Academic journal article Attention, Perception and Psychophysics

Retinotopy of Visual Masking and Non-Retinotopic Perception during Masking

Academic journal article Attention, Perception and Psychophysics

Retinotopy of Visual Masking and Non-Retinotopic Perception during Masking

Article excerpt

Published online: 14 March 2015

© The Psychonomic Society, Inc. 2015

Abstract Due to the movements of the observer and those of objects in the environment, retinotopic representations are highly unstable during ecological viewing conditions. The phenomenal stability of our perception suggests that retinotopic representations are transformed into non-retinotopic representations. It remains to show, however, which visual processes operate under retinotopic representations and which ones operate under non-retinotopic representations. Visual masking refers to the reduced visibility of one stimulus, called the target, due to the presence of a second stimulus, called the mask. Masking has been used extensively to study the dynamic aspects of visual perception. Previous studies using Saccadic Stimulus Presentation Paradigm (SSPP) suggested both retinotopic and non-retinotopic bases for visual masking. In order to understand how the visual system deals with retinotopic changes induced by moving targets, we investigated the retinotopy of visual masking and the fate of masked targets under conditions that do not involve eye movements. We have developed a series of experiments based on a radial Ternus-Pikler display. In this paradigm, the perceived Ternus-Pikler motion is used as a non-retinotopic reference frame to pit retinotopic against non-retinotopic visual masking hypothesis. Our results indicate that both metacontrast and structure masking are retinotopic. We also show that, under conditions that allow observers to read-out effectively non-retinotopic feature attribution, the target becomes visible at a destination different from its retinotopic/spatiotopic location. We discuss the implications of our findings within the context of ecological vision and dynamic form perception.

Keywords Visual masking · Motion perception · Reference frames

Introduction

Retinotopic and non-retinotopic representations in human vision

The optics of the eye map neighboring points in the environment to neighboring photoreceptors in the retinae, and these neighborhood relations, known as retinotopic organization, are preserved in early visual cortical areas. Under normal viewing conditions, due to the movements of the observer's body, head, eyes, and due to the movements of objects, the stimuli impinging on retinotopic representations are highly dynamic and unstable. Thus, understanding ecological vision requires an understanding of how visual processes operate under these dynamic conditions. In order to explain the phenomenal stability of our environment, it is often postulated that the brain constructs non-retinotopic representations wherein the ego-centric representations (i.e., based on the observer, such as retinotopic representations) are transformed into exo-centric representations (i.e., based outside of the observer, such as spatiotopic representations). However, determining whether a given visual process operates in retinotopic or non-retinotopic representations and which visual processes operate in non-retinotopic representations remains one of the fundamental challenges in understanding ecological vision.

Retinotopy of visual masking assessed with the Saccadic Stimulus Presentation Paradigm

Saccadic eye movements constitute a major source for retinotopic instability. However, during these eye movements, the world appears phenomenally stable suggesting that retinotopic shifts caused by saccades are either dismissed or compensated by the visual system. Theories of dismission propose that very little information is kept from one saccade to another and vision starts tabula rasa after each saccade. Theories of complete compensation propose that all information is remapped across the saccade by taking into account the global shift caused by the saccade. Theories that take intermediate positions between these two extremes have also been proposed (Bridgeman, van der Heijden, & Velichkovsky, 1994). …

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