Coarse Disparity Processing Does Not Shift Fine Scale Processing

Several stereomatching algorithms posit that processing on coarse (low spatial frequency) scales constrains processing on fine (high spatial frequency) scales by shifting the disparity range over which fine mechanisms operate. To test this hypothesis, we measured stereoacuity and stereo increment thresholds for high spatial frequency test stimuli in the presence of low spatial frequencies. If high spatial frequency mechanisms are always shifted to an optimal range for disparity processing, as proposed in the coarse-to-fine models, stereo increment thresholds for high frequencies in the presence of low frequencies should be constant, regardless of base disparity. In contrast, we find that in the presence of low spatial frequencies, increment thresholds for high spatial frequencies increase with base disparity as do increment thresholds for high frequencies alone. As a further test of whether information on coarse scales enhances processing on fine scales, diplopia thresholds were measured. In the presence of low frequencies, fusion ranges for high frequencies are severely reduced.