We have been conducting the psychophysio-logical studies on form perception by means ofthe visual evoked potentials (VEPs) (Ito &Sugata, 1995; Ito, Sugata, & Kuwabara, 1997)

and other researchers have also investigated theeffects of form or shape upon VEPs (Jeffreys,1969, 1989; John, Herrington, & Sutton, 1967;Kakigi, Miyazaki, & Mori, 1972; Moskowitz,

Japanese Psychological Research1998, Volume 40, No. 2, 111–116 Short Report

Visual evoked potentials to the geometric formsin the randomized presentation1

MOTOO ITO2

Department of Psychology, Faculty of Letters, Aichi Gakuin University, Iwasaki-cho, Nisshin, Aichi 470-01, Japan

HIROSHI KUWABARA3

Suzuka Hospital, National Sanatorium, Kasado, Suzuka, Mie 513, Japan

TATSUYA SUGATA4

Department of Social Welfare, Holy Cross College, Komono-cho, Mie-gun, Mie 510-12, Japan

KAZUYA SUZUKI5 and YUKO KAWAI6

Department of Psychology, Faculty of Letters, Aichi Gakuin University, Iwasaki-cho, Nisshin, Aichi 470-01, Japan

Abstract: Two outlined geometric figures, an equilateral triangle and a circle, of equal contourlength, were randomly presented at a fixed position in the lower or upper part of the visualfield (LVF and UVF). Transient visual evoked potentials (VEPs) were recorded monopolarly fromthe inion (I), 5, 10, 15 cm above it (I5, I10, I15) and Fz, for 12 subjects. Grand-averaged VEPswere computed. A negative (N) wave (averaged peak latency 155 ms) was identified in the LVFand a positive (P) wave (130 ms) in the UVF. In the LVF, the N amplitude of the triangle wassignificantly larger than that of the circle at I5 and I. Regarding the P wave in the UVF, thetriangle was of a significantly longer latency than the circle at I15, I10 and I5. The enhance-ment of the N amplitude for the triangle in the LVF is not attributable to the arousal caused bythe preparatory state for the figure, since the subject could not predict the figure to bepresented next or its position.

Key words: form perception, geometric figures, transient visual evoked potentials, arousallevel, preparatory state.

1 Some of the data in the present article were reported at the 58th Annual Convention of the Japanese PsychologicalAssociation (1994).2 The authors are deeply indebted to Professor K. Tsuji of Nagoya University for his critical reading and comments onthis manuscript and Mr. H. Ohashi for his cooperation in running the experiments and analyzing the data. Thanks arealso expressed to Professor M. Kida of Aichi Gakuin University for his advice and encouragement. E-mail may beaddressed to motoo@dpc.aichi-gakuin.ac.jp.3 Now at Mie National Hospital (Osatokubota-cho, Tsu 514, Japan).4 Now at Nagoya Welfare College (Nagakute-cho, Aichi-gun, Aichi 480-11, Japan).5 Now at Institute for Science of Labour (Sugao, Miyamae-ku, Kawasaki 216, Japan).6 Now at Kyoto City Mental Health Center (Mibu, Nakagyo-ku, Kyoto 604, Japan).

© 1998 Japanese Psychological Association. Published by Blackwell Publishers Ltd, 108 Cowley Road, Oxford OX4 1JF, UK and 350 Main Street, Malden, MA 02148, USA.

Armington, & Timberlake, 1974; Rietveld,Tordoir, Hagenouw, Lubbers, & Spoor, 1967;Spekreijse, Van der Tweel, & Zuidema, 1973;White, 1969). Since the various findings havebeen incongruent, we need to accumulate sys-tematic data from similar experiments andreplication studies (Ito & Sugata, 1995).

Ito and Sugata (1995) compared the VEPsobtained with three geometric figures: a triangle,a square and a circle. The triangle elicited asignificantly larger negative (N1) response thanthe square or the circle. Ito et al. (1997) exam-ined the effects of geometric form and orienta-tion, and found that the upright triangle, theinverted triangle and the diamond evoked sig-nificantly larger N1 responses than the squareand the circle.

However, the following problem stillremains unsolved. The subjects of our previousstudies (Ito & Sugata, 1995; Ito et al., 1997) hadprior knowledge of the differential psycho-logical effects of geometric figures, for examplethat the triangle is the most visible of them(Torii, 1969; Yokose, 1968). When a figure isrepeatedly presented at a fixed position on thevisual field, such related knowledge may leadsubjects to have different preparatory states,which in turn result in different levels ofarousal. The N1 enhancement could have beencaused by such a difference in arousal levels.The possibility has not completely beendiscounted (Karlin, 1970; Näätänen, 1975).

To confirm that our previous results wereattributable to the difference of figural feat-ures, the present experiment was designed toexamine VEPs by an improved procedure inwhich triangle and circle were randomly pre-sented at either of two positions in visual field.

Method

SubjectsTwelve psychology students (six men, sixwomen; mean age 24.2 years, range 22–33years) participated. They all had normalvisual acuity by wearing optical aid wherenecessary.

Stimulus presentationTwo outlined geometric figures, an equilateraltriangle and a circle of equal contour length(8.6 cm), were randomly presented at a fixedposition in the lower or upper part of the visualfield (LVF or UVF) on the cathode-ray displayof an audio-visual tachistoscope (Iwatsu ISELIS-701A) (Figure 1). A personal computer (NECPC-9801DX) was used to control the spatial andtemporal parameters. Subjects were exposed tothe dark field against which a stimulus figurewas presented for 48 ms. Stimulus-onset asyn-chrony (SOA) was varied randomly in the range408–688 ms, in 40-ms steps. Stimulus figures(line width 1.3 mm) were presented in green onthe dark background. Subjects binocularlyobserved the figure from a chin rest at a dis-tance of 57 cm. Stimulus luminance was 7 cd/m2.

A small fixation point (FP) of green lightwas constantly presented at the center of the

112 M. Ito, H. Kuwabara, T. Sugata, K. Suzuki, and Y. Kawai

© Japanese Psychological Association 1998.

Figure 1. Spatial relations of the stimulus figuresin the present experiment.

Upper

Lower

2°52'

2°29' 2°44'

2°

FP

2°

2°29' 2°44'

2°52'

display. The angular separation between the FPand the top (bottom) of the figure was heldconstant at 2° in the LVF (UVF) (Figure 1).Four sessions were conducted. Each consistedof 32 random presentations of each of the fourstimuli.

VEP recordingElectroencephalograms (EEGs) were obtainedby referential recording. Five Ag-AgCl elec-trodes were placed on the midline at the inion(I), 5, 10, 15 cm above it (I5, I10, I15) and Fz.The earlobes were linked and used as the refer-ence, and Cz was used for ground. The EEGs(0.5–30 Hz) were amplified with an eight-channel polygraph (NEC San-ei System 360)and monitored with an oscilloscope.

A vertical electro-ocolugram (EOG) fromthe right eye was also amplified (DC) and mon-itored in order to cancel any trials which con-tained artifacts of eye movement and blinking.The cancellation level was set at ±100 µV. Ag-AgCl electrodes were placed just below andabove the right eye. EEGs and EOGs wererecorded together with the signal of stimulusonset, by using a 14-channel data recorder(TEAC XR-510). VEPs were obtained off line with a personal computer (NEC PC-9801FX). Averaging time was 740 ms (100 msfor prestimulus period and 640 ms for stimulusperiod) and the sampling interval was 2 ms.The mean number of summations in 32 stimu-lus presentations was 25.6 both for VEPs andEOGs. VEPs were printed out with an x-yplotter (Roland DXY-1300).

The peaks of the wave components wereindividually determined for the 12 subjects.

Results

Figure 2 shows the grand-averaged VEPs andEOGs for the four conditions. The waves weresuperimposed on the prestimulus baselines ofaveraged potentials. Changes in EOGs werenegligible, which indicated the stability of fixa-tion. A negative (N) wave was clearly identi-fied in the LVF and a positive (P) wave in theUVF, peaking at about 155 ms and 130 ms,respectively. Both waves showed the monopolar

potential distribution on the scalp, with thepeaks at I5. The N wave is what we called N1 inour previous studies (Ito & Sugata, 1995; Ito et al., 1997).

Figure 3 shows the averaged peak latenciesof the N and P waves at four locations exceptFz. At Fz, since neither peak was clear in somecases, they were discarded from the present dataanalysis. The averaged peak latencies of the twowaves were again at about 155 ms and 130 ms.

Figure 4 shows the averaged scalp distribu-tions of both N and P amplitudes. One-way ana-lysis of variance (ANOVA) on the figure effectwas made for the averaged peak latency andamplitude of both waves. In the LVF, the N

Visual evoked potentials to geometric forms 113

© Japanese Psychological Association 1998.

Figure 2. Grand-averaged VEPs for the triangleand the circle randomly presented atfixed positions in the lower or upperpart of visual field (LVF and UVF).

Lowertriangle

Lowercircle

Uppertriangle

Uppercircle

Fz

I15

I10

I5

I

E0G

–

+

5µV

0 600ms

Loca

tion

EOG

amplitude of the triangle was significantly largerthan that of the circle at I5 and I , F(1, 11) =31.96 and 24.06, p ,.001, respectively. How-ever, there was no significant difference in theP amplitudes at any location in the UVF. Onthe other hand, the P peak latency of the tri-angle was significantly longer than that of thecircle at I15, I10 and I5 in the UVF, F(1, 11) =11.38, 14.21 and 6.94, p ,.01, .01 and .05,

respectively, although no significant differencein the N latency was found at any location inthe LVF.

According to Figure 2, another positive wavepeaking at about 235 ms, which we called P2 inour previous studies (Ito & Sugata, 1995; Ito et al., 1997), is also observed for both figures inthe LVF. Figure 5 shows the averaged peaklatencies of this wave. In the UVF, there seemsno distinct wave of similar latency.

Regarding the later positive wave in the LVF,one-way ANOVA on the figure effect was con-ducted. There was no significant difference inlatency at any location, but the circle was of asignificantly larger amplitude than the triangleat I15, F(1,11) = 10.85, p ,.01 (Figure 6).

114 M. Ito, H. Kuwabara, T. Sugata, K. Suzuki, and Y. Kawai

© Japanese Psychological Association 1998.

Figure 4. Averaged scalp distributions of the N amplitude in the LVF and the Pamplitude in the UVF for the triangleand the circle. Vertical lines indicate ±1 standard deviation.

Am

plitu

de (

µv)

I15 I10 I5 I

Lower triangleLower circle

Upper triangleUpper circle

N

P

–10

–8

–6

–4

–2

0

2

4

6

Location

Figure 3. Averaged peak latencies (ms) of thenegative (N) wave in the LVF and the positive (P)wave in the UVF for the triangle and the circle.Vertical lines indicate ±1 standard deviation.

190180170160150140130120110100 90

Late

ncy

(ms)

I15 I10 I5 I

Lower triangleLower circle

Upper triangleUpper circle

NN

P

Location

Figure 5. Averaged peak latencies (ms) of the later P wave in the LVF for the triangleand the circle. Vertical lines indicate ±1standard deviation.

270260250240230220210200190180

I15 I10 I5 I

Lower triangle Lower circle

Location

P

Late

ncy

(ms)

Figure 6. Averaged scalp distributions of the laterP amplitude in the LVF for the triangleand the circle. Vertical lines indicate ±1standard deviation.

I15 I10 I5 I

Lower triangle Lower circleLocation

0

2

4

6

Am

plitu

de (

µv)

P

Discussion

The results of the present experiment may besummarized as follows: (1) In the LVF, theamplitude of the N wave (or the N1 wave) wassignificantly larger for the triangle than for thecircle at I5 and I, but in the UVF no significantdifference of the P amplitude was shown be-tween the two figures at any location. (2) Re-garding the P wave in the UVF, the triangle wasof a significantly longer latency than the circleat I15, I10 and I5, although on the N (or the N1) latency in the LVF no significant differ-ence was shown between the figures at anylocation. (3) As to the later positive wave (orthe P2 wave) in the LVF, there was no sig-nificant difference in its latency at any location,but the circle was of a significantly larger ampli-tude than the triangle at I15.

As clearly shown, the triangle evoked alarger N amplitude than the circle at I5 and I inthe LVF. This result is in accordance with thedata of the N1 wave in our previous experi-ments in which the particular figure was repeat-edly presented at a fixed position in the LVF(Ito & Sugata, 1995; Ito et al., 1997). It alsoshows that the larger N amplitude for the tri-angle in the LVF is not attributable to the arousalcaused by the preparatory state, since thesubject could not predict which figure would bepresented next, or its position (Karlin, 1970;Näätänen, 1975). In a similar experimentalsituation, we examined the effect on the VEPsof selective attention (Ito, Kuwabara, Sugata,Suzuki, & Kawai, 1996). An equilateral tri-angle or a circle of equal contour length wasrandomly presented at a fixed position in theLVF or the UVF. The subjects were asked topush a button quickly whenever the target figure(triangle or circle) appeared in the attendedvisual field (LVF or UVF). In the LVF, the tri-angle elicited a significantly larger N amplitudethan did the circle in all the relevant and irrel-evant combinations of figure and field. Theresult showed that the enhancement of the Nwave for the triangle was not attributable toselective attention, but to a nonattentive process.

In the current study, there was no differencein the P amplitude between the two figures in

the UVF. This result also supports the findingof our previous study (Sugata, Ito, Kuwabara,& Osaka, 1992), where the effects of both formand location upon VEPs were examined by theconventional presentations.

The facilitation of the later positive wave inthe LVF for the triangle was not observed in the present experiment. Although the circleevoked a significantly larger response than thetriangle at I15, it should be noted that no sig-nificant difference was shown between the twofigures around the occipital area.

Between the N wave in the LVF and the P wave in the UVF, polarity reversal seems tohave occurred (Jeffreys, 1977; Jeffreys & Smith,1979). In spite of the difference of peak latencybetween the two waves, the scalp distributionshowed a similar pattern and the onset latencywas the same. These lead to a prediction thatthe figure effect should be symmetrical witheach other for the two presentations. However,the present results were incongruent with theprediction. The N amplitude for the trianglewas larger than that for the circle in the LVF,while the P amplitude did not differ betweenthe figures in the UVF. Contrarily, the P latencyfor the triangle was longer than that for thecircle in the UVF, while the N latency did notdiffer between the figures in the LVF. Theremay be functional differentiation between the LVF and the UVF, although it is hard atpresent to give a clear explanation for such anasymmetry in the responses. In this regard, thestudy of Previc (1988) seems suggestive.

Previc examined the effect of spatial fre-quency, contrast and hemifield stimulation onthe reversal VEPs by analyzing the behavior of N1 (peak latency about 60–90 ms) and P1(about 90–120 ms) components. The N1 com-ponent showed band-pass spatial tuning andno contrast saturation, while the P1 was low-pass spatially tuned and dominant at low con-trasts. The N1 wave was marked in the UVFand the P1 wave was distinct in the LVF. Previcsuggested that information processing differedbetween the UVF and the LVF. Undoubtedly,his study cannot be compared directly withours, but further discussion of the behavior of the VEPs in connections with functional

Visual evoked potentials to geometric forms 115

© Japanese Psychological Association 1998.

116 M. Ito, H. Kuwabara, T. Sugata, K. Suzuki, and Y. Kawai

© Japanese Psychological Association 1998.

differentiation of the UVF and the LVF wouldbe significant for our study.

References

Ito, M., & Sugata, T. (1995). Visual evoked potentialsto geometric forms. Japanese PsychologicalResearch, 37, 221–228.

Ito, M., Kuwabara, H., Sugata, T., Suzuki, K., &Kawai, Y. (1996). Visual-evoked potentials togeometric forms: Examination of the effect ofselective attention. In C. Ogura, Y. Koga, & M. Shimokochi (Eds.), Recent advances in event-related brain potential research (pp. 67–71).Amsterdam: Elsevier.

Ito, M., Sugata, T., & Kuwabara, H. (1997). Visualevoked potentials to geometric forms: Effects of spatial orientation. Japanese PsychologicalResearch, 39, 339–344.

Jeffreys, D. A. (1969). Characteristics of visual andauditory EPs. Neuroscience Research ProgramBulletin, 7, 205–227.

Jeffreys, D. A. (1977). The physiological significanceof pattern visual evoked potentials. In J. E.Desmedt (Ed.), Visual evoked potentials inman: New developments (pp. 134–167). Oxford:Clarendon Press.

Jeffreys, D. A. (1989). Evoked potential studies ofcontour processing in human visual cortex. In J. J. Kulikowski, C. M. Dickinson, & I. J. Murray(Eds.), Seeing contour and colour (pp. 529–545).London: Pergamon Press.

Jeffreys, D. A., & Smith, A. T. (1979). The polarityinversion of scalp potentials evoked by upperand lower half-field stimulus patterns: Latencyor surface distribution differences? Electroence-phalography and Clinical Neurophysiology, 46,409–415.

John, E. R., Herrington, R. N., & Sutton, S. (1967).Effects of visual form on the evoked response.Science, 155, 1439–1442.

Kakigi, S., Miyazaki, M., & Mori, T. (1972). Effects ofstimulus rotation, shape, and visual angle upon

human visual evoked response. Japanese Psycho-logical Research, 14, 153–157.

Karlin, L. (1970). Cognition, preparation, andsensory-evoked potentials. Psychological Bulletin,73, 122–136.

Moskowitz, A. F., Armington, J. C., & Timberlake, G.(1974). Corners, receptive fields, and visuallyevoked potentials. Perception & Psychophysics,15, 325–330.

Näätänen, R. (1975). Selective attention and evokedpotentials in humans: A critical review. Bio-logical Psychology, 2, 237–307.

Previc, F. H. (1988). The neurophysiological signi-ficance of the N1 and P1 components of thevisual evoked potential. Clinical Vision Science,3, 195–202.

Rietveld, W. J., Tordoir, W. E. M., Hagenouw, J. R. B.,Lubbers, J. A., & Spoor, Th. A. C. (1967). Visualevoked responses to blank and to checkerboardpatterned flashes. Acta Physiologica et Pharma-cologica Neerlandica, 14, 259–285.

Spekreijse, H., Van der Tweel, L. H., & Zuidema, T. (1973). Contrast evoked potentials in man.Vision Research, 13, 1577–1601.

Sugata, T., Ito, M., Kuwabara, H., & Osaka, R.(1992). The relationship between figure per-ception and visual evoked potentials: Effects offigure form (8). The Proceedings of the 56thAnnual Convention of the Japanese Psycho-logical Association, 849 (in Japanese).

Torii, S. (1969). Form perception. In Y. Wada, T. Oyama, & S. Imai (Eds.), Handbook of sens-ory and perceptual psychology (pp. 478–503).Tokyo: Seishin-shobo (in Japanese).

White, C. T. (1969). Evoked cortical responses andpatterned stimuli. American Psychologist, 24,211–214.

Yokose, Z. (1968). Psychology of visual percep-tion (2nd ed.). Tokyo: Kyoritsu-shuppan (inJapanese).

(Received Nov. 29, 1995; accepted May 10, 1997)