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).