Visual processing deficits in acute and chronic schizophrenics.

Psychophysical techniques have been used to assess the duration that brief visual stimuli remain in visual memory. At the earliest "iconic" stage the duration depends on several parameters, one of which is spatial frequency. In the present experiment, a two-pulse temporal resolution task was used to evaluate the duration of iconic persistence in schizophrenics as a function of spatial frequency. Normal controls, acute, and chronic schizophrenics viewed achromatic gratings of different spatial frequencies. Their objective was to discriminate between a single or double flash of these gratings. Signal detection analysis was used to control for psychological factors. Repeated measures analyses of variance revealed that schizophrenics (i) do not conform to the typical relationship between iconic persistence and spatial frequency of the grating and (ii) have longer iconic persistence than normals on all spatial frequencies. The results are discussed in terms of the different sensitivities of transient and sustained neurophysiological mechanisms involved in spatiotemporal frequency visual analysis.