Bioplausible multiscale filtering in retino-cortical processing as a mechanism in perceptual grouping

Abstract

Why does our visual system fail to reconstruct reality, when we look at certain patterns? Where do Geometrical illusions start to emerge in the visual pathway? How far should we take computational models of vision with the same visual ability to detect illusions as we do? This study addresses these questions, by focusing on a specific underlying neural mechanism involved in our visual experiences that affects our final perception. Among many types of visual illusion, ‘Geometrical’ and, in particular, ‘Tilt Illusions’ are rather important, being characterized by misperception of geometric patterns involving lines and tiles in combination with contrasting orientation, size or position. Over the last decade, many new neurophysiological experiments have led to new insights as to how, when and where retinal processing takes place, and the encoding nature of the retinal representation that is sent to the cortex for further processing. Based on these neurobiological discoveries, we provide computer simulation evidence from modelling retinal ganglion cells responses to some complex Tilt Illusions, suggesting that the emergence of tilt in these illusions is partially related to the interaction of multiscale visual processing performed in the retina. The output of our low-level filtering model is presented for several types of Tilt Illusion, predicting that the final tilt percept arises from multiple-scale processing of the Differences of Gaussians and the perceptual interaction of foreground and background elements. The model is a variation of classical receptive field implementation for simple cells in early stages of vision with the scales tuned to the object/texture sizes in the pattern. Our results suggest that this model has a high potential in revealing the underlying mechanism connecting low-level filtering approaches to mid- and high-level explanations such as ‘Anchoring theory’ and ‘Perceptual grouping’.

The Café Wall Illusion: Local and Global Perception from Multiple Scales to Multiscale

“…The edge maps are at seven different scales (σc =4, 8,12,16,20,24,28) and a fixed set of Hough parameters are used as NumPeaks=100, Threshold=3, FillGap=40, and MinLength=450 (Reproduced with permission from [23]; based on [19]). wider range of horizontal lines detected and a fairly broad range of vertical lines, and this fits as a transition stage between the 'horizontal groupings' of identically colored tiles with the mortar lines at a focal view, and the 'zigzag vertical groupings' of the tiles [22] at a more peripheral/global view. Fig 11 (b) (center-column) shows the near vertical lines detected.…”

“…A low-level filtering approach [17,19,22,23] have been explored here modelling the retinal/cortical simple cells in our early vision for revealing the tilt cues involved in the local and global perception of the Café Wall stimulus. The model has an embedded processing pipeline utilizing Hough transform to quantify the degrees of the inducing tilts appeared in the low-level representation for the stimulus in our model, referred to as the edge map at multiple scales.…”

“…The range of tilt angles increases along the following scales of the edge maps reaching to a wide range of variations at scale 32 (σc = 32 or DoG32) that is not reflected in our subjective experience of tilt in the pattern (it is overestimated at this scale). In the literature [18,19,22,25,37] it is noted that the size of DoG filter should be close to the size of the mortar for the Twisted Cord elements to be appeared [20] for the resolution analysis and its effect on the Hough parameters; Reproduced with permission from [23]). along the mortar lines, here DoG16 (σc =16).…”

Informing Computer Vision with Optical Illusions

“…Tile Illusions are Geometric Illusions with second-order tilt effects which arise from the contrast of background tiles and tilt cues such as in the Café Wall illusion. A quanti ed model for detecting the illusory tilts in the Café Wall illusion has been reported [2,3] and we are going to generalize this approach for more complex Tile Illusions such as Complex Bulge pattern which was introduced in [4,5] and more generally to a range of Geometric Illusions that will be explored as the primary new contribution in this work.…”

“…We explore the response of a simple bioplausible model of low-level vision we named it Vis-CRF [1] as a generalize vision model, tested here on Geometric/Tile Illusions, reproducing the misperception of their geometry, that we reported for the Café Wall and some Tile Illusions [2,5] and here will report on a range of Geometric illusions. The model has until now not been veri ed to generalize to these other illusions, and this is what we show in this paper.…”