Peripheral hyperacuity: three-dot bisection scales to a single factor from 0 to 10 degrees

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Abstract
Performance of three-dot bisection was determined as a function of the feature separation at eccentricities of 0–10 deg along the inferior vertical field meridian by using dot stimuli scaled in size to compensate for eccentricity. For these briefly flashed dot stimuli, the entire function of three-dot bisection acuity against dot separation worsens away from the fovea with a single scaling factor that is compatible with the change of the cortical magnification factor in area V1. When the presentation duration of the stimulus was lengthened from 150 msec to 1 sec, the improvement was much greater in the fovea than at 10-deg eccentricity for closely separated stimuli. We attribute this difference to a luminance cue (detection of a brightness change) that is present for a long stimulus duration at small separations in the fovea, but not in the periphery.