Early and Late Modulation of Saccade Deviations by Target Distractor Similarity

Abstract

In this study, we investigated the time course of oculomotor competition between bottom-up and top-down selection processes using saccade trajectory deviations as a dependent measure. We used a paradigm in which we manipulated saccade latency by offsetting the fixation point at different time points relative to target onset. In experiment 1, observers made a saccade to a filled colored circle while another irrelevant distractor circle was presented. The distractor was either similar (i.e., identical) or dissimilar to the target. Results showed that the strength of saccade deviation was modulated by target distractor similarity for short saccade latencies. To rule out the possibility that the similar distractor affected the saccade trajectory merely because it was identical to the target, the distractor in experiment 2 was a square shape of which only the color was similar or dissimilar to the target. The results showed that deviations for both short and long latencies were modulated by target distractor similarity. When saccade latencies were short, we found less saccade deviation away from a similar than from a dissimilar distractor. When saccade latencies were long, the opposite pattern was found: more saccade deviation away from a similar than from a dissimilar distractor. In contrast to previous findings, our study shows that task-relevant information can already influence the early processes of oculomotor control. We conclude that competition between saccadic goals is subject to two different processes with different time courses: one fast activating process signaling the saliency and task relevance of a location and one slower inhibitory process suppressing that location.

Interaction between Visual- and Goal-related Neuronal Signals on the Trajectories of Saccadic Eye Movements

“…We showed the first evidence of robust deviation away in the monkey that is comparable to findings from several human studies (Van der Stigchel, 2010;Mulckhuyse et al, 2009;Van der Stigchel et al, 2007;McSorley et al, 2006;Walker et al, 2006;Ludwig & Gilchrist, 2003;Doyle & Walker, 2001). The dominant explanation for this result has been based on a hypothesis that deviation away is because of a form of top-down inhibition of the neurons representing the distractor.…”

“…(2) The competitive interaction between target and distractor should be reduced, which might facilitate deviation away, because the visual transient associated with the distractor would have ended before the target appearance. We predicted that monkeys would quickly build an expectation of the distractor locus, and that the eyes would consequently deviate away from this location, consistent with human studies (Van der Stigchel, 2010;Mulckhuyse et al, 2009;Van der Stigchel et al, 2007;McSorley et al, 2006;Walker et al, 2006;Ludwig & Gilchrist, 2003;Doyle & Walker, 2001). Simultaneously, we measured distractor-evoked activation of SC visuomotor neurons leading up to the time of a saccade, because these neurons project directly to the brainstem saccade circuitry (Rodgers, Munoz, Scott, & Paré, 2006).…”

“…Interestingly, the trajectories between successively fixated locations during natural viewing are rarely straight (see, e.g., the classic freeviewing studies by Yarbus, 1967). In recent years, human studies have shown that saccade trajectories can deviate toward or away from salient visual distractors depending on visual and cognitive parameters (Van der Stigchel, 2010;Mulckhuyse, Van der Stigchel, & Theeuwes, 2009;Van der Stigchel, Meeter, & Theeuwes, 2007;Ludwig & Gilchrist, 2003;Doyle & Walker, 2001). This has popularized a view that saccade deviation reflects a dynamic interaction between visual-and goal-related processes, but the neural basis for it remains largely unknown.…”

Oculomotor capture by stimuli that signal the availability of reward

“…When the activity somewhere on the map passes a certain threshold, a saccade toward that location is executed. Modulations of activity are thought to occur through an integration of early bottom-up (e.g., physical salience) and late top-down (e.g., task-relevance) signals that evolve after the onset of the search display (e.g., Mulckhuyse et al 2009;Trappenberg et al 2001). Accordingly, when a physically salient distractor activates a certain location on the map early in time, activity from stimuli in other locations is inhibited because of lateral inhibition.…”

“…The gap effect describes the phenomenon whereby saccade latencies typically reduce when there is a gap between the offset of the fixation stimulus and the onset of the target. In other words, when the fixation cross is removed before the onset of the search display and the moment in time at which the target may appear is uncertain [e.g., by varying stimulus onset asynchronies (SOA)], it is more likely that participants will make fast saccades (see, e.g., Mulckhuyse et al 2009). …”