While recognizing a face appears to be a natural and usually effortless process, deficiency in this behavioral capacity can have profound consequences in everyday life. Because of the great importance of recognizing faces, a distinct and highly efficient brain system has been developed for processing and utilizing facial information.1–4
In schizophrenia, impairments in recognizing different aspects of facial information have been reported,5–8
and such impairments may play a crucial role in poor social interaction in patients. Understanding the nature of facial processing impairment can facilitate the development of effective intervention to improve the quality of patients' social life.
Facial processing comprises multiple functional components, namely, visual processing, analysis of facial identity, and recognition of facial expressions.9
The visual processing component presumably involves detection of physical features of faces, not the features used in other component processes. The visual detection of a face may occur prior to or without the acquisition of other features embedded in faces.10,11
Previous studies have shown that schizophrenia patients were deficient in judging facial identity12
and facial emotion,5,6,13
suggesting that compromised facial processing is not limited to a single component. Yet, the functional integrity of visual processing of facial information, which provides sensory signals for analyzing facial identity and emotional expression, remains an open question. Parsing impaired behavioral performance, such as face recognition, into elementary components, such as visual detection and cognitive and emotional analysis, will help in probing into the pathophysiological processes underlying schizophrenia.14
Visual processing in schizophrenia is altered in several domains including responses in the early visual pathway (contrast detection and backward masking),15,16
and motion discrimination.18–20
Presumably, the abnormalities in the visual system could compromise sensory processing of facial information, which might provide deviant signals to subsequent cognitive and emotional processes involved in face recognition. It is known that the processes involved in face recognition are qualitatively different from those involved in recognition of other visual objects.21–23
Examining the visual component involved in facial processing in schizophrenia is important not only for identifying the mechanisms for detecting a face as a special class of visual objects but also for understanding the sensory, cognitive, and emotional processes associated with the mental disorder. Further, the knowledge about the visual mechanisms of facial processing may provide clues for developing targeted intervention strategies that help patients to improve their social functioning.
The focus of the present study is to examine the process involved in analyzing the visual information fundamental for perceiving a face as such in schizophrenia. To differentiate from other components of face recognition, such as identity or expression information analysis, we use the term face detection to indicate the awareness of the mere presence of a face.
In order to examine the visual process for face detection, it is crucial to limit those clues used in analysis of facial identity and emotion, while probing into face-specific processes. We employed several experimental strategies.
- We used a line-drawn schematic face as the stimulus. The line-drawn images, unlike photo images, simply present a face-like object and contain minimal clues about individual identity or emotional expression.
- We used brief durations for the presentation of the stimulus. It has been shown that formation of the first general impression of a face requires at least 100 ms of viewing time.24
- The task we used was to detect the presence of the face-like stimulus. The simple detection nature of the task, in combination with the primitive features and brief presentation of the stimulus, helped to remove other features, such as gender, age, or expression, that are normally associated with regular face images.
- We measured the performance in detecting a nonface visual object, a tree, in addition to face detection. Like the line-drawn faces, the line-drawn trees are made of same number of line segments, rendering the two types of stimuli similar visual properties (such as brightness and complexity).
- To access the face-specific visual process, we measured the stimulus inversion effect. One hallmark of facial information processing is that recognition of faces is disproportionately disrupted by stimulus inversion, compared with recognition of other visual objects.25 Application of this stimulus inversion approach can help to delineate the specificity of facial processing deficit associated with schizophrenia.