Motion discrimination around the visual field

Abstract

Rationale. There are several perceptual asymmetries associated with motion sensitivity, each of which has been investigated independently. Sensitivity is greater: (1) for directions toward/away from the center of gaze than for tangential trajectories (radial direction advantage); (2) for locations in the lower than upper visual field (LVF advantage); and (3) for cardinal than oblique directions (cardinal direction advantage). Goal. We systematically investigated whether the radial direction advantage occurs across polar angle locations, and first tested whether the radial and LVF advantages interact. Then, we addressed whether, and to what extent, sensitivity is enhanced for directions along the primary axes of an absolute reference frame (cardinal vs oblique) and a relative reference frame (radial-tangential vs directions that are neither radial nor tangential). Method. Observers discriminated the drift direction of a Gabor target at 7 degrees eccentricity, at 1 of 8 polar angle locations. At each location, subjects judged motion direction (clockwise/counterclockwise) relative to 1 of 8 motion directions. Sensitivity was derived from psychometric curves fit to data for each direction per location. Radial and tangential performance was computed by averaging sensitivity for the 2 corresponding test directions at each location. In a separate analysis, we averaged sensitivity for 4 cardinal and 4 oblique directions per location. Results. (1) The radial direction advantage is location-specific, primarily occurring in the LVF. (2) The LVF advantage is direction-specific, occurring primarily for radial motion. (3) Sensitivity is increased for directions along the primary axes of an absolute reference frame for all observers (cardinal better than oblique) and along the primary axes of a relative reference frame for some observers (radial/tangential better than other directions). Discussion. These interactions between directional and location asymmetries provide a nuanced characterization of motion discriminability around the visual field.