stemorv & Cognition1976. Vol. 4 (1).6-10

The storage of physical and name propertiesin short-term visual memory

ROBERT A. REEVEUniversity of Sydney, Sydney. New South Wales, Australia :;006

andRALPH HALL

University ofNell' South Wales. Kensington, Australia :;0]]

Two experiments investigated the hypothesis that short-term visual memory is based primarily onphysical features of the visual input. Subjects were required to recall visually presented figures or thenames of those figures presented either visually or aurally at a number of different retention intervals.Subjects shadowed words during the retention interval presented aurally in Experiment I and visually inExperiment II. In both experiments, figures were recalled better than names and no differences in recallof names were found due to presentation modality. Recall of both names conditions showed a steadydecline across retention intervals whereas recall of figures remained at a relatively high level. Thesefindings were interpreted as providing further support for the existence of short-term visual memory notsubject to auditory recoding and based primarily on physical features of the input. It was suggested thatsuch visual memory is limited in capacity so that input exceeding this capacity is recoded into anauditory-verbal-linguistic form.

1 The persistence of short-term memory for visualinformation has been demonstrated in a number ofstudies (e.g., Kroll, 1972: Kroll, Parks, Parkinson,Bieber. & Johnson, 1970; Parkinson, 1972; Parkinson,Parks, & Kroll, 1971). Evidence that the storage is of avisual nature was provided by the finding that a singleletter (Kroll et al., 1970), and four letters (Parkinson,1972), showed less forgetting if presented visually thanif presented aurally when subjects shadowed aurallypresented material during the retention interval. Inaddition, Kroll (1972) and Parkinson et al. (1971) foundthat shadowing phonemically similar material during theretention interval interfered with recall of a letterpresented aurally, but not with one presented visually.

Hall, Swane, and Jenkins (1973) maintained that suchshort-term visual storage was based on the physical asopposed to the auditory-verbal-linguistic features of theinput. They found that visually presente d geometricfigures were recalled better than the visually presentednames of those figures when subjects were required toshadow unrelated words during the retention interval.Hall et al. (1973) argued that this provided evidence thatphysical properties are held in a nonverbal visualmemory not subject to interference fromauditory-verbal-linguistic rnemc 'Y. The present studywas designed to further investigate this hypothesis,especially in the light of Parkinson's (1972) finding thatfour letters can be held in a visual memory store notsubject to interference from an auditory shadowing task.In particular. it is argued that if names of shapespresented visually are transfonned into ana uditory-verbal-linguistic code then the retention

Requests for reprints should be addressed to the first author.now at the School of Behavioural Sciences. MacquarieUniversity. North Rvde , New South Wales. Australia 2113.

characteristics of material should be similar to that ofthe same names presented aurally, at least over the rangeof retention intervals beyond the duration of echoicmemory. This hypothesis was investigated in bothexperiments of the study.

In Experiment I different groups of subjects werepresented with a single slide containing either geometricfigures, the names of those figures. or were presentedaurally with the figures' names. Subjects were thenrequired to shadow aurally presented unrelated wordsduring the retention interval. It was predicted, in linewith the findings of Hall et al. (1973), that thegeometric figures should show little, if any, retentionloss while the two name groups should show similarmarked retention losses over the retention intervals used.

Experiment II was a replication of Experiment I withthe exception that the shadow task was presentedvisually. This was included to determine whether thevisual storage was dependent critically on theinterpolated task being auditory in nature. If "physical"storage is more efficient when subjects are required to"process" other materials in an auditory fashion then itmight reasonably be asked what the effect would be of alimited amount of visual processing of other materials on"physically" stored material. The qualification "limitedamount of visual processing" seems necessary since,although the intervening task in the experiment is visualin nature, a priori it would seem to require the sametype of processing as in Experiment I, i.e., subjects arerequired to repeat words out loud as they see or hearthem. On these grounds it was predicted that both taskswould interfere with memory material in a similar way.

EXPERIMENT IMethod

Forty-five first-year undergraduate students in psychology at

6

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Figure 1. Proportion of correct recall responses over retentionintervals for Experiment I.

the University of Sydney served as subjects, participation inexperiments being part of the course requirement. They wereassigned randomly to three groups, 15 subjects per group, withthe groups differing in the nature of the to-be-rememberedmaterial. Group VS received slides of geometric figures;Group VN received slides of the names of those figures; andGroup AN received the figure names aurally. The figures wereconstructed from four dimensions, the dimensions and valuesbeing: shape (square, circle, or triangle), number of figures (twoor three), color (black or white), and size (large or small).Twenty-four slides were obtained by combining all the aboveattributes. A second set of 24 slides contained the four wordsnecessary to name each of the figures displayed in the naturalreading order, i.e., number, followed by size, followed by color,followed by form, This presentation order was the same for theauditory memory material. This was recorded in a male voice soas to clearly distinguish it from material to be shadowed, whichwas recorded in a female voice. The presentation time of thememory material was 1.5 sec in all conditions based on the timeneeded for aural presentation for Group AN. A 1000-Hz tonewas sounded 2 sec before presentation of memory material,again immediately prior to presentation, and also immediatelyfollowing presentation.

Visual material was projected onto a screen on the wall of thelaboratory by means of a manual slide projector controlled by adecade interval timer. Aural material was prerecorded on aHanimex twin track tape recorder.

The words to be shadowed were two-syllable words chosenfrom Australian daily newspapers on the assumption that thesewords were more likely to conform to Australian norms andusage. They were presented at a rate of two words per secondover stereo headphones to the seated subject.

Subjects first completed 10 practice trials to accustom themto the shadowing task. A single random order of the practiceshadowed lists was used for all subjects. The rust 4 of theseinvolved shadowing only and consisted of 32-word lists. Thenext 6 practice trials included presentation 'of memory materialaurally in Group AN and visually in groups VS and VN. Thememory material consisted of single digits for the first 3 suchpractice trials and letters for the next 3 where the letters couldvary in size and number. The subject was instructed tocommence shadowing immediately following offset of thememory material and to be as accurate as possible in theshadowing task. The end of the shadowing list was marked by a1000-Hz tone, after which the subject was instructed to writedown the memory material, guessing where necessary.

SHORT-TERM VISUAL MEMORY 7

Following these practice trials, each subject received 24experimental trials composed of 6 trials at each of four retentionintervals, the intervals. being 1, 5, 10, and 20 sec. The order inwhich retention intervals were assigned to the 24 experimentaltrials was random, subject to the constraint that anyoneretention interval did not occur on more than 2 successive trials.A single random order of the shadowed lists and associatedmemory material was used for all subjects. The subjects wereinformed of the attribute-value composition of the memorymaterial and, as in the practice trials, all subjects were requiredto write their responses on a slip of paper and hand it to theexperimenter. All experimental trials were separated by arandom time interval between 45 and 70 sec to minimizebuild-up of proactive inhibition (Kincaid & Wickens, 1970).

ResultsTo insure all groups had received an equivalent level

of performance in shadowing, a one-way analysis ofvariance was carried out on the arcsine transformedproportions of words correctly shadowed over Trials 24.No significant differences were found among the groups(F = 0.31, df= 2, 42, p> .05) which means that allgroups were equated for shadowing performance.However, a significant difference was obtained on theexperimental trials (F= 14.9, df=2,42,p< .00l).Posthoc Scheffe tests on the means revealed that thedifference was due to poorer shadowing inCondition AN (73% correct) than in the otherconditions (87% and 84% for conditions VN and VS,respectively).

Recall performance of each group is shown inFigure 1.

In counting the recall errors for the experimentaltrials each attribute was scored separately, so that a totalof four errors was possible on each trial. A square roottransformation of the number of errors at each of thelongest three retention intervals was then subjected to atwo-way analysis of variance. The shortest retentioninterval was deleted from this analysis due to the almostperfect recall in all groups. This interval was includedsimply to insure all memory material is equally perceivedin the different memory modalities (Kroll et a1.. 1(70).

The square root transformation (x' =Vi +VX+l) wascarried out as there was some tendency for cell meansand variances to be correlated (Winer, 1971, P. 400).The results of this analysis showed that the main effectfor retention intervals reached significance (F = 33.8,df = 1, 42, P < .00 I) (standard error = .82), with recallshowing a steady decline with increasing retentionintervals for all groups. There was no significantinteraction between groups across retention intervals(F = 0.54, df = 4, 84, p > .05). Instead of testing themain effect for between groups, two planned contrastswere set up in order to test the predictions moredirectly. The first compared Groups VN and AN. Nosignificant difference was obtained (F = 2.5, df = I, 42,p > .05). The second compared Group VS with theother two Groups combined. Group VS showed betterrecall than Groups VN and AN (F = 22.8, df= 1,42,P < .00l).

8 REEVE AND HALL

DiscussionThe findings in this experiment support the

hypothesis that visual short-term memory is basedprimarily on the physical properties of a visuallypresented stimulus as recall of figures was superior torecall of the namesof those figures both when they werepresented visually and aurally. The finding that recall offigure names was no different when presented visuallythan when presented aurally is consistent with thehypothesis that these are stored in the same manner.That both suffered interference from the shadowingtaskwhereas the figures suffered very little interferencesuggests that both are stored in anauditory-verbal-linguistic code. This conclusion may,however, need to be revised in view of the fact that theshadowing performance of subjects in Group AN waspoorer than that of subjects in Group VN. This pointwillbe taken up further in the general discussion.

EXPERIMENT II

MethodExperiment II was the same in all respects as Experiment I

with the exception that the shadowing task was visual in natureand there were fewer practice trials.

The visual material for shadowing was presented using aTelefunken magnetophon 300TS half-frame filmstrip projectorwhich consists of a combined continuous projector and 2-tracktape recorder unit. The projector and tape recorder could besynchronized by recording pulses on one track of the tape.

A continuous 35-mm film strip was made up using the samewords for shadowing material as in Experiment 1. Thepresentation rate was three words/sec. It was found in apreliminary studty that subjects had no difficulty shadowingaccurately at the two words/sec rate used in auditory shadowing(Experiment O. The faster presentation rate for visual materialgave approximately the same error rate as in Experiment 1. Theincreased presentation rate necessitated the presentation of morewords at each retention interval thanin Experiment 1.The samewords were used in both experiments although in Experiment IIsome words were used twice.

Blank black frames were spliced into the film strip to separatethe trials and allow presentation of a visual slide inConditions 'IS and VN. The same set of slides was used in thisexperiment as in Experiment I. Tones were also presented as inExperiment 1.

A further 45 first-year undergraduate students in psychologyserved as subjects with 15 being randomly assigned to each ofthree groups: VS, VN, and AN as in Experiment 1.

ResultsNo significant differences between groups were found

in shadowing during practice trials (F = 0.38, df= 2, 42,P > .05). nor during the experimental trials (F = 0.70,df= 2,42, r-> .05). Thus, in contrast to Experiment I,shadowing was not affected by presentation modality ofthe memory material.

Recall performance is shown in Figure 2. Analysis ofvariance of the square root transformed number oferrors at each of the longest three retention intervalsrevealed a significant drop in recall across retentionintervals (F = ; 1.2, df = 2, 84, P < .001) (standard

error = .99), but no significant interaction betweengroups across retention intervals (F = 0.15, df = 4, 84,p > .05). Groups VN and AN did not differ significantly,(F = 0.18, df = I, 42, p > .05), whereas Group VSshowed better recall than Groups VN and AN combined(F = 13.96, df = 1,42, P < .001).

DiscussionThe results of this experiment are consistent with

those of Experiment I. Figures were recalled better thannames, both when the latter were presented visually andaurally, and recall of names was not affected bymodality of presentation of those names.

Visual shadowing was used in this experiment to testthe hypothesis that visual short-term memory does notdepend critically on interveningmaterial being presentedin modalities other than visual. The findings confirmedthis hypothesis. That is, it is the act of repeating wordswhich causes interference in the case of recall of thefigure names, not the input modality.

Unl ike Experiment I, analysis of shadowingperformance on the experimental trials shows thatpresentation modality of memory material did not affectshadowing performance. It can thus be asserted moreconfidently in the present experiment that names offigures are stored in a similar manner, i.e. in anauditory-verbal-linguistic code.

GENERAL DISCUSSION

The findings in both experiments provide support forthe hypothesis that visual short-term memory is basedprimarily on physical properties of the input. Four-worddescriptions are apparently recoded into anauditory-verbal-linguistic code even when presentedvisually. This finding would seem at variance with

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Figure 2. Proportion of correct recall responses over retentionintervals for Experiment II.

studies which have compared visual with auditorymemory letters. The finding that four-word visualdescriptions of figures are not retained as well as theactual figures is suggestive of the fact that visualshort-term memory, as well as being based on physicalproperties, may be limited in capacity. That is, it mayonly be able to hold a limited amount of visualinformation at anyone time. If this limited caoacitvhypothesis is true then it would help to explaindiscrepancies in previous findings.

Conrad (1964), Dale and Gregory (1966), andSperling (1967), among others, have demonstrated thatacoustic confusions occurred even when memory letterswere presented visually. Typically, these experimentshave presented six to eight items for recall. However,experimenters who claim to have demonstrated theexistence of short-term visual memory have typicallypresented between one and four items for recall (e.g.,Kroll et al., 1970; Parkinson, 1972; Scarborough, 1972)and have not found acoustic confusions. This differencewould suggest that with memory letters the short-termmemory system can hold a maximum of approximatelyfive items. After this maximum has been passed itemsare recoded into an auditory or acoustic form and arethus likely to show acoustic confusion on recall. On thishypothesis it should also be possible to overload thememory capacity by presenting greater numbers ofvarieties of figures for recall.

One problem associated with postulating a visualshort-term memory which is limited in capacity lies inaccounting for the continuous visual recognitionmemory type studies (e.g., Kirsner, 1973) which suggestthat many items can be held in visual memory. Thispossible anomaly may be tied to the paradigm used inthe investigation of visual memory. Just how much thisis the case is a matter for further empiricalinvestigation.

The finding that visual short-term memory wasunaffected by the modality of presentation of theshadowing material does not mean that interpolatedvisual material will not interfere with such memory. It ispossible that material with similarphysicalproperties tothe material to be recalled will result in retention loss.This possibility seems worthy of investigation in viewofthe present findings regarding visual shadowing.

It seems a reasonable working hypothesis to suggestthat when the same memory material is present indifferent ways, resulting in a similarrecall decrement forthe two types of material following an interveningtask,that the decrement is due to the same kind ofinterference and/or storage. It is a suggestion, however,which should be regarded with some degree of caution,as evidenced by the shadowing performances inExperiment I.

In Experiment I, although there was no significantdifference in recall between Groups AN and VN, therewas significant difference in shadowing performance

SHORT-TERM VISUAL MEMORY 9

between these two groups. Group VN shadowedsignificantly better than Group AN. The finding thatshadowing performance was affected by presentationmodality of the memory material in Experiment I couldmean either that shadowing differences were unrelatedto memory storage of the names or that auralpresentation of the shadowing material caused someparticular difficulty in storing the aurally presentedmemory material over and above the act of repeating thematerial. While the present study was not ableunequivocally to distinguish between these twopossibilities, or other interpretations, postexperimentalprotocols do provide some weak evidence for a possibleinterpretation. After the experiment, subjects wereasked how they had retained the memory material. InExperiment I, where the presentation rate of shadowedmaterial was two words per second, subjects' responses,independent of group condition, separated into twodistinct categories; they either claimed to have"visualized" or to have "verbalized" the memorymaterial. This breakdown showed that all SUbjects withina group who claimed to have "visualized" did betterthan all subjects who claimed to have "verbalized."However, in Experiment II, where the presentation rateof shadowed material was three words per second, nosuch group independent division of subjects' responseswas noted. That is, all subjects in Group VS claimed tohave "visualized," while all subjects in Groups VN andAN claimed to have "verbalized." This weak findingwould seem to imply that in Experiment I, somesubjects were able to further process the memorymaterial to a more efficient type of storage whileshadowing, resulting in a slight decrement in shadowingperformance. Although this essentially subjectiveanalysis does offer a partial solution to the problem ofpoorer shadowing in Experiment I for Group AN, ifit iscorrect it would seem to raisea number of problems forstudies using a similar paradigm to the presentexperiment, the most notable beingthe exact nature andeffect of subjects' "control processes" given thedifferent types of memory materials frequently used inconjunction with the different types of interveningtasks.

REFERENCES

Conrad, R. Acoustic confusion and immediate memory. BrttimJoumal of PsYchology, 1964. 65, 76-84.

Dale, H. C. A•• 8< Gregory, M. Evidence of semantic codlnc inshort-term memory. Psychonomic Science. 1966.5,76-76.

Hall. R .• Swane. D. 8< Jenkins, R. A. Memory for physical andsemantic features of visual material in a shadowinll task.Joumal of Experimental PsYcholollY, 1973, 100, 426-428.

Kincaid, J. P.• 8< Wickens. D. D. Temporal aradient of releasef.rom proactive inhibition. Joumal of ExperimentalPsYchology. 1970,86,313-316.

Kirsner, K. An analysis of the visual component in recoanittoDmemory for verbal stimuli. Memory 8< CognitiOD, 1973 1449-453. ' ,

Kroll. N. E. Short-term memory and the nature of interferencefrom concurrent sh adowing, Quarterly Journal ofExperimental PsYchology, 1972, 24,414-419.

10 REEVE AND HALL

Kroll, N. E.. Parks, T., Parkinson, S. R., Bieber, S. L., &<Johnson, A. L. Short-term memory while shadowing: Recallof visually and aurally presented letters. Joumal ofExperimental Psychology, 1970, 85, 220-224.

Parkinson, S. R. Short-term memory while shadowing: Multipleitem recall of visually and or aurally presented letters. Journalof Experimental PsYchology, 1972, 92,256-265.

Parkinson, S. R.. Parks, T., & Kroll, N. E. A. Visual and auditoryshort-term memory: The effects of phonemically similarauditory shadow material during the retention interval.Journalof Experimental Psv chologv, 1971, 87, 274-280.

Scarborough, D. L. Stimulus modality effects on forgetting inshort-term memory. Joumal of Experimental PsYchololY,1972,95,285-289.

Sperling, G. Successive approximations to a model for short-termmemory. Acta PsYchologica, 1967, 27, 285-292.

Winer, B. J. Statisticol principle. in experimental de.itn. 2nd Ed.New York: McGraw-HUl, 1971.

(Received for publication October 18,1974.Revision received March 17,1975.)