Attentional selection in judgments of stereo depth

Abstract

Stereoscopic depth is most useful when it comes from relative rather than absolute disparities. However, the depth perceived from relative disparities can vary with stimulus parameters that have no connection with depth or are irrelevant to the task. We investigated observers' ability to judge the stereo depth of task-relevant stimuli while ignoring irrelevant stimuli. The calculation of depth from disparity differs for 1-D and 2-D stimuli and we investigated the role this difference plays in observers' ability to selectively process relevant information. We show that the presence of irrelevant disparities affects perceived depth differently depending on stimulus dimensionality. Observers could not ignore disparities of irrelevant stimuli when they judged the relative depth between a 1-D stimulus (a grating) and a 2-D stimulus (a plaid). Yet these irrelevant disparities did not affect judgments of the relative depth between 2-D stimuli. Two processes contributing to stereo depth were identified, only one of which computes depth from a horizontal disparity metric and permits attentional selection. The other uses all stimuli, relevant and irrelevant, to calculate an effective disparity direction for comparing disparity magnitudes. These processes produce inseparable effects in most data sets. Using m u l t i p l e d i s p a r i t y d i re c t i o n s a n d comparing 1-D and 2-D stimuli can distinguish them.

What's special about horizontal disparity

“…For 1-D stimuli, the surprise is muted because of directional ambiguity associated with the aperture problem. But little or no training is required to carry out the same tasks with 2-D stimuli (e.g., Farell & Ng, 2018 ; Farell & Ng, 2019 ; Stevenson & Schor, 1997 ), in apparent disregard for years of exposure to contrary statistical regularities. This might be attributed to the generality, flexibility, and robustness of a component analysis of disparity, which in principle is isotropic.…”

“…The RDA is presumably regional, encompassing the stimuli whose relative disparity is to be calculated and perpendicular to the average orientation of the non-horizontal components within the region. How large a spatial area this includes, we do not know, but it appears to receive input from both task-relevant and unattended irrelevant stimuli within this area ( Farell & Ng, 2019 ). A judgment of relative depth would be a report of a comparison of the RDA components of the relevant stimuli.…”

“…Attention, however, appears not to be a factor. Attention has access to computations carried out on the RDA, not to input to the RDA ( Farell & Ng, 2019 ; see also Chopin et al, 2016 ).…”