Anti Saccades

The antisaccade task has been introduced by Hallett (1978). Normal subjects have slower antisaccade velocities, prolonged reaction times, make some erratic prosaccades, especially in a gap task, and express saccades cannot be obtained. Patients with frontal lobe lesions have great difficulties in suppressing such erratic prosaccades. The unusual task of suppressing a saccade to a suddenly appearing stimulus in the absence of a fixation point and looking to no where takes extra effort and critically depends on brain structures like the tectal fixation system and the frontal lobe.

Antisaccade performance can be altered with peripheral cues (valid, invalid, non-informative) regarding the direction of the subsequent saccade, with different cue lead times (time between cue onset and stimulus onset), and by voluntary attention to a particular location. Unexpectedly, spatially valid cues for antisaccades increase both error rate and reaction time. Background and stimulus luminance, timing parameters, stimulus eccentricity, previous trial performance and instructions are also critical for the antitask performance. The performance of the anti gap task develops with age until 15-20 years.

The antisaccade task is quickly becoming a very popular paradigm and may be used as a differential diagnostic tool for many disorders including Affective Disorder, Alzheimer, HIV, Huntington, Obsessive Compulsive Disorder, Parkinson, Schizophrenia, and Attention-Deficit Hyperactivity Disorder. Relationships to Dyslexia are established. The antisaccade task allows to distinguish between the reflexes and the voluntary saccades (frontal lobe component) by commanding these saccades in opposite directions.

When using the antisaccade task for diagnostic purposes, it is of importance to count not only the number errors but also the percentage of corrections of these errors and the corresponding correction times.

Most recently it has been shown that healthy adult subjects make about 15-20% errors (on average) and about halt of these escape the conscious perception of the subjects.

Erratic prosaccades often (about 50% of the cases) escape the subject's conscious perception (see Exp.Brain Res. 125(4):511-6, 1999). In this situation the subject's direction of attention and the direction of the saccade are dissociated in space.

See also this review article by Everling and Fischer 1998.

Author: Prof.Dr.B.Fischer & Jenny Goldring
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