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Forward and backward visual masking in schizophrenia: influence of age
M F Green1, K H Nuechterlein, B Breitmeyer
1Department of Psychiatry and Biobehavioral Sciences, Harbor Medical Center, UCLA, and VA Greater Los Angeles Health Care System, Los Angeles, CA, USA.
Background:
Visual masking tasks assess the earliest stages of visual processing. This study was conducted to address: (1) whether schizophrenia patients show masking deficits after controlling for sensory input factors; (2) whether patients have relatively intact forward masking (when the mask precedes the target) compared with backward masking (when the mask follows the target); and (3) whether the masking deficits in schizophrenia reflect an accelerated age-related decline in performance.
Method:
A staircase method was used to ensure that the unmasked target identification was equivalent across subjects to eliminate any confounding due to differences in discrimination of simple perceptual inputs. Three computerized visual masking tasks were administered to 120 schizophrenia patients (ages 18-56) and 55 normal comparison subjects (ages 19-54) under both forward and backward masking conditions. The tasks included: (1) locating a target; (2) identifying a target with a high-energy mask; and (3) identifying a target with a low-energy mask.
Results:
Patients showed deficits across all three masking tasks. Interactions of group by forward versus backward masking were not significant, suggesting that deficits in forward and backward masking were comparable. All three conditions showed an age-related decline in performance and rates of decline were comparable between patients and controls. Two of the masking conditions showed increased rates of decline in backward, compared to forward, masking.
Conclusions:
We found age-related decline in performance that was comparable for the two groups. In addition, we failed to find evidence of a relative sparing of forward masking in schizophrenia. These results suggest that: (1) early visual processing deficits in schizophrenia are not due to a simple perceptual input problem; (2) sustained channels are involved in the masking deficit (in addition to transient channels); and (3) for the age range in this study, these deficits in schizophrenia are not age-related.