the development of discourse mapping processes: the on...

Cognition, 13 (1983) 309-341 2

The developm nt of discourse mapping processes: fhe on-line interpretation of anaphoric expressiopkT*

LORRAINE KOMISARJEVSKY TYLER

Max-Planck-lnstitu t fiir Psycholinguistik

Abstract

The present research focuses on how children integrate the antecedent of different kinds of anaphor into their on-going interpretation of an utterance, and on the kinds of cues they use to help them to do this. Theae issues were studied by examining the on-line processing of three types of anaphoric devices -repeated noun phrases, general terms and pronoun anaphors. The data showed that by the age of five, anaphoric mapping processes in general are well-mastered, although all age-groups (5, 7, 10 year olds and adults) found general term anaphors more difficult to interpret. The major developmental differences concerned the processing of anaphoric pronouns. For five year olds, pronouns were primarily interpreted as devices which maintained the themaric subject (If the discourse, but ,:hen there was no thematic subject they relied primarily on pragmatic plausibility in their assignment of pronominal co-reference. As children get older, thev are able to take advantage of the lexical properties of pronouns and all three sources of information-lexical, pragmatic inference and the thematic structure of the discourse-p1a.v contributory roles in the assignment of reference to a pronoun.

introduction

A fundamental aspect of natural language is that each utterance is produced within an interpretative context. Thus, to properly interpret an utterance, the listener has to determine its relationship to its immediate and preceding

*This research was primarily supported by a grant from the Dutch Science Foundation (ZWO). I am very grateful to Peter Jeurissen, Pienie Zwitserlood and Colin Brown for testing the 360 children who participated in the three experiments. I also wish to thank Merrill Garrett, Marie-Louise Kean, Eve Clark, William Marslen-Wilson and Annette Karmiloff-Smith, for their careful and critical reading of an earlier version of this paper. Reprint requests should be sent to: Dr. L. K. Tyler, Max-Planck-Institut fiir Psycholinguistik, Berg en Dalseweg 79,6522 BC Nijmegen, The Netherlands.

0010-0277/83/$10.40 0 Elsevier Sequoia/Printed in The Netherlands

310 L. Komisarjevsky Tyler

linguistic and non-linguistic context. The research described here is concerned with the psycholinguistic consequences of a major aspect of these relationships between an utterance and its context; specifically, with what can be called anuphoric mapping processes. These processes are defined as the mental events involved in the processing of those linguistic items that are co-referential with (and that depend for their interpretation on) other items that have previously been mentioned, either explicitly or implicitly, in the preceding discourse (c.f., Halliday and Hasan, 1976; Lyons, 1977). The linguistic devices that are used to make this kind of discourse connection are anaphoric devices. These include not only pronouns and nominals, but also full definite noun phrases linked in some way to an antecedent (for example, the use of the tree as a textual linkage to an entity previously mentioned as an elm).

The present research focusses on the development of these anaphoric mapping processes after the age of five years. It is concerned with the consequences of different kinds of discourse anaphor for a child”s subsequent processing of an utterance. How do children integrate the antecedent of an anaphor into their on-going analysis of an utterance, and what kinds of cues do they use to help them to do this?

To be able to answer such questions about the nature of the on-going representation which the listener is constructing requires the use of an experimental paradigm which is sensitive to the properties of this on-line constructive process. As has been argued elsewhere (Marslen-Wilson and Tyler, 1980~; 1981), tasks which force the listener to respond rapidly while in the process of listening to an utterance are most directly sensitive to the properties of this developing representation. This is because fast response tasks tan the listener’s representation of the input at a specific moment in time. Given the input available to the listener when she or he makes the response, it is then possible to infer what types of analysis must have been performed upon this input to produce the effects reflected in the response.

These so-called ‘on-line’ tasks can be contrasted with ‘off-line’ tasks in which little or no constraint is placed upon the listener to respond rapidly to the speech input. These latter tasks provide a much less direct source of data about the language understanding process. Although they can provide information about the types on’ representation eventually available, they can only indirectly answer questions about the processes involved in constructing these representations.

I therefore used one of these on-line tasks-the mispronunciation detection task (Cole, 1973)-to investigate three major issues, The first issue is whether there are developmental changes in the ability to integrate a sequence of utterances into a coherent discourse by means of anaphoric

The development of discourse mapping processes 311

referring expressions. The existing data are unclear on this issue, mainly because It has not been systematically investigated. Past studies have usually focussed either on the development of discourse integration skills indepen- dent of the issue of anaphora, \?r on the comprehension of potentially anaphoric referring expressions, such as pronouns, but not on the two together.

Of the former studies, the data are equivocal as to whether or not there are developmental changes in the ability to rapidly integrate utterances during comprehension. Some data suggest that five year olids can only achieve the rapid integration of utterances when the linkages between utterances are relatively simple and direct (Tyler, 198 1; Tyler and Marslen- Wilson, 197&, b). But there is no evidence that it is by exploiting the anaphoric properties of definite noun phrases and pronouns that the child achieves this integration. On the contrary, some recent data from production experiments (Karmiloff-Smith, 1980) suggest that five year olds are not yet able to use pronouns in their true anaphoric function to maintain the intra- linguistic cohesion of a discourse. But this has never been established for comprehension, since none of thf work on the interpretation of anaphoric expressions has set out to investigate the development of discourse mapping processes by means of anaphoric devices. Indeed, most studies in this area have focussed on sentence-internal anaphora and have thus neutralised the potential discourse function of anaphors by using isolated sentences (Chomsky, 1969; Maratsos, 1973; Scholes, 1981). Although there arc a few studies which have used materials consisting of two consecutive sentences (i.e., the minimum discoune unit), what these experiments in fact amount to are demonstrations of the deictic as opposed to the anaphoric function of pronouns (Chipman and de Dardel, 1974; Tanz, 1977). That is, in these studies, the first sentence the child hears typically names a co-present referen& the second contains a pronoun, and the child’s task is to pick out the referent in the extralinguistic context. It is likely that children pick out the correct object by means of the deictic relationship between the object and the pronoun rather than by means of the anaphoric relationship between the pronoun and its discourse antecedent. Therefore, at least for the comprehension of spoken language, the issue of whether and how the anaphoric properties of pronouns and repeated definite noun phrases are used by children is still open.

A second issue, closely related to the first, is the extent to which different kinds of anaphors vary in their effectiveness as cohesive devices in discourse. Here the question is whether there are developmental changes in the ability to bring the properties of the appropriate antecedent into play in the subsequent processing of an utterance as a function of the directness of the

312 L. KomisaMevsky Tyler

relationship between an anaphor and its antecedent. Once again, there are few previous data which bear on this issue and from which we can derive specific hypotheses. The developmental aspect of the question has not been studied, and there is only one experiment using adult subjects which compares the relative effectiveness of different kinds of anaphor during spoken language comprehension (Tyler and Marslen-Wilson, 1982)l. This experiment suggests that anaphors as diverse as proper names, pronouns and zero forms can all be equally effective for adults in co-indexing the appropriate referent in the prior discourse.

But there is no evidence that this is also true for children iis young as five years. Indeed, one might reasonably assume that young children will find anaphoric mapping easier when the relationship between anaphor and antecedent is most direct -as in the case of a repeated definite noun phrase which, in the simplest analysis, merely requires a match between two identical labels-and more difficult when it depends upon a less direct mapping process, as in the case, for example, of anaphoric pronouns. Although there is no clear consensus on the processes involved in the interpretation of anaphoric pronouns in discourse-for example, one proposal is that it involves detailed linguistic knowledge such as the identification of the lexical properties of number and gender (Scholes, 1981), while another is that it depends upon an understanding of the thematic structure of a discourse (if one draws an analogy from the processes Karmiloff-Smith (1986) has suggested for production)-nevertheless, all of the proposals clearly suggest a set of more indirect mapping processes than is the case for repealted definite noun phrases.

The third issue to which the present experiments are addressed concerns developmental changes in the relative contribution of the many different factors influencing anaphoric mapping. In interpreting an anaphoric expres- sion., children, like adults, must identify it as having anaphoric properties. They must also have available in memory some representation of the discourse, and they have to link the anaphor with its appropriate antecedent in this discourse model. Being able to accomplish this linkage successfully depends on whether children can use a variety of different sources of information which are present either in the discourse or in the utterance containing the anaphor. Thus, they have to be able to exploit the lexical properties of anaphors, the syntactic structure of the utterance, the structural properties of the discourse, pragmatic inference, and the presuppositions

‘Other related studies have used. written rather than spoken material (e.g., Sanford and Garrod, 1981). Since the relationship between the two modalities is by no means clear, these studies are not diitly relevant to our present concerns which are exclusively with spoken language understanding (see Tyler and Ma&en-Wilson, 1982).

The developmerrt of discourse mapping processes: 313

about shared knowledge which are inherent within any discourse. All of these sources of information clearly contribute towards successful co-referentiality (Clark and Marshall, 1978; Ehrliclt, 1980; Lasnik, 1976; Marslen- Wilson and Tyler, 19806; Sidner, 19’79; Silverstein, 19764 b), and the extent to which children are sensitive to any or all of them will determine how well they are able to interpret an anaphoric device.

In investigating this third issue, I will look in particular at children’s use of lexical, discourse and pragmatic inferential information in the in’terpreta- tion of several types of anaphoric expressions. Are there developmental changes in the extent to which these factors influence the assignment of co- reference? Does, for example, the successful interpretation of anaphors depend primarily on children’s use of the linguistic distinctions inherent in pronouns and noun phrases- as, for example, Solan (1978) and Chomsky (1969) would claim? Or, do children interpret anaphors by primarily using more global types of linguistic information, such as the structural organisa- tion of the discourse--as Karmiloff-Smith (1980) has recently argued for production? Yet a third possibility, based upon the claim that young children rely heavily upon pragmatic inference in the interpretation of spoken language (Chapman, 1978; Tyler and Marslen-Wilson, 1$7&r), is that this is a major source of information they use in resolving anaphoric reference.

In summary, three main issues are investigated in the expeiiments to be reported here. These are:

(i) Are there developmental changes in the ability to link utterances into a coherent discourse by means of anaphoric expressions?

(ii) Do different kinds of anaphors vary in their effectiveness as cohesive devices in discourse?

(iii) Are there developmental changes in the relative contribution of various sources of information which influence the assignment of anaphoric reference?

No one is&e is dealt with in a single experiment. Rather, all three issues are recurrent themes throughout the three experiments.

Experiment One

The first expelriment was partly exploratory in nature. Its primary aim was to determine whether ttke study of on-line anaphoric mapping processes in five year olds was feasible. Its second aim was to determine whether anaphoric mapping processes are more or less successful as a function of the directness with which an anaphor indexes its antecedent. The directness of

314 L. KomisaHewky Tyler

the relationship between an anaphor and its antecedent was defined in terms of the extent to which the properties of an anaphor explicitly included those of its antecedent. Examples of three anaphors which vary along this dimen- sion are given in sentence-pairs (l)-(3) below. In each case, the anaphor (in italics) occurs at the beginning of the second sentence of each pair.l

(1) Mother saw the postman coming from a distance. The postman brought a letter from Uncle Charles who lives in Canada.

(2) Mother saw the postman coming from a distance. The man brought a letter from Uncle Charles...

(3) Mother saw the postman coming from a distance. He brought a letter from Uncle Charles...

Comparing these three different anaphors, it is clear that the anaphor which is most directly related to its antecedent is the repeated definite noun phrase the postman in (1). This type of anaphor merely requires the listener to establish a match between two identical labels. In both (2) and (3), however, the relationship is less direct. In (2) the anaphor is a general classificatory term preceded by a definite article. In order to make the correct link between anaphor and antecedent the child has to identify the antecedent as being semantically coextensive with that term (cf., Stenning, 19’75), as well as interpreting the definite article as implying anaphoricity. In (3), where the anaphor is an unambiguous personal pronoun, the child has to locate an antecedent which matches the pronoun in number and gender.

To determine whether the anaphoric mapping process is accomplished just as readily for the three types of anaphor, I took advantage of the fact that word-recognition processes are facilitated when the word in question is predictable. There were two steps involved here, First of all, a situation was set up in which selected target words were predictable on the basis of the prior context. Then, secondly, I used the mispronunciation detection task to measure the extent to which the on-line processing of the target words was facilitated as a function of this contextual predictability. The

2These are loose translations of the Dutch originals. The Dutch sentences (context sentence followed by each of the three continuations) with 1itera.I gloss were:

0 Moeder zag de postbode a! van verre aankomen. mother saw the postman already from a distance coming)

1) Deposlbode bracht een brief van oom Karel, die... Whepostman brought a letter from Uncle Charles, who...)

2) De man bracht een brief... Wre man brought a letter...)

3) Hij bracht een brief... He brought a letter...)

The dcveloptnen t of discourse nrapping proct-wcs 315

mispronunciation detection task involves the subject listening to speech and pressing a response button when she or he hears a mispronounced word. The mispronunciation is placed after the first two or three phonemes and it turns the original word into a non-word in the language. In the examples above, the target word fetter would be mispronounced as kffer.’ Earlier experiments by Cole and Perfetti (1980) had used this task successful%y with seven year olds, and my own pilot studies established that it could be reliably used with children as yc,ng as five years.

The reason for using the mispronunciation detection task here is because the task is sensitive to the effects of predictability. That is, reaction times to detect mispronounced words are facilitated when the original word-the source for the mispronounced word- is more contextually predictable. When a word is predictable on the basis of prior context, then the word is more likely to be identitied before the mispronunciation occurs. In this case, since listeners think that they know what the word is, as, soon as they hear the mispronunciation and detect a mismatch with the word that has already been identified, the de lection response can be made. Detection latencies will be faster here thzrl in the case where the word ‘s not predictable. In this latter case the mispronunciation will tend to occ~lr before the listener has identified the word and consequently the detection response will be slower. This is because the listener has to wait longer for the information nece.:sar\/ either to identify the word or to decide that it is a non-word.

Bcsause the task is sensitive to the effects of contextual predictability, it car1 be used hzre to determine whether listeners perform anaphoric mapping processes on-line, If we consider the examples above, the word letter (the source word for Zeffer) becomes predictable if one knows that it is H!e postman that is the subject of the second sentence. This is a baseline condition, in which the source word is predictable without the necessity of ansphoric mapping processes. However, in sentences like (2) and (3) the word letter can only be predictable if one has established that the antecedent of the anaphor in each case is indeed the postman. Thus, if there are any diffc.:rences in the ability to make the appropriate discourse mapping in order to rosolve these different types of anaphor, then this should produce slower responses in (2) or (3) relative to (1) where tke postman is explicitly mentioned in the second sentence and anaphoric mapping is not strictly necessary.

A fourth experimental condition was also included in which the target word was not predictable. In this condition the target word was pragmatically implausible when the utterance was mapped onto its discourse context. This was to ensure that children were indeed integrating utterance and context. An example is given below:

316 L. Komisurjevsky Tyler

(4) Mother saw the postman coming from a distance. Mother brought a letter from Uncle Charles...

Here the anaphor refers to Mother in the context sentence rather than to postmwz, as in the other conditions. The situation depicted in the continuation sentence is not, by itself, implausible, but it becomes implausible when the utterance is interpreted with respect to the prior context.3

If condition (4) had not been included and no difference had been found between conditions (l), (2) and (3), then it would not have been clear whether children were performing any discourse mapping at all. However, if responses in (4) are generally longer than those in (2) and (3), then this would provide evidence that children are indeed mapping at least one kind of anaphor onto its antecedent and finding, in consequence, that the target word is pragmatically implausible.

Method

Mu terials

28 stimulus sets were constructed, each of which consisted of a context sentence and 4 possible continuation sentences. Following the continuation sentence were 2 or 3 additional sentences, which made each sequence into a short story. Each of the continuation sentences contained an anaphor in subject position, with the target word the direct or indirect object of the verb following the anaphor. The target word was always a noun which mentioned a specific attribute or property of the referent of the anaphor. By pairing each continuation sentence with the context oentence, 4 sentence- pairs were obtained. An example of one of these sets was given earlier.

As in the example, the first sentence of each sentence-pair provides a scene-setting context which contains two potential antecedents (Mother, postman) for the set of possible continuations. Continuation sentences in (1) (2) and (3) contain anaphors whose antecedent is postman. However, 1s explained earlier, each anaphor varies in the directness with which it indexes it antecedent. In (1) the anaphor is a definite noun phrase which repeats the description of the antecedent, in (2) it is a general classificatory term preceded by a definite article, and in (3) it is an unambiguous personal

3A few of the items in condition (4). were actually pragmatically anomalous rather than simply implausible. However, when these items were analysed separately, they were found to be indistinguish- able from the implausible sentences -both latency.

in number of missed detections and in mean response

The devclopmerr~ of discourse mapping processes 317

pronoun. In contrast to these three conditions, the anaphor (a repeated nominal or repeated definite noun phrase) in (4) refers to mother in the context sentence.

TO ensure that the target words were only predictable when the anaphor had indexed its appropriate antecedent, pre-tests were carried out on five year olds using an auditory cli;ze procedure, In these pre-tests three things were established. Firstly, I made sure that children consistently. produced the source word (e.g., letter) in response to the sequence: ‘Mother saw the postman coming down the street. The postman brought...* The przdictability rating here was 85%. This is a measure of predictability in the baseline condition. The second point that was established in the pre-test was the predictability of targets when the general classificatory term (e.g., the man) was mentioned following the context sentence (e.g., as in (2)). In this condition, 80% of the children produced the correct target. Moreover, using the same procedure, I ascertained that targets were not prOdictable when the context sentence was omitted from (2) so that children heard the continuation sentence in isolation. The predictability rating here was only 6.5%. This procedure was carried out in order to ensure that when no time constraints were imposed on the subjects, the general classificatory terms could, ‘in principle, function to locate the correct referent in the prior discourse.

Finally, a pre-test was carried out on condition (3) to determine whether, when the child was under no time constraints, the pronoun anaphor was successfully mapped onto its referent. The predictability rating here was 76%. Since this result indicates that pronouns can often be correctly interpreted when no time pressure is imposed on the 5 year old, any reaction- time differences in the mispronunciation detection experiment can be seen to reflect the relative effectiveness of pronoun anaphors in indexing the correct refer2:nt under the time constraints imposed by natural speech.

The target words in each of the four continuation sentences, for all 28 sets, were then mispronounced towards the end of the first syllable. Mis- pronunciations conSisted of changing a single phoneme so that the source word become a non-word in the language. Thus, for example, the Dutch word for letter, Ilric,?, would become briek.

Each target word appeared in four conditions. So that each child would only hear a target word once, four versions of the materials were constructed. Each version contained eight sentence-pairs in each of the four conditions, pseudo-randomly distributed across a version. 12 filler sentences were interspersed between the test sentences in order to obscure their regularity.

The four versions of the materials were recorded by a female native speaker of Dutch at a normal conversational rate. After recording the

318 L. Komis@vsky Tyler

stimuli, timing pulses wfere placed on the non-speech channel of the tape at the exact onset of the mispronounced phoneme. These pulses could not be heard by the subject, and their function was to start a digital timer which was stopped when the child pressed the response key.

Design and procedure

Ten children of five, seven and ten years of age were tested on each version of the materials, making a total of 40 children in each age group. 40 adults were also tested on the same materials to provide comparison data.

Each child was tested individually in his or her school by an experimenter who was a native speak’er of Dutch. The children were told to listen to short stories which they would hear over headphones, and to press the response button as soon as they heard the story-teller say a wrong word. They were then given an example of a mispronounced word, and the contrast between the mispronounced word and its correct form was pointed oat to them. Each child was then given S-10 practice sentences, depending on how quickly he or she grasped the requirements of the task.

Subjects

The 120 children who participated in the experiment attended schools in and around the Nijmegen area. The 40 adult subjects were students at the Katholieke Universiteit, Nijmegen, and they were paid for their services.

Results and discussion

Detections

Before examining the reaction-time data, the occasions on which subjects failed to detect the mispronunciation at all will be discussed. Table 1 presents a breakdown of these data by age and condition. There are two points of interest here. Firstly, the five year olds fail to detect mispronunciations more frequently than any other group, indicating that they find the task more difficult than the older children. But, more noteworthy is the distribution of missed detections across conditions. The five year olds clearly have the most difficulty in condition (4) where the number of missed detections equals the combined total of missing responses in the other three conditions. Although there is a tendency for the older children to exhibit a similar pattern, it is more extreme in the five year olds and clearly diminishes with age.


Table 1. Experiment One: Number of failures to detect mispronunciations+

Age-group Type of continuation Total

5 years 7 years

10 years Adults

ApprorMate General noun f hrase term

--_

17 19 11 11 6 14 1 5

Pronoun

24 9

11 3

inappropriate noun phrase

64 28 19 1

124 59 50 10

Total 35 49 47 112 Z!4 3

+Total possible N = 280 in each condition for each age-group.

Such poor performance in condition (4) suggests that the five year olds have great difficulty in recovering the target word when it is not predictable. In fact, the high percentage of missing responses suggests that five year olds may have frequently failed to recover the word at all, thinking that they had heard a non-word. This lack of predictability was presumably due to the pragmatic implausibility of the target word. given the properties predicated of the anaphor in the context sentence. For example, in the stimulus set above, on the basis of the properties predicated of the antecedent Mother in the context sentence, and the fact that the existence of the postman has been established, it is unlikely, in Dutch culture, that mother would be bringing a letter.

Although the older children and adults missed fewer mispronunciations in condition (4) than the five year olds, their response to targets was also clearly (although less strongly) slowed down when targets were not predictable, since for all ages reaction-times in condition (4) were longer than in condition ( 1).4

Reaction-time data

Condition (4) was not included in the full analysis of the reaction-time data because 23% of the five year old data in that condition was missing. Since I did not feel justified in replacing such large quantities of missing data, and the error analysis was sufficient to make the point here, it was not included in the statistical analyses.

4The mean reaction times in condition (4) were 846 msec, 627 msec, 590 msec, and 441 msec for the 5.7, 10 year olds and adults, respectively.

320 L. Komisa@evsky Tyler

The mean mispronunciation detection reaction-times for the other three conditions are given in Table 2. Note that absolute differences in reaction- times between age-groups are not central here; what matters are the relative differences between the three conditions within any one age-group.

Table 2. Experiment One: Mean mispronunciation detection latencies (msec)

Age-group Type of continuation

Noun phrase General term Pronoun

5 years 749 807 801 7 years 578 631 593

10 years 500 548 507 Adults 379 424 404

Before computing the statrstical analyses, missing and extreme values were replaced using the method recommended by Winer (1971). Extreme v&es were defined as those which were two standard deviations either above or below the mean for each age-group and condition. The percentage cf replaced data for the five year olds was 11 .l%‘, and for the seven, ten year olds and adults it was 6.3%, 6.1% and 4.5%, respectively.

Two analyses of variance, one with subjects and one with items as random variables, were computed on the means of the raw data. These analyses were then combined into MinF’ ratios (Clark, 1973). In the subject analysis, subjects were nested within Age and crossed by Type of Anaphor. In the item analysis, items were crossed by both Age and Type of Anaphor.

There was a highly significant main effect of Age (hlinF’ (3,237) = 80.63, p < 0.001) reflecting the finding that as subjects get older, reaction-times get faster. Thus, the overall mean for the five, seven, ten year olds and adults were 786 msec, 600 msec, 518 msec and 403 msec, respectively. The main effect of Type of Anaphor was also significant (MinF’ (2,83) = 3.75, p < 0.05), but there was no interaction with Age (MinF’ < 1).

Before discussing individual aspects of the data, I should point out that one general aspect of the experiment was successful. That is, the fact that fast and reliable reaction-times were obtained in this experiment clearly

‘A large proportion of the replaced data (48%) came from S particular sentences. Without these sentences, the percentage of replaced data for the five year olds (6.1%) is very similar to that of the seven and ten year olds. However, these 5 sentences did not change the pattern of reaction-times. Computing the mean reaction-times for the 5 year olds without these 5 sentences, the overall pattern remains the same, but absolute reaction-times are slightly faster-71 1 msec, 794 msec, and 770 msec, in conditions 1,2, and 3, respectively.

The developttten t of discourse mapping processes 321

establishes the feasibility of using this type of task to study the processes involved in anaphoric mapping in children as young as five years.

General term anaphors

The main effect of Type of Anaphor can be specifically attributed to the fact that reaction-times to sentences containing general terms were slower than those to the repeated noun phrase baseline condition [I ). The overall difference here of 50 msec was significant on the Newman-Keuls test. The other differences between conditions were too small to reach significance. Thus, responses to utterances containing general term anaphors averaged 25 msec longer than those containing pronoun anaphors, and these latter were, on average 25 msec longer than the repeated noun phrase baseline. Moreover, there were no age-related differences in the extent to which responses in the repeated noun phrase condition were facilitated over those in the general term condition. For the five, seven, ten year olds and adults the differences between the two conditions were 58 msec, 53 msec, 48 msec and 45 msec, respectively. All of these differences were significant at the 0.05 level or beyond on the Newman-Keuls statistic, using an error term derived from the MinF’ value.

There are at least two reasons which might be given 3s explanations for the slower responses to utterances containing general term anaphors. One explanation is that the listener did not interpret the general terms as anaphoric referring expressions at all, but rather as new entities in the discourse. However, this is an improbable explanation: general terms do function successfully as anaphoric devices when the antecedent is a definite noun phrase. This is clear from the results of Garrod and Sanford (1977) as well as from the results of the cloze pre-test.

A more plausible explanation is that a general term is, nonetheless, a less effective anaphoric device. The reason for this concerns the ass#umptions that a listener makes about the linguistic forms speakers will use INhen referring to entities that have been previously mentioned in a discourse. When an entity is established in a discourse by means of a definite noun phrase, this creates a presupposition about the existence of a definite and specific referent (Donnellan, 1971). This in turn means that the listener expects future reference to that entity to be made by linguistic forms which are more presupposing, such as pronouns and zero forms (c.f., Silverstein, 197ti; 19766). However, when this expectation is violated, as is the case when the entity is referred to by a less presupposing linguistic form such as a general term anaphor, then establishing co-referentiality between the general term and its antecedent is more difficult.

322 L. Komisatjevsky Tyler

Before concluding this section, I will briefly discuss one methodological issue- the contrast between the cloze pre-test data (as discussed in the Method section) and the mispronunciation detection latencies. On the basis of the cloze data alone (80% predictability rating), we could argue that general term anaphors are rather successful anaphoric devices. However, when we consider the reaction-time data, we find that in fact they cause some difficulty. The reaction-time data force us to modify conclusions drawn from the cloze data. The two sorts of data together imply that although general terms do function to index the appropriate referent, this process is more difficult, or more time-consuming, than is the case for some other types of anaphor. This is not a trivial observation. Since the listener’s task is to interpret the speech input fast enough to keep abreast of the subsequent incoming speech, delays and difficulties of interpretation will undoubtedly affect the representation which is being constructed. This conclusion could not have been drawn from the cloze data alone, but needed data which reflect the properties of real-time comprehension processes6

Pronoun anaphors

Turning to the result for the pronoun anaphors, we find clear developmental differences. The five year olds were 58 msec slower in responding to the pronoun anaphor condition than to the repeated noun phrase baseline, and this difference was significant at the 0.01 level on the Newman-Keuls test. This difference disappears by seven years of age: For the seven, ten year olds and adults, the differences between the pronoun and repeated noun phrase conditions of 15, 7 and 25 msec, respectively, fell far short of significance on the Newman-Keuls statistic.

This result means that for the older children and adults, the word letter-- the source for the mispronounced leffer-was predictable whether the continuation sentence contained a repeated definite noun phrase or a pronoun in subject position. This implies, furthermore, that the pronoun was functioning successfully to bring the properties of its antecedent into play in the subsequent processing of the utterance. In this respect, the five year olds were clearly not as successful as the older children. What we now have to consider is what specific aspect of the process was responsible for the five year olds’ difficulty with anaphoric pronouns,

0ne possibility is that five year olds have problems in identifying or using the lexical information which is carried by the pronoun. That is, they may

%he same contrast in the five year old data between cloze and reaction-time responses can also be seen with pronoun anaphors, suggesting that although pronouns can function successfully as anaphors, the processes involved cause some difficulty and this costs the listener in processing time.


not have fully developed the processing skills needed to exploit properly the lexical information of number and gender marked on the pronoun, and to match these properties to those of the antecedent. No data in the present experiment bears directly on this issue, but it is clearly a crucial aspect of anaphoric pronoun mapping and will be take11 up again in Experiment Two.

An alternative explanation for the five year olds’ difficulties with pronouns is that this might be symptomatic of a broader problem with anaphoric mapping processes in general, rather than with *anaphoric pronouns in particular. The present data do not resolve this issue. The only reaction-time data which might suggest that five year olds are performing discourse mapping is the finding that responses to utterances containing repeated noun phrases are facilitated relative to those containing pronouns. However, this facilitation may not be a consequence of discourse mapping processes at all, but may instead be due to sentence-internal effects. That is, to the fact that the postman is mc.ntioned within the same sentence as tke

letter in condition (l), rather thcln to its potential anaphoric properties. _ Note that: this problem does not arise for the older groups. They are clearly

integrating the utterance with the discourse context, since responses to utterances containing pronouns are not significantly different from those to the repeated noun phrase baseline.

Given the problems just discussed, two additional studies were carried out: Experiment Two to determine whether the source of the five year olds’ difficulties with pronouns stemmed from an inability to exploit the lexical properties carried by a pronoun, and Experiment Three to detemrine whether their problem with pronouns was part of a more general problem with discourse mapping processes.

Experiment Two

This experiment had two main aims. First, to explore the possibility that ,the

five year olds’ difficulties with anaphoric pronouns, as found in the first experiment, was caused by an insensitivity to, or an inability to use, the lexical properties of pronouns, and second, to investigate the interplay between lexical information and pragmatic inference in the assignment of reference to a pronoun. Pragmatic inference is taken to mean here the plausibility of potential antecedents with respect to the properties predicated of the anaphor elsewhere in the utterance in which the anaphor occurs. If there are developmental changes in children’s ability to use the lexical properties of a pronoun to guide them in assigning co-reference relations,


is there also a corresponding change in their reliance upon this kind of pragmatic inference? To investigate these issues, we constructed short stories of the following form : ’

(5s) Every now and then, the prince goes to see the old shepherd. He takes good care of the sheep, and...

(5b) Every now and then, the princess goes to see the old shepherd. He takes good care of the sheep, and...

(SC) Every now and then, the princes go to see the old shepherd. He takes good care of the sheep, and...

(Sd) Every now and then, the princess goes to see the old shepherd. She takes good care of the sheep, and...

These materials contained three critical manipulations: the number and gender ‘of the potential antecedents in the context sentence, the number and gender of the anaphoric pronoun in the continuation sentence,” and the

‘The Dutch originals with literal gioss (pronouns in italics):

(Sir) De prins gaat af en toe bij de oude herder op bezoek (Ihe prince goes now and then by the old shepherd to visit) L/Q past altrjd goed op de schafen maar...

(He looks always good out for the sheep and...) (Sb) De prinses gaat af en toe bij de oude herder op bezoek

(‘The princess goes now and then by the old shepherd to visit) Hij past altijd goed op de schafen maar...

(He looks always good out for the sheep and...) 6c) De prinsen gaan af en toe bij de oude herder op bezoek

(‘The princes go now and then by the old shepherd to visit) Hij past altijd goed op de schafen maar...

(He looks always good out for the sheep and...) 04 De princes gaat af en toe bd de oude herder ap bezoek

(The princess goes now and then by the old shepherd to visit) .ZU past altijd goed op de schafen maar...

(She looks always good out for the sheep and...) 8A note on number and gender on personal pronouns appearing in subject pa&ion in Dutch.

Sinmlar Plural

Durch English Dutch English

1 person: ik I wii WC 2person: jij you (familiar) jullie you (familiar)

3 person: :ij you (polite) u you (polite) he zij they

zij she het it

(i) Prcmouns referring to inanimate entities in Dutch have one of two genders. The pronoun her is used only for those nouns which are neuter (as marked by the definite article), and h# is used for all others.

(ii) For animate entities, the gender of the pronoun agrees with the biological gender of its referent. (iii) The pronoun for she and they is identical but the form of the accompanying verb always

indicates which is intended.

The development of discourse mapping processes 3 2 5

pragmatic plausibility of the antecedent relative to the continuation sentence. In condition (Sa), both potential antecedents in the context sentence are singular and male and therefore the pronoun in subject position in the continuation sentence, which is also singular and male, is lexically ambiguous. However, the most pragmatically plausible interpretation of the pronoun is for it to be co-referential with the shepherd. In conditions (5b) and (5c), the pronouns are both lexically unambiguous--on the basis of gender marking in (5b) and number marking in (Sc)---and pragmatically appropriate since they both index the shepherd. In contrast, condition (5d) presents a different case. Mere the pronoun is unambiguous on the basis of its gender marking, but its correct referent is the princess rather than the shepherd. Thus, if the listener uses the gender marking on the pronoun to index the princess, then the continuation sentence is pragmatically implausible.

Method

Ma teriuls

The materials consisted of 24 sets of 4 sentence-pairs, as illustrated above. Each sentence-pair consisted of a context sentence, followed by a continuation sentence containing an anaphoric pronoun in subject position and a target word (in italics) in the following verb phrase. Two or three additional sentences followed on from the continuation sentence to make the sequence into a more-or-less complete story. As in the previous experiment, the target word in the continuation sentence was only predictable if the pronoun indexed a specific referent in the context sentence. In the example set above, the shepherd is the antecedent which makes sheep predictable.

All of the target word-antecedent pairs (e.g., sheep-shepherd) had been pre-tested for either Experiments One or Three to ensure that the target word was predictable when the critical definite noun phrase (e.g., the shepherd) was actually mentioned in the continuation sentence. The mispronunciations occurring in the target words were therefore also the same in other experiments.

Four versions of the materials were constructed in order to counter- balance conditions across subjects, so that each child only heard each target word once. The stories were then recorded and timing pulses were placed at the onset of each mispronounced phoneme.

326 L. Komisarjeusky l)ler


The design and procedure replicated that of the previous experiment, and the same number of children in each of the 3 age-groups, plus a group of adults, were tested on the materials.

Subjects

120 children from Nijmegen, and 40 undergraduates from the Katholieke Universiteit, Nijmegen, participated in the experiment. None of these subjects had taken part in the first experiment.


Before performing the statistical analyses, we replaced missing and extreme values (Winer, 1977). The percentage of replaced data for the 3 groups of children was 12.4% 12.4% and 8.6% for the five, seven and ten year olds, respectively. Missing and extreme values each accounted for approximately half of the total amount of the replaced data for each of the 3 age-groups. Only 4.2% of the adult data was replaced and, of this, 95% was due to extreme values. For all age-groups, the replaced data were distributed evenly across the four experimental conditions.

The statistical analyses were computed on the means of the raw data. As in the first experiment, there was a large difference in overall reactlon- times between the four age-groups (MinF’ Age (3,222) = 94.5, p < O.OII ) with reaction-times becoming progressively faster as children got older. ‘The means for each group of subjects in order of ascending age were 838 msec, 661 msec, 538 msec and 429 msec. Collapsing across age-groups, the main effect of Condition was not significant (MinF’ (3,167) = 1.188, p < O.OS), nor was the interaction between Condition and Age (MinF’ < 1). However, there are clear indications in the data that the role of both pragmatic pla.usi- bility and lexical information in the assignment of pronominal reference changes with age. This can be seen in Table 3 which presents the overall means for each age-group and condition.

Interphy of pragma tic plausibility and the lexical properties of pronouns

For adult listeners, some earlier work suggests that the constraints on anaphor resolution that derive from the lexical properties of the pronoun are only one aspect of the resolution process (Marslen-Wilson and Tyler,


Table 3. Experiment Two: Mean mispronunciatio~l detection latencies (msec)

Age-group

A

Condition*

B C D

5 years 844 812 853 842 7 years 6% 653 650 685

1;3 years 526 542 524 559 Adults 428 423 412 454

*cTondition A = Ambiguous p[ronoun; pragmatically plausible antecedent. Condition B = Unambiguousj pronoun (gender); pragmatically plausible antecedent. Condition C = Unambiguousi pronoun (number); pragmatically plausible antecedent. Condition D = Unambiguous! pronoun (gender); pragmatically implausible antecedent.

19806; Sidner; 1979). An equally important factor is what we can call pragmatic inference -those processes that assess the interpretative plausibility of potential antecedents relative to the properties predicated of the anaphor in the continuation sentence. When the outcome of these processes is inconsistent with the outcome of lexical matching of the pronoun (as was the case in condition (5d)), then processing of the utterance is more difficult (Tyler et al., 1982).

This is exactly the outcome that was obtained for the seven, ten year olds and adults in condition (Sd), where the properties predicated of the antecedent selected on the basis of the pronoun’s lexical properties were pragmatically inconsistent with the subsequent discourse. Condition (Sd) was compared with the mean of conditions (Sa), (Sb), and (5~) taken together. since in each of these three cases lexical and pragmatic inf’ormation were consistent with each other. For the three oldest age-groups, condition (5d) was slower than the. mean of the other three conditions combined, and this difference was significant for each age-group at the 0.05 level or beyond, using planned orthogonal contrasts (Kirk, 1968), with an error-term derived from the MinF’ value. Moreover, the extent to which each age-group was slower on (Sd) remained remarkably constant across all three age-groups. For both the seven year olds and adults, condition (5d) was 33 msec slower than conditions (Sa), (5b) and (5~) combined, and for the ten year olds it was 29 msec slower.

The five year olds present a very different picture. Their performance was not affected when the lexical information carried by the pronoun was incompatible with the subsequent pragmatic plausibility of the referent. Combining conditions (5a), (5b) and 5c), and comparing this with (5d), I found that the five year olds were unaffected by the pragmatic implausibility


in (5d). There was a negligible difference between rhe two conditions of 6 msec. This suggests that, fol the youngest children, the lexical properties of the pronoun do not function to the same extent as for older children and adults in selecting an anteced.ent.

The data also sLlggest th;lt the five year olds an: nonetheless beginning to be able to use the lexicid information carried by the pronoun. If (5b) is compared to (5~) (where the pronoun is unambiguous either because of its gender (5b) or its number (SC) marking), there is a tendency for the five year olds to be faster on condition (5b) than (5c)-although this difference falls short of significance (t, = 1.393, df = 78, p < 0.1; t2 = 1.255, df = 46, p < 0.2). This suggests that Dutch children may be able to use gender markings on pronouns developmentally earlier than they are able to use number markings.

Related results for English have been reported recently by Scholes (198 1) and Wykes (1978), using very different tasks- a picture-verification task in the case of Scholes, and an acting-out task in the case of Wykes. Both Wykes (1978) and Scholes (1981) found that children were sensitive to gender m,arkings on pronouns by five years of a,ge, but in addition, Scholes found that mastery of number marking was delayed until six years. After the age of seven, he argues, there appears to be no difference in children’s sensitivity to both types of lexical information.

An important general point to nose here is that the results of the present mispronunciation detection experimen’ts cannot be accounted for in terms of simple lexical priming effects. That is, a sceptical reader might argue that the target word is not facilitated by means of discourse mapping processes, but rather because a semantically related word appears in the prior context. This is clearly not the case, given the results for the older children and adults in condition (Sd). Here responses were slowed down relative to condition (5a)--even though in both cases the target was preceded by the same semantically, related word-because the pronoun’s antecedent was pragmatically implausible. This clearly establishes that the effects here are due to discourse mapping processes, and not simple lexical priming.

Experiment Three

The purpose of Experiment Three was to determine whether five year olds have specific problems with anaphoric pronouns, or whether their difficulty is wit1h establishing co-referentiality between any type of anaphor and its appropriate antecedent in the prior discourse. I therefore compared the

The development @discourse mapping processes 329

processing of anaphoric pronouns with anaphoric noun phrases in discourse contexts, where the correct interpretation of each type of anaphor could only be achieved if the listener established co-referentiality with the appro-

priate antecedent in the prior discourse. For this reason sequences of the following type were constructed : 9

(6a) The skater in the orange suit was our nephew. The skater fell on the ice and broke his leg...

(6b) The skater in the orange suit was our nephew. He fell on the ice and broke his leg...

(6~) The skater in the orange suit was our nephew.

(6dj Our nephew fell on the ice and broke his leg... The boy in the orange suit was our nephew. Our nephew fell on the ice and broke his leg...

Each sequence consists of a context sentence followed by a continuation sentence. Each of the continuation sentences contains a target word (ice) which can only be predictable if the listener knows that somebody skating is the subject of the continuation sentence. In condition (6a), the information that makes ,he target predictable is contained within the continuation sentence itself and therefore discourse mapping is not essential here. However, in conditions (6b) and (6~) the crucial predictability information is only present in the context sentence and must be indexed by the two types of anaphor. If five year olds find anaphors in general difficuit to process, then there should be no differen:e in the predictability of the target word in these two conditions, and in both cases the target should be less predictable than in (6a). However, if their difficulty is restricted to pronoun anaphors, then the target word should be less’ predictable in (6b) than in

9Dutch originals with literal T9rglish gloss (anaphor in italics):

(64 De schaatser met het oranje pak was onze neef (The skater with the orange suit was our nephew) De schuutrer vie1 op het i]s en brak zijn been...

(The skater fell on the ice and broke his leg...) 030 De schaatser met het oranje pak was onze neef

(The skater with the orange suit was our nephew) H(/ vie1 op het ijs en brak zijn been...

(He fell on the ice and broke his leg...) (6~) De schaatser met het oranje pak was onze neef

(The skater with the orange suit was our nrphew) Onze neefviel op het ijs en brak zijn been...

(Our nephew fell on the ice and broke his leg...) (6d) De jongen met het oranje pak was onze neef

(The boy with the orange suit was our nephew) Onzc neefviel op het ijs en brak zijn been... (Our nepirew fell on the ice and broke his leg...)

330 L. Komiwjevsky Tyler

(6~). Moreover, to the extent that anaphoric definite descriptions are successful anaphors, the predictability of the target in (6~) should be similar to that in (6a).

In contrast to the other 3 conditions, the context sentence in (6d) does not contain the relevant predictability information. Therefore, by comparing (6~) and (6d), which share the same anaphor in the continuation sentence, we can evaluate the contribution of discourse context to the on- line interpretation of the anaphor.

Method

Materials

I constructed 28 sets of 4 sentence-pairs, similar in structure to the example given above (6a-6d). Each sentence-pair consisted of a context sentence followed by a continuation sentence. Preceding each sentence-pair were 2-3 short sentences that provided a minimal discourse context for the interpretation of the test sentences. In conditions (6a), (6b) and (6c), the Mame context sentence is followed by one of three different continuation sentences, each of which contains the target word ice which can be predictable if the listener knows that the skater is the subject of the continuation sentence. The information which makes the target word predictable always occurs in subject position in the context sentence, while additional information about the same individual is given in object position. In half of the context sentences, this additional information takes the form of an attribute or property of the individual (e.g., that he is our nephew), and in the other half it takes the form of a person’s name (e.g., that the butcher in the village is called Mr. Jones).

The three continuation sentences differ in the way in which this information (which makes the target word predictable) can be brought to bear on the interpretation of the sentence. As explained earlier, the information is either contained within the continuation sentence itself (6a) or must be indexed in the discourse sentence by an anaphor ((6b) and (6~)).

Condition (6~) can be contrasted with (66). In both cases the anaphors in the continuation sentences are identical, but in one case (6~) the information that makes the target predictable (the skater) is mention.ed in the context sentence, whereas in the other (6d) it is not and therefore the target word cannot be predictable.

The materials were pre-tested on five year olds, using an auditory cloze procedure, to ensure that target words were predictable in conditions (6a)

The development of discourse mupping procesws 331

and (6~) but not in (6d). Predictability ratings for these 3 conditions were 87.5%, 73% and 3%, respectively. These ratings mean that the definite description, the skater, was sufficient to make the target word predictable whether it occurred in the continuation sentence ‘,tself (6a), or was merely mentioned in the context sentence and subsequently indexed by an anaphoric definite description in the continuati0.n sentence (6~). Further- more, when ,the skater was not mentioned in the context sentence (6d), the target word was clearly not predictable.

Target words were mispronounced towards the end of the first syllable by changing a single phoneme so that the word became a non-word in the language. Four versions of the materials were then constructed so that each child <would only hear one occurrence of each of the 28 target words. Each version contained 8 sentence-pairs in each of the 4 conditions, and 12 filler sentences pseudo-randomly dispersed among the test sentences.

The 4 versions of the materials were recorded by a native Dutch female reader, and timing pulses were then placed at the onset of each mispronounced phoneme,


The design and procedure were identical to those of Experiments One and Twco, and the same numbler of subjects of each of the 4 age-groups were tested. .

Subjects

The 120 children who took part in the experiment attended schools in and around the Nijmegen area. The 40 adult subjects were students at the Katholieke Univeristeit, Nijmegen, and they were paid for their participa- tion. None of these subjects had taken part in the other two experiments.


The first step was to replace missin.g and extreme reaction-times using the same procedure as in the earlier experiments. The overall percentage of replaced data was similar for the three groups of children- 11.7%, 11.8% and 9.7% for the five, seven and ten year olds, respectively. Only 4.3% of the adult data was replaced.

For the 3 groups of children the percentage of replaced data was equally divided between missing and extreme values. Of the missing reaction-times,

332 L. Komiwfevsky Tyler

the largest proportion of these fell in condition (dd). The percentage of occasions on which children failed to detect the mispronunciation in condition (6d) was 12.5%~~ 11.1% and 6.1% for the five, seven and ten year olds, respectively. Since the total number of missing responses in this condition was much smaller than in the comparable condition in Experiment One (i.e., condition (4)), it was not excluded from the statistical analyses. The extreme values which had to be replaced were evenly distributed across the four experimental conditions for each age-group.

The mean mispronunciation detection latencies for each age-group and condition are given in Table 4. Two analyses of variance were performed on the means of the raw data -one with subjects and one with items as the random variable-from which MinF’ ratios were derived.

As before, there was a significant main effect of Age (MinF’ (3,223) = 88.0, p C 0.001). Overall mean reaction times for the five, seven and ten year olds and adults were $07 msec, 688 msec, 558 msec and 404 msec, respectively.

Table 4. Experiment Three: Mean mispronunciation de tee tion Iatencies (msec).

Age-group Condition*

A B C D

5 year5 746 781 770 931 7 years 643 699 669 741

10 years 519 568 548 596 Adults 379 412 373 453

*Condition A = Repeated definite noun phrase + predictive context. Condition B = Unambiguous pronoun + predictive context. Condition C = Repeated property/name + predictive context. Condition D = Repeated property/name + non-predictive context.

The second main effect of Condition was also highly significant (MinF’ (3,187) = 14.45, p < 0.001). This reflected, first of all, the finding that responses in (6a), (6b) and (6~) were all significantly faster than those in th.e neutral context condition (6d) where the predictability information was not mentioned in the context sentence. Secondly, reaction-times to pronouns (6b) were slower than to definite repeated noun phrases (6a) (t = 2.43, df = 187, p < 0.01). Although the interaction of Age by Condition just failed to reach signiticance on the MinF’ statistic (MinF’ (9,661) = 1.754, p > O.OS), it was significant on both the subjects (F’ = 3.327, df = 9,468, p = 0.0006) and the items analysis (F* = 3.7082, df = 9,243, p =

The develqment of discourse mapping processes 333

0.0002)10. Some of the age-related differences between conditions emerge in the individual comparisons, which will now be described.

Definite descriptions: Proper names versus properties

The context sentence in conditions (6a), (6b) and (6~) contained either a proper name or a property in object position. This meant that the continuation sentences used in condition (6~) included two types of anaphoric definite descriptions -repeated properties (e.g., our nephew) and repeated proper names (e.g., Mr. Jones). In order to determine whether they were differentially effective as anaphoric devices, I analyzed each type of device separately. The results showed that there were no differences between them (F < l), and that both types of definite descriptions were equally good anaphoric devices.

Discourse mapping: anaphoric definite descriptions

Latencies were equally fast whether the target word was predictable on the .basis of sentence-internal information (6a) or information which could only be retrieved from the context (6~). The difference between these conditions was small for each group (25 msec, 27 msec, 29 msec and 7 msec for the five, seven and ten year olds and adults) and did not approach significance using planned orthogonal contrasts (Kirk, 1968).

There are two important aspects to this result. Firstly, it shows that from the age of five years listeners can successfully make the appropriate utterance-discourse links by means of anaphoric definite descriptions. l[n other words, the five year olds’ difficulties in Experiment One were not due to problems with the mapping of anaphors in general, but must instead be restricted to anaphoric pronouns.

Secondly, for the anaphors in condition (6~) to have successfully indexed the critical predictability information from the discourse, the two definite descriptions which were used to refer to the same individual in the context sentence in condition (6c)-that is, the skater ix~ subject position; our nephew in object position- must have been integrated into a unitled representation, which was then accessed by the anaphor in the continuation sentence, If such a representation had not been constructed, the anaphor in (6~) would only have indexed our nephew in the context sentence. In this case, ice would not have been predictable and reaction times in (6~)

“Since, on the basis of the earlier experiments, I had (I priori hypotheses of differences between conditions for different age-groups, it was not necessary to follow the Geiser-Greenhouse procedure for possible violations of the variance-covariance matrices (see Kirk, 1968, p. 263).

334 L. Komisnrjevsky ;rLler

would have been longer than those in (6a), and equal to those in (6d) where the skater was not mentioned in the context sentence.

Anaphoric pronouns

1 now turn to the effects of anaphoric pronouns in condition (6b). At first glance the results here seem rather surprising. Contrary to the outcome in the first experiment, five year olds’ performance on pronouns did not appear to be significantly impaired. Although they were 3s msec slower on pronouns than on repeated noun phrases (condition (6a)), this difference was not significant. On the other hand, all other age-groups were slower on pronouns than on repeated noun phrases. The differences here of 56 msec, 49 msec and 33 msec for the seven, ten year olds and adu!ts, respectively, were all significant at thz 0.05 level or beyond using planned orthogonal contrasts (Kirk, 1968).

This set of results can be explained in terms of the discourse properties of the stimulus materials used in the experiment. As mentioned earlier, the materia’ls here differed from those in Experiments One and Two in that each sentence-pair was preceded by two or three sentences, thus making short stories. A post-hoc analysis of these stories showed that in 16 out of 28 cases, the referent of the pronoun in the continuation sentence was not clearly the main topic, or theme, of the discourse, so that various other antecedents could easily have been pronominalised in subject position in the continuation sentence. However, for the other 12 stories, the referent of the pronoun was clearly the topic of the discourse, and pronominalising any other antecedent at that point would have violated discourse constraints.

Analysing these two sets of items separately, I found that the three older age-groups were consistently slower on pronouns whether or not the antecedent was discourse topic. The five year olds presented a rather different picture. When the antecedent of the anaphor was not the main discourse topic, reaction-times to pronouns were 57 msec slower than to anaphoric noun phrases (this result is analogous to the outcome in Experiment One where there was also no clear discourse topic). However, when the referent of the pronoun was clearly the discourse topic, then they were not at all slower to respond to pronouns. Pronouns in this case were only 6 msec slower th,an the anaphoric noun phrases in (ba).

The five year olds’ dissociation here can be accommodated quite readily by certain recent proposals made by Karmiloff-Smith (1980). She argued that when children produce connected discourse, they observe what she terms the ‘thematic subject constraint’, which roughly corresponds to the di.scourse topic. This means that children select a thematic subject for the

The developmen r of discourse mapping procesxs 335

discourse and then keep all subsequent utterance-initial slots for reference to the thematic subject. Moreover, all references to the thematic subject are made by pronouns and zero anaphors. An important point here is that whereas 5-6 year olds adhere strongly to the principle that uterrance-initial slots must be reserved for reference to the thematic subject, this ccdnstraint is relaxed as children get older.

This proposal has clear implications for the present results. If, as Karmiloff-Smith has suggested, five year olds in particular expect a pronoun in utterance-initial position to refer to the thematic subject of the discourse, then, when it does not, their ability to correctly interpret the pronoun should be impaired. This differential difficulty -with pronouns in utterance- initial position as a function of the discourse status of the antecedent is exactly what was found in the present experiment. This result, moreover, has the more general implication that, at least for language comprehension, young children arc more dependent on the thematic structure of a discourse than are older children.

What remains to be explained here is why the 3 older age-groups were slower to respond to pronouns. Although there is no conclusive answer. one reasonable possibility concerns the number of pote:?tial referents for the pronoun. Unlike the first experiment, the lead-in sentences in the present set of stimuli introduced up to four referents other than those mentioned in the context sentence of each sentence-pair. It is quite possible that when there are a large number of potential antecedents present in the discourse, listeners have greater difficulty in assigning pronominal reference than when the number of potential antecedents is small.

Contextual effects on immediate processing

For all age-groups, the detection of mispronunciations was facilitated by the presence of a prior constraining context. The releva.nt result here is the difference between conditions (6~) and (6d), which measures the difference between latencies as a function of the presence (6~) or absence (6d) of a constraining discourse context. In all age-groups latencies in condition (6~) were significantly faster than those in condition (6d).

However, the degree of facilitation derived from the context sentence clearly changes during development, since the difference between the two conditions was more than twice as large for the five year olds as compared to any other age-group (161 msec, 72 msec, 48 msec and 80 msec for the five, seven and ten year olds and adults). Thus, for the youngest children the processes involved in detecting a mispronunciation are considerably slowed down when there is no constraining prior context. _+ similar finding has been

336 L. Komisarjevsky Tyler

reported by Cole and Perfetti (1980) with children aged between 7-l 1

JWES.

This result clearly implies that for five year olds in particular the word- by-word processing of the input is strongly dependent upon the relationship between the incoming utterance and its discourse context.

General discussion

The aim of the three experiments reported here was to trace the development of anaphoric mapping processes after the age of five years. The specific questions addressed in the experiments were whether children can integrate utterances into a discourse by means of anaphoric devices; whether some devices are developmentally more effective anaphors than others; and what is the relative contribution of different sources of constraint to anaphoric mapping processes? Since the five year olds’ performance was different from that of the older children and adults, it will be discussed separately.

Five year olds

Taken together, the experiments reveal that at least some of the processes involved in anaphoric mapping are clearly mastered by the age of five. By that age definite repeated noun phrases and proper names function equally well as anaphors and succeed in integrating consecutive utterances into a discourse. The five year olds did show some difficulty in correctly interpreting general term anaphors, but this was true for the older age-groups as well.

The main distinction between the five year olds and older subjects tvas with respect to anaphoric pronouns -with five year olds finding these more difficult under some circumstances than older children and adults. There seemed to be two reasons for this. Firstly, the five year olds were unable to fully exploit the lexical information carried by pronouns. Although they were beginning to be able to use gender markings by that age, the consistently correct use of number was delayed until about seven years of age. This is consistent with the comprehension data of Scholes (1981) and Wykes (1978), while Karmiloff-Smith’s (1980) work suggests that the anaphoric use of both of these lexical cues in production does not emerge until about seven.

A second factor which emerged in the experiments as influencing five year olds’ difficulties with pronouns was their adherence to the ‘thematic subject constraint’. They had particular difficulty with pronouns when the discourse

The development of discourse nlapping processes 337

did not provide a clear thematic subject. Striking evidence of this appeared in Experiment Three where a pronoun was a march more effective anaphoric device in those stories in which the discourse provided a clear topic.

Further support for the importance of the thematic subject is shown by the finding that the existence of a prominent, thematic subject seems to affect the point during processing at which the pronoun brings the properties of the antecedent into the subsequent processing of the utterance. When the discourse has a clear thematic subject, then the properties of the antecedent are brought into play soon after the pronoun is heard, but this process seems to be delayed when a thematic subject is not clearly established.

The critical data here consist of a comparison of condition (4) in Exper- iment One with condition (Sd) in Experiment Two. The relevant examples are repeated below (with anaphors in italics).

(4) Mother saw the postman coming from a distance. Mother brought a letter from Uncle Charles who...

(Sd) Every now and then, the princess goes to see the old shepherd. S?re takes good care of the sheep and...

In both sets of materials there was only a single context sentence introducing a number of potential referents, none of which was clearly marked as thematic subject. Therefore, ary one of them could lhave been pronominalised in subject position in the continuation sentence. In both conditions the target word was pragmatically implausible given the properties predicated of the antecedent of the anaphor. The only difference between the two conditions was that in condition (4) the anaphor in the continuation sentence was a repeated noun phrase (either a proper name as in the example abcve, or a detinite noun phrase), whereas in condition (Sd) it was an UT. ambiguous personal pronoun.

l’he important point here is that tive year olds were extremeljr disturbed by the implausibility in the noun phrase condition (4)-where the anaphor clearly designated a unique antecedent in the discourse-but showed no effect at all of the implausibility in the pronoun condition (Sd). In contrast, older children and adults were affected in both the noun phrase an.d the pronoun conditions. If, for the five year olds, the presence of a pronoun had functioned to immediately index a unique referent, then their performance should have been as poor in the pronoun case as in the noun phrase case. Since it was not, this suggests that pronominal reference had not been definitely assigned by the time the children heard the mispronounced word. Older children and adults, in contrast, were disturbed in the pronoun case, implying that they must have assigned reference by the time they heard the target.

338 L, Komisarjevsky Tyler

Taken together, what the data from these comprehension experiments and Karmiloff-Smith’s production work suggests is that the thematic structure of the discourse plays a primary role for five year olds in determining the functional role assigned to an anaphoric pronoun. When the discourse provides a clear thematic subject, then the pronoun functions as an “empty’ element in that its lexical properties are not used as the basis for a match with the lexical properties of potential antecedents. In fact, it is not clear that any sort of matching process is ever attempted in such conditions, or that the pronoun functions as a referential device at all. Rather, it seems that the pronoun is interpreted as a device which merely maintains the thematic subject in the utterance in which it appears. In Karmiloff-Smith’s terms, the pronoun is taken as the ‘default case’ for the thematic subject. Thus, the pronoun is both serving to maintain the thematic subject, and functionin[- as a place-holder which contributes towards the cohesion of a discourse by providing structural links between utterances.

What we now have to consider is what happens when five year olds encounter a pronoun in discourse contexts where a thematic subject has not yet emerged. One possibility is that in such conditions the pronoun functions referentially. That is, it is used to index a specific location in the child’s mental representation of the discourse. Under these circumstances five year olds will need to take more advantage of other potential sources of constraint--such as the pragmatic plausibility of potential antecedents and the lexical properties of pronouns. The data show that the five year olds have no difficulty with pragmatic plausibility, therefore one can assume that it is their problem in using lexical information which contributes towards the increased difficulty of pronominal reference w!ien a discourse does n’ot contain a prominent thematic subject.

Older children and adults

The first point to mention is that there is no evidence of any developmental change in the processes underlying anaphoric mapping in comprehension after the age of seven. In these experiments, seven and ten year olds behaved essentially as adults.

By the age of seven, pronouns and different kinds of repeated noun phrases (e.g., definite noun phrases and nominals) are effective anaphoric devices, functioning to bring the properties of antecedents in the prior discourse into the current processing of the utterance. By this age, then, children can successfully integrate a sequence of utterances into a coherent discourse by means of anaphoric mapping processes.

The development of discourse mapphg processes 339

In assigning reference to a pronoun, older children, unlike five year olds, use a variety of different sources of information. The lexical properties of pronouns, the pragmatic plausibility of potential antecedents and the thematic structure of the discourse all contribute towards the selection of a referent. Moreover, there was no suggestion in the present data that the thematic structure of the discourse plays as d0minac.t a role for older children as it does for five year olds. Recall that for older children and adults in Experiment Three, latencies to utterances containing pronouns did not change as a function of the prominence of a thematic subject in the discourse.

Other research supports this general picture (Tyler et al., 1982). In this experiment, which was carried out with adults, subjects heard short stories followed by a continuation sentence, similar to the stories used in the experiments described earlier. Three sources of constraint on pronominal co-reference were contrasted with each other. These were: the discourse focus, the lexical information carried by the pronoun and thl: pragmatic plausibility of the verb in the continuation sentence rt:lative to different potential antecedents. The results showed, first, that each of the three factors played an immediate role in assigning pronominal refererce. Second, the discourse focus was the ‘weakest’ factor when pitted against the other two. However, the effects of the lexical properties of the pronoun and pragmatic inference were approximately equal in strength, and tended to cancel each other out when the materials brought them into conflict.

The general picture which emerges from all of this research is that the listener’s mental representation of the discourse is organised in such a way that certain mental knowledge structures-corresponding to potential discourse antecedents -will be preferentially accessible for the processing of the subsequent input. The presence of a pronoun alerts the listener to the existence of an anaphor in the speech. Given the antecedents previously mentioned, these will be assessed for their pragmatic plausibility-irrcspec- tive of whether the pronoun is ambiguous or unambiguous. In this frame- work, the function of the pronoun is not to select, in an all-or-none fashion, a single antecedent, but rather to give a positive weighting to the antecedent that is consistent with its lexical properties. Thus, no one source of information is necessarily, by itself, sufficient to determine co-reference, but all contribute to the weighting in favour of an antecedent.

What the present series of studies show is that it is just this weighing UP of different sources of information which is still developing in the five year old. The interpretation of a pronoun in these children is primarily driven either by discourse structural considerations or by deictic lexical infonna- tion, and what they yet have to learn is how to exploit all of the constraints which are available.

340 L. Komisu@evsky Tyler

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University of Sussex, England.

On dtudic chez Ies enfants la ma&e c?‘int<grer Pant&dent de differents types d’anaphora dans I’intcrpretation dcs 6nonces et le type d’indices utilises pour cet ‘c tiche. La recherche portc sur Ic traitement en t,cmps rOeI de trois types c!.e mdcanismes anaphoriq ACS: syntagmes nominaus, repdtes. termcs gt%raux et pronoms anaphoriquer. A cinq ans les enfants maitrisent bien en general lcs proces- sus de projection anaphorique, cependant Ie terrnc gin&al d’anayl: ,re est trouve difflcile 1 interprdter par tous Its groupes d’iige (S-7 -10 ans 4 adultcs). Les principales differences au tours du divelop- pement portent sur le traitement des pronoms anaphoriques. A 5 ans les enfants interpretcnt d’abord les pronoms comme dcs mdcanismes maintenant le sujet thdmatique du discours; en l’absence de celui-ci ils se rapportcnt principalcmcnt i la plausibilit@ pragmatiquc pour assigner la co-rdfdrcncc pronominale. Plus tard, les enfants utilisent les proprietis lexicales des pronoms et les trois sources d’information-lexicale. inf&ence pragmatique et structure thematiquc du discours-contribucnt pour affecter la rbference $ un pronom.

the development of discourse mapping processes: the on...

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