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Richard S. Watson, Robert F. Hess; Spatial summation depends on spatial scale. Journal of Vision 2004;4(8):862. doi: 10.1167/4.8.862.
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© ARVO (1962-2015); The Authors (2016-present)
Richard Watson, Robert Hess: McGill Vision Research. Purpose: Spatial summation of motion signals has previously been shown to occur over large regions of visual space such as those stimulated by optic flow (Burr et al 1998). However the use of spatially broadband stimuli has concealed whether information from one spatial scale dominates performance, or whether all spatial scales are exploited. We explored the role of spatial scale in spatial summation using spatially limited Gabor stimuli. Design and Methods: Stimulus. A Random Dot Kinematogram comprised a central Signal region (of variable size:1.85 to 22.4 degrees squared) surrounded by a Noise region (size: 50.2 degrees squared). The Signal region contained dots with coherent motion direction (up or down) plus dots with random direction. Only randomly moving dots appeared in the Noise region. Dots were Gabors, speed =1.5 deg/sec. Three conditions of dot spatial frequency were explored: 5.97, 10.61, 23.88 cycles/degree. Constant bandwidth was maintained. Observers performed a 2AFC direction discrimination task, the quantity of signal dots being varied to establish motion coherence thresholds. Results: Discrimination thresholds rose monotonically with decreasing Signal area. However the rate of increase depended on the centre spatial frequency of the stimuli. Low frequencies produce the highest rate of increase, with medium frequencies producing a lower rate, and high frequencies the lowest rate. Conclusions: Spatial summation for this global task depends upon spatial scale.
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