Perception of contours and shapes: Low and intermediate stage mechanisms

Abstract

This review focuses on low and intermediate stages of contour shape processing. It is split into two main sections, 'Contour Detection' and 'Shape Discrimination and Representation'. The first section examines contrast detection of elements within a contour ("collinear facilitation") and the detection of contours in noise ("contour integration"). The second section deals with the discrimination and representation of simple and complex shapes. Perceptual effects on contour detection have been linked to low-level, long-range lateral interactions between neighbouring neurons in V1. Experimental results suggest a complex network of interactions that are context dependent, with collinearity being the dominant factor. While lateral connections are an obvious candidate for linking contour elements into spatially extended contours, the long-range interactions are insufficient to account for human performance in a variety of tasks. Data suggest the existence of global mechanisms that integrate information beyond that of neighbouring cells and are influenced by the overall features of a stimulus. Evidence from psychophysics and physiology is converging towards the identification of an intermediate level of shape processing, where sensitivity to such global attributes emerge.

Individual differences in the dynamics of collinear facilitation?

“…It has been suggested that collinear facilitation plays a role in higher-level contour integration (see Loffler (2008) for a review). When target and flankers are presented simultaneously (SM), top down signals based on the expectation that there is a single object present might drive facilitation to enhance the target and integrate the Gabor elements to make a coherent line (Blake & Lee 2005).…”

Global Shape Processing Deficits Are Amplified by Temporal Masking in Migraine

“…25 Psychophysical, [26][27][28] monkey physiology, 29 and human fMRI 30 studies support the view that the high sensitivity may be a result of processing at intermediate, extrastriate stages. 31 According to the reduced inhibition hypothesis, if masking was a consequence of inhibition, migraineur performance should be similar to controls without a mask, but better than controls when masked. If, however, migraineurs have raised internal noise levels, they should perform equally poorly in both conditions.…”

Estimating the usefulness of distorted natural images using an image contour degradation measure

“…In contrast with VIF, NICE detects the edges in the reference and test images and can be viewed as performing spatially global variance normalization, collinear facilitation [29], and hard thresholding. NICE and MS-NICE perform global variance normalization by normalizing the channel responses based on the average channel response energy [108].…”

“…The second objective estimator is the newly proposed natural image contour evaluation (NICE) utility estimator, which was inspired by the importance of contour information to the HVS for object perception [28][29][30]. NICE is based on the hypothesis that degradations to image contours restrict the content that an image conveys to a human and decrease perceived utility.…”