Perception of object trajectory: Parsing retinal motion into self and object movement components

Abstract

A moving observer needs to be able to estimate the trajectory of other objects moving in the scene. Without the ability to do so, it would be difficult to avoid obstacles or catch a ball. We hypothesized that neural mechanisms sensitive to the patterns of motion generated on the retina during self-movement (optic flow) play a key role in this process, "parsing" motion due to self-movement from that due to object movement. We investigated this "flow parsing" hypothesis by measuring the perceived trajectory of a moving probe placed within a flow field that was consistent with movement of the observer. In the first experiment, the flow field was consistent with an eye rotation; in the second experiment, it was consistent with a lateral translation of the eyes. We manipulated the distance of the probe in both experiments and assessed the consequences. As predicted by the flow parsing hypothesis, manipulating the distance of the probe had differing effects on the perceived trajectory of the probe in the two experiments. The results were consistent with the scene geometry and the type of simulated self-movement. In a third experiment, we explored the contribution of local and global motion processing to the results of the first two experiments. The data suggest that the parsing process involves global motion processing, not just local motion contrast. The findings of this study support a role for optic flow processing in the perception of object movement during self-movement.

How Moving Backgrounds Influence Interception

“…Not necessarily, because the only conclusion that we can be certain of is that if motion of the background’s retinal image plays a role in updating goal positions in response to self-motion, it does so by relying on local changes near the target rather than by analysing the whole optic flow to separate self from object motion [37,38] or by combining retinal background motion with extra-retinal information about the eye movements [31]. We often interact with objects that are supported by horizontal surfaces or are attached to vertical surfaces, such as cups on tables and light switches on walls, in which case the direct surrounding is close to the object of interest and therefore influenced in a similar manner by self-motion.…”

“…Perhaps pursuing the moving target with one’s eyes changed matters by making it more difficult to separate the motion on the retina into components caused by eye movements, by changes in the vantage point and by object motion, thereby making it more difficult to determine an appropriate response. To make the required distinctions one would have to decompose the optic flow [37,38] or consider vestibular information [39] and information from the eye muscles [31]. …”

Guiding locomotion in complex, dynamic environments

“…By this account, the component of the object's optical motion that is due to self-motion is determined by global optic flow and factored out by the visual system, leaving the component that is due to object motion. Rushton and Warren (2005; Warren and Rushton, 2007, 2009) coined the term flow parsing to describe this process. In a series of psychophysical studies, they and other researchers (e.g., Matsumiya and Ando, 2009) have demonstrated that observers are capable of using global optic flow from the stationary background to recover object motion in world coordinates.…”

A Neural Model of MST and MT Explains Perceived Object Motion during Self-Motion

“…The proposal that self-motion information is used to globally discount the component of the object's retinal motion due to self-motion has been termed flow parsing (Rushton and Warren, 2005) and represents the most wellestablished explanation to date of how the visual system recovers world-relative object motion. Flow parsing has been suppor-ted by a series of psychophysical experiments wherein subjects judged the direction of a vertically moving object on a computer screen while viewing optic flow patterns that simulate selfmotion (Rushton and Warren, 2005;Warren and Rushton, 2007, 2008). As would be expected if the visual system "subtracted" the global optic flow pattern from the retinal optic flow, humans judge the vertical object trajectories as slanted.…”