scholarly journals Reversal of a Distractor Effect on Saccade Target Selection After Superior Colliculus Inactivation

2008 ◽  
Vol 99 (5) ◽  
pp. 2694-2702 ◽  
Author(s):  
Robert M. McPeek
Keyword(s):  
Superior Colliculus ◽  
Search Task ◽  
Target Location ◽  
Target Selection ◽  
Saccade Target ◽  
Search Array ◽  
Distractor Effect ◽  
Normal Trend ◽  
Winner Take All ◽  
Take All

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.

Competition Between Saccade Goals in the Superior Colliculus Produces Saccade Curvature

2003 ◽  
Vol 89 (5) ◽  
pp. 2577-2590 ◽  
Author(s):  
Robert M. McPeek ◽  
Jae H. Han ◽  
Edward L. Keller
Keyword(s):  
Superior Colliculus ◽  
Search Task ◽  
Visual Target ◽  
Temporal Structure ◽  
Saccade Target ◽  
Stimulation Site ◽  
Electrical Microstimulation ◽  
Saccade Onset ◽  
Significant Difference ◽  
Increased Activity

When saccadic eye movements are made in a search task that requires selecting a target from distractors, the movements show greater curvature in their trajectories than similar saccades made to single stimuli. To test the hypothesis that this increase in curvature arises from competitive interactions between saccade goals occurring near the time of movement onset, we performed single-unit recording and microstimulation experiments in the superior colliculus (SC). We found that saccades that ended near the target but curved toward a distractor were accompanied by increased presaccadic activity of SC neurons coding the distractor site. This increased activity occurred ∼30 ms before saccade onset and was abruptly quenched on saccade initiation. The magnitude of increased activity at the distractor site was correlated with the amount of curvature toward the distractor. In contrast, neurons coding the target location did not show any significant difference in discharge for curved versus straight saccades. To determine whether this pattern of SC discharge is causally related to saccade curvature, we performed a second series of experiments using electrical microstimulation. Monkeys made saccades to single visual stimuli presented without distractors, and we stimulated sites in the SC that would have corresponded to distractor sites in the search task. The stimulation was subthreshold for evoking saccades, but when its temporal structure mimicked the activity recorded for curved saccades in search, the subsequent saccades to the visual target showed curvature toward the location coded by the stimulation site. The effect was larger for higher stimulation frequencies and when the stimulation site was in the same colliculus as the representation of the visual target. These results support the hypothesis that the increased saccade curvature observed in search arises from rivalry between target and distractor goals and are consistent with the idea that the SC is involved in the competitive neural interactions underlying saccade target selection.

Target Selection for Saccadic Eye Movements: Direction-Selective Visual Responses in the Superior Colliculus

2001 ◽  
Vol 86 (5) ◽  
pp. 2527-2542 ◽  
Author(s):  
Gregory D. Horwitz ◽  
William T. Newsome
Keyword(s):  
Superior Colliculus ◽  
Eye Movement ◽  
Discrimination Task ◽  
Visual Motion ◽  
Target Selection ◽  
Small Population ◽  
Saccade Target ◽  
Visual Responses ◽  
Direction Discrimination ◽  
Deep Layers

We investigated the role of the superior colliculus (SC) in saccade target selection in rhesus monkeys who were trained to perform a direction-discrimination task. In this task, the monkey discriminated between opposed directions of visual motion and indicated its judgment by making a saccadic eye movement to one of two visual targets that were spatially aligned with the two possible directions of motion in the display. Thus the neural circuits that implement target selection in this task are likely to receive directionally selective visual inputs and be closely linked to the saccadic system. We therefore studied prelude neurons in the intermediate and deep layers of the SC that can discharge up to several seconds before an impending saccade, indicating a relatively high-level role in saccade planning. We used the direction-discrimination task to identify neurons whose prelude activity “predicted” the impending perceptual report several seconds before the animal actually executed the operant eye movement; these “choice predicting” cells comprised ∼30% of the neurons we encountered in the intermediate and deep layers of the SC. Surprisingly, about half of these prelude cells yielded direction-selective responses to our motion stimulus during a passive fixation task. In general, these neurons responded to motion stimuli in many locations around the visual field including the center of gaze where the visual discriminanda were positioned during the direction-discrimination task. Preferred directions generally pointed toward the location of the movement field of the SC neuron in accordance with the sensorimotor demands of the discrimination task. Control experiments indicate that the directional responses do not simply reflect covertly planned saccades. Our results indicate that a small population of SC prelude neurons exhibits properties appropriate for linking stimulus cues to saccade target selection in the context of a visual discrimination task.

Dissociating oculomotor contributions to spatial and feature-based selection

2013 ◽  
Vol 110 (7) ◽  
pp. 1525-1534 ◽  
Author(s):  
Donatas Jonikaitis ◽  
Jan Theeuwes
Keyword(s):  
Visual Perception ◽  
Target Location ◽  
Target Selection ◽  
Visual Selection ◽  
Saccade Target ◽  
Perceptual Discrimination ◽  
Spatial Selection ◽  
Feature Based ◽  
Selection Mechanisms ◽  
Saccade Preparation

Saccades not only deliver the high-resolution retinal image requisite for visual perception, but processing stages associated with saccade target selection affect visual perception even before the eye movement starts. These presaccadic effects are thought to arise from two visual selection mechanisms: spatial selection that enhances processing of the saccade target location and feature-based selection that enhances processing of the saccade target features. By measuring oculomotor performance and perceptual discrimination, we determined which selection mechanisms are associated with saccade preparation. We observed both feature-based and space-based selection during saccade preparation but found that feature-based selection was neither related to saccade initiation nor was it affected by simultaneously observed redistribution of spatial selection. We conclude that oculomotor selection biases visual selection only in a spatial, feature-unspecific manner.

Superior Colliculus Activity Related to Concurrent Processing of Saccade Goals in a Visual Search Task

2002 ◽  
Vol 87 (4) ◽  
pp. 1805-1815 ◽  
Author(s):  
Robert M. McPeek ◽  
Edward L. Keller
Keyword(s):  
Superior Colliculus ◽  
Rhesus Monkeys ◽  
Search Task ◽  
Visual Search Task ◽  
Saccadic System ◽  
Concurrent Processing ◽  
Initial Saccade ◽  
Preparatory Activity ◽  
Winner Take All ◽  
Initial Movement

Saccades are typically separated by inter-saccadic fixation intervals (ISFIs) of ≥125 ms. During this time, the saccadic system selects a goal and completes the preparatory processes required prior to executing the subsequent movement. However, in tasks in which competing stimuli are presented, two sequentially executed movements to different goals can be separated by much shorter ISFIs. This suggests that the saccadic system is capable of completing many of the preparatory requirements for a second saccade concurrently with the execution of an initial movement. We recorded single neurons in the superior colliculus (SC) during rapid saccade sequences made by rhesus monkeys performing a search task. We found that during the execution of an initial saccade, activity related to the goal of a quickly following second saccade can be simultaneously maintained in the SC motor map. This activity appears to signal the selection or increased salience of the second saccade goal even before the initial saccade has ended. For movements separated by normal ISFIs (≥125 ms), we did not observe activity related to concurrent processing, presumably because for these longer ISFI responses, the goal of the second saccade is not selected until after the end of the first saccade. These results indicate that, at the time of an initial saccade, the SC does not necessarily act as a strict winner-take-all network. Rather it appears that the salience of a second visual goal can be simultaneously maintained in the SC. This provides evidence that selection or preparatory activity related to the goal of a second saccade can overlap temporally with activity related to an initial saccade and indicates that such concurrent processing is present even in a structure which is fairly close to the motor output.

Close interactions between “When” and “Where” in saccade target selection: Multiple saliency and distractor effects

1999 ◽  
Vol 22 (4) ◽  
pp. 693-694
Author(s):  
Christian Olivers ◽  
Dietmar Heinke ◽  
Glyn Humphreys ◽  
Hermann Müller
Keyword(s):  
Visual Search ◽  
Target Selection ◽  
Saccade Target ◽  
Spatial Selection ◽  
Distractor Effect ◽  
Selection Processes ◽  
Remote Distractor Effect ◽  
Saccade Generation

A model of when and where saccades are made necessarily incorporates a model of the “When” and “Where” of target selection. We suggest that the framework proposed by Findlay & Walker does not specify sufficiently how (and by what means) selection processes contribute to the spatial and temporal determinants of saccade generation. Examples from across-trial priming in visual search and from the inhibition of temporally segmented distractors show linkage between the processes involved in computing when and where selection operates, so that there is cooperation rather than competition between so-called Where and When pathways. Aspects of spatial selection may also determine the remote distractor effect on saccades. The detailed relations between the processes involved in selection and saccade generation may be best understood in relation to detailed computational accounts of the processes.

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