Temporal segregation deficit in visual perception: a single case study

The patient (LD) presents a visual deficit in temporal segregation. PET scan showed a bilateral hypometabolism in the superior parietal, temporal and occipital cortex. Neuropsychological data revealed that memory, attention and language functions were almost completely preserved. Visual sensory tests showed that visual acuity, depth and colour perception were normal, whereas detection of apparent motion direction, flicker fusion and saccadic eye movements were abnormal. Shape drawing was impaired whereas shape recognition (and naming), with either static or dynamic stimuli, was good. LD failed in tasks requiring integration of elements to produce a whole image (line drawings, degraded and textured shapes). On the other hand, LD’s performance was good in tasks not involving spatial integration, such as visual search and letter-by-letter reading. The main finding is that LD failed in tasks requiring temporal segregation. These tasks involved shape recognition when different shapes (Experiment 1a) or different parts of either a word or a shape presented successively on the same retinal locus with (Experiments 2b, 3a, 3b) and without (Experiments 4a, 4b) eye movements. Finally, LD has no problems in tasks (4c) involving temporal integration alone. Taken together, these results suggest damage to a general mechanism involved in temporal segregation.