“Heron and colleagues sought to address the question of how humans compute estimates of sub-second visual duration. Historical attempts to answer this question have taken inspiration from the observation that different brain areas are functionally specialised for the processing of specific stimulus attributes such as spatial location. This led to the dominance of ‘dedicated’ models of duration perception: central, specialised mechanisms whose primary function is duration encoding.
Recently, these models have been challenged by the emergence of ‘distributed’ models which posit the localised encoding of duration alongside other, non-temporal stimulus features. This raises the possibility that some neurons might perform ‘double duty’ by (for example) encoding information about spatial location and temporal extent. However, given the potentially vast number of non-temporal stimulus features implicated, isolating those functionally tied to duration encoding represents a challenge.
Heron and colleagues attempted to quantify contributions to duration processing from three different strata within the visual processing hierarchy: monocular, depth-selective and depth-invariant. They began by isolating the duration information presented to left and right monocular channels. When this information induced duration aftereffects, strong aftereffects were also observed in the non-adapted eye. Nevertheless, a small but significant amount of adaptation did not show interocular transfer. Next, they used a novel class stimuli to present duration defined by the presence or absence of retinal disparity information. These stimuli allow the first demonstration of duration perception under conditions where stimuli are only visible to mechanisms that allow the integration of spatial information from both eyes.
They found robust duration aftereffects could be generated by viewing disparity-defined durations, revealing duration selective mechanisms entirely independent from monocular processing. Importantly, these aftereffects showed only partial selectivity for the visual the duration information’s depth plane. For example, adaptation to durations defined by crossed disparity information followed by testing with uncrossed disparity-defined stimuli produced aftereffects that were significantly greater than zero but significantly smaller than conditions were adapting and test durations were defined by the same type of retinal disparity.
Heron and colleagues findings provide clear support for duration selectivity at multiple stages of the visual hierarchy. They suggest that duration processing may have similarities with the well documented ‘serial cascade’ type processing documented in the spatial domain. In this scenario, downstream duration encoding mechanisms apply cumulative adaptation to effects inherited from their upstream counterparts.”
—-blog post by James Heron, University of Bradford
Heron J, Fulcher C, Collins H, Whitaker D & Roach NW (2019). Adaptation reveals multi-stage coding of visual duration. Scientific Reports (9), Article number: 3016 (pdf)
Publisher’s link: https://www.nature.com/articles/s41598-018-37614-3