First, while N1 reduction to tones has been found in psychotic patients during periods of auditory hallucinations compared to symptom-free intervals (Hubl et al., 2007), it is not limited to the auditory modality but occurs for visual processing as well, and appears to be largely independent of specific stimulus features (i.e., words or faces). Patients who are prone to auditory hallucinations also showed decreased activation in temporoparietal regions compared to nonhallucinators during a visually-presented verbal WM task (Wible et al., 2009), and showed poorer performance than nonhallucinators in both an auditory and visual word serial position test (Bruder et al., 2011). Thus, any interference caused by experiencing auditory hallucinations is not likely due to direct acoustic interference (i.e., hearing voices). However, visually-presented stimuli may be rehearsed using the verbal language system and interference from the “inner voice” could occur in hallucinators (Ford et al., 2001; Wible et al., 2009). Interestingly, restricted perceptual processing may itself cause hallucinatory symptoms, as seen after depriving healthy individuals from visual experience for several days (Merabet et al., 2004).
