Object Substitution Masking in Schizophrenia: An Event-Related Potential Analysis

Abstract

Schizophrenia patients exhibit deficits on visual processing tasks, including visual backward masking, and these impairments are related to deficits in higher-level processes. In the current study we used electroencephalography techniques to examine successive stages and pathways of visual processing in a specialized masking paradigm, four-dot masking, which involves masking by object substitution. Seventy-six schizophrenia patients and 66 healthy controls had event-related potentials (ERPs) recorded during four-dot masking. Target visibility was manipulated by changing stimulus onset asynchrony (SOA) between the target and mask, such that performance decreased with increasing SOA. Three SOAs were used: 0, 50, and 100 ms. The P100 and N100 perceptual ERPs were examined. Additionally, the visual awareness negativity (VAN) to correct vs. incorrect responses, an index of reentrant processing, was examined for SOAs 50 and 100 ms. Results showed that patients performed worse than controls on the behavioral task across all SOAs. The ERP results revealed that patients had significantly smaller P100 and N100 amplitudes, though there was no effect of SOA on either component in either group. In healthy controls, but not patients, N100 amplitude correlated significantly with behavioral performance at SOAs where masking occurred, such that higher accuracy correlated with a larger N100. Healthy controls, but not patients, exhibited a larger VAN to correct vs. incorrect responses. The results indicate that the N100 appears to be related to attentional effort in the task in controls, but not patients. Considering that the VAN is thought to reflect reentrant processing, one interpretation of the findings is that patients’ lack of VAN response and poorer performance may be related to dysfunctional reentrant processing.

Impaired conscious access and abnormal attentional amplification in schizophrenia

“…In our work, no significant difference between patients and controls was observed for the N1. This finding contrasts with several previous studies that found a reduced N1 amplitude in the auditory modality ( Brockhaus-Dumke et al 2008 ; Turetsky et al 2008 ) and in several visual masking paradigms ( Neuhaus et al 2011 ; Wynn et al 2013 ). Careful examination of the present results suggests that a non-significant difference in N1 amplitude may be observable in Fig.…”

Visual masking & schizophrenia

“…It is important to note that we do no attribute masking deficits to slips of attention such as missed stimuli but to a diminished gain of attention and/or neuromodulation. This proposal is in accordance with other studies on masking and attention ( Lalanne et al, 2012 ) and studies pointing to attentional dysfunctions ( Green et al, 2011a , Rassovsky et al, 2005b , Wynn et al, 2013 ), or short term memory ( Wynn et al, 2006 ; see also Knight et al, 1985 for poor premorbid schizophrenia patients).…”

Impaired conscious access and abnormal attentional amplification in schizophrenia

“…In our work, no significant difference between patients and controls was observed for the N1. This finding contrasts with several previous studies that found a reduced N1 amplitude in the auditory modality (Brockhaus-Dumke et al, 2008;Turetsky et al, 2008) and in several visual masking paradigms (Neuhaus et al, 2011;Wynn et al, 2013). Careful examination of the present results suggests that a non-significant difference in N1 amplitude may be observable in Figure 4A for SOA > 27 ms.…”