Role of spatio-temporal distortions in the visual periphery in disrupting natural attention deployment

Abstract

Human visual system based quality metrics and perceptually optimized video coders often use principles of foveation and saliency to weigh the distortion in certain regions more heavily or hide the artefacts in regions where they are less noticeable. These approaches however fail to consider the impact such a tuning produces on the non-salient surroundings usually incident on the para, peri and extra-peri foveal visual regions. Vision studies on the other hand, have highlighted the enhanced sensitivity of these peripheral visual regions towards spatio-temporal artefacts: more so in the supra-threshold region. Because such analysis has often been performed using controlled synthetic stimuli and forced fixation based experimental approaches, that assume perfect luminance adaptation, tracking and semantic comprehension of underlying content, a thorough understanding of the impact of peripheral disturbances in a natural viewing scenario is missing. The present work therefore uses a Gaze Contingent Display to study the impact of spatiotemporal distortions in the peri foveal and extraperi foveal regions in a free-viewing scenario, using natural scene stimuli. Using four state of the art gaze analysis-techniques to analyze the gaze data collected from 48 observers, spatio-temporally and semantically, confirms and extends our previous understanding of distortion perception in the periphery. Our observations indicate that non-flickering spatial distortions seem to have less of a disruptive effect in the visual periphery as compared to the temporally flickering artefacts and second, the threshold at which disruptions begin to occur is higher in the visual periphery as compared to that of the fovea, both of these effects being strongly scene dependent and prone to natural scene masking. The results highlight the need for sufficient consideration of the supra-threshold effects of peripheral distortions, in order to achieve an optimum perceptual experience.