The tell-tale tasks: a review of saccadic research in psychiatric patient populations

Abstract

This review focuses on saccade research with adult psychiatric patients. It begins with an introduction of the various types of saccades and the tasks used to evoke them. The functional significance of the different types of eye movements is briefly discussed. Research findings regarding the saccadic performance of different adult psychiatric patient populations are discussed in detail, with particular emphasis on findings regarding error rates, response latencies, and any specific task parameters that might affect those variables. Findings regarding the symptom, neurocognitive, and neural correlates of saccadic performance and the functional significance of patients' saccadic deficits are also discussed. We also discuss the saccadic deficits displayed by various patient groups in terms of circuitry (e.g. cortical/basal ganglia circuits) that may be implicated in the underlying pathophysiology of several of these disorders. Future directions for research in this growing area are offered.

Figures

Figure 1

Saccadic eye movement tasks. Each panel shows the salient events occurring in different saccade tasks over time. The line marked Right and Left in each panel indicates the hemifield in which the target appears. The bottom line labeled ‘eye’ in each panel is a schematic of the eye position. Upward deflections of the eye position trace indicate rightward eye movements and downward deflections indicate leftward eye movements. The grey bar in each panel labeled ‘fixation’ indicates the onset and duration of the fixation stimulus, usually located in the center of a screen. The black bar labeled ‘target’ in each panel indicates the onset and duration of the target which is usually located in the periphery. A. Visually-guided saccade task. The fixation stimulus appears (grey bar) and the subject is required to maintain gaze on its location. After a fixation time a peripherally located target (black bar) appears and at the same time the fixation stimulus disappears. The subject is required to make a saccade to the target. This task is also referred to as a reflexive prosaccade. B. Visually-guided, delayed-saccade task. The fixation stimulus appears and after a fixation time the target appears. A further delay is imposed during which the subject maintains fixation. After the delay, the fixation stimulus disappears signaling the subject to make a saccade to the target. C. Memory-guided saccade task. The fixation stimulus appears and the subject is required to maintain gaze on its location. After a fixation time a target appears transiently. The subject is required to maintain fixation and only after another delay does the fixation stimulus disappear signaling the subject to make a saccade to the location of the previously flashed target. This task is also referred to as the oculomotor delayed response task (ODR). D. Antisaccade task. This task is identical to the reflexive saccade task except that a peripheral stimulus appears in one hemifield (now called cue) and the required saccade is to the opposite hemifield. In this example, the cue appears in the right hemifield and the saccade is leftward. E. Gap saccade task. The fixation stimulus appears and after a fixation time it disappears. The subject maintains gaze at the center where the fixation stimulus was. After a ‘gap time’ a second stimulus appears in the periphery and the subject is required to make a saccade to the location of the second stimulus. Note that this task differs from all others in that the cue to make a saccade is the onset of the peripheral stimulus whereas in the other tasks the cue to make a saccade is the offset of the fixation stimulus. F. Antisaccade with gap task. This task is a combination of those shown in D and E. The peripheral stimulus (cue) appears in one hemifield and the saccade occurs toward the opposite hemifield. The onset of the cue occurs after a ‘gap time’ in which the fixation stimulus is no longer present on the screen.