Saccadic suppression in schizophrenia

Abstract

About 40% of schizophrenia patients report discrete visual disturbances which could occur if saccadic suppression, the decrease of visual sensitivity around saccade onset, is impaired. Two mechanisms contribute to saccadic suppression: efference copy processing and backwards masking. Both are reportedly altered in schizophrenia. However, saccadic suppression has not been investigated in schizophrenia. 17 schizophrenia patients and 18 healthy controls performed a saccadic suppression task using a Gabor stimulus with individually adjusted contrast, which was presented within an interval 300 ms around saccade onset. Visual disturbance scores were higher in patients than controls, but saccadic suppression strength and time course were similar in both groups with lower saccadic suppression rates being similarly related to smaller saccade amplitudes. Saccade amplitudes in the saccadic suppression task were reduced in patients, in contrast to unaltered amplitudes during a saccade control task. Notably, smaller saccade amplitudes were related to higher visual disturbances scores in patients. Saccadic suppression performance was unrelated to symptom expression and antipsychotic medication. Unaltered saccadic suppression in patients suggests sufficiently intact efference copy processing and backward masking as required for this task. Instead, visual disturbances in patients may be related to restricted saccadic amplitudes arising from cognitive load while completing a task.

Figure 1

(1-1) Summary of target locations across all trials and participants (indicated by different colors). The distance between two successive target locations was always 7°. (1-2) Example of a saccadic suppression trial with a probe displayed by a Gabor appearing halfway (3.5°) along the saccade trajectory (depicted as arrow). Gabor grating was oriented parallel to saccade trajectory.

Figure 2

(2-1) Distribution of Gabor flashes relative to saccade onset in patients with schizophrenia (yellow) and healthy controls (blue). Overlap between groups is indicated in brown. Note, distribution of Gabor flashes was similar in both groups. (2-2) Mean probe detection rates with standard deviations related to saccade onset in patients with schizophrenia (N = 17) and healthy controls (N = 18). Detection rates are depicted as running averages. Detection rate around saccade onset did not differ between patients and controls, nor was there any evidence for prolonged backwards masking starting earlier in patients. However, baseline detection rate in the interval 200 ms to 70 ms before saccade onset was slightly, but significantly, lower in patients than controls. (2-3) Distribution of saccade amplitudes in patients with schizophrenia (yellow) and healthy controls (blue) during the saccadic suppression task. Overlap between groups is indicated in brown. Black bar indicates range of amplitudes used in the analysis below (2-4). (2-4) Similar to (2-2) but based on only amplitudes > 4°. Note, the suppression at saccade onset is even more similar between the groups than in (2-2).

Figure 3

In both groups, smaller saccade amplitudes were related to a smaller suppression index.