Abstract
Aim. Humans are sensitive not only to interocular positional disparities, the basis of stereopsis, but also disparities in contrast or hue. Here we ask whether the mechanisms for detecting such disparities are adaptable. Evidence of adaptability would support the idea that there are dedicated channels for detecting interocular disparities in contrast or hue. Here we term such disparities 'interocular decorrelations'. Methods. Stimuli were horizontally-oriented multi-spatial-frequency sine-wave luminance gratings, subject to interocular differences in their component sine-wave phase Ø. Observers adapted to various Ø, specifically correlated (Ø= 0o), uncorrelated (Ø = 90o) and anticorrelated (Ø = 180), as well as to monocular patterns (adaptor to just one eye) and to a blank screen (the no-adaptor condition). During the test period observers discriminated between a correlated pattern and one with a Ø>0 that was adjusted by a staircase procedure that converged on 79% correct detections. Ø values were then converted to an index of interocular decorrelation (ID) that ranged from 0-1 so that psychometric functions could be fitted to the proportion correct data and threshold IDs with bootstrap errors estimated. Results. ID thresholds for the no-adaptor and correlated adaptor conditions were not significantly different, but thresholds increased significantly as a function of adaptor ID, by approximately a factor of 6 when going from correlated (ID=0) to anticorrelated (ID=1) adaptor conditions. Thresholds were higher for the uncorrelated compared to monocular adaptors (even though both had an ID of 0.5). The difference between the monocular and uncorrelated adaptor was accounted for when the ID values were converted into interocular RMS contrast differences. Conclusion. Interocular decorrelation is an adaptable dimension of vision, likely mediated by the binocular differencing channel posited in previous studies.
Meeting abstract presented at VSS 2018