Effects of Motion Pattern Characteristics on the Perception of Visual Acceleration

The ability to perceive visual motion is one that we use every day to perform goal-directed activities, such as intercepting or avoiding objects. As objects and observers rarely move at constant velocities, it is important to be able to detect changes in velocity. However, little attention has been paid to how we perceive visual acceleration in the literature. This thesis explored the influence of real world-relevant motion pattern characteristics on visual acceleration perception. Observers rarely see object motion with an unlimited field of view, and therefore we first examined how physically constraining the horizontal distance over which a stimulus can move affects the ability to detect and pursue horizontal acceleration and deceleration at different average velocities. Results indicated that detection improves and smooth pursuit worsens as average velocity increases. Moreover, both improve as the horizontal aperture size increases. Given our asymmetrical experience with the frequency and relevance of upward compared to downward events due to gravity, we then investigated whether acceleration and deceleration detection vary as a function of vertical direction. We also tested whether the effects of aperture size on detection and pursuit persist on the vertical axis. Our data suggested that detection is better for downward than upward motion, and both detection and smooth pursuit improve as the vertical aperture size increases. Considering that we tend to see translation as well as more complex motion patterns outside the laboratory, we subsequently explored whether acceleration and deceleration detection vary between horizontal translation and radial optic flow, which is similar to the motion we see when moving forward or backward while looking straight ahead. We found that detection is better for radial than horizontal motion, although direction within each pattern type has no effect. Finally, we verified that sensitivity to the presence of acceleration is uniform across the optic flow field, regardless of radial direction. In summary, although we detect acceleration and deceleration similarly across a wide range of conditions, overall perception appears to be affected by the unique characteristics of the motion pattern