The Role of Spatial Structure in Human Duration Processing

Abstract

This thesis presents a series of human psychophysical experiments designed to examine the interaction between the reliability of spatial form information and the neural mechanisms responsible for the processing of sub-second durations. Duration discrimination sensitivity was found to be lower when event durations were defined by stimulus characteristics that caused reductions in spatial form sensitivity. This form-duration sensitivity coupling persisted across stimuli defined both by crossed and uncrossed retinal disparity and within monocularly visible texture-defined stimuli. The interaction was also observed when spatial form was degraded by physical instability within shape borders, and when physically stable borders became perceptually unstable. These effects could not be attributed to artefacts of stimulus visibility, temporal coherence or stimulus size. Adaptation experiments generated aftereffects of perceived duration within stimuli whose durations were defined solely by retinal disparity, providing the first demonstration of duration selectivity within exclusively cortical duration encoding mechanisms. The selectivity of these aftereffects was then investigated using adapting and testing durations defined by matching or opposing retinal disparities. Duration aftereffects were maximal when adapt and test disparities were matched. However, there was partial transfer of duration aftereffects across large changes in retinal disparity, implicating contributions from higher-level extra-striate mechanisms. Collectively, these experiments provide support for duration processing mechanisms that are inextricably linked to the mechanisms underpinning spatial processing across multiple levels of the visuo-spatial hierarchy.