A generalised deficit can account for problems in facial emotion recognition in schizophrenia
Introduction
Since it was first shown that patients with schizophrenia are impaired in categorising facial stimuli of different emotional expressions (Shannon, 1970, Dougherty and Izard, 1974), research interest in face processing abilities in schizophrenia has increased. The reasons for this are twofold. First, it has been suggested that this deficit may have important clinical consequences (e.g. misreading social cues may contribute to social avoidance, delusion formation, etc.). Second, if dissociations exist between patients’ performance on facial emotion processing and other related cognitive functions (i.e. recognition of facial identity; categorisation of other complex visual stimuli, etc.), this could offer a valuable window into the relationship between cognitive and emotional aspects of psychological functioning (Mandal et al., 1998, Leventhal and Scherer, 1987).
Over the last three decades a wealth of data has emerged pertaining to the ability of patients with schizophrenia to identify emotions. This work has focused on the ability to categorise facial stimuli as well as verbal and postural cues of emotional state. The following review is restricted to studies where the categorisation or recognition of facial expression of emotion has been a principal aim of the experimental method. Overall, these studies have shown that schizophrenia patients are impaired in recognising facial emotion. However, debate continues regarding whether the observed impairment represents a generalised performance deficit, a problem in the processing of facial stimuli, or a deficit in emotion recognition (Bryson et al., 1997, Mandal et al., 1998).
Integration of the findings in this area is problematic because differences between studies have often been greater than their similarities (Kerr and Neale, 1993). Differences occur in subject and stimulus-related variables, and methodological approach. Stage of illness, medication status, duration of illness, clinical subtyping, age and composition of clinical and control groups have all varied. Studies have also differed in terms of the emotions that have been examined, both in number and valence. For example, some studies have considered only happy, sad and neutral (Mandal et al., 1999b); others have examined seven universally recognised emotions (Bryson et al., 1997); still others have included emotions such as shame, curiosity, etc. (Walker et al., 1980). Methodological variations across studies have spanned a wide spectrum. These include posed versus natural emotional stimuli, duration of stimulus presentation, still versus motion stimuli, response requirements (e.g. free response, forced-choice, match/non-match), and whether or not a differential deficit design (Chapman and Chapman, 1978) was used. Further variations include use of other neuropsychological measures as covariates and examination of performance differences in relation to emotional valence.
Despite these problems, studies using differential deficit designs and distinct categories of emotion can give a relatively coherent picture of the deficit. The main issue is how this deficit may be interpreted.
Section snippets
Early research in emotion recognition
Early studies established that patients with schizophrenia had a deficit in the recognition of facial emotion (Dougherty and Izard, 1974, Muzekari and Bates, 1977, Shannon, 1970). Although the results were relatively consistent, interpretation is actually difficult. The major criticism has been the failure to adopt a differential deficit design (Chapman and Chapman, 1978). Because there have been no comparisons between the tasks used in these studies and others involving similar or related
Differential deficit design studies
Most of this research has used facial recognition as a control task (Addington and Addington, 1998, Salem et al., 1996, Novic et al., 1984), but some studies have also used age discrimination based on face stimuli (Gessler et al., 1989, Habel et al., 2000, Schneider et al., 1995). At least one study has addressed the hypothesis that the deficit may be an impairment in labelling rather than discrimination (Walker et al., 1984). Emotion matching or emotion discrimination tasks have often been
Selection of an appropriate modelling strategy
Feedforward neural networks, or multi-layered perceptrons using the backpropagation learning algorithm have been widely used on tasks of categorisation (Rumelhart and McClelland, 1986). The basic task fulfilled by such networks is classification through the transformation of an input vector into an output vector on the basis of weighted associations between the activation of processing units. Here it was felt that this type of neural network architecture was suitable as a model of degraded
Results
The threshold for statistical significance was set at the P<0.001 level as a partial control for the number of tests.
Discussion
The simple neural network model presented in this paper is capable of learning to discriminate facial emotions on the basis of 12 measures of salient relationships between configurational features of the face derived from real facial expressions. The network exhibited a similar pattern of relative accuracy to different emotions as that seen in healthy subjects. Moreover, when lesioned, the network's performance was degraded such that the consequence of lesioning on measures of accuracy was most
Acknowledgements
The authors would like to thank the Neuroscience Institute for Schizophrenia and Allied Disorders (NISAD) for their support, and Terry Lewin for his helpful comments regarding data analysis and preparation of the manuscript.
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