Release of saccades in schizophrenics: Inattention or inefficiency?

Summary

This paper attempts to distinguish between inattention and inefficiency as the cause of the eye movement problems of schizophrenic subjects. It focuses on their release of fast saccadic eye movements in four different situations: interrupting smooth tracking, as double-jumps in refixation, and as inadvertent departures from steady fixation or too-early prediction moves. If an attention deficit causes saccades during tracking, they should be reduced only for schizophrenic subjects in the dark, when there is no constrasting background. Instead the reduction was present for all groups. If double-jumps in saccadic refixations were caused by inattentional instability, they should increase in schizophrenic subjects when the target is a temporary flash of light. Instead, they were reduced in all groups to almost none, suggesting a perceptual processing cause for the excess double jumps. If a global attentional problem of schizophrenia caused saccade release, saccade number should be correlated across the four situations. Instead, there were significant correlations only between departures and predictions in paranoid schizophrenic subjects (r = 0.728) and between predictions and looking in nonparanoid schizophrenic subjects (r = −0.855). This lack of over-all correlations suggests that a common inattentional problem does not produce these eye movement deficiencies. Instead, the perceptual influence on tracking and looking suggests that processing inefficiency is responsible for at least part of the deficit.