Independent speed-tuned global-motion systems.
Several experiments were conducted to investigate the role of speed in global-motion processing; the extraction of the direction of motion of a small subset of coherently-moving (signal) dots in a stimulus in which the other (noise) dots move in random directions. The specific aim of the experiments was to determine whether multiple speed-tuned global-motion systems exist. The results of these experiments are: (1) when the signal dots were chosen from a group of dots moving at 1.2 degrees s-1, the speed of additional-noise dots had to be below 4.8 degrees s-1 for them to affect global-motion extraction; (2) the addition of static dots did not impair the extraction of a global-motion signal carried by dots moving at 1.2 degrees s-1; (3) noise dots moving at 1.2 degrees s-1 impaired the extraction of a global-motion signal from dots moving at 10.8 degrees s-1, though not to the same extent as dots moving at a higher speed; and (4) these results were dependent upon speed, not spatial-step size or luminance contrast. These results are interpreted as indicating that global-motion extraction occurs within at least two independent speed tuned systems. One of these systems is sensitive to high speeds and the other to low speeds.
Edwards
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Information Science Research Laboratory, NTT Basic Research Laboratories, Kanagawa, Japan. mark@hering.berkeley.edu
Badcock
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Smith
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D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors