Perception of circular heading from optical flow

Observers viewed random-dot optical flow displays that simulated self-motion on a circular path and judged whether they would pass to the right or left of a target at 16 m. Two dots in two frames are theoretically sufficient to specify circular heading if the orientation of the rotation axis is known. Heading accuracies were better than 1.5 degrees with a ground surface, wall surface, and 3D cloud of dots, and were constant over densities down to 2 dots, consistent with the theory. However, there was an inverse relation between the radius of the observer's path and constant heading error, such that at small radii observers reported heading 3 degrees to the outside of the actual path with the ground and to the inside with the wall and cloud. This may be an artifact of a small display screen.

Perception of circular heading from optical flow

Observers viewed random-dot optical flow displays that simulated self-motion on a circular path and judged whether they would pass to the right or left of a target at 16 m. Two dots in two frames are theoretically sufficient to specify circular heading if the orientation of the rotation axis is known. Heading accuracies were better than 1.5 degrees with a ground surface, wall surface, and 3D cloud of dots, and were constant over densities down to 2 dots, consistent with the theory. However, there was an inverse relation between the radius of the observer's path and constant heading error, such that at small radii observers reported heading 3 degrees to the outside of the actual path with the ground and to the inside with the wall and cloud. This may be an artifact of a small display screen.

Age differences in perceiving the direction of self-motion from optical flow

Patterns of optical flow produced at the eye of a moving observer are important for the guidance of locomotion. This study examined age-related changes in the ability to perceive one's direction of self-motion, or heading, from optical flow, using computer displays that simulate translational or curvilinear movement parallel to a random-dot ground surface. We found small but significant decrements in performance with age, such that the mean heading threshold rises from 1.1 degrees in younger observers to 1.9 degrees in older observers for translation, and from 1.4 degrees to 2.9 degrees for curvilinear movement, under comparable dot density and speed conditions. The absence of an age by dot density interaction indicates that there is no age-related shift in strategy, but rather a general decline in the ability to detect and localize global optical flow patterns. The decrement appears to be due to higher level losses in the visual system rather than ocular or low-level sensory losses. The results may have implications for the control of high-speed locomotion and falls in older adults.