The time course and specificity of perceptual deterioration

Abstract

Repeated within-day testing on a texture discrimination task leads to retinotopically specific decreases in performance. Although perceptual learning has been shown to be highly specific to the retinotopic location and characteristics of the trained stimulus, the specificity of perceptual deterioration has not been studied. We investigated the similarities between learning and deterioration by examining whether deterioration transfers to new distractor or target orientations or to the untrained eye. Participants performed a texture discrimination task in three one-hour sessions. We tested the specificity of deterioration in the final session by switching either the orientation of the background or the target elements by 90 degrees. We found that performance deteriorated steadily both within and across the first two sessions and was specific to the target but not the distractor orientation. In a separate experiment, we found that deterioration transferred to the untrained eye. Changes in performance were independent of reported sleepiness and awareness of stimulus changes, arguing against the possibility that perceptual deterioration is due to general fatigue. Rather, we hypothesize that perceptual deterioration may be caused by changes in the ability for attention to selectively enhance the responses of relatively low-level orientation-selective sensory neurons, possibly within the primary visual cortex. Further, the differences in specificity profiles between learning and deterioration suggest separate underlying mechanisms that occur within the same cortical area.

Fig. 1.

Example stimuli. Shown are the horizontal background with right-leaning horizontal array (Left), vertical background with right-leaning vertical array (Center), and horizontal background with left-leaning horizontal array (Right). A background and target element orientation combination was randomly assigned to each subject for the first and second testing session. This combination became the control combination for the third testing session, which tested for changes in background and target orientation.

Fig. 2.

Experimental design. Each trial consisted of a brief target followed by a mask after an ISI. Blocks consisted of 50 trials with the same ISI. A threshold was obtained over eight blocks, with decreasing ISIs across blocks. A session consisted of three threshold measurements, and a day of testing contained three sessions, starting at 10 a.m., 2 p.m., and 6 p.m.

Fig. 3.

The time course of perceptual deterioration is spread across six thresholds in two sessions at 10 a.m. and 2 p.m.

Fig. 4.

Test of specificity of deterioration for stimulus features. Differences scores for background orientation change (left bar) and target orientation change (right bar) show significant improvement (specificity) with target orientation change but not background orientation change. **, P < 0.01.

Fig. 5.

Transfer of deterioration in trained eye (T2 - T1) and the untrained eye (T3 - T1).