Ricco's diameter for line detection increases with stimulus velocity.
The purpose of this study was to determine whether Ricco's diameter, the spatial extent within which sensitivity demonstrates a perfect reciprocity between contrast and area, enlarges as the stimulus velocity increases. Detection thresholds were measured for a single line of length 10 arcmin as a function of linewidth that varied between 0.31 and 21.7 arcmin and for velocity ranging from 0 to 6 deg/s. We fitted the detection threshold versus linewidth data with two power functions of slope 0 and 1 and defined the intersection of these two functions as Ricco's diameter. For an increase in velocity from 0 to 6 deg/s, Ricco's diameter increases in dimension by approximately a factor of 4. Similar results were obtained when Ricco's diameter was estimated by comparing detection threshold of a thin line to that of an edge. The increase in Ricco's diameter with stimulus velocity suggests that the spatial-frequency mechanism that mediates line detection shifts progressively toward lower spatial frequencies for faster moving stimuli.
College of Optometry, University of Houston, Texas 77204-6052, USA.
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D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D009039:Motion Perception / Q000502:physiology*; D012684:Sensory Thresholds; D013028:Space Perception / Q000502:physiology*