Reduced multisensory integration in patients with schizophrenia on a target detection task

A growing body of literature demonstrates impaired multisensory integration (MSI) in patients with schizophrenia compared to non-psychiatric individuals. One of the most basic measures of MSI is intersensory facilitation of reaction times (RTs), in which bimodal targets, with cues from two sensory modalities, are detected faster than unimodal targets. This RT speeding is generally attributed to super-additive processing of multisensory targets. In order to test whether patients with schizophrenia are impaired on this basic measure of MSI, we assessed the degree of intersensory facilitation for a sample of 20 patients compared to 20 non-psychiatric individuals using a very simple target detection task. RTs were recorded for participants to detect targets that were either unimodal (auditory alone, A; visual alone, V) or bimodal (auditory+visual, AV). RT distributions to detect bimodal targets were compared with predicted RT distributions based on the summed probability distribution of each participant's RTs to visual alone and auditory alone targets. Patients with schizophrenia showed less RT facilitation when detecting bimodal targets relative to non-psychiatric individuals, even when groups were matched for unimodal RTs. Within the schizophrenia group, RT benefit was correlated with negative symptoms, such that patients with greater negative symptoms showed the least RT facilitation (r(2)=0.20, p<0.05). Additionally, schizophrenia patients who experienced both auditory and visual hallucinations showed less multisensory benefit compared to patients who experienced only auditory hallucinations, indicating that the presence of hallucinations in two modalities may more strongly impair MSI compared to hallucinations in only one modality.