Psychophysical and saccadic information about direction for briefly presented visual targets

Area of Science:

• Neuroscience
• Ophthalmology
• Cognitive Psychology

Background:

• Saccadic eye movements involve constant error (difference between intended and actual movement) and variable error (amplitude variability).
• These errors are thought to stem from sensory (target position processing) and motor (execution) components.
• Understanding if the saccadic system uses the same target position information as visual perception is crucial.

Purpose of the Study:

• To compare how the saccadic system and visual perception process target position information under varying presentation durations.
• To determine if sensory and motor error components in saccades are influenced similarly by target presentation conditions.

Main Methods:

• Subjects performed saccades towards targets and made psychophysical judgments about target locations.
• Targets were presented for brief durations (17-200 msec) and sometimes followed by a spatial mask.
• Psychophysical tasks included vernier and bisection judgments to assess perceived target position.

Main Results:

• Brief target presentation and masking significantly decreased mean saccadic amplitude and increased inter-trial variability.
• Perceived target position also shifted to lesser eccentricities and showed increased variability under these conditions.
• Changes in saccadic constant errors were proportionally larger than observed in psychophysical judgments.

Conclusions:

• The saccadic and perceptual systems process target position information similarly but separately.
• Differences in saccadic error changes suggest distinct processing mechanisms, potentially related to collicular receptive field properties.
• Collicular receptive field characteristics may explain saccadic amplitude changes and undershoots related to target duration.