Visual Figural Aftereffect as a Function of Stimulation Interval and Decay Time

Abstract

Several recent reviews (2, 5, 6) show that FAE (figural aftereffecc) increases as a function of fixacion or inspection time, and decays as a function of time following fixacion. I11 vision, a single continuous period of fixation generally produces maximal FAE within 60 sec. or less (5). [There is some evidence, at least with kinesthetic FAE, that a series of inspection periods interspersed with rests may yield larger amouncs of FAE than can be obtained with a single contin~~ous period ( 1, 7) .] Inspeccion times beyond 60 sec. or so generally do not produce further increases in magnitude of visual FAE, but it has been suggested (2) that longer inspection times, to 5 min. or more, may cause FAE to persisc longer over rest. More recently, Sagara and Oyama (5, Fig. 5) summarize several studies which tend to support this suggestion. Specifically, rate of decay of visual FAE over cime following a single concinuous fixation period may vary inversely as a funccion of fixation time, both for fixacion times shorter and longer than the point at which maximal FAE is developed. The presenc study attempted to test this possibility. METHOD Apparatz~s.--The inspection stimulus was a black outline circle with a gap at the 9 o'clock position and a fixation point to the left (S's view) of the gap. Each of the 10 test stimuli consisted of two gapped circles with a fixation point between. The circle to the right of the fixation point was an exact duplicate of the inspection circle. The gap in the left circle, which was at [lie 3 o'clock position, varied in size stepwise. Four of the circles had gaps smaller than, flue larger than, and one the same size as the gap in the inspection circle. All stimuli were drawn in India ink, photographed, reduced in size, and reproduced as glossy positive prints. The prints were dry mounted on heavy posterboard. In this form all circles were 5/4 in. in diameter and 1/32 in. in width of contour. The gap in the inspection circle was 8/128 in. wide (about 28 of arc). The gaps in the test circles varied in steps of l/l28 in. from 4/128 through 13/128. The fixation point, a dot 1/64 in. in diameter, was Vg in. to the left of the gap of both the inspection circle and the right-hand test circle, and the same distance to the right of the left-hand test circle. The over-all linear width of the test circles, measured from their outside edges, was 3/4 in., or about 2 of visual angle at the viewing distance used. The card bearing the inspection stimulus was mounted in the pre-exposure field of a Gerbtands tachistoscope. The 10 cards bearing the test stimuli could be presented one at a time in the exposure field. The luminance of both pre-exposure and exposure fields, measured through the eyepiece of the tachistoscope with MacBeth illurninometer, was 2.52 ml. Design.-There were three inspection times, 4 sec., min., and 5 min., and chree test periods ( times elapsed from end of inspection to beginning of testing), 0 (immediate rest), 1 dxy, and 7 days. An independent group of 40 Ss was tested in each of these nine conditions. In addition, a concrol group of 40 Ss