Abstract
Many locomotor tasks involve interactions with moving objects. When observer (i.e., self-)motion is accompanied by object motion, the optic flow field includes a component due to self-motion and a component due to object motion. For moving observers to perceive the movement of other objects relative to the stationary environment, the visual system could recover the object-motion component – that is, it could factor out the influence of self-motion. In principle, this could be achieved using visual self-motion information, non-visual self-motion information, or a combination of both. In this study, we report evidence that visual information about the speed (Experiment 1) and direction (Experiment 2) of self-motion plays a role in recovering the object-motion component even when non-visual self-motion information is also available. However, the magnitude of the effect was less than one would expect if subjects relied entirely on visual self-motion information. Taken together with previous studies, we conclude that when self-motion is real and actively generated, both visual and non-visual self-motion information contribute to the perception of object motion. We also consider the possible role of this process in visually guided interception and avoidance of moving objects.
Highlights
When humans and other animals move through the world, their own movement is often accompanied by the movement of other objects
For moving observers to perceive how other objects are moving relative to the stationary environment, the visual system could recover the object-motion component of optic flow
This could be achieved by factoring out the influence of self-motion using visual self-motion information, non-visual self-motion information, or some combination of both
Summary
When humans and other animals move through the world, their own movement is often accompanied by the movement of other objects. When self-motion is accompanied by object motion, the resultant optic flow includes a self-motion component caused by the observer’s movement through the world and an object-motion component caused by the movement of objects; that is, the optic flow field (Figure 1A) is the vector sum of the self-motion (Figure 1B) and object-motion components (Figure 1C). The optical motion of the stationary background (represented by the gray vectors in Figure 1A) contains only the self-motion component and is characterized by a radially expanding pattern with a focus of expansion aligned with the direction of self-motion [1,2]. The optical motion of the moving object (represented by the yellow vector in Figure 1A) includes both the self-motion and object-motion components. Unless the object is moving parallel to the observer, the direction of optical motion deviates from the radially expanding background flow, allowing for the detection of moving objects during self-motion [3]
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