The distribution of human motion detector properties in the monocular visual field

The detection of coherent movement in stroboscopically (100 Hz) displayed moving random checkerboard ("Julesz-") patterns is studied psychophysically for eccentricities up to 48 degrees in the temporal visual field. Starting from the assumption that the studied visual subsystem consists of ensembles of 'bilocal' movement detectors ("Reichardt-detectors"), the parameters of these elementary detectors are deduced from the experimental results. This leads to the following interesting insights into the functional architecture of the system. At any eccentricity there is a critical velocity value Vc (near the center of the range of detectable velocities) at which both the spans and the delays reach their minimum value. Thus Vc can be defined as the ratio of the minimum span to the minimum delay values. At velocities below Vc the spans are constant and the delays are inversely proportional to V. At velocities above Vc the delays are constant and the spans increase proportional to V. The critical velocity Vc at any given eccentricity equals N times Vco, where Vco, is the critical velocity for foveal vision and N an eccentricity scaling factor. (N is the inverse normalized "cortical magnification factor"). Thus there is a complete structural invariance in terms of eccentricity-scaled units. Given the eccentricity scaling factor, the determination of two subject dependent constants of foveal vision, the minimum span and minimum delay, suffices to predict the main properties of the motion detection system at any eccentricity.