Letter to the Editor

An integrated eye movement score as a neurophysiological marker of schizophrenia

Interpersonal communication is a specific scenario in which patients with psychiatric symptoms may manifest different behavioral patterns due to psychopathology. This was a pilot study by eye-tracking technology to investigate attentive bias during social information processing in schizophrenia. We enrolled 39 patients with schizophrenia from Shanghai Mental Health Center and 42 age-, gender- and education-matched healthy controls. The experiment was a free-viewing task, in which pictures with three types of degree of interpersonal communication were shown. We used two measures: 1) initial fixation duration, 2) total gaze duration. The Positive and Negative Syndrome Scale (PANSS) was used to determine symptom severity. The ratio of first fixation duration for pictures of communicating vs. non-communicating persons was significantly lower in patients than in controls (Mann-Whitney U = 512, p = 0.004). We found that male patients showed a significantly lower ratio of first fixation duration than male controls (Mann-Whitney U = 190, p = 0.028), while it was marginally lower in female patients than female controls (Mann-Whitney U = 77, p = 0.057). The ratio of first fixation duration for pictures of communicating persons vs. no persons was negatively correlated with PANSS negative symptoms in male patients (rho = −0.458, p = 0.024).

In contrast, it was negatively correlated with PANSS positive symptoms in female patients (−0.701, p = 0.004). These findings suggest altered attentive bias during social information processing with a pattern of avoidance at first sight towards pictures of communicating persons in schizophrenia. It is worthwhile to note that social functioning impairment is associated with the severity of symptoms.

Abnormalities of global visual scanning have been well-recognized in schizophrenia patients. However, its relevance to various cognitive domains is still understudied. In the present study, we identified the association between global visual scanning and cognitive function in schizophrenia.

Eye movement was captured and analyzed in 28 individuals with schizophrenia and 21 healthy controls in free viewing test. The MATRICS consensus cognitive battery (MCCB) was applied to evaluate cognitive function.

Consistent with previous reports, schizophrenia patients exhibited several eye movement abnormalities during global visual scanning and showed cognition deficits in MCCB test as compared with healthy controls. Fixation duration was significantly related to cognitive dysfunction in schizophrenia. Moreover, there was a potential that eye movement measures during landscape scanning, rather than face scanning, were preferentially related to cognitive dysfunction.

This study indicated the association between free visual scanning and various cognitive functions in schizophrenia, shedding light on the possibility that some eye movement measures during visual exploration could be a biomarker for cognitive deficits in schizophrenia.

Eye movement abnormalities have been effective biomarkers that provide the possibility of distinguishing patients with schizophrenia from healthy controls. The existing methods for measuring eye movement abnormalities mostly focus on synchronic parameters, such as fixation duration and saccade amplitude, which can be directly obtained from eye movement data, while lack of considering more thorough features. In this paper, to better characterize eye-tracking dysfunction, we create a dataset containing 100 images with eye movement data of 40 patients and 30 healthy controls via a free-viewing task, and propose two types of features for effective schizophrenia recognition, i.e. the hand-crafted discriminative eye movement features and the model-metric based features via utilizing the computational models of fixation prediction and the metrics of evaluating their prediction performance. Using the proposed features, two commonly used classifiers including support vector machine and random forest have been trained for classification between patients and controls. Experimental results demonstrate the effectiveness of the proposed features for improving classification performance, and the potential that our method can serve as an alternative and promising approach for the computer-aided diagnosis of schizophrenia.

Alteration of visual scanpaths under emotional facial expression in schizophrenia patients has been described in recent years; however, it is not clear whether such results are different when they transfer to faces in natural social scenes. The present study was designed to investigate the effects of emotional faces in natural social scenes on the gaze patterns of patients with schizophrenia, compared to gaze at isolated faces. A novel theme identification task was used where participants selected a positive, neutral or negative word to describe an emotional picture. Participants were 29 patients with schizophrenia and 31 healthy controls. The Positive and Negative Syndrome Scale (PANSS) and the Scale of Social Function in Psychosis Inpatients (SSPI) were used to assess symptoms and social functioning. In total, patients with schizophrenia showed significantly fewer fixations, saccades numbers and decreased fixations in areas of interest. As expected, patients showed shorter scanpath length, but only in the pictures with social settings. Furthermore, the effect size of scanpaths parameters under social scene was all greater than isolated face. In addition, patients compared to controls showed more abnormal scanpath parameters processing negative and neutral faces than positive faces, especially in social scene. The present study suggests that scanpath length for social scene faces may be more sensitive than for isolated face pictures. Our findings further support restricted scanpath whilst recognizing emotional facial expressions in natural social scenes as a favorable topic for further investigation as a trait marker.

Attribution of abnormally heightened salience to daily-life stimuli is considered to underlie psychosis. Dopaminergic hyperactivity in the midbrain-striatum is thought to cause such aberrant salience attribution. A “salience network” comprising the bilateral insula and anterior cingulate cortex is related to the processing of stimulus salience. In addition, visual and auditory attention is well described by a “saliency map”. However, so far there has been no attempt to clarify these different domains of salience in an integrated way. This article provides an overview of the literature related to four domains of salience, tries to unite them, and attempts to extend the understanding of the relationship between aberrant salience and psychosis.

Eye movement abnormalities have been identified in schizophrenia; however, their relevance to cognition is still unknown. In this study, we explored the general relationship between eye movements and cognitive function.

The three eye movement measures (scanpath length, horizontal position gain, and duration of fixations) that were previously reported to be useful in distinguishing subjects with schizophrenia from healthy subjects, as well as Wechsler Adult Intelligence Scale-III (WAIS-III) scores, were collected and tested for association in 113 subjects with schizophrenia and 404 healthy subjects.

Scanpath length was positively correlated with matrix reasoning and digit symbol coding in subjects with schizophrenia and correlated with vocabulary and symbol search in healthy subjects. Upon testing for interaction effects of diagnosis and scanpath length on correlated WAIS-III scores, a significant interaction effect was only observed for matrix reasoning. The positive correlation between scanpath length and matrix reasoning, which was specific to subjects with schizophrenia, remained significant after controlling for demographic confounders such as medication and negative symptoms. No correlation was observed between the two other eye movement measures and any of the WAIS-III scores.

Herein, we reveal novel findings on the association between eye-movement-based measures of visual exploration and cognitive scores requiring visual search in subjects with schizophrenia and in healthy subjects. The association between scanpath length and matrix reasoning, a measure of perceptual organization in subjects with schizophrenia, implies the existence of common cognitive processes, and subjects with longer scanpath length may be advantageous in performance of perceptual organization tasks.