Abnormalities in rapid, automatic aspects of attention in schizophrenia: blunted inhibition of return.

When a visual cue is presented at the same location but 100 ms prior to presentation of a visual stimulus, reaction time to the stimulus is decreased. However, in healthy subjects if the interval between the cue and the stimulus is between 500 and 1500 ms, reaction time is increased ('inhibition of return'). The present experiment compared inhibition of return in 11 medicated and clinically stable schizophrenic outpatients and 11 healthy control subjects screened by SADS-L. Healthy subjects responded faster to true cues than false cues when the interval between cue and stimulus was 100 ms, but responded equally fast in the two conditions with a 200 ms interval and responded faster to false than true cues at 700 and 1200 ms intervals. Schizophrenics, in contrast, responded faster to true than false cues at both 100 and 200 ms intervals and showed lower than normal advantages on false as compared to true cues at 700 and 1200 ms intervals (group x cue type x interval interaction p < 0.01). Thus while schizophrenics showed 'inhibition of return' it did not begin until greater than normal intervals between cue and stimulus and was blunted in magnitude. This suggests failure of inhibitory mechanisms that are important in very rapid and automatic aspects of normal attention.