End stopping in V1 is sensitive to contrast

Abstract

Common situations that result in different perceptions of grouping and border ownership, such as shadows and occlusion, have distinct sign-of-contrast relationships at their edge-crossing junctions. Here we report a property of end stopping in V1 that distinguishes among different sign-of-contrast situations, thereby obviating the need for explicit junction detectors. We show that the inhibitory effect of the end zones in end-stopped cells is highly selective for the relative sign of contrast between the central activating stimulus and stimuli presented at the end zones. Conversely, the facilitatory effect of end zones in length-summing cells is not selective for the relative sign of contrast between the central activating stimulus and stimuli presented at the end zones. This finding indicates that end stopping belongs in the category of cortical computations that are selective for sign of contrast, such as direction selectivity and disparity selectivity, but length summation does not.Vision is an active integrative process: information from one part of the scene can drive the interpretation of features in other parts 1 . The information in an image is concentrated at contours and terminations 2 . Line ends, corners and junctions are singularities that are crucial for form perception, object recognition, depth ordering and motion processing (refs. 1 ,3-7 ). The physiological correlates of the perceptual phenomena of terminator detection and contour completion must begin with the well-known single-cell physiological properties of end stopping and length summation. Selective responsiveness to terminators (by end-stopped cells) probably provides the initial step both in depth ordering of contours and surfaces, and in solving the aperture problem for stereo and motion 8-10 . Similarly, the physiological property of length summation must provide the initial step in the process of contour integration.To identify correctly the end of a contour, the brain must ignore changes in contrast caused by nonuniform illumination and respond only to those changes caused by the ending of the contour. Contrast polarity can be used to differentiate between these situations. If a change in contrast is due to an alteration in illumination, such as a shadow, then contrast polarity will be preserved along the contour. Conversely, contrast polarity inversion along a contour usually signals the end of the contour. Many instances of surface stratification and border ownership, such as shadow, transparency, occlusion and neon color spreading, have different ordinal contrast configurations at T and X junctions (Fig. 1). A long-standing issue is how the visual cortex uses contrast information to distinguish among different ordinal relations within these junctional singularities. Are there explicit junction detectors in the visual cortex?Although, perceptually, sign-of-contrast information at junctions is crucial, it is generally assumed that by the complex-cell stage of V1 information about sign of contrast has been pooled 11 and is t...

Perspectives on science and art

“…Our tolerance of multiple points of view in a single painting suggests that one characteristic of this alternative (psycho) physics is that depth cues are processed locally; that is, it is not necessary for the perspective cues to be consistent across the entire image. This idea is consistent with the plausibility at first glance of impossible figures, like Penrose's triangle, and with observations from psychophysics and neurophysiology that figure-ground segregation, depth ordering, and surface stratification are processed at early stages in the visual system, where receptive fields are small and processing is necessarily local [20][21][22][23][24][25][26][27].…”

Terminator Disparity Contributes to Stereo Matching for Eye Movements and Perception

“…As far as we are aware, ours is the first investigation of the binocular equivalent of the barber-pole illusion. The advantage of this approach is that it rules out explanations based on the disparity of contrast envelopes (McKee et al, 2004;Wilcox and Allison, 2009), since the contrast envelopes for the stimuli used in our experiments either had no disparity (Figs. 2, 6), or could account only for a fraction of the response (Fig.…”

“…For example, our ability to localize in depth a horizontal bar might be based on the disparity of the two bar endings (or terminators). However, as previously pointed out (McKee et al, 2004;Wilcox and Allison, 2009), under such conditions mechanisms that match the location of the bar in its entirety could also be used. Accordingly, hard evidence for the role played by terminators per se in extracting depth information is currently lacking.…”

Generalization of Figure-Ground Segmentation from Binocular to Monocular Vision in an Embodied Biological Brain Model

“…4) consists of -from the left column to the right column -V1, V1C end-stop cells [13] and figure layers. The figure layers correspond to the zero-disparity region of foveation.…”

“…There are three sets of layers at three interacting spatial resolutions. The first set corresponds to V1, the second set to V1C end-stop cells [13], and the third set learns to extract the figure from the background. The network is connected in a feedforward fashion from left to right and the figure-ground layers have both recurrent and bidirectional connectivity.…”