Study Of Visual Search Performance In Patients With First-episode Schizophrenia

Background:Schizophrenia is usually considered as a complex illness with multiple impairment of social cognition,including memory,executive function,attention,and so on.Recently,facial affect perception is also found to be impaired in schizophrenic patients,and such a deficit could probably be a specific cognitive marker for schizophrenia.It is proposed that the face perception deficit was not a specific marker for schizophrenia and might result from the deficits in earlier visual processing stages.Although evidence showed that both the face and other perceptions were impaired in schizophrenia,the evidence is not consistent for general face processing.It should be noted that numerous neurophysiological studies found abnormalities in anatomical structures and functional activities related to face processing.It is still in debating whether the deficiency of visual processing in schizophrenia is general across stimuli or stimulus specific.Existing neurophysiological evidence reveals that schizophrenia may cause physiological changes related to face processing.We adopted a visual search task to examine both kinds of processing with the same experimental design,in order to determine if the deficit in face processing is related to the deficit in early visual processing.Objectives:We adopted a visual search task,to explore if the deficit of first-episode schizophrenic patients in face processing is related to the deficit in early visual processing.Then we performed correlation analysis on the psychophysical measurement and the score of symptom,social function.Methods:Eighteen first-episode schizophrenia patients and eighteen age and gender matched healthy control were enrolled in this study.Subjects sitting quietly in a dimly lit room were asked to search a target among two or four items presented on a monitor.Every trial began with a fixation of a random period within 1000 to 2000 ms.Then,two or four triangles were presented for 600 ms at two or four possible positions in the visual field.Subjects were asked to press one of two keys to indicate whether there was a target.There were three experiments in our study.In Experiment 1,subjects were recruited to search a target triangle which pointed downward.In Experiment 2,the task was to search a specific face identity.And in Experiment 3,subjects were instructed to search a happy face among the neutral faces.In each kind of set size,we calculated for the averaged accuracy and reaction time.The psychiatric symptoms were evaluated based on the Positive and Negative Syndrome Scale(PANSS).The subjects' social functioning were assessed based on The Personal and Social Performance scale(PSP).Independent t-tests were used to compare the basic demographic and descriptive characteristics between patients and healthy controls.A mixed design ANOVA was performed on each dependent variable in each experiment.Pearson correlation analysis was then performed on the psychophysical measurement and the symptom scores.Results:Behavioral performance of visual search tasks: In Experiment 1,the interactions between the subject group and the set size were not significant for either the accuracy(P=0.001)or the reaction time(P<0.001).In Experiment 2,for the accuracy,the interaction was significant(P=0.008),as well as the main effects of the set size(P<0.001)and subject group(P=0.028).Post-hoc analysis showed that the accuracy was lower for SZ than HC only when the set size was 2(P=0.009).For the reaction time,the main effect of the set size was significant(P<0.001).In Experiment 3,the interaction for the accuracy was not significant.However,both the main effects of the set size(P<0.001)and the subject group(P=0.005)were significant.Post-hoc tests showed that the accuracies of SZ were lower than those of HC for both the set size of 2(P=0.007)and 4(P=0.006).For the reaction time,the interaction was not significant,nor the main effect of the subject group.However,the main effect of the set size was significant(P<0.001).The interaction among group,set size and experiment was not significant,the main effect of the experiment was significant(P<0.001).Post-hoc tests showed that the RT was fastest in Experiment3 and slowest in Experiment 2(all P<0.05).In summary,the search accuracy results showed that the search performance of SZ and HC was only different in searching the face related target.The reaction times of SZ were not different from those of HC.Correlation between the behavioral performance and the symptom scores: The schizophrenic patients had deficits in searching face identity(at the set size of 2)and facial expression(at the set size of 2 and 4).There was a significant correlation between the negative symptom score and the accuracy of searching a happy face at the set size of 4(P=0.012),which indicated that the severer the schizophrenia was,the harder the patients were in searching a happy face in the crowd of neutral faces.Besides,there was a significant correlationbetween the positive symptomscoreand the reaction time in searching face identity(at the set size of 4)(P=0.018)and facial expression(at the set size of 2(P=0.027)and 4)(P=0.049).Conclusions:Compared to healthy controls,the accuracies for face identity search and facial affect search were significantly lower in schizophrenia while the performance of triangle search was the same.The accuracy for facial affect search was negatively correlated to the negative symptoms in schizophrenia.The reaction time of face processing was positively correlated to the intensity of positive symptoms.These results revealed a face related deficit in schizophrenia and were in favor of the view that the deficits derived from schizophrenia in visual processing were specific to the stimuli.