Abstract
Involuntary ocular tracking responses to background motion offer a window on the dynamics of motion computations. In contrast to spatial attention, we know little about the role of feature-based attention in determining this ocular response. To probe feature-based effects of background motion on involuntary eye movements, we presented human observers with a balanced background perturbation. Two clouds of dots moved in opposite vertical directions while observers tracked a target moving in horizontal direction. Additionally, they had to discriminate a change in the direction of motion (±10° from vertical) of one of the clouds. A vertical ocular following response occurred in response to the motion of the attended cloud. When motion selection was based on motion direction and color of the dots, the peak velocity of the tracking response was 30% of the tracking response elicited in a single task with only one direction of background motion. In two other experiments, we tested the effect of the perturbation when motion selection was based on color, by having motion direction vary unpredictably, or on motion direction alone. Although the gain of pursuit in the horizontal direction was significantly reduced in all experiments, indicating a trade-off between perceptual and oculomotor tasks, ocular responses to perturbations were only observed when selection was based on both motion direction and color. It appears that selection by motion direction can only be effective for driving ocular tracking when the relevant elements can be segregated before motion onset.
Highlights
A CENTRAL QUESTION IN UNDERSTANDING how perception and action may be articulated is whether perceptual selection and eye movement control rely on similar filtering mechanisms
Among involuntary tracking eye movements, ocular following is a quasireflexive response to motion covering a large part of the visual field (Kawano 1999; Miles et al 1986), which is believed to reflect the unfolding of visual motion processing, providing a window on the link between neural computation and behavior (Ilg 1997; Lisberger et al 1987; Masson and Perrinet 2012)
Arman et al (2006) showed that the motion aftereffect is stronger for motion in an attended direction even when the test appears at a nonattended location, indicating enhancement of motion processing by selection of same-direction motion signals
Summary
Undergraduate psychology students at the University of Geneva participated in the experiments for class credit (ages 18 – 42 yr, mean age 24 yr). In two dual task blocks, observers were asked to pursue the target and to report whether the vertical motion of dots in a designated color deviated to the left or to the right. The attended color and the vertical direction of motion of the attended dots in the first block were counterbalanced across participants. Observers were instructed to report the horizontal deviation of the cloud of dots moving in a specified direction. The to-be-attended dots moved to the left or right from vertical relative to a reference centered on the pursuit target (oblique motion, third line in C). B: mean horizontal and vertical eye movement velocity (group averages) locked to pursuit target motion onset. Because the vertical direction of motion was blocked, we tested whether there was anticipation of the vertical motion pulse by analyzing the interval from vertical motion onset until 80 ms thereafter, which is too early for a visually driven response
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