Motion Perception and the Co-incidence of Spatial Structure at High and Low Spatial Frequencies

Abstract

Abstract: : Purpose: To examine how the visual system integrates motion signals that are generated by moving structure defined at different spatial frequencies. Methods: Stimuli were low or high spatial frequency (SF) band-pass filtered movies: either natural scenes or binary noise whose element size or density were systematically varied. Compound images were produced by summing low and high SF filtered images either from the same source image (producing a compound equivalent to the source image) or from independent source images (producing a compound containing uncorrelated edge structure at high and low SFs). The upper displacement limit of motion (Dmax) and motion coherence sensitivity were measured with 2AFC direction discrimination. Results: 1. Increasing the size of noise elements or enhancing low spatial frequencies increased Dmax; this is consistent with previous findings. 2. Dmax and motion coherence sensitivity were unaffected by the relative location of edges defined by high and low spatial frequencies. 3. Direction discrimination was possible between low and high SF band-pass filtered random dot patterns whose peak frequencies were separated by up to four octaves. Conclusion: The first and second results implicate spatial frequency selective motion detectors that operate independently of motion analysers selective for other spatial scales. The final result implicates a unitary motion system that can integrate the change in location of edges defined by widely separated spatial frequencies. Both mechanisms are required to account for all results, and they appear to operate under very similar conditions.

Keywords: 477 motion-2D • 586 spatial vision • 596 temporal vision