Absolute Depth Sensitivity in Cat Primary Visual Cortex under Natural Viewing Conditions.

Ivan N Pigarev,Ekaterina V Levichkina

doi:10.3389/fnsys.2016.00066

Abstract

Mechanisms of 3D perception, investigated in many laboratories, have defined depth either relative to the fixation plane or to other objects in the visual scene. It is obvious that for efficient perception of the 3D world, additional mechanisms of depth constancy could operate in the visual system to provide information about absolute distance. Neurons with properties reflecting some features of depth constancy have been described in the parietal and extrastriate occipital cortical areas. It has also been shown that, for some neurons in the visual area V1, responses to stimuli of constant angular size differ at close and remote distances. The present study was designed to investigate whether, in natural free gaze viewing conditions, neurons tuned to absolute depths can be found in the primary visual cortex (area V1). Single-unit extracellular activity was recorded from the visual cortex of waking cats sitting on a trolley in front of a large screen. The trolley was slowly approaching the visual scene, which consisted of stationary sinusoidal gratings of optimal orientation rear-projected over the whole surface of the screen. Each neuron was tested with two gratings, with spatial frequency of one grating being twice as high as that of the other. Assuming that a cell is tuned to a spatial frequency, its maximum response to the grating with a spatial frequency twice as high should be shifted to a distance half way closer to the screen in order to attain the same size of retinal projection. For hypothetical neurons selective to absolute depth, location of the maximum response should remain at the same distance irrespective of the type of stimulus. It was found that about 20% of neurons in our experimental paradigm demonstrated sensitivity to particular distances independently of the spatial frequencies of the gratings. We interpret these findings as an indication of the use of absolute depth information in the primary visual cortex.

Highlights

It is generally recognized that reconstruction of 3D information from 2D retinal representations is one of the most important functions of the visual system
Neuronal responses from the primary visual cortex were recorded while the trolley with the cat sitting on it and facing the visual scene slowly approached the visual scene, which consisted of stationary sinusoidal gratings rear-projected over a large screen
From 81 neurons studied in Cat 2, 20 neurons had a significant increase of firing rate dependent on distance/spatial frequency, while 61 cells did not have significant changes in mean firing rate

Summary

Introduction

It is generally recognized that reconstruction of 3D information from 2D retinal representations is one of the most important functions of the visual system. Absolute Depth Preference in V1 visual area V1 (Barlow et al, 1967; Nikara et al, 1968; von der Heydt et al, 1978; Ferster, 1981; Gonzalez et al, 1993; Poggio, 1995; Prince et al, 2000), and in various extrastriate cortical areas (Poggio and Fischer, 1977; Maunsell and Van Essen, 1983; Andersen et al, 1985; DeAngelis and Newsome, 1999; Janssen et al, 2000; Thomas et al, 2002; Watanabe et al, 2002; Anzai et al, 2011; for the review see DeAngelis, 2000; Uka and DeAngelis, 2002; Tsutsui et al, 2005; Roe et al, 2007; Otero-Millan et al, 2014) Another powerful mechanism for 3D reconstruction is the analysis of motion parallax (Toyama et al, 1986; Xiao et al, 1997; Cao and Schiller, 2003; Nadler et al, 2008). Several studies explored other monocular cues of depth estimation (Tsutsui et al, 2002; Liu et al, 2004; Rosenberg and Angelaki, 2014)

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Conclusion