Therefore, he concluded that in the The role of accommodation in the case of direct stimulation of the two eyes with rivalry patterns, BR control control of binocular rivalry 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 pupils (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 eye 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 afterimage 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 pupil 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 afterimages. 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 Perception & 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.