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Howard P Collins, Neil W Roach, Andrew J Logan, Samantha L Strong, James Heron; Asymmetric time perception across visual depth planes and degrees of spatial certainty. Journal of Vision 2019;19(10):208. doi: https://doi.org/10.1167/19.10.208.
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© ARVO (1962-2015); The Authors (2016-present)
Typically, greater numbers of neurons encoding a stimulus characteristic provide greater perceptual sensitivity to changes in that characteristic (e.g., cardinal vs oblique orientation discrimination (Orban et al, 1984)). Within extrastriate cortex, neurons selective for crossed retinal disparity are more abundant than their uncrossed counterparts, which is associated with higher sensitivity to changes in the spatial characteristics of crossed disparity-defined stimuli (CDDS) (DeAngelis & Uka, 2003; Regan & Hamstra, 1994). Recent models of time perception (e.g. Eagleman & Pariyadath, 2009) propose that perceived duration scales with neural response magnitude, suggesting a metric for estimating duration may arise via the encoding of (potentially) non-temporal stimulus features. The current study used dynamic luminance noise to measure differences in perceived duration of stimuli defined solely by crossed or uncrossed disparity (±6 arcmins). Observers (n=9) made 2AFC judgements about the relative durations of a constant (333ms) 500Hz auditory tone and a variable (333ms ±Δms) disparity-defined disc-shaped stimulus. Duration discrimination thresholds were significantly higher for uncrossed disparity-defined stimuli (UDDS) than CDDS (p< 0.05), suggesting a possible link between the relative paucity of neurons selective for uncrossed disparity and the encoding of duration. However, UDDS are associated with greater spatial uncertainty which may also be contributing to reductions in reliability of temporal encoding. To test this, the relative spatial uncertainty of CDDS vs UDDS was measured using a disparity-defined shape discrimination task. Observers were significantly more sensitive to shape deformations (circle vs ellipse) within CDDS (p< 0.05). This suggests spatial uncertainty may be driving duration sensitivity; potentially implying that CDDS vs UDDS sensitivity may be equated by degrading the spatial reliability of the former. In a follow-up experiment, when CDDS diameter was jittered during stimulus presentation, duration discrimination thresholds elevated to match UDDS performance (p=0.57). Taken together, our findings reveal a hitherto unexplored link between spatial and temporal reliability.
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