ABSTRACTMETAPHOR COMPREHENSION IN RIGHT BRAIN-DAMAGED SUBJECTS WITH VISUO-VERBAL AND

VERBAL MATERIAL: A DISSOCIATION (RE)CONSIDERED

M. Cristina Rinaldi 1, Paola Marangolo2 and Francesca Baldassarri1

(1Dipartimento di Psicologia, Università “La Sapienza”, Roma, Italy; 2Fondazione I.R.R.C.S. Santa Lucia, Roma, Italy)

INTRODUCTION

The right hemisphere plays a major role in the regulation of the pragmaticdimension of verbal communication. In particular, studies on normal subjects(Bottini et al., 1994; Pynte et al., 1996; Faust and Weisper, 2000) indicate adirect involvement of the right hemisphere in metaphorical language processing.

Winner and Gardner (1977), who first investigated metaphor comprehension inbrain-damaged subjects, found a dissociation in right-hemisphere damaged (RHD)subjects between a pictorial and a verbal condition: while in the pictorial conditionRHD subjects tended to interpret the metaphors literally (choosing the literalpicture), when requested to explain the same metaphors verbally they chose thecorrect metaphorical interpretation. Unfortunately, the authors could not rule outthat the result obtained in the pictorial condition was due to the spatial and perceptualproblems typical of RHD subjects (Heilman et al., 1983). Subsequent studiesinvestigating RHD subjects’ tendency to literalness with exclusively verbal materialcame to contradictory results (Brownell et al., 1984; Tompkins, 1990).

Here we report the results from two tests on metaphor comprehension, avisuo-verbal and a verbal test, carried out by RHD and control subjects.

MATERIALS AND METHODS

Subjects

Fifty RHD subjects and 39 control subjects matched for age and education were tested.

Neuropsychological Examination

Each RHD subject underwent a Neuropsychological Examination which classified 29/50subjects as having personal neglect syndrome, 9/50 subjects as defective in logic reasoningon visuo-spatial material, 5/50 subjects as defective in visuo-perceptual integration. Of the50 subjects, 18 had a constructive apraxia deficit. No subject was classified as aphasic. Sixof the 50 subjects had a slightly impaired auditory verbal comprehension.

Stimuli 1) Visuo-verbal Test

The test consisted of 20 sentences including a simple metaphorical expression andfurther verbal elements creating a context favoring a metaphorical interpretation. Each

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sentence was matched with a table containing 4 black and white drawings representingrespectively the correct metaphorical meaning, the literal meaning, an incorrect alternativemetaphorical meaning and an incorrect alternative literal meaning.

2) Verbal Test

The test consisted of 20 metaphorical sentences realized with the same criteria of thevisuo-verbal test. The metaphorical expressions differed from those of the visuo-verbal test.Each sentence was written on a card and matched with three sentences written on a differentcard and representing respectively the correct metaphorical meaning, the literal meaningand an incorrect control meaning which referred to aspects of both the literal and themetaphorical meaning.

In both tests, the metaphors used were common Italian metaphorical expressionsdetectable in any Italian dictionary; this kind of metaphors are more akin to idiomaticexpressions, defined by Cruse (1986) “dead metaphors” (syntactically frozen). Incomparison to new metaphors, frozen metaphors are processed more automatically. It shouldbe noted however that the pioneering study carried out by Winner and Gardner (1977) onthe comprehension of ‘metaphors’ used this same kind of metaphors.

Procedure

1) Visuo-verbal Test

The table with the four drawings was placed in front of the patient. The examiner readaloud the corresponding sentence and asked the patient to indicate the picture which bestrepresented the meaning of the sentence.

2) Verbal Test

The card with the metaphorical sentence was placed in front of the patient, and theexaminer read it aloud. Soon after, the second card with the possible interpretations wasplaced below the first card and the examiner read them aloud. The subject was asked tochoose the interpretation that best represented the meaning of the sentence.

RESULTS

1) Visuo-verbal Test

Respectively, RHD subjects gave 51.2% correct responses, 33.5% literalresponses, 7.1% metaphorical control responses, and 8.2% literal controlresponses. Control subjects gave 83% correct responses, 10.13% literalresponses, 2.95% metaphorical control responses, and 1.54% literal controlresponses (see Figure 1).

An ANOVA was carried out (factors: ‘subject group’, ‘type of response’).The main effect of factor ‘type of response’ was significant (p < .001). Theinteraction ‘type of response’ x ’subject group’ was also significant (p < .001):contrariwise to control subjects, when choosing the wrong response RHDsubjects tended to choose the literal response.

A different ANOVA was carried out to verify the influence of the aboveneuropsychological deficits respectively on the correct metaphorical and theincorrect literal responses of RHD subjects: none of the deficits considered hadany significant influence.

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2) Verbal Test

Respectively, RHD subjects gave 73% correct responses, 14,8% literalresponses and 2.95% control responses. Control subjects gave 92.05% correctresponses, 5% literal responses and 2.95% control responses.

An ANOVA was carried out (factors: ‘subject group’, ‘type of response’).The main effect of ‘type of response’ was significant (p < .001). The interaction‘type of response’x’subject group’ was also significant (p < .001): control andRHD subjects differed in the type of response given in the verbal test, but notendency to select the literal response when choosing the wrong answer wasevident in either group of subjects.

Visuo-verbal Test vs. Verbal Test: Comparative Results:a chi-square analysisshowed that RHD subjects’ total number of correct responses was significantlylower in the visuo-verbal than in the verbal test (p < .01). Moreover, a secondchi-square analysis showed that RHD subjects chose the incorrect literalresponse significantly more often in the visuo-verbal than in the verbal condition(p < .001). Finally, the correlation between the number of correct responses inthe two tests was significant (r = .60, p < .001).

Further observations:to exclude that a difference in performance might stemfrom a difference in the metaphors used in the two tests, at the end of theexperimental session the examiner asked for a verbal explanation of some of themetaphors presented in the visuo-verbal test. Interestingly, RHD subjects alwaysgave a correct metaphorical interpretation, although on the same item they couldchoose the incorrect literal picture.

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Fig. 1 – Mean number of correct and incorrect responses of control and RHD subjects at theVISUO-VERBAL TEST.

DISCUSSION

Our data confirm the presence of a dissociation in metaphorical processing ofRHD subjects with visuo-verbal and with verbal material, a dissociation first notedby Winner and Gardner (1977). RHD subjects not only chose the literal wrongresponse more often in the visuo-verbal than in the verbal condition, but also gavesignificantly more correct responses in the verbal than in the visuo-verbal test.

Our results rule out any causal influence of visuo-spatial and visuo-perceptual deficits in determining the bias towards the literal responses shownby RHD subjects in the visuo-verbal test.

Actually, the peculiarity of RHD subjects of processing metaphors literallywhen faced with visuo-verbal material has not been properly explained yet.

According to Huber (1990), a problem with pictured assessment of metaphorcomprehension arises from the difficulty in judging the plausibility of the foils:in fact, while the literal representation of the metaphor is univocal, severaldifferent situations can be used to represent the metaphorical meaning of asentence, so that an additional difficulty is given by having to consider theplausibility of many more than one possible situation versus the single literal one.

If so, this difficulty might be greater in the visuo-verbal (where there are fourpossible answers = situations) than in the verbal test (only three possibleanswers). This might account for the lower performance and the high frequencyof the wrong literal answers observed in the visuo-verbal test.

Anyway, also alternative explanations are possible. In our opinion, if thesame patients perform differently in the two experimental conditions, it might besomething in the conditions themselves which determines such difference. Thebasic difference between the two tests is that while the visuo-verbal test requiressubjects to process information from two different representational codes, thevisuo-spatial and the linguistic one, the verbal test involves the processing ofinformation coming from only the linguistic code.

Recent results suggest that the right hemisphere is directly involved in theintegration of information from different sensory modalities (Raji et al., 2000;Calvert et al., 2001). Both our tests involve two modalities of input, the auditoryand the visual sensory modality. As far as we know, until now there are nostudies suggesting that this integration could also involve different informationrepresentational systems at a more abstract level than the sensory level(information related to language with information related to vision). Wespeculate that a difficulty in integrating information coming from the visual andthe linguistic representational systems might be the responsible factor for thelower performance observed in RHD subjects on the visuo-verbal test. If this isthe case, the deficit observed in RHD subjects would not be specific tometaphors but would affect any task requiring the integration of informationrelated to different representational systems (in our case, language and space).

As to the specific bias observed towards the literal wrong response, Pynte et al.(1996) show that the literal meaning of a metaphor is anyway accessed even whenunrequired and incongruous with the context. So, if the correct metaphoricalinterpretation is not accessed due to a integration deficit, the subject might selectthe simultaneously activated literal interpretation.

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M. Cristina Rinaldi, Dipartimento di Biologia. Università “La Sapienza” Roma, Italy.

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