[Basic cognitive-perceptive module in schizophrenics]

A specific deficit in gaze discrimination has been hypothesized for schizophrenic patients (Rosse et al., 1994). Gaze discrimination is a basic ability for animals as well as for human beings. It plays an important role in mutual control of social interactions. According to Baron-Cohen (1995), sensitivity to eye gaze relies on a specific cognitive module, the Eye Direction Detector (EDD). The author distinguishes three basic functions of the EDD; first, the EDD is involved in eyes detection; second, the EDD is used in order to establish direction of gaze, and specially to compute whether the eyes one is looking at are directed to the subject or somewhere else; third, the EDD is implied in interpretation of gaze as seeing. Rosse et al. (1994) tested subjective impressions concerning gaze discrimination in a group of schizophrenic patients. Schizophrenics reported the subjective impression of being looked at by the portraits significantly more often than controls. The authors concluded that a specific impairment in gaze detection is present in the patients, and that it may be responsible for the paranoid symptoms often reported in schizophrenia. However, it seems difficult to assert that a response bias in schizophrenics toward perceiving faces as looking at them results from the deficit of an elementary perceptual module responsible for the detection of eye-direction. Rather we suspect such a bias to be the consequence of an impairment of the more complex level of mindreading, responsible for the interpretation of gaze as seeing in terms of mental states. The aim of the present experiment was to test in a more specific way the elementary gaze discrimination system. A series of portraits of models looking at five different directions (-30 degrees, -15 degrees, 0 degree, 15 degrees, 30 degrees), have been presented to 22 schizophrenic patients and 36 normal control subjects. In each trial one portrait was presented. Subjects were asked to determine the direction of its gaze by pressing the "z-key" (left side of the keyboard) if the portrait was looking to the left, and the "/-key" (right side of the keyboard) if the portrait was looking to the right. For each trial, we recorded both the side of the response (left key or right key) and the corresponding reaction time (RT). For the purpose of the analysis, the mean numbers of left responses were computed for each subject. The mean numbers of left responses recorded for each direction of gaze did not significantly differ between patients and controls. That is schizophrenic patients are not impaired in the gaze discrimination task used in the present study. In Rosse's experiment, subjects were required to decide whether the portrait on the screen was looking at them or not. On the contrary, in our task, subjects were simply required to state whether gaze was directed to the right or to the left. No explicit judgment was required as to whom or what gaze was directed. Therefore, we can assume that the present paradigm investigated the functioning of a more basic process than that tested by Rosse et al. Our data are consistent with those reporting that basic cognitive processes are unimpaired in schizophrenia, whereas explicit processes are extensively affected.