Visual and cognitive processing of face information in schizophrenia: detection, discrimination and working memory

Abstract

Face recognition involves several physiological and psychological processes, including those in visual, cognitive and affective domains. Studies have found that schizophrenia patients are deficient at recognizing facial emotions, yet visual and cognitive processing of facial information in this population has not been systematically examined. In this study, we examined visual detection, perceptual discrimination and working memory of faces as well as non-face visual objects in patients. Visual detection was measured by accuracy when detecting the presence of a briefly displayed face, image which contained only the basic configural information of a face. Perceptual discrimination was measured by discriminability scores for individual facial identity images, in which the degree of similarity between images was systematically varied via morphing. Working memory was measured by the discriminability scores when two comparison face images were separated by 3 or 10 s. All measurements were acquired using a psychophysical method (two-alternative forced choice). Relative to controls, patients showed significantly reduced accuracy in visual detection of faces (p=0.003), moderately degraded performance in perceptual discrimination of faces (p=0.065), and significantly impaired performance in working memory of faces (p<0.001 for both 3 and 10 sec conditions). Patients' performance on non-face versions of these tasks, while degraded, was not correlated with performance on face recognition. This pattern of results indicates that greater signal strength is required for visual and cognitive processing of facial information in schizophrenia.

Figure 1

Schematic illustration of stimuli used in (a) face detection and (b) face discrimination and working memory. For face detection, the testing sessions were blocked according to duration for which stimuli were displayed (13, 26, 52 or 104 msec). Face signal strength here is modulated by display time. Note that the face signal is limited to configural face information. In each session, 42 stimuli were presented. Presentation order of the sessions was randomized across subjects. This procedure contains no requirement for judging or memorizing facial identity or expression. For face discrimination and working memory, the difference between the two comparison face images in the second presentation, or the similarity level, could be 5, 12.5, 25, 50, or 100%. A 100% difference would entail a comparison of the two original face photographs (i.e. of two different faces). The larger a difference (i.e. the greater face signal strength for discrimination), the more easily the task can be performed. The similarity levels varied across trials according to the method of constant stimuli. Stimulus presentation and response recording were programmed within a VisionShell and controlled by a Macintosh G3 computer. All task procedures employed a two alternative forced choice method. The order of the tasks was counter-balanced across subjects. Subjects practiced on each task before data collection began. The face and the non-face tests each took about 60 minutes to complete.

Figure 2

Averaged percent correct score or accuracy in detecting faces. The abscissa denotes subject groups. The ordinate denotes subject accuracy in face detection. Higher accuracy means better performance. Open symbols are for normal controls and filled symbols for schizophrenia patients. The dark bars represent the mean accuracy of each group. When the outliers, (defined as points that were 2 standard deviations below and above the group mean) were removed, the group difference remained similarly significant.

Figure 3

Discriminability scores for perceptual discrimination of similar faces. The ordinate denotes the discriminability score. The higher the score, the better performance is. The abscissa denotes subject groups. The dark bars represent the mean score of each group. See legend of Figure 2 for additional information.

Figure 4

Discriminability scores for working memory of similar faces. The left panel is for the inter-stimulus interval of 3 sec, and the right panel is for the inter-stimulus interval of 10 sec. See legends of Figures 2 and 3 for additional information.