In Press, International Journal of Psychophysiology

Deficits in the early stages of visual information processing have consistently been found on the backward masking task in patients with schizophrenia, but the nature of this impairment remains unclear. Pupillography was used to measure attentional allocation during visual backward masking task performance in patients with schizophrenia (n=16) and nonpsychiatric controls (n=16). Schizophrenia patients detected significantly fewer targets than controls only when the stimulus onset asynchrony (SOA) between targets and masks reached 317 msec. For both groups, peak pupil dilation responses were also significantly larger in the 317 msec SOA condition relative to a no-mask condition, suggesting that the processing load of the 317 SOA masking condition was greater than the no-mask condition. In addition, a principal components analysis of pupillary response waveforms identified time-related components that appeared to differentially index attentional allocation to targets versus masks. Patients with schizophrenia showed less dilation than controls on a middle component that appeared to index attentional allocation to targets, but patients showed greater dilation than controls on a late component that appeared to index attentional allocation to masks. That is, controls attended more to targets than to masks, but patients attended more to masks than to targets. These findings suggests that masking impairments at SOA intervals greater than 100-200 msec may be due abnormalities in attentional allocation mechanisms.