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Visual beats: Differential brightness of the stimuli and estimation of brightness
Vision Res. Vol. 9, pp. 429-433.
Pergamon Press 1969. Printed in Great Britain.
VISUAL
BEATS: DIFFERENTIAL BRIGHTNESS OF THE STIMULI AND ESTIMATION OF BRIGHTNESS 1 RATHE KARRER
Illinois State Pediatric Institute, 1640 Roosevelt Road, Chicago, IlL 60608
(Rece&ed 24 June 1968; in final form 11 November 1968) INTRODUCTION THE STUDY o f beat p h e n o m e n a arising from the combination o f intermittent stimuli has a long history in audition and even cutaneous sensation (VON B~g:~SY, 1960). While analogous p h e n o m e n a can be found in vision there has been little investigation. Recent studies (KARRER, 1965; 1967) have indicated the usefulness o f visual beat p h e n o m e n a for analysis o f the temporal characteristics in vision and have shown similarities between visual and auditory beats. Beats arising from the presentation of a different flicker frequency (F~ and F2) to each eye can indicate the rate o f temporal processing o f the system by the correspondence o f perceived beat rate (Br) to the physical beat frequency (Bf). This correspondence has been shown in flickering stimuli to hold up to flicker frequencies as fast as 80 H z and to flicker fusion (KARRER, 1967). Beats were also observed under scotopic and photopic conditions and under conditions in which the brightness o f the two flicker frequencies are slightly different. Since brightness affects the perceived rate o f flicker (cf. BARTLEY, 1959; BROWN, 1965) implicating temporal processing, it is possible that differential brightness o f the two stimuli m a y affect both perceived beat rate and beat perception. Information is needed o f the extremes o f differential brightness still capable o f producing a perceptible beat equal to the beat frequency and, therefore, accurate temporal following o f flashes. STUDY 1 Method and procedure Two General Radio Strobotacs (Model 1531A) served as sources of flicker. All frequencies were monitored by a Hewlett-Packard electronic counter (Model 522B). The flicker sources were placed in a viewing box which contained ground glass behind two holes (2 in. dia.) fitted with rubber eye pieces. A removable center partition isolated the two sources for dichoptic viewing. The viewing screens were 1-2 in. from the eye which resulted in the flicker filling all but the extreme peripheral visual field when in frontal view. At fusion of the flicker (in my conditions as high as 85 Hz) the brightness was approximately 400 mL as determined with a Macbeth illuminometer. Wratten neutral density filters were inserted to reduce the brightness of one of the fundamental frequencies by 1 log unit steps. This large decrease in brightness was done for both left and right eyes separately for the two fundamental frequencies of 20 Hz (F1) and 21 Hz (]72). 1 Part of this work was included in a Ph.D. dissertation submitted to the New School for Social Research, 1965. I thank HOWARDGROBER, JOHS CLAUSEN,JAY BELL and NANCY KARRERfor their counsel and assistance. 429
430
RATHE KARRER
To provide a continuous record of the combined flicker frequencies of the two sources and the beat frequencies, the output of a Bradley selenium photocell (Model 1-1A), mounted above and between the two flicker sources was led through an EMG preamplifier (Model 5p3) into a Grass polygraph (Model 5A). A telegraph key was provided for S to tap in synchrony with the perceived beats. The S's tapping rate was fed into another polygraph channel. The paper speed was 25 mm/sec to allow reading to the nearest ½mm or 0.02 sec. To mask the possible cues to beat frequency from the clicks produced by the strobotacs, S's wore earphones through which 75-db SPL (re: 0.0002 dyn/cm2, measured with a General Radio soundlevel meter, Model 1551A) of white noise was presented from a Grayson Stadler white noise generator (Model 522B). This white noise was 35-db SPL above the intensity of the clicks so that S's could not judge by sound cues when the strobotacs were turned on or off. The subject tapped the rhythm of the perceived beat at each successive brightness step until no beat was reported. A minimum of 30 taps was obtained for each brightness step. The criterion for no perceptible beat was 3 presentations of any brightness step. Five adult male subjects took part. The perceived beat rate (Br) and the beat frequency (Bf) were determined from the polygraph record for each brightness step and for each S. The Bf was divided by the mean Br of each series of taps to determine the ratio Bf/Br for each series. This ratio indicates the correspondence of perceived beat rate to beat frequency. A ratio larger than unity indicates a Br faster than Bf, while a ratio smaller than unity indicates a Br slower than Bf.
Results A l l subjects r e p o r t e d beats with an intensity difference o f 2 log units. The m e a n ratio o f perceived b e a t rate to physical b e a t frequency was only slightly less t h a n u n i t y ( m e a n Bf/Br = 0.99). One subject r e p o r t e d beats with an intensity difference o f 3 log units (mean Bf/Br = 0.96) b u t n o t beyond. These gross d a t a indicate t h a t the Br to B f e q u a l i t y is n o t affected b y widely divergent brightness o f the two flickering stimuli. T h e b e a t was no longer perceived when the brightness decrease caused one frequency to a p p e a r fused.
STUDY 2 W h e n the F1-F2 frequencies are in-phase there is a d o u b l i n g o f energy a n d brightness increases are perceived with the beating. A l t h o u g h this brightness increase is a m a j o r characteristic o f the perceived b e a t (KARRER, 1968), it often a p p e a r s as a m i n i m a l change r a t h e r t h a n a t w o - f o l d one. A second experiment was carried o u t to m e a s u r e this brightness change. Brightness estimates were o b t a i n e d for the b e a t p r o d u c e d b y various Ft-F2 frequencies a n d b e a t frequencies.
Method andprocedure Stimulus F1 frequencies of 5, 10, 15, 20, 25, 35 and 45 Hz (well below the CFF of 85 Hz) were paired with appropriate F2 frequencies to give a beat frequency of 1.0 Hz. In addition, for the F1 frequencies of 10, 25 and 45 Hz, beat frequencies of 0. 5 and 2. 0 Hz were used. The two stimulus sources were presented both binocularly and dichoptically. The subject estimated the brightness change of the beat by assigning the darker phase a value of I0 and estimating the brighter phase from this standard. A two-fold brightness increase obtained a value of 20 while a value of 15 indicated an increase by one half. If no change in brightness was perceived the value of the standard, 10, was given. After practice, subjects were able to perform this difficult judgment with reasonable reliability. Two judgments of each condition replicated at least one day later gave a total of four estimations per subject for each of the 13 conditions. Rank order correlations between the replications were generally of the magnitude 0.7--0.8. All eonditiom were presented randomly except that successive judgments of the same condition were never allowed to occur. Ten adults (8 males and 2 females) served as subjects.
Results W i t h a b e a t frequency o f 1.0 the brightness o f the b e a t decreases as the frequency o f the two stimuli increases (Fig. 1A). W i t h b i n o c u l a r presentation, the brightness is seen
Visual Beats: Differential Brightness of the Stimuli and Estimation of Brightness ____ Binocular
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5 - - Hz FIG. I. Magnitude estimation of heat brightness: (A) as a function of lower stimulus (Fz) frequency, and (B) as a function of beat frequency at selected F1 frequencies. Broken line, binocular presentation; solid line, dichoptic presentation; dots, 0.5 Hz; crosses, 1.0 Hz; circles, 2. 0 Hz. to double at 5 Hz but drops to about 75 per cent change at 15 Hz. With dichoptic presentation, the brightness is considerably less than double, about 75 per cent at 5 Hz, and falls to about 25 per cent by 15 Hz. An interesting small rise in brightness occurs at 20 Hz (perhaps also reflected in the binocular data) which may indicate some facilitation at this frequency. 2 Binocular beat brightness also reaches its minimum in this region. Beat brightness drops off not only as a function of the stimulus frequencies but also as a function of beat frequency (Fig. 1B). Slow beat frequencies are judged brighter than fast beat frequencies. Moreover, with dichoptic presentation the beat brightness falls to about 25 per cent by 25 Hz stimulus frequency or above 1 Hz beat frequency. Discussion
Brightness differences between the stimuli appear to have no effect on perceived beat rate. Since beat rate is an index of the fundamental frequencies, it follows that the central 2 This may be related to other findings that the thresholds for electric (CLAUSEN,1955) and photic (KELLY, 1962) flicker tend to be lowest in this region. BARTLEY(1959) has also given some special importance to this frequency.
432
RATHEKARRER
representation o f these frequencies is accurate so long as both are seen to flicker. CLAUSEN and VANDERBILT (1957), using the combination of electric mad photic flicker, also found no effect o f brightness on perceived beat rate so long as flicker was present. The results imply that the a m o u n t o f differential brightness necessary to obscure the beat must also be a function o f the stimulus frequencies and beat frequency. F o r instance, greater differential brightness should be tolerable at an F1 frequency o f 5 H z and also with a 0.5 Hz beat frequency. The decrease in beat brightness with increasing stimulus frequencies m a y indicate a decrease in the number o f neural channels activated at each pulse (BARTLEY, 1958, 1964) even though the stimulus frequency is accurately followed by each channel. Such a process would maintain perceived beat frequency but give fewer channels for interaction during in-phase and, thus, reduced beat brightness. Since brightness has no apparent effect on perceived beat rate the neural representations o f stimulus brightness and stimulus frequency are relatively independent in flickering stimuli.
REFERENCES
BARTLEY,S. H. (1958). Some facts and concepts regarding the neurophysiology of the optic pathway. Archs Ophthal. 60, 775-791. BARTLEY,S. H. (1959). Central mechanisms of vision, inHandbookofPhysiology(editedbyH.W.MAC,OUN), Vol. 1, Sect. 1, Neurophysiology, Washington, D.C.; Am. Physiol. Soc. BARTLEY, S. H. (1964). Some sensory end results and the neural activity of the optic pathway. Am. J. Optom. Archs Am. Acad. Optom. Monogr. No. 328. B~K/~SY,G. VON(1960). Experiments in Hearing, McGraw Hill, New York. BROWN, J. L. (1965). Flicker and intermittent stimulation, in Vision and Visual Perception (edited by C. H. GRAHAM),John Wiley, New York. CLAUSEN, J. (1955). Visual Sensations (Phosphenes) Produced by a.c. Sine Wave Stimulation, Ejnar Munksgaard, Copenhagen. CLArOs~rq, J. and VANDERBrLT,C. (1957). Visual beats caused by simultaneous electrical and photic stimulation. Am. J. PsychoL 70, 577-585. KAga~R, R. (1965). Visual beat phenomena and their relation to the temporal characteristics of perception. Unpublished doctoral dissertation, Graduate Faculty, New School for Social Research. KAggER, R. (1967). Visual beat phenomena as an index to the temporal characteristics of perception. J. exp. PsychoL 75, 372-378. ~R, R. (1968). Visual beats: phenomenology and preliminary data as a function of age. Psychonom. Sei. 11, 269-270. I~LI.Y, D. H. (1962). Visual responses to time dependent stimuli: II. Amplitude sensitivity measurements. J. opt. Soc. Am. 52, 89-95.
Abstract--Visual beats, arising from dichoptic presentation of a different flicker frequency to each eye, are unaffected by widely divergent brightness of the two frequencies. Estimated perceived brightness of beats decreases as a function of flicker frequency and beat frequency. The data indicate that temporal processing is somewhat independent of brightness registration in flickering stimuli. R~sumr---Les battements visuels qui sent produits par une prrsentation dichoptique d'une frrquence de papillotement diff~rente pour chaque oeil, ne sent pas affect~s par une grande diffrrence de luminosit6 entre les deux frrquences. L'estimation de la luminosit~ pereue des battements diminue en fonction de la fr~quence de papillotement et de la frrquence des battements. Les donn~es indiquent que le processus temporel est dans une certaine mesure indrpendant de la luminosit6 enregistr~e pour les stimuli papillotants. Zusammenfassung--Sichtbare Schl~ige, die aus der dichoptischen Reizung beider Augen mit je verschiedenen Flimmerfrequenzen entstehen, sind nicht durch weitliiufige HeUigkeitsunterschiede der beiden Frequenzen beeinflusst. Die gesch~itzte Helligkeit der Schlfige verringect
Visual Beats: Differential Brightness of the Stimuli and Estimation of Brightness sich mit der Flimmer- und Schlagfrequenz. Die Resultate zeigen, dass die zeitliche Analyse v o n d e r Helligkeitsregistrierung der Flimmerreize gr6sstenteils unabh~ingig ist. Pe310Me - - 3pHTe.rlbHble <<6rIeHH~>>, BO3HHKalOIIIHe rlpI,I O~HOBpeMeHHO~ CTHMyJDII.U4H ~ByX FYla3 MeYlbKatouIHM CBeTOM pa3HOl~ qaCTOTbI, He H3MeHfllOTC~ rlprl 6OJIbIIIOM pacxo~eHIa~d CBeTJIOT Ka~O~l IIX 3THX ,/I~ByXqaCTOT. CBeTnOTa 6HermtL onpenen~eMa~ B BocHpH~THH, yMeHbIHaeTc~l rlpH yMeHbIJJeHHn qaCTOTbI MenbKaI-i~ H qaCTOTbI 6 n e a ~ . [~TH ~aHI-Ible IIOKa3blBalOT, tITO BpeMerm6e npoTeKarme rIpotlecca B H3BeQTHOFI Mepe He 3aBHCHT OT perHcTprlpyeMofi CBeTYlOTbl MenbKa~OtlinX CTHMy.rIOB.
433
Pergamon Press 1969. Printed in Great Britain.
VISUAL
BEATS: DIFFERENTIAL BRIGHTNESS OF THE STIMULI AND ESTIMATION OF BRIGHTNESS 1 RATHE KARRER
Illinois State Pediatric Institute, 1640 Roosevelt Road, Chicago, IlL 60608
(Rece&ed 24 June 1968; in final form 11 November 1968) INTRODUCTION THE STUDY o f beat p h e n o m e n a arising from the combination o f intermittent stimuli has a long history in audition and even cutaneous sensation (VON B~g:~SY, 1960). While analogous p h e n o m e n a can be found in vision there has been little investigation. Recent studies (KARRER, 1965; 1967) have indicated the usefulness o f visual beat p h e n o m e n a for analysis o f the temporal characteristics in vision and have shown similarities between visual and auditory beats. Beats arising from the presentation of a different flicker frequency (F~ and F2) to each eye can indicate the rate o f temporal processing o f the system by the correspondence o f perceived beat rate (Br) to the physical beat frequency (Bf). This correspondence has been shown in flickering stimuli to hold up to flicker frequencies as fast as 80 H z and to flicker fusion (KARRER, 1967). Beats were also observed under scotopic and photopic conditions and under conditions in which the brightness o f the two flicker frequencies are slightly different. Since brightness affects the perceived rate o f flicker (cf. BARTLEY, 1959; BROWN, 1965) implicating temporal processing, it is possible that differential brightness o f the two stimuli m a y affect both perceived beat rate and beat perception. Information is needed o f the extremes o f differential brightness still capable o f producing a perceptible beat equal to the beat frequency and, therefore, accurate temporal following o f flashes. STUDY 1 Method and procedure Two General Radio Strobotacs (Model 1531A) served as sources of flicker. All frequencies were monitored by a Hewlett-Packard electronic counter (Model 522B). The flicker sources were placed in a viewing box which contained ground glass behind two holes (2 in. dia.) fitted with rubber eye pieces. A removable center partition isolated the two sources for dichoptic viewing. The viewing screens were 1-2 in. from the eye which resulted in the flicker filling all but the extreme peripheral visual field when in frontal view. At fusion of the flicker (in my conditions as high as 85 Hz) the brightness was approximately 400 mL as determined with a Macbeth illuminometer. Wratten neutral density filters were inserted to reduce the brightness of one of the fundamental frequencies by 1 log unit steps. This large decrease in brightness was done for both left and right eyes separately for the two fundamental frequencies of 20 Hz (F1) and 21 Hz (]72). 1 Part of this work was included in a Ph.D. dissertation submitted to the New School for Social Research, 1965. I thank HOWARDGROBER, JOHS CLAUSEN,JAY BELL and NANCY KARRERfor their counsel and assistance. 429
430
RATHE KARRER
To provide a continuous record of the combined flicker frequencies of the two sources and the beat frequencies, the output of a Bradley selenium photocell (Model 1-1A), mounted above and between the two flicker sources was led through an EMG preamplifier (Model 5p3) into a Grass polygraph (Model 5A). A telegraph key was provided for S to tap in synchrony with the perceived beats. The S's tapping rate was fed into another polygraph channel. The paper speed was 25 mm/sec to allow reading to the nearest ½mm or 0.02 sec. To mask the possible cues to beat frequency from the clicks produced by the strobotacs, S's wore earphones through which 75-db SPL (re: 0.0002 dyn/cm2, measured with a General Radio soundlevel meter, Model 1551A) of white noise was presented from a Grayson Stadler white noise generator (Model 522B). This white noise was 35-db SPL above the intensity of the clicks so that S's could not judge by sound cues when the strobotacs were turned on or off. The subject tapped the rhythm of the perceived beat at each successive brightness step until no beat was reported. A minimum of 30 taps was obtained for each brightness step. The criterion for no perceptible beat was 3 presentations of any brightness step. Five adult male subjects took part. The perceived beat rate (Br) and the beat frequency (Bf) were determined from the polygraph record for each brightness step and for each S. The Bf was divided by the mean Br of each series of taps to determine the ratio Bf/Br for each series. This ratio indicates the correspondence of perceived beat rate to beat frequency. A ratio larger than unity indicates a Br faster than Bf, while a ratio smaller than unity indicates a Br slower than Bf.
Results A l l subjects r e p o r t e d beats with an intensity difference o f 2 log units. The m e a n ratio o f perceived b e a t rate to physical b e a t frequency was only slightly less t h a n u n i t y ( m e a n Bf/Br = 0.99). One subject r e p o r t e d beats with an intensity difference o f 3 log units (mean Bf/Br = 0.96) b u t n o t beyond. These gross d a t a indicate t h a t the Br to B f e q u a l i t y is n o t affected b y widely divergent brightness o f the two flickering stimuli. T h e b e a t was no longer perceived when the brightness decrease caused one frequency to a p p e a r fused.
STUDY 2 W h e n the F1-F2 frequencies are in-phase there is a d o u b l i n g o f energy a n d brightness increases are perceived with the beating. A l t h o u g h this brightness increase is a m a j o r characteristic o f the perceived b e a t (KARRER, 1968), it often a p p e a r s as a m i n i m a l change r a t h e r t h a n a t w o - f o l d one. A second experiment was carried o u t to m e a s u r e this brightness change. Brightness estimates were o b t a i n e d for the b e a t p r o d u c e d b y various Ft-F2 frequencies a n d b e a t frequencies.
Method andprocedure Stimulus F1 frequencies of 5, 10, 15, 20, 25, 35 and 45 Hz (well below the CFF of 85 Hz) were paired with appropriate F2 frequencies to give a beat frequency of 1.0 Hz. In addition, for the F1 frequencies of 10, 25 and 45 Hz, beat frequencies of 0. 5 and 2. 0 Hz were used. The two stimulus sources were presented both binocularly and dichoptically. The subject estimated the brightness change of the beat by assigning the darker phase a value of I0 and estimating the brighter phase from this standard. A two-fold brightness increase obtained a value of 20 while a value of 15 indicated an increase by one half. If no change in brightness was perceived the value of the standard, 10, was given. After practice, subjects were able to perform this difficult judgment with reasonable reliability. Two judgments of each condition replicated at least one day later gave a total of four estimations per subject for each of the 13 conditions. Rank order correlations between the replications were generally of the magnitude 0.7--0.8. All eonditiom were presented randomly except that successive judgments of the same condition were never allowed to occur. Ten adults (8 males and 2 females) served as subjects.
Results W i t h a b e a t frequency o f 1.0 the brightness o f the b e a t decreases as the frequency o f the two stimuli increases (Fig. 1A). W i t h b i n o c u l a r presentation, the brightness is seen
Visual Beats: Differential Brightness of the Stimuli and Estimation of Brightness ____ Binocular
p A/ 20
431
Dlchoptlc
\
| ",,
1.0
o
E .--. 0.5 Hz x--x tO Hz o..--o 2.0Hz
B/ o
._E
"~" .~.... 2.0
,
~.
1.5
t.o
5
I
10
I
15
I
20
I
25
I
I
35
I
I
45
5 - - Hz FIG. I. Magnitude estimation of heat brightness: (A) as a function of lower stimulus (Fz) frequency, and (B) as a function of beat frequency at selected F1 frequencies. Broken line, binocular presentation; solid line, dichoptic presentation; dots, 0.5 Hz; crosses, 1.0 Hz; circles, 2. 0 Hz. to double at 5 Hz but drops to about 75 per cent change at 15 Hz. With dichoptic presentation, the brightness is considerably less than double, about 75 per cent at 5 Hz, and falls to about 25 per cent by 15 Hz. An interesting small rise in brightness occurs at 20 Hz (perhaps also reflected in the binocular data) which may indicate some facilitation at this frequency. 2 Binocular beat brightness also reaches its minimum in this region. Beat brightness drops off not only as a function of the stimulus frequencies but also as a function of beat frequency (Fig. 1B). Slow beat frequencies are judged brighter than fast beat frequencies. Moreover, with dichoptic presentation the beat brightness falls to about 25 per cent by 25 Hz stimulus frequency or above 1 Hz beat frequency. Discussion
Brightness differences between the stimuli appear to have no effect on perceived beat rate. Since beat rate is an index of the fundamental frequencies, it follows that the central 2 This may be related to other findings that the thresholds for electric (CLAUSEN,1955) and photic (KELLY, 1962) flicker tend to be lowest in this region. BARTLEY(1959) has also given some special importance to this frequency.
432
RATHEKARRER
representation o f these frequencies is accurate so long as both are seen to flicker. CLAUSEN and VANDERBILT (1957), using the combination of electric mad photic flicker, also found no effect o f brightness on perceived beat rate so long as flicker was present. The results imply that the a m o u n t o f differential brightness necessary to obscure the beat must also be a function o f the stimulus frequencies and beat frequency. F o r instance, greater differential brightness should be tolerable at an F1 frequency o f 5 H z and also with a 0.5 Hz beat frequency. The decrease in beat brightness with increasing stimulus frequencies m a y indicate a decrease in the number o f neural channels activated at each pulse (BARTLEY, 1958, 1964) even though the stimulus frequency is accurately followed by each channel. Such a process would maintain perceived beat frequency but give fewer channels for interaction during in-phase and, thus, reduced beat brightness. Since brightness has no apparent effect on perceived beat rate the neural representations o f stimulus brightness and stimulus frequency are relatively independent in flickering stimuli.
REFERENCES
BARTLEY,S. H. (1958). Some facts and concepts regarding the neurophysiology of the optic pathway. Archs Ophthal. 60, 775-791. BARTLEY,S. H. (1959). Central mechanisms of vision, inHandbookofPhysiology(editedbyH.W.MAC,OUN), Vol. 1, Sect. 1, Neurophysiology, Washington, D.C.; Am. Physiol. Soc. BARTLEY, S. H. (1964). Some sensory end results and the neural activity of the optic pathway. Am. J. Optom. Archs Am. Acad. Optom. Monogr. No. 328. B~K/~SY,G. VON(1960). Experiments in Hearing, McGraw Hill, New York. BROWN, J. L. (1965). Flicker and intermittent stimulation, in Vision and Visual Perception (edited by C. H. GRAHAM),John Wiley, New York. CLAUSEN, J. (1955). Visual Sensations (Phosphenes) Produced by a.c. Sine Wave Stimulation, Ejnar Munksgaard, Copenhagen. CLArOs~rq, J. and VANDERBrLT,C. (1957). Visual beats caused by simultaneous electrical and photic stimulation. Am. J. PsychoL 70, 577-585. KAga~R, R. (1965). Visual beat phenomena and their relation to the temporal characteristics of perception. Unpublished doctoral dissertation, Graduate Faculty, New School for Social Research. KAggER, R. (1967). Visual beat phenomena as an index to the temporal characteristics of perception. J. exp. PsychoL 75, 372-378. ~R, R. (1968). Visual beats: phenomenology and preliminary data as a function of age. Psychonom. Sei. 11, 269-270. I~LI.Y, D. H. (1962). Visual responses to time dependent stimuli: II. Amplitude sensitivity measurements. J. opt. Soc. Am. 52, 89-95.
Abstract--Visual beats, arising from dichoptic presentation of a different flicker frequency to each eye, are unaffected by widely divergent brightness of the two frequencies. Estimated perceived brightness of beats decreases as a function of flicker frequency and beat frequency. The data indicate that temporal processing is somewhat independent of brightness registration in flickering stimuli. R~sumr---Les battements visuels qui sent produits par une prrsentation dichoptique d'une frrquence de papillotement diff~rente pour chaque oeil, ne sent pas affect~s par une grande diffrrence de luminosit6 entre les deux frrquences. L'estimation de la luminosit~ pereue des battements diminue en fonction de la fr~quence de papillotement et de la frrquence des battements. Les donn~es indiquent que le processus temporel est dans une certaine mesure indrpendant de la luminosit6 enregistr~e pour les stimuli papillotants. Zusammenfassung--Sichtbare Schl~ige, die aus der dichoptischen Reizung beider Augen mit je verschiedenen Flimmerfrequenzen entstehen, sind nicht durch weitliiufige HeUigkeitsunterschiede der beiden Frequenzen beeinflusst. Die gesch~itzte Helligkeit der Schlfige verringect
Visual Beats: Differential Brightness of the Stimuli and Estimation of Brightness sich mit der Flimmer- und Schlagfrequenz. Die Resultate zeigen, dass die zeitliche Analyse v o n d e r Helligkeitsregistrierung der Flimmerreize gr6sstenteils unabh~ingig ist. Pe310Me - - 3pHTe.rlbHble <<6rIeHH~>>, BO3HHKalOIIIHe rlpI,I O~HOBpeMeHHO~ CTHMyJDII.U4H ~ByX FYla3 MeYlbKatouIHM CBeTOM pa3HOl~ qaCTOTbI, He H3MeHfllOTC~ rlprl 6OJIbIIIOM pacxo~eHIa~d CBeTJIOT Ka~O~l IIX 3THX ,/I~ByXqaCTOT. CBeTnOTa 6HermtL onpenen~eMa~ B BocHpH~THH, yMeHbIHaeTc~l rlpH yMeHbIJJeHHn qaCTOTbI MenbKaI-i~ H qaCTOTbI 6 n e a ~ . [~TH ~aHI-Ible IIOKa3blBalOT, tITO BpeMerm6e npoTeKarme rIpotlecca B H3BeQTHOFI Mepe He 3aBHCHT OT perHcTprlpyeMofi CBeTYlOTbl MenbKa~OtlinX CTHMy.rIOB.
433