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Updated: Jul 6, 2026
Investigating the Deployment of Visual Attention Before Accurate and Averaging Saccades via Eye Tracking and Assessment of Visual Sensitivity
Published on: March 18, 2019
Reversal of a distractor effect on saccade target selection after superior colliculus inactivation
1The Smith-Kettlewell Eye Research Institute, 2318 Fillmore Street, San Francisco, CA 94115, USA. rmm@ski.org
Abstract:
Recent evidence indicates that inactivation of the primate superior colliculus (SC) results in an increase in saccade target-selection errors. The pattern of errors suggests that a winner-take-all competition selects the saccade goal and that SC inactivation perturbs this process by biasing the competition against stimuli in the inactivated field. To investigate this idea, the difficulty of target selection was manipulated in a color-oddity search task by varying the number of homogeneous distractors in the search array. Previous studies have shown that target selection is easier when a greater number of homogeneous distractors is present, due to perceptual grouping of the distractors. These results were replicated when testing with the SC intact. Surprisingly, during SC inactivation, this normal trend was reversed: target-selection performance declined significantly with more distractors, resulting in a greater proportion of errant saccades to distractors. Examination of the saccade endpoints indicates that after SC inactivation, many errant saccades were directed to distractors adjacent to the target. This pattern of results suggests that the salience signal used by the SC for target selection is relatively broad in spatial scope. As a result, when the area of the SC representing the target location is inactivated, distractors near the target are at a competitive advantage relative to more distant distractors and, consequently, are selected more often as the saccade goal. This contributes to the trend of worse performance with more distractors due to the greater proximity of distractors to the target.
Insights
Inactivating the superior colliculus (SC) impairs saccade target selection. This study reveals SC inactivation reverses normal search trends, increasing errors when distractors are closer to the target.
Area of Science:
- Neuroscience
- Oculomotor control
- Visual attention
Background:
- The superior colliculus (SC) plays a critical role in guiding eye movements (saccades) by selecting targets.
- Inactivating the SC leads to increased errors in choosing the correct saccade target.
- Existing models suggest a competitive process for saccade goal selection, potentially disrupted by SC inactivation.
Purpose of the Study:
- To investigate how superior colliculus (SC) inactivation affects target selection in a visual search task.
- To determine if SC inactivation alters the influence of distractor number on search performance.
- To explore the spatial scope of the salience signal processed by the SC.
Main Methods:
- A color-oddity search task was employed with varying numbers of homogeneous distractors.
- Target selection difficulty was manipulated by adjusting distractor density.
- Performance was assessed with the SC intact and during SC inactivation in primates.
Main Results:
- With the SC intact, increased distractors improved target selection, consistent with perceptual grouping.
- During SC inactivation, this trend reversed: performance declined significantly as distractor number increased.
- Errant saccades were frequently directed to distractors adjacent to the target following SC inactivation.
Conclusions:
- Superior colliculus (SC) inactivation disrupts the normal facilitatory effect of distractors on target selection.
- The SC's salience signal appears to have a broad spatial scope, making nearby distractors more competitive when the target representation is inactivated.
- This broad spatial influence contributes to increased saccade errors towards distractors near the target during SC inactivation.
