Volume 8 Issue 11 November, 2018
Eyes are our windows to the world. The current focus of attention on the role of eye movements underpinning adaptive functioning as well as psychopathology has certainly been a very unique development. This has been made possible by the advent of modern eye-tracking techniques.
Simply put, to process a visual scene, movement of the eyes in vertical and horizontal planes in a bid to acquire, fixate, and track the stimulus is necessary. High acuity information about aspects of the scene is derived through fixation that allows for visual signals to be concentrated on the fovea. Less detailed information is collected by parafoveal and peripheral retinal fields and these areas also help to locate the next fixation point. Eye rotations are calibrated in degrees of visual angle, and several successive rotations are required for a complete scan of the visual scene. Depending on whether the visual stimulus is in motion or stationary, 2 respective classes of eye movements, namely, smooth pursuit and saccades have been founded.
Fixed characteristic order of sequential eye movements known as scanpaths, help to note the features of a visual stimulus and subsequently lead to laying down of memory traces. Internal representation of visual stimulus is a sensory trace + memory trace. This continues along with external scanning consisting of motor shifts of the eyes which helps to form a feature ring. Memory traces help in successful pattern recognition. More than the visual input per se, the visual scanpaths and sequences is determined by the top-down cognitive factors of selective attention, expectations, contingencies and memory.
- Visual stimuli eye movements first work towards gathering the gist of the scene later, interpretation of the scene and task at hand (categorization or memory/recognition).
- When it comes to face perception, initially there is a registration of the overall face percept or general framework of the face and then salient features of foveal interest are inserted into the framework. This is in contrast to processing in a serial, piecemeal manner. It is known as gestalt perception.
- For neutral faces, typical inverted triangular pattern of scanning occurs with most fixations being focused on the eyes, nose and mouth. Older adults exhibit fewer overall fixations, which are disproportionately focused on the lower parts of the face, especially the mouth. Age – related frontal lobe atrophy has been elucidated as the cause.
Relevance in Psychiatric Disorders:
Eye tracking has been used to investigate disorder specific attentional bias. Attention combines early and late stage processing. Early attention -> initial viewing of stimulus; indicates initial vigilance important in threat detection. Late attention -> viewing pattern that occurs later; reflects rumination or maintenance.
In Major Depressive Disorder, individuals have an attentional bias to sad faces during late processing denoted as greater number of fixations. This may be indicative of the elaborative processing of dysphoric stimuli, akin to a ruminative cognitive style partially liable for the maintenance of MDD. Depression and bipolar disorder have been associated with prefrontal and cerebellar disturbances of oculomotor control during major depression.
Individuals high in body dissatisfaction have restricted and extensive scanning behaviours with a facial preoccupation. They attend more to their own perceived unattractive features and to the perceived attractive features of others (negative attention bias).
Endophenotype of Schizophrenia? In Schizophrenia, two discrete styles of visual scanning — “extensive” Vs “minimal” have been identified and are possibly related to positive and negative schizophrenia symptoms. They have reduced number of fixations of increased durations, visuospatial working memory deficits, superimposed upon a faulty oculomotor processing system. In contrast to gestalt facial perception, extraneous areas of the face are treated as equally critical as salient feature regions. Among non-neutral faces, they display restricted scanpaths, notably reduced for happy faces, yet with superior recognition accuracy, and increased attentional focus to salient facial features for sad faces. All of this may contribute towards misinterpretations of real-life social interactions.
Socially anxious participants were found to fixate more on the eye regions, and moreover, respond to direct gazes with increased physiological arousal. People with autism orient to different kinds of contingencies. Scanpaths are erratic, undirected, and disorganized, often reflecting the processing of only one or two relatively unimportant features of the face (e.g., an ear, the chin, or region of the hair line) but not the saccading between the eyes which is essential for face and affect recognition.
In this way, further eye tracking paradigms research can help in linking behavioral disturbances with underlying neurobiological correlates and assist in the identification of specific endophenotypes underpinning related psychological disorders.
Dr. YAMINI. D
SENIOR RESIDENT, DEPARTMENT OF PSYCHIATRY VICTORIA HOSPITAL, BMCRI
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