Time discrimination in the mentally retarded: Latency changes in the evoked potentials with visual masking paradigm

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The research was composed of two sections. First analyzed the regulation of attention transfer in time (in a split of a second). Second analyzed the relationship between memory accessibility and target context (the effect of priming).First section: Visual ERPs were measured in relation to selective attention directed to positions in time. Two target pairs (S1-S2 and S3-S4), each composed of a number (N) and a checkerboard (C) with short ISI, were flashed successively. NC-NC and CN-CN sequences were presented with the same probability in random order. A subject's task was naming for the number and pattern-matching for the checkerboard. The target was the number in a session, while the checkerboard in another session. Effects of two attentional conditions on the requlation of attention transfer in time were measured by the amplitude of the occipital N1 to the target and nontarget stimuli. One attentional condition was Focused in which a subject knew the target position prior to S1 presentation and another was Divided in which the subject did not know the target position prior to S1. The data suggested that (1) the normal subject regulated his attention transfer, that is, attending to the target and disregarding the nontarget, (2) mentally retarded and schizophrenia attended to the nontarget as well as to the target.Second section: Two pictures (S1 and S2) of familiar animals/objects were presented with short intervals. Reaction time (RT) for the S2 naming and the ERP N400 to S2 were analyzed. Parameter was closeness or distance in meaning between S1 and S2. The data suggested that (1) RT was longer and N400 was larger in amplitude when S1 and S2 were distant in meaning and (2) the same tendency was found for the retarded people as for the normal subjects.