Symposia introduction

Abstract

Due to the movements of the eyes and those of the objects in the environment, natural vision is highly dynamic. An understanding of how the visual system can cope with such complex inputs requires an understanding of reference frames, used in the computations of various stimulus attributes. It is well known that the early visual system has a retinotopic organization. It is generally thought that the retinotopic organization of the early visual system is insufficient to support the fusion of visual images viewed at different eye positions. Moreover, metacontrast masking and anorthoscopic perception show that a retinotopic image is neither sufficient nor necessary for the perception of spatially extended form. How retinotopic representations are transformed into more complex non-retinotopic representations has been long-standing and often controversial question. The classical paradigm to study this question has been the study of memory across eye movements. As we shift our gaze from one fixation to another one, the retinotopic representation of the environment undergoes drastic shifts, yet phenomenally our environment appears stable. How is this phenomenal stability achieved? Does the visual system integrate information across eye movements and if so how? A variety of theories ranging from purely retinotopic representations without information integration to detailed spatiotopic representations with point-by-point information integration have been proposed. Talks in this symposium (Crawford, Melcher, Cavanagh) will address the nature of trans-saccadic memory, the role of extra-retinal signals, retinotopic, spatiotopic, and objectopic representations for information processing and integration during and across eye movements. In addition to the challenge posed by eye movements on purely retinotopic representations, recent studies suggest that, even under steady fixation, computation of moving form requires non-retinotopic representations. This is because objects in the environment often move with complex trajectories and do not stimulate sufficiently retinotopically anchored receptive fields. Moreover, occlusions can ‘blank out’ retinotopic information for a significant time period. These failures to activate sufficiently retinotopically anchored neurons, in turn, suggest that some form of non-retinotopic information analysis and integration should take place. Talks in this symposium (Nishida, Herzog) will present recent findings that show how shape and color information for moving objects can be integrated according to non-retinotopic reference frames. Taken together, the talks at the symposium aim to provide a recent perspective to the fundamental problem of reference frames utilized by the visual system and present techniques to study these representations during both eye movement and fixation periods. The recent convergence of a variety of techniques and stimulus paradigms in elucidating the roles of non-retinotopic representations provides timeliness for the proposed symposium. Since non-retinotopic representations have implications for a broad range of visual functions, we expect our symposium to be of interest to the general VSS audience including students and faculty.