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Gestalt Closure and the Human Visual Evoked Cortical Potential William Z. Anthony

a b

& Jerry W. Lester

a b


Department of Psychology , University of Houston , USA b

Department of Psychiatry , Baylor College of Medicine , USA Published online: 06 Jul 2010.

To cite this article: William Z. Anthony & Jerry W. Lester (1978) Gestalt Closure and the Human Visual Evoked Cortical Potential, The Journal of General Psychology, 99:2, 243-249, DOI: 10.1080/00221309.1978.9710509 To link to this article:

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The Journal of G e w a l Psychology, 1978, 99, 243-249.

GESTALT CLOSURE AND THE HUMAN VISUAL EVOKED CORTICAL POTENTIAL* Department of Psychology, University of Houston; Department of Psychiatry, Baylor College of Medicine

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Previous research examined the relationship between perceptual psychological content and the human visual evoked cortical potential (VECP). Each study suffered a common methodological problem. The stimuli’s properties covaried with their perceptual-psychological content. To circumvent this problem, VECP’s were recorded before and after Ss (14 men and women) “closed” Gestalt figures. A small, consistent increase in amplitude was observed after figures were organized.

A. INTRODUCTION The present study will support the position that changes in perceptual organization alter the human visual evoked cortical potential (VECP). Although previous research suggests the presence of such a relationship, methodological difficulties have precluded firm interpretations of those findings. Lifshitz (4) studied the effects of “higher order” functioning on the VECP in man using a series of slides which included three different categories (indifferent scenic, repulsive medical, and nude female photographs). The VECP to the pictorial slides differed measurably from VECP’s to these same slides made nonassociational by defocusing, or to blank light flashes; the amplitude of the late component was larger for the focused slides. The VECP to the three different pictorial categories also differed, though not as markedly and were clearly replicable only for some Ss. These results should be interpreted cautiously, however, because of an inherent confounding of the stimuli’s physical parameters and the psychological-perceptual parameters. Beatty and Uttal(1) noted significant reduction of VECP amplitude as grouping of visual stimuli was increased. John, Herrington, and Sutton (3) noted differences in the late

* Received in the Editorial Office, Provincetown, Massachusetts, on August 19, 1977. Copyright, 1978, by The Journal Press. 243

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components of the VECP which depended on the perceptual forms presented. The potentials (a) differed for a blank visual field and one containing a geometric form; (b) differed for different geometric forms of equal area; (c) were similar for versions of the same geometric form of unequal area; and (d) differed for two printed words equated for total letter area. John, Herrington, and Sutton suggest that this was evidence that the waveform of VECP is not determined solely by the set of peripheral receptors which is stimulated, but it also reflects the perceptual content of the stimulus. Buchsbaum and Fedio (2) investigated the possibility of hemispheric differences in the VECP as a function of visual information using three groups of test material: three letter words, random dot patterns, and designs. The VECPs for verbal and nonverbal stimuli distinctively differed when recorded over the left hemisphere. Verbal stimuli generally resulted in shorter latencies. In their discussion, they noted that artifact due to eye movements was unlikely because of the short stimulus duration (40 msec) and the far posterior placement of the EEG leads (0102;10/20 system). Sandler and Schwartz (7) reported unspecified waveform changes associated with different organizations of ambiguous figures and a Gestalt closure figure. This study was significant in that the properties of the physical stimuli remained constant, and changes were still noted in the VECP as a function of perceptual organization. The authors suggested that these differences could possibly be accounted for by attentional factors, since different instructions were given at different points in the experiment. Excepting Sandler and Schwartz, these studies confounded the physical and psychological stimulus dimensions by having them covary. The present study specifies the effect on the VECP of varying the single psychological dimension described as perceptual organization, while holding the physical stimulus constant and controlling for attention by using a single set of instructions throughout. Changes in perceptual organization called Gestalt closure, although never adequately defined, may be thought of as a change in the perception of an unchanged physical structure which simplifies or organizes the character of the stimulus. Mooney (5) used such incomplete figures as invariant stimuli to produce Gestalt closure. It is hypothesized here that the amplitude of the VECP to such invariant incomplete figures would vary as a function of whether or not Gestalt closure had occurred. B.


1. Subjects and Stimuli

There were 14 Ss, nine males and five females, 19 to 33 years old. All Ss were naive with respect to the hypothesis to be tested.



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Twelve 35 mm slides of incomplete or Gestalt closure figures were presented to the Ss in a fixed sequence. An example of this type of figure is shown in Figure 1 , which may be seen as either a collection of simple elements or as a faucet in side view. An optical system presented the slide as a Maxwellian view field sub-tending a visual angle of 40' 38'. Each slide contained a central fixation point. Illumination through the system without a slide in position was measured and calculated as 42.7 trolands. 2.


Every second a 28 msec duration stimulus presentation, producing the evoked potentials, was created by interrupting the illumination to the slide with an episcotister driven by a variable speed motor. A monopolar recording system using an active electrode placement 1 cm above the inion on the midline, referenced to the right ear and grounded to the left ear, recorded evoked potentials which were averaged on an FT-1060Fabritek computer and plotted by an X-Yplotter.

FIGURE 1 MOONEY-TYPE FIGUREDEPICTINGA WATER FAUCETIN SIDE VIEW Faucet handle is at top center, spout is at lower left.



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Each S was fitted with a mouthpiece made by having an impression taken of his teeth in softened dental wax. After the electrodes were applied, S was escorted into the electrostatically shielded test chamber. S’s position was adjusted to the optical system by varying the mouthpiece location to produce the proper stimulus alignment and focusing. Gestalt closure was demonstrated by having S organize or “close” one incomplete figure slide. To help control for eye movements and attentional factors, S was instructed to fixate the constantly illuminated dot centered in each slide and to signal theEs when he recognized the subject of the slides by tapping on the table. These instructions applied to the period both before and after closure. To assure reliability in the VECP’s,64 flash presentations of each slide were made before closure and 64 presentations after closure. If S signalled before 64 presentations that he had closed the figure being presented, that slide was excluded from that S’s data. After 64 presentations, if the S had not previously reported closure, he was allowed to inspect the slide under continuous illumination until he could adequately describe the subject of the slide to E . Then 64 postclosure presentations for that slide were made. Although all Ss closed some slides before the 64 preclosure presentations were completed, no S closed more than six of 12 slides before the criterion. Two Ss were given more extensive presentations than the other Ss. These two viewed all of their slides for two sets of 64 presentations preclosure trials and for two sets of 64 presentations postclosure trials. They had a total of four sets totalling 256 presentations of each slide. Four other Ss viewed each of their slides for an additional 64 presentations postclosure. These additional presentations failed to show any systematic effect due to sequence or number of presentations.

C . RESULTS The critical test for this study was a comparison between the amplitude of the VECP before closure and the amplitude of the VECP after closure. The results for all completed slides for a given S were averaged to give a preclosure and a postclosure amplitude measure. The major effect of Gestalt closure on the VECP was a small but consistent increase in amplitude of the surface positive component which occurred from 100 to 180 msec latency, as exemplified in Figure 2 . The mean preclosure peak to trough amplitude of this component was 5.59 microvolts and the mean postclosure amplitude was 6.78 microvolts (t for paired data = 6.310A,df = 12, p < .001).N o consistent differences in latency or waveform were present.






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1 FIGURE 2 RESPONSESEVOKED BY 64 PRESENTATIONSOF THE SAME GESTALT CLOSURE FIGUREBEFORE (PRE)AND A ~ E (POST) R Ss IDENTIFIEDOR CLOSEDTHE FIGURE The major effect is seen in the increased peak to trough amplitude at 100-180 msec.(A = 100 msec, B = 5 microvolts.)

Although the differences in amplitude were not large, they were very consistent, since 13 of 14 Ss had a greater postclosure mean amplitude than preclosure mean amplitude for the 100-180 msec component which was significant as shown with a sign test ( p < .001). Since each S had a slightly



different sample of the 12 slides due to the deletion of slides organized before 64 presentations, differences across the slides were not tested.

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In this study three classes of variables were dealt with; physical or stimulus events, physiological events, and psychological events. To explore the effect of the psychological (i.e., centrally mediated) events on the measured electrophysiological processes, the physical stimulus was held constant. Sandler and Schwartz (7) suggested that changes in the VECP waveform that correlated with perceptual organization, may have been due to attentional factors. The present study also indicates changes in the VECP as a function of perceptual organization (closure), but did not support an attentional explanation. S s here were instructed to attempt to close the figures during the “pre” condition, as well as the postclosure condition. Their continued attentiveness was indicated by the fact that all Ss closed some figures throughout the experiment. Hence, the observed changes are unlikely to be due to differences in attention. Although eye movements were not monitored in this study, it is unlikely that they contributed significantly to the results. The short flash duration used, along with a central fixation point, prevented more than a single fixation during any presentation of the stimulus. To further elucidate the mechanisms which may account for the observed changes in the VECP that accompany perceptual organization, future research might use multiple EEG leads. Buchsbaum and Fedio (2) found left hemispheric differences in the VECP to verbal stimuli vs. nonverbal stimuli. An analog of this finding may be uncovered in the right hemisphere if Gestalt figures are used as stimuli. In general, as Naatanen (6) has recommended, future research concerning correlates between centrally mediated psychological phenomena and the VECP should attempt to keep physical properties of the stimuli constant. In conclusion, organized and disorganized percepts produce different VECP amplitudes for a 100-180 msec component.

REFERENCES BEATTY, J., & UTTAL,W. R. The effects of grouping visual stimuli on the cortical evoked potential. Percept. 6 Psychophys., 1968, 4, 214-216. 2 . BUCHSBAUM, M., I3 FEDIO, P. Visual information and evoked responses from left and right hemispheres. Electroenceph. Cj. Clin. Neurophysiol., 1969, 26, 266-272. 3. JOHN,E. R., HERRINGTON, R. N., I3 SUTTON,S. Effects of visual form on the evoked response. Science, 1966, 155, 1439-1442. 1.



LIFSHITZ,K. The averaged evoked cortical response to complex visual stimuli. Psychofihysiology, 1966, 3, 55-68. 5 . MOONEY, C. M. A factorial study of closure. Can. J . Psychot., 1954, 8, 51-60. 6. NMTANEN, R. Selective attention and evoked potentials in humans: A critical review. B i d .


Psychol., 1975 (May), 2(4), 237-307. 7.

SANDLER,L. S., &SCHWARTZ,M. Evokedresponsesandperception:Stimuluscontentversus stimulus structure. Psychophysiology, 1971, 8, 727-739.

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USAF Hospital K Z Sawyer I( Z Sawyer AFB, Michigan 49843

Gestalt closure and the human visual evoked cortical potential.

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