Luminance flicker sensitivity in positive- and negative-symptom schizophrenia

The aim of the present research was to investigate magnocellular and parvocellular channel disorders using luminance-flicker sensitivity in normal observers and a group with schizophrenia. The threshold sensitivity for a sine wave-modulated patch of achromatic flickering light in a gaussian envelope was measured as a function of its temporal frequency (1.0 Hz, 4.0 Hz, 8.0 Hz, 16.0 Hz, 32.0 Hz) and three space average luminance levels (mesopic 3.0 cd/m2, photopic 33.0 cd/m2 and 66.0 cd/m2). The Andreasen scales for the assessment of positive and negative symptoms in schizophrenia were used to classify subjects into subgroups with predominantly positive and negative symptoms. The results showed that there were no significant differences between the control and positive-symptom group in flicker sensitivity as a function of temporal frequency and luminance level, and there were no differences in flicker sensitivity between the three groups at 1.0 Hz at each of the three luminance levels. At 3.0 cd/m2 the negative-symptom group showed significant reductions in flicker sensitivity at 4.0 Hz, 8.0 Hz, 16.0 Hz and 32.0 Hz in comparison with the control and positive-symptom group. At 33.0 cd/m2 the negative-symptom group showed significant reductions in flicker sensitivity at 4.0 Hz and 32.0 Hz, and at 66.0 cd/m2 they showed significant reductions in flicker sensitivity at 4.0 Hz, 8.0 Hz and 32.0 Hz only in comparison with the control. It was concluded that the non-significant differences in flicker sensitivity in the positive-symptom group showed that the processing of temporal information in parvo- and magnocellular channels was unimpaired. Furthermore, the non-significant differences in flicker sensitivity at 1.0 Hz at each of the three luminance levels in the three groups provided evidence that functioning in parvocellular channels was unimpaired in the positive- and negative-symptom group. Finally, it was concluded that the significant reductions in flicker sensitivity at medium and high temporal frequencies in the negative-symptom group provided evidence for an impairment in magnocellular channels.