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Therefore, he concluded that in the The role of in the case of direct stimulation of the two with rivalry patterns, BR control control of is effected through accommodation by the blurring of retinal images. However, Fry (1936) has not in fact shown that accommodation changes LEONC. LACK do take place during BR control with Flinders University of South Australia, Bedford Park, South Australia 5042 the eyes in the normal unparalyzed state. He infers that accommodation is The role of accommodation in the control of binocular rivalry (BR) has been the basis of BR control because granted various degrees of importance by Es in the past. The most recent control is lost when his S's eyes are investigation by Fry (1936) concluded that accommodation provides the basis of paralyzed. However, neither BR control through the blurring of retinal images. However, the present study McDougall (1903) nor George (1936) found that the introduction of very small artificial (0.5 mm) did not found BR control to be obliterated by reduce BR control. It was concluded that if accommodation changes are paralyzing the intrinsic muscles. occurring with large pupils, the resulting image blurring plays no part in control Indeed, McDougall found hardly any of rivalry. Experiment 2 tested the effect of paralyzed intrinsic eye muscles and effect and warned (1906) against the found almost the same degree of control as in the normal state. The slight overemphasis of peripheral motor decrease of control that was present was attributed to a general performance systems in the control of attention. decrement, since slight performance decrements with eye paralysis were also Both Fry (1936) and McDougall found in a visual reaction-time task and hand dynamometer test. In (1903) reported the data from one Experiment 3, it was found that the increased control that was obtained over experimental S-presumably several practice sessions was mostly retained during subsequent eye paralysis. themselves in each case. In studying These findings and, in addition, a very significant control of rivaling factors affecting voluntary control of stimuli under eye paralysis strongly suggest a central component of BR control attention, it is obviously desirable to rather than one based on accommodation. minimize Ss' expectations and to take care to control motivation or If dissimilar patterns stimulate increased predominance for the right instructional conditions. A necessary corresponding retinal areas of the two eye was slightly greater than that for prerequisite would be to use a eyes, the observer perceives an the left eye but was proportionately sufficient number of Ss naive to the alternation between these two patterns similar to the original passive purposes of the experiment. The known as binocular rivalry (BR). predominance of each eye. McDougall purpose of the following experiments Helmholtz (1925), Breese (1899), (1906) concluded that even in the was to overcome past experimental McDougall (1903), DeVries and improbable case of its existence in deficiencies in clarifying the role of Washburn (1909), and Washburn and normal conditions, differential accommodation in BR control. Gilette (1933) have shown that the accommodation activity between the predominance of one of the patterns two eyes would play at the most a EXPERIMENT 1 could be increased temporarily by a secondary role in the control of The first experiment was to test the voluntary effort as compared to the attention in BR. effect of artificial pupils on BR passive viewing condition. George George (1936), in a series of tests control. Fry (1936) found that the (1936), Fry (1936), Meredith and measuring reversible perspective and reduction of artificial size from Meredith (1962), and Lack (1969) BR rates, mentioned briefly the effects 3.94- to 2.06-mm pupils was sufficient have shown that control can also be of paralyzing the intrinsic eye muscles. to abolish control in his S. In any case, demonstrated by decreasing or This had "relatively little effect on with artificial pupils smaller than increasing the rate of alternation as voluntary control in tests of reversible 0.5 mm in diam, BR control would compared with the rate during passive perspective, but in tests of binocular necessarily be abolished, since viewing. Helmholtz (1925) classified rivalry the control was noticeably accommodation changes would BR as a phenomenon of alternating decreased." Intrinsic eye muscle become completely ineffective in attention, and attributed BR control paralysis also "noticeably affected" blurring the retinal images. In the to the willful concentration of the voluntary control of rivaling present experiment, Ss were tested for attention. .. Despite the potential . Rather than attribute this their degree of control of BR under significance of BR control to the study decrease of BR control specifically to the conditions of no artificial pupils, of attention, there have been only a the loss of accommodation, he made and with 2.8-mm artificial pupils, 1.7-, few experiments, of dubious value, the more general conclusion that BR is 1.0-, and 0.5-mm pupils. and no recent experiments to a "lower level function" than that of investigate the mechanism of BR perspective reversal. Unfortunately, Method control. since George (1936) provides no data Subjects. Nine (five males and four Most concern in the past has been or statistics, it is impossible to assess females) volunteer Ss were obtained with the role of ocular the degree to which BR control was from the nonacademic staff of the accommodation as the mediator of BR affected by eye paralysis in his Psychology Department. All Ss had control. McDougall (1903) tested the experiment. normal vision without the use of effect of accommodation in BR by Fry (1936), in a rather bold corrective lenses. The natural pupil paralyzing the intrinsic eye muscles of interpretation of the earlier articles, diameters of all Ss were measured to one eye with the use of atropine. The assumed that accommodation the nearest 0.5 mm in the viewing subsequent predominance of the right "provides the basis for the voluntary condition of no artificial pupils. The eye was attributed to the loss of suppression of vision in one eye or in mean natural pupil size was 5.7 mrn, accommodation ability in the left eye. the favoring of vision in the other." with no S having natural pupils less By voluntary control, McDougall Hence, accommodation would be the than 4.5 mm in diam, Thus, it seems (1903) could increase the basis of BR control. He found that BR reasonable to assume that all the predominance of either the right eye control was nearly abolished in his S artificial pupil conditions produced or paralyzed left eye. The extent of when small artificial pupils were used. reductions of effective pupil size in all

38 Copyright 1971, Psychonomic Journals, Ine., Austin, Texas & Psychophysics, 1971, Vol. 10 (1) Table 1 30-sec test trial. Ss who did blink Mean Slow Rates and Rapid Rates in Alternations Per Minute and Mean BR Control occasionally during test trials did so at Percentages for the Six Conditions of Both Test Sessions about the same low frequency regardless of the viewing condition or Natural Natural Pupils Pupils instructions. I 2.8mm 1.7mm II 1.0mm 0.5mm The measure of rivalry rate under the "slow rate" and "rapid rate" Slow Rate 14.6 13.4 12.8 14.0 12.3 13.0 instructions in alternations per minute Rapid Rate 33.9 32.9 32.9 32.4 31.1 31.1 and the percentage BR control Percentage Control 38.3 39.6 40.1 41.2 42.7 40.5 measure, (100)(rapid - slow)/(rapid + [100(R - S)/(R + S)l slow), were the same as described in a previous article (1969). Ss. No Ss had ever practiced BR look into the stereoscope and fixate at Table 1 gives the mean slow rates, control, and only three had any the apparent intersection point of the rapid rates, and percentage control previous experience of BR. All Ss were vertical and horizontal lines," measures for both test sessions. Since naive to the purpose of the (2) "after the (start) signal press the there was no practice effect between experiment. counter once for each alternation in the two test sessions, presentation Stimuli. The fusion stimuli rivalry," and (3) "at the (stop) signal order was not included in the consisted of left and right black rings, stop pressing and look away." Ss were subsequent data analysis. An analysis 58 mm apart, with inner diameters of instructed to keep their heads of variance applied to the slow rate 8.5 deg and outer diameters of stationary and not to blink excessively and rapid rate measures showed a 10.5 deg, Each ring was centered on a during test trials. In addition, Ss significant difference (F = 27.9, 28-deg square white field. The white received one of three different df = 1/8, p < .001) between the rivalry fields were on black surrounds of a instructions for anyone test trial. The rates but no significant effect stereocard which provided a second instructions were identical to those (F = 0.98, df = 5/40, p > .50) of fusion contour for the two fields. The detailed in an earlier article by the pupillary conditions on the rivalry rate rivalry contours were a black vertical present author (Lack, 1969) of measures. A S by Condition analysis of diameter, 1 deg in width, in the right "passive rate," "slow rate," and "rapid variance applied separately to the BR fusion ring and a black horizontal rate." .The "slow rate" and "rapid control measures found no significant diameter, 1 deg in width, in the left rate" instructions were essentially the effect (F = 0.11, df = 5/40, p> .50) fusion ring. The fusion rings and same as Fry's (1936) "attempted due to pupillary conditions. In rivalry lines were inked on thin white retardation" and "attempted summary, the instructions of "slow paper and mounted in the black acceleration" conditions. They were rate" and "rapid rate" consistently stereocard. then given 2-min viewing in the produced a very significant difference Apparatus and procedure. The no-pupil condition to familiarize them of rivalry rates in all pupillary apparatus consisted mainly of a with counting alternations during BR conditions. In this experiment, the Stereoking Model HN-44 stereoscope, and to allow the BR rate to stabilize reduction of artificial pupil size had no in which could be fixed a 4 x 10 em after what Cogan and Goldstein effect on BR control. stereocard, 5.5 em from refracting (1967) found to be an initial increase The discrepancy of the present lenses, providing fixation at infinity. of BR rate commonly observed in results with Fry's (1936) findings are Immediately in front of the refracting naive Ss, In each viewing condition, all unlikely to be due to differences in lenses, artificial pupils could be Ss followed the same sequence of stimulus conditions. The retinal area mounted and adjusted to the instructions over nine test trials: the subtended and the black-white intraocular distance of any S. The "passive rate" for the first 30-sec test contrasts were about the same in both stimuli were transilluminated by a trial, the "slow rate" for the next four cases. The main difference in stimulus 500-W incandescent bulb placed trials, and the "rapid rate" for the last conditions was that Fry (1936) had behind the stereocard. To keep retinal four trials. Initially, all nine Ss were three bars in each rivalry stimulus illumination constant for all pupil tested under the three viewing compared to one bar in the present conditions, adjustments were made in conditions of no artificial pupils, experiment. In any case, according to the distance of the incandescent bulb 2.8-mm pupils, and L 7-inm pupils in the retinal blurring hypothesis, the BR from the stereocard and the input balanced order so that each condition control of any illuminated stimuli voltage to the bulb by the use of a appeared three times in each position should be lost with the use of the very Variac transformer. The effective of order. Approximately 2 months small artificial pupils, luminance was measured at the later, all nine Ss were tested in the A second source of discrepancy may for the no-pupil condition or behind viewing conditions of no artificial be due to differences in the the artificial pupil with an S.E.I. spot pupils, 1.0-inm pupils, and 0.5-mm experimental Ss. As far as possible, the photometer. In all conditions, the pupils in a similar balanced order. A Ss in the present experiment were kept luminance of the black fusion rings, complete testing session was about naive and free from expectations vertical, and horizontal diameters was 45 min in duration. Ss were given no about their ability to control the 0.31 fL. The white background knowledge of results throughout the rivalry in any of the pupillary viewing luminance was a uniform 4.0 fL. A experiment. conditions. The fact that the overall chinrest and nose slot were adjusted mean slow rate, rapid rate, and for the S in order to provide a Results and Discussion percentage control is nearly identical comfortable and fairly stable head After the initial 2-min to these respective measures in a naive position. During a test trial, S pressed familiarization period, all Ss reported unpracticed group of eight Ss in the a small event counter in his preferred no difficulty in indicating rivalry similar conditions of an earlier hand to indicate each alternation in alternations of the vertical and experiment (Lack, 1969) suggests that BR. Rate of alternation was measured horizontal lines. E observed no head the Ss in the present experiment were for 30-sec timed trials which were movements of Ss during all the test a representative naive sample. On the separated by 30-sec rest periods. trials. Ss also followed the instructions other hand, any prior expectations on All Ss were given the general not to blink excessively. Most Ss, in the part of Fry's (1936) S may have instructions: (1) "at the (ready) signal fact, did not blink at all during any made it difficult for him to exert equal

Perception & Psychophysics, 1971, Vol. 10 (1) 39 amounts of effort under the two Table 2 pupillary conditions. Whatever the Means for Both Groups Combined of Rivalry Rates, Percentage BR Control, Reaction case, the reliability of Fry's (1936) Time, and Squeeze Strength Under Normal Conditions and With results with respect to the effect of the Intrinsic Eye Muscles Paralyzed small artificial pupils on BR control BR Squeeze would now seem to be in question. Slow Rapid Control RT Strength 2 The lack of any difference due to (Alternations/Min) (Percent> (Msec) (lbs/in. ) artificial pupils does not exclude the Normal 12.6 32.8 42.8 260 18.4 possibility that accommodation Paralyzed 13.8 30.5 37.9 269 17.8 changes do provide the basis of BR Difference n.s. < .10 < .10 < .05 < .10 control. It only suggests that if there are accommodation changes concomitant with BR control, the BR control were the same as that in Mydrilate administered 20 min prior resulting image blurring in the natural Experiment 1, except that only the to testing. pupil or large pupil condition has no 0.5-fum artificial pupils were used. hi The 20 Ss were divided randomly effect on BR control as compared to addition, Ss were instructed to into two groups so that both Group A the small artificial pupil condition in maintain for all three instructional and Group B contained five males and which retinal image blurring is conditions the same criterion of what five females. Group A first had the eliminated. One is left with the they considered to be a BR normal test session followed by the necessity of developing alternative alternation. This instruction was to treatment test session; Group B had explanations if accommodation is still test the extent to which Ss in the reverse order of conditions. At no held as the basis of BR control. Iri any Experiment 1 may have enhanced time were any Ss given any knowledge case, BR control should be abolished their BR control measures by of results. when the accommodation function is distorting their criterion under the eliminated due to paralysis of the "slow rate" and ''rapid rate" Results and Discussion intrinsic eye muscles. The next instructions. In the BR task the same measures as experiment, therefore, examines the The apparatus for the visual RT task used in Experiment 1 were taken of effect of intrinsic eye muscle paralysis consisted of telegraph key, reaction passive rate, slow rate, and rapid rate on BR control. stimulus, reaction timer, and electrical in alternations per minute, and the circuitry, in addition to the chinrest percentage BR control calculated from EXPERIMENT 2 and stereoscope used in the BR task. the formula (100)(R - S)/(R + S). Iii. A mydriatic and cycloplegic named Ss viewed the stimulus through the the RT task, the first 10 trials from Mydrilate was used. One drop in each stereoscope with the stereocard and each S in each test session were eye was sufficient to produce artificial pupils removed. The stimulus considered as warm-up trials and were complete paralysis and (a 24-V 3-W red light bulb placed excluded from the results. The median pupillary dilation commencing 60 em behind the stereoscope) RT from the remaining 25 trials was approximately 15 min after provided a binocularly viewed red disk used as the S's RT in each test session. administration and lasting. of 25-fL uniform illumination. Ss were In the squeeze strength task, the mean approximately 6 h. Its effects could be positioned at the stereoscope in a of the three trials in lbs/in," was used more rapidly reversed after a testing lightproof and sound-deadened room. as the S's squeeze strength for each session with the administration of one S was instructed to hold the fingers of test session. drop in each eye of 0.5% solution his preferred hand immediately above The mean values of each of these physostigmine. The present author the telegraph key and to respond as measures for the 20 Ss under each initially tested the effect of Mydrilate quickly as possible at the onset of the treatment condition are shown in on himself and observed that the reaction stimulus by tapping the Table 2. inability to focus was subjectively telegraph key. Thirty-five reaction The effect of intrinsic eye muscle disturbing and seemed to produce trials were presented in serial order paralysis tends to be the same as that increased caution. These with no warning signals. The onset of found by Fry (1936)-a reduction of introspections suggest that intrinsic reaction stimuli followed previous rapid rate and an increase of slow rate. eye muscle paralysis may produce a trials by varying intervals of time on a However, the changes are so slight that generalized motivational decrement in semirandom schedule. The intertrial neither reaches the .05 level of Ss, To test for this possibility, a visual intervals of 3, 4, 5, 6, and 7 sec significance with a one-tailed test. The task (simple reaction time, RT) and a occurred an equal number of times in mean reduction of the BR control nonvisual task (hand squeeze strength) the total of 35 trials. Ss were warned measure approached significance were included in addition to the test to wait for the onset of the reaction (t =1.62', df =19, .10> p> .05), but of BR control. If BR control was stimulus to avoid anticipatory tapping. the mean increase of reaction time is abolished but the RT task and squeeze The apparatus for the squeeze task significant (t =1.8T, df =19, p < .05), strength task were unchanged with consisted simply of a hand and the mean decrease of squeeze Mydrilate, it would be clear dynamometer hydraulically connected strength also approaches significance confirmation of accommodation as the to a pressure gauge. Ss were instructed (t =1.64, df =19, .10> p> .05). basis of BR control. to squeeze the dynamometer bulb as Therefore, the effect of eye paralysis strenuously as possible on each of produces a slight decrement in Method three trials, separated by 30-sec rest performance, which reaches about the Subjects. Twenty (10 males and 10 intervals. same level of significance for all three females) Ss with uncorrected normal All Ss performed the three tasks in tasks. The differences between the vision and under 30 years of age were the same order (BR control, RT task, mean slow rate and mean rapid rate is obtained from an introductory and squeeze strength task) on each of still very significant (t =6.5, df =19, psychology class. No S had an;' prior two separate test sessions held 1 week p < .0001) in the eyes-paralyzed experience with BR. All were naive as apart at the same time of day. For condition. to the purpose of the experiment. both sessions, the instructions and The only difference in procedure Stimuli. The apparatus, procedures were exactly the same between the otherwise identical testing illumination, and testing procedure for except that in one session Ss had conditions of the Experiment 1

40 Perception & Psychophysics, 1971, Vol. 10 (1) 0.5-mm pupil condition and Group A were naive with respect to BR and the According to the findings of the in the normal condition of the present purposes of the experiment. author (Lack, 1970), this procedure experiment was the additional Stimuli. One pair of rivalry stimuli gives the maximum increase of BR instruction given to Group A to use (single vertical and horizontal control. Following the 12th practice the same criterion for alternations diameters of fusion rings, H-V), was day, Group P was given a final test day under both rivalry rate instructions. the same as that of Experiments 1 and with Mydrilate and without knowledge The two groups have almost identical 2. A second pair of rivalry stimuli of results. Ss were tested with the mean values of slow rate, rapid rate, (3H-3V) was produced by adding two single line rivalry stimuli, then triple and BR control. Therefore, it seems equally spaced lines parallel to each of line rivalry stimuli, and finally with reasonable to conclude that Ss do not the rivalry diameters of the first pair. the afterimage rivalry stimuli, distort their criterion to obtain fewer The additional rivalry lines were 7 deg following the normal test trial alternations in the slow rate and more in length and 1 deg in width and had sequence in each case. For the alternations in the rapid rate. the same illumination as the other afterimage stimuli, the 30-sec rest In conclusion, intrinsic eye muscle black fusion and rivalry lines. Instead periods were extended to 100 sec. paralysis does not produce a specific of producing one intersection point of Group U was tested under the same loss of BR control. On the contrary, rivalry as the first rivalry pair, this pair conditions and procedure as the final very significant BR control is present produced the intersection of three test day of Group P. with the complete abolition of vertical and three horizontal lines, or accommodation activity. If the nine rivalry intersections. The Results and Discussion nonsignificant tendency of decreased afterimage rivalry stimuli consisted of The Ss found no difficulty in BR control with eye paralysis is real, it a single vertical bar on the right eye indicating BR alternations of the is probably due to some central factor and a single horizontal bar on the left afterimage stimuli on the final test that produced performance eye, which bisected each other in the day. The alternations were reported as decrements in all three tasks. binocular condition. Both bars were being unambiguous, with a complete 4 deg in width and 28 deg in length. disappearance of one afterimage bar EXPERIMENT 3 They were produced by a photoflash usually occurring with the appearance Fry (1936) found that BR control behind the stereoscope projected of the other. This virtually eliminated of afterimage stimuli was practically through cut-out slots of a black the possibility of criterion problems abolished with the use of stereocard. for Ss, homatropine. He reasoned that BR Apparatus and procedure. The The main results of this experiment control of afterimages was mediated apparatus, instructions, and stimulus are illustrated in Fig. L' Group P's through the intraocular pressure illumination for the two pairs of practice of the "slow rate" and "rapid changes resulting from illuminated rivalry stimuli were the rate" instructions showed very accommodation. Although research same as in Experiment 2. The significant effects between Practice investigating the effects of apparatus for the test of afterimage Day 1 and Practice Day 12. The mean accommodation on intraocular rivalry control was the same as that of slow rate showed a very significant pressure (Armaly & Rubin, 1961) did Experiments 1 and 2, except that the decrease (t = 9.73, df = 13, not find the sort of pressure-changing artificial pupils were removed and the P < .0001); the mean rapid rate mechanism envisaged by Fry, it is still black stereocard with the vertical and showed a very significant increase possible that intrinsic eye muscle horizontal bar slots was inserted in the (t = 1l.2,df = 13, p < .0001); and the paralysis does abolish control of stereoscope. A Blaupunkt manually percentage control measure showed a afterimage rivalry. Therefore, this triggered photoflash was mounted very significant increase (t = 21.0, ' possibility needed to be reinvestigated. 20 cm behind the stereoscope df = 13, p < .0001). The effects due to It was also decided to include a test of equidistant from the two eyepieces. If practice are very similar to the results the comparative controllability of produced a flash with a constant of the author's earlier studies (Lack, single line and triple line rivalry stimuli output of 150 J for a duration of 1969, 1970). The fact that this during eye paralysis to determine if approximately 1 msec, The Ss were increase of BR control, using the the discrepancy of the findings of the instructed to close their eyes O.5-mm pupils, is at least as great as present experiments with Fry's (1936) immediately after the flash and to that without artificial pupils is further was due to the difference in rivalry view the afterimages. The "start" confirmation of the conclusions of stimuli. ' signal for the beginning of rivalry Experiment 1. The present author (1969) found alternation counting was given always Comparisons between the initial test that spaced practice of the "slow rate" 5 sec after the flash. day and Practice Day 1 found no and "rapid rate" instructions produced The 28 Ss were allotted randomly significant differences of slow rate, a decrease in the measured slow rate, to two groups so that a well-practiced rapid rate, and BR control. This an increase in the measured rapid rate, Group P and an unpracticed Group U confirms the results of Experiment 2, and hence an increase in the measure each contained seven males and seven that eye muscle paralysis has no effect of BR control. Because this result was females. Group P was initially tested on unpracticed control. On the other obtained with eyes normal and with Mydrilate, using only the single hand, the differences between Practice without the use of small artificial vertical and horizontal rivalry stimuli, Day 12 and the final test day did reach pupils, it is possible that an and without knowledge of results. significance (p < .01'). It is doubtful if accommodation mechanism provided Group P was then given 12 consecutive these differences can be attributed to a the basis for the increased control of practice days with eyes normal. Prior specific loss of an accommodation role well-practiced Ss, This possibility was to each practice day after Practice in well-practiced control because there also tested in the present experiment. Day 1, each S was given knowledge of are other factors which would tend to his previous day's performance in decrease the performance of Group P Method terms of mean slow rate, mean rapid on the final test day. A general Subjects. Twenty-eight (14 males rate, and percentage BR control, S 'was performance decrement with and 14 females) Ss with uncorrected then given knowledge of results after Mydrilate would be expected to normal vision and r nder 30 years of each trial and was reinforced with mild produce the same proportional age were obtamed from an praise for any improved performance decrement with unpracticed control, introductory psychology class. All Ss at the end of the practice day. but this would produce a greater

Perception & Psychophysics, 1971, Vol. 10 (1) 41 100 In any case, he is implying that the AFTERIMAGES AI main source of control still accessible ...J 90 to BR is a component that can be o GROUP P• affected on a higher level. This c: 80 I- GROUP U 0 corresponds with McDougall's (1906) Z conclusions that despite the slight o 70 U effect of atropine in reducing 60 voluntary attention in BR, the role of c: motor adjustment of sense organs is III 50 one that is only secondary to what he calls "cerebro-ideational activity." The . W 40 results of the present experiments also . o suggest that the peripheral mechanisms ~ 30 Z of accommodation, pupillary activity, ~ 20 blinking, and retinal image movement, c: if they have a real effect at all, play W 10 Q. only a secondary role in the control of binocular rivalry.

STIMULI H-V H-V H-V 3H-3V AI REFERENCES ARMALY, M. F., & RUBIN, M. L. DAYS I I 2 3 4 S 6 7 8 9 10 II 12 F Accommodation and applanation tonometry. Archives of Ophthalmology, PRACTICE DAYS 1961, 65, 415-423. BREESE, B. B. On inhibition. Psychological Monographs, 1899, 3, 1-65. Fig. 1. Mean SR control percentages with eyes paralyzed for Group P on the COGAN, R., & GOLDSTEIN, A. G. The initial test day (I) and for Group P and Group U on the final test day (F) and stability of binocular rivalry during spaced and massed viewing. Perception & means for Group P with eyes normal on the 12 practice days. Psychophysics, 1967, 2,171-174. De VRIES, A.. & WASHBURN, M. F.Minor absolute reduction of well-practiced (p < .001) elevated above these studies from the Psychological Laboratory of Vassar College: X. A study control. The absence of knowledge of respective values for Group U. of retinal rivalry in the after-image. results and reinforcement on the final What is most important with respect American Journal of Psychology, 1909, test day must also tend to decrease to the original purpose of the 20,131-138, . Group P's performance in comparison experiment is that the naive FRY, G. A; The relation of accommodation to the suppression of vision in one eye. with Practice Day 12. unpracticed Group U with Mydrilate American Journal of Ophthalmology, Although the effect of eye paralysis and using very small artificial pupils 1936, 19, 135-138. is a significant decrease of BR control had very significant control with all GEORGE, R. W. The significance of the fluctuation experienced in observing from a mean of 84.0% on Day 12 to a BR stimuli. The rapid rate/slow rate ambiguous figures and in binocular mean of 74.3% on the final test day, a difference with the H-V stimuli is very rivalry. Journal of General Psychology, comparison with the initial test day significant (t = 5.73, df =13, 1936, 15, 39-61. HELMHOLTZ, H. von. Treatise· on mean of 32.0% shows that what p < .0005), as is the difference with physiological . Vol. 3.J. P. Southall control was developed through the 3H-3V stimuli (t =7.75, df =13, (Ed.) New York: Dover, 1925. practice has been mostly retained. The p < .0005), and also with the LACK, L. C. The effect of practice on comparison between the initial test afterimage stimuli (t = 5.84, df = 13, binocular rivalry control. Perception & Psychophysics, 1969, 6, 397-400. day and final test day for Group P p < .0005). With the afterimage LACK, L. C. Effect of knowledge of results showed very significant (p < .0005) stimuli, the peripheral factors of and spacing of practice trials in training differences of slow rate, rapid rate, accommodation, pupillary activity, of control of binocular rivalry. Perceptual & Motor Skills. 1970, 31, 827-830. and BR control, as did the comparison retinal image movements, and blinking McDOUGALL, W. Physiological factors of between the unpracticed Group U and are eliminated, as is the possibility of the attention process (III). Mind, 1903, the Group P final test day. In criterion distortions. Even in this 12.473-488. . summary, the practice of "slow rate" condition there is very significant BR McDOUGALL, W. Physiological factors of the attention process (IV). Mind 1906, and "rapid rate" instructions with eyes control by naive unpracticed Ss and 15, 329-359. ' normal produces a very significant even more significant control MEREDITH, G. M., & MEREDITH, C. G; increase of control between the initial (t = 10.6, df = 13, P < 00001) by W. Effect of instructional conditions on rate of binocular rivalry. Perceptual & and final eyes-paralyzed conditions. In well-practiced Ss, This argues strongly Motor Skills, 1962, 15, 655-664. addition, it seems unlikely that this for the existence of some component WASHBURN, M, F., & GILETTE A. increased control is dependent on of control that is exerted on a higher, Studies from the Psycholo'gical nonperipheral level, Laboratory of Vassar College: LXII. accommodation. Motor factors in voluntary control of The effect of practice with the H-V George (1936) concluded that BR cube perspective fluctuations and retinal stimuli clearly transferred to the represents a "lower level function" rivalry fluctuations. American Journal of control of the 3H-3V stimuli and than reversible perspective, and, as a Psychology, 1933, 45, 315-319. afterimage stimuli since the BR result, BR is under less voluntary (Accepted for publication January 10, control measures were significantly control than is reversible perspective. 1971.)

42 Perception & Psychophysics, 1971, Vol. 10 (1)