2. Methods
2.1. Participants
The patients and controls in this data set have already been fully
characterized (Zemon et al., 2020; see also Table 1), but key details
are repeated. Participants included 75 healthy controls and 68 patients
with schizophrenia (n = 54) and schizoaffective disorder
(n = 14). Participants were excluded if they met the criteria for
alcohol or substance dependence within the last six months, abuse within
the last month, or had any neurologic or ophthalmic disorders affecting
contrast sensitivity. Participants had 20/32 or better corrected visual
acuity at 4m based on the Logarithmic Visual Acuity Chart (Precision
Vision, La Salle, IL). Patients were recruited from the Nathan Kline
Institute for Psychiatric Research, and diagnoses were obtained using
the Structured Clinical Interview for the Diagnostic and Statistical
Manual of Mental Disorders, 4th edition and available clinical
information. Healthy controls were excluded if they had an Axis I
psychiatric disorder. Figure 1 reproduces the demographic and clinical
characteristics of the sample.
2.1. Measures and Procedures
The stimulus and procedural details have been described but are repeated
for expository purposes. The mean background luminance was 100 cd/m²,
the viewing distance was 190 cm, and the presentation duration was
either 33 or 500 ms. Horizontal sine-wave gratings with spatial
frequencies of 0.5, 1, 4, and 7 cycles/degree (cpd) and a square-wave
grating of 21 cpd were presented randomly on the left or right side of
the screen. A two-down, one-up staircase procedure determined stimulus
contrast (± .15 log-unit steps). Contrast sensitivity corresponded to
the inverse of the contrast threshold, which itself was calculated as
the mean of the contrast values of the last ten staircase reversals
(Levitt, 1971).