Local spatial scale for three-dot alignment acuity

Three-dot alignment discrimination thresholds were determined for blobs with Gaussian spatial and temporal contrast envelopes. The stimuli were presented at detection threshold luminance contrast. Thresholds were determined as a function of the blur parameter of the stimuli. This was done for a range of eccentricities in the visual field (from 45 degrees nasal to 65 degrees temporal). The thresholds were corrected for variations of the stimulus extent with the blur parameter. The results were used to estimate the local spatial scale for three-dot alignment acuity. This was done by a method recently introduced by Watson (1987). It was found that the local spatial scale for three-dot alignment acuity is approximately linearly proportional to eccentricity.