A potential qualitative endophenotype for schizophrenia: backward masking response to red light.

Past research with unaffected relatives of individuals with schizophrenia has suggested a new qualitative endophenotype for schizophrenia that involves a unique change in visual processing response to red light. The current study provides the first report of this "red light effect" in individuals with schizophrenia (N=15), compared with nonpsychiatric controls (N=16), using a location backward masking by pattern paradigm with red and green background conditions. Analyses revealed a statistically significant group difference in the overall change in accuracy to a red background. Controls tended to show an increase in accuracy with the red (compared with green) background, although the medium effect size was not statistically significant in the small sample. In contrast, participants with schizophrenia showed a statistically significant decrease in accuracy with the red background. Results support recent reports which have suggested that a unique change in visual processing in response to red light may represent a new endophenotype for schizophrenia. This effect is unique from most existing endophenotypes in that it represents a distinct qualitative performance pattern rather than simply poorer performance relative to a comparison group.