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Infant saccadic eye movements to visible and previously visible targets
Insights
Infant saccadic eye movements for target localization are pre-programmed. The number and size of saccades (eye movements) were determined before the first movement, regardless of target visibility.
Area of Science:
- Developmental neuroscience
- Oculomotor control
- Infant visual perception
Background:
- Infants localize peripheral targets using multiple saccades.
- Saccade step size relates to target distance but is constant within a series.
- The timing of saccade programming relative to target presentation is unclear.
Purpose of the Study:
- To investigate if saccade parameters are pre-determined before the initial saccade in a localization series.
- To examine the role of target visibility in saccade programming during infant visual localization.
Main Methods:
- Two-month-old infants viewed peripheral targets.
- Targets were either continuously visible or extinguished before localization.
- Saccadic eye movements were recorded and analyzed for step size and number.
Main Results:
- Infants predominantly used multiple saccades towards the target hemifield in both conditions.
- Saccade size within a series was consistent but varied with initial target distance.
- The pattern of multiple saccades was similar whether targets remained visible or were extinguished.
Conclusions:
- Saccade parameters for target localization appear to be pre-programmed before the first saccade.
- The oculomotor program for saccadic localization operates similarly regardless of continuous target presence.
- This suggests a robust, pre-determined strategy for visual target acquisition in young infants.
Abstract:
Recent evidence has shown that 1- and 2-month-old infants localize a peripheral target by means of a series of saccades. Step size in a series was directly related to target distance, but within a localizing series did not vary appreciably as the line of sight approached the target. The current study examined whether, during localization of a peripheral target, step size and number of steps were determined prior to the first saccade in a localizing series. 2-month-olds viewed peripheral targets which either remained on (continuous condition) or were extinguished (interrupted condition) prior to target localization. It was found that on the majority of trials a series of saccades was made toward the target hemifield. In both conditions the size of each saccade in a multiple saccadic series was approximately equal within a given trial, but varied with initial target distance. Multiple saccades on both continuous and interrupted trials were similar in form, differing only in the total extent of eye rotation. This suggests that a similar oculomotor program was operating under both conditions.