The prospects for the clinical application of exploratory eye movement among patients with psychotic disorders

Tianhong ZHANG, Yangyang XU, Yu LI, Jijun WANG*

·Forum·

The prospects for the clinical application of exploratory eye movement among patients with psychotic disorders

Tianhong ZHANG, Yangyang XU, Yu LI, Jijun WANG*

psychotic disorders; exploratory eye movements; free-viewing mode; visual scanpaths;eye-tracking

Laboratory examinations which relate to mental illness such as schizophrenia have been criticized for lack of specificity. Although the biological endophenotypes of mental illness receive much psychiatric focus, the heterogeneities of mental illness devalue the clinical significance of various examination tools. Eye tracking,with non-invasive, quick, and visual characteristics, is gradually gaining the attention of psychiatrists. Although early eye tracking studies found that several eye movement dysfunctions (EMDs) such as smooth pursuit dysfunctions occurred among patients with psychotic disorders (approximately 50% to 80% EMD of the patient group compared with only nearly 1% to 8% EMD of the control group),[1]there is no further breakthrough with eye-tracking application. With the development and application of new types of eye tracking facilities in recent years, various eye tracking examination tools have been upgraded. The present study discusses eye tracking’s applicability in the diagnoses of psychotic disorders.

1. Significance of the eye tracking indicators

In the common eye tracking studies, the frequently used indicators reflecting the visual scanpath are based on two fundamental components: fixation and saccade (as shown in Figure 1; the circle represents fixation and the arrow represents saccade), which include the frequencies of fixation and saccade, the fixation duration, the saccade amplitude, and so forth.Fixation shows the way that subject receives external information and reflects characteristics about degrees of freedom in attention and the information processing speed. Saccade depicts the integrated eye movement process and represents the eye movement sequence and the subtle eye movement control ability of the subject. Generally speaking, the subject completes the information gathering about the visual image with the help of the intergration between fixation and saccade,so there is subjectivity and reliability of systematically evaluating features of fixation and saccade within a certain period.

2. The exploratory of eye movement characteristics with schizophrenia

We discuss among patients. In many eye tracking experiment paradigms (such as free-viewing task),patients with schizophrenia mostly displayed atypical scanpaths.[2]Several studies found that compared with normal controls, patients with schizophrenia usually demonstrated a limited scan pattern, including a decrease of the fixation and saccade frequencies, a increase in the mean of fixation duration, a reduction ofthe saccade range, a decrease of the scanpath length,and so on.[3-5]On the contrary, the scan strategies among healthy controls were more comprehensive and global when compared with those of patients with schizophrenia. The scanpath among patients with schizophrenia was significantly poorer in the space scope than that among healthy controls. Besides, patients with schizophrenia paid less attention to the informative areas with full of meaning and characteristics than did healthy controls. This atypical scanpath feature was found in many studies investigating schizophrenia, and those studies showed high degrees of homogeneity,especially in the indicators such as fixation number,saccade amplitude, and scanpath length. Moreover,the feature was examined by different tasks, stimulant patterns, recording ways, and research teams. For example, considerable similarities in the scanpath results existed among patients with schizophrenia under the free-viewing pattern which presented patients with images such as personal emotion expressions,locations, and meaningless unreadable codes. Although conclusions remain relatively consistent, different studies still had various results concerning the specific numeric ranges, especially on the task and stimulant conditions and the ways of analyzing the data. Also,some studies had the same measurement, but the differences in the definitions of several variables influenced differences within results. For instance,some studies defined the total scanpath length as the summed distance between several fixation loci, but other studies defined it as the true path of the direct measured fixation loci. The existence of different methodologies not only influences results but also hinders the promotion of the examination tool in clinical settings. The formulation and implementation of standardized experiments are important considerations for the future.

Figure 1. Illustration of the results in eye movements

3. The evaluations of the clinical applicability of eye tracking

The diagnostic value of an examination tool can generally be evaluated by its sensitivity and specificity.Research showed that visual scanpath may be an indicator for distinguishing patients with schizophrenia from other patients with other mental disorders even exhibiting more value than the relatively traditional potential markers such as smooth eye tracking. Benson and colleagues[6]reported the results of the applicability of eye tracking among patients with schizophrenia in clinical practice in 2012. After combining three eyetracking measurements (multivariate eye movement phenotypes)—the stability of fixation, the freeviewing pattern, and smooth eye tracking—they thought the identification rate could maximally reach 98.3%. The result has already proven far superior to traditional psychophysiological and neuropsychological examinations. In their conclusions, they also suggested that the atypical scanpath was common in the freeviewing pattern among patients with schizophrenia instead of only being demonstrated in the personal emotion expression pictures or the social settings as suggested by traditional views. In addition, they thought that among all types of paradigm, the free-viewing produced the most specific results. Other benefits of eye tracking include the non-invasive nature of the procedure, the low cost, and the short amount of time required for an examination. The general procedure does not last more than 15 minutes. Contrary to magnetic resonance and electroencephalogram (EEG),eye tracking has relatively few requirements for the physical setting where it is carried out, so it has the potential for widespread application in clinical practice.

Apart from the benefit of distinguishing patients with schizophrenia from healthy controls, the value of exploratory eye tracking in detecting different types of mental illness has also gained much attention from researchers. Matsushima and colleagues[7]applied the indicators of the response search score and fixation frequency to distinguish patients with schizophrenia,patients with depression, methamphetamine psychosis,alcohol psychosis, anxiety disorder, temporal lobe epilepsy, frontal lobe lesions, and healthy controls. The results showed a sensitivity of 76.7% and a specificity of 81.4%. A study[8]compared the visual scanning performance between patients with schizophrenia and patients with bipolar disorder. Temporal and spatial features of scan paths with different types of stimuli(with or without social content) were compared.Patients with schizophrenia differed significantly on the spatial features from that of patients with bipolar disorder, which indicated that spatial scanning features may serve as biomarkers in psychotic disorders. So the visual scanpath may be a rather valuable clinical characteristic marker of psychotic disorders. But there were not enough studies comparing the eye movement characteristics among the different types of mental illnesses and there were inconsistent findings. We need to address these problems in future studies.

Another problem is the shortage of a sole eye tracking indicators to explain the biological mechanisms of mental illness. The process of eye movement usually reflects the process of early cognitive processing. Once the process has been fixed and formed to a certain characteristic, it may be reflected in the corresponding functional neuroimaging studies. Eye movement may be a key interconnecting locus between the evidence from cognitive behavioral science and the evidence from functional brain mechanisms. Eye tracking can act as a direct tool for identifying the mechanisms of cognitive dysfunction and its related cerebral impairments.Moreover, it is a desirable choice to be used in combination with EEG, magnetic resonance imaging(MRI), near-infrared spectroscopy (NIRS) and a series of other examination tools in future studies.

In summary, there are differences between patients with psychotic disorders in the eye tracking process when compared to patients with other mental disorders. The detection and identification of this atypical visual scanpath can benefit both the clinical diagnoses of mental illness and the research of psychotic endophenotypes. This tool can even become a specific and sensible biomarker. From the perspective of clinical applicability, the identification of this characteristic is more practical than other biological examination tools(such as genetic analysis, functional magnetic resonance imaging ect.), especially for its easy use in the early recognition of psychosis.[9]

Funding

The manuscript was supported by the National Natural Science Foundation of China (81201043, 81671329,81671332, 81171267, 81171280, 81261120410 and 81361120403), the Science and Technology Committee of Shanghai Municipality program (15411967200 and 14411961400), the Shanghai Jiaotong University Science and Social Science Intersection Program(14JCRY04), the Shanghai Jiaotong University Medicine and Industry Intersection Program (YG2014MS40), the Shanghai Jiaotong University School of Medicine - the Shanghai Institute For Biological Sciences, Chinese Academy of Science (SHSMU-ION) brain collaboration program (2015NKX001), Division of early psychosis(2013-YJTSZK-05), the Shanghai Municipal Excellent Leader in Academics planning program (16XD1402400)and the Shanghai Health System Advanced Applicable Promotion Techniques (2013SY003).

Conflict of interest statement

The author reports no conflict of interest related to this manuscript.

Author contributions

TZ was in charge of drafting the manuscript; YX and YL were in charge of conducting the literature reviews and summaries; and JW offered advice and revision feedback for the initial manuscript.

Reference

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Dr Tianhong Zhang obtained a bachelor’s degree in clinical medicine from China Medical University in 2004. He then obtained a master’s degree and a doctorate degree in psychiatry and mental Health at the Shanghai Mental Health Center, Shanghai Jiaotong University School of Medicine in 2007 and 2015, respectively. He has been working at the Shanghai Mental Health Center since 2007. Presently he is working as a chief physician at the Research Institute of Electroencephalogram and Eye Tracking of the Shanghai Mental Health Center. His main research interests are early recognition and intervention for psychotic disorders.

精神病性障碍患者眼动探索特征的临床应用展望

张天宏，许扬扬，李瑜，王继军

精神病性障碍；探索性眼动；自由视图；视觉扫描路径

The present study analyses recent reports on exploratory eye movement characteristics in patients with psychotic disorders and predicts the future value of using eye tracking in clinical settings as a laboratory examination tool. We hope researchers will gain further understanding about the characteristics and clinical importance of this new examination tool.

[Shanghai Arch Psychiatry. 2016; 28(4): 218-221.

http://dx.doi.org/10.11919/j.issn.1002-0829.216029]

Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine, Shanghai, China

*correspondence: Professor Wang Jijun. Mailing address: Department of Eye Movement in Brain Image, RD South Wanping 600, Shanghai, China.Postcode: 200030. E-Mail: jijunwang27@163.com

概述：本文回顾总结了近年来文献报道的精神病性障碍患者在自由视图模式下的探索性眼动特征，并且对其作为一种实验室诊断工具的临床应用价值进行了分析与展望，以期对这一新的检测方法的特点和临床意义有更深入的了解。