How long range is contour integration in human color vision?

Abstract

We quantified and compared the effect of element spacing on contour integration between the achromatic (Ach), red-green (RG), and blue-yellow (BY) mechanisms. The task requires the linking of orientation across space to detect a contour in a stimulus composed of randomly oriented Gabor elements (1.5 cpd, s ϭ 0.17 deg), measured using a temporal 2AFC method. A contour of ten elements was pasted into a 10 ϫ 10 cells array, and background elements were randomly positioned within the available cells. The effect of element spacing was investigated by varying the mean interelement distance between two and six times the period of the Gabor elements (l ϭ 0.66 deg) while the total number of elements was fixed. Contour detection was measured as a function of its curvature for jagged contours and for closed contours. At all curvatures, we found that performance for chromatic mechanisms declines more steeply with the increase in element separation than does performance for the achromatic mechanism. Averaged critical element separations were 4.6 6 0.7, 3.6 6 0.4, and 2.9 6 0.2 deg for Ach, BY, and RG mechanisms, respectively. These results suggest that contour integration by the chromatic mechanisms relies more on short-range interactions in comparison to the achromatic mechanism. In a further experiment, we looked at the combined effect of element size and element separation in contour integration for the Ach mechanism. We found that the critical separation decreases linearly with the spatial frequency, from about 5 deg at low spatial frequency (larger elements) to about 1 deg at high spatial frequency (smaller elements) suggesting a scale invariance in contour integration. In both experiments we also found no differences between closed and open jagged contours detection in terms of element separation. The neuroanatomical implications of these findings relatively to area V1 are discussed.

Aging and the integration of orientation and position in shape perception

“…Their results showed that the minimum aspect ratio required to discriminate an ellipse from a circle decreased with increasing contour sampling at the same rate for younger and older subjects. Interelement spacing has also been shown to affect the detectability and discriminability of elongated contours embedded in cluttered backgrounds (e.g., Beaudot & Mullen, 2003;Kovács & Julesz, 1993;Li & Gilbert, 2002). Interestingly, similar to the current results, the effect of interelement spacing on contour grouping was the same in younger and older subjects (Hadad, 2012;Roudaia et al, 2013), even though overall ability to detect and discriminate contours in noise declines with aging (Del Viva & Agostini, 2007;Roudaia et al, 2011Roudaia et al, , 2013.…”

Perceptual grouping in Gabor lattices: Proximity and alignment

“…Subject performance was measured as a function of interelement angle in a 2AFC paradigm. This experimental approach has proven very popular in subsequent studies (reviewed by Field, 1999, andField, 2003) in which a large number of local or global stimulus properties have been assessed, such as contour closure (Kovacs & Julesz, 1993), polarity and luminance contrast along the path (Field, Hayes, & Hess, 2000), chromaticity and color contrast (Beaudot & Mullen, 2003;McIlhagga & Mullen, 1996), spatial frequency tuning , eccentricity (Hess & Dakin, 1999;Nugent, Keswani, Woods, & Peli, 2003), temporal properties of the presentation (Beaudot, 2002;Hess, Beaudot, & Mullen, 2001), and stationary motion (Bex, Simmers, & Dakin, 2001). Most relevant in the context of this article is the consistent finding that contour saliency increases with element alignment and proximity.…”

Digital Camouflage Images Using Two‐scale Decomposition

“…Perception studies [BM03,EM98] show that long coherent-edges are perceptually salient to the HVS even they are faint. Long edges may reveal the important information about the object.…”

“…The importance of edges is considered using the Gaussian scale space analysis to ensure the structures of the objects are preserved through camouflage manipulations. Perception research [BM03,EM98] shows that long coherent-edges, even when faint, are perceptually salient to the human visual system (HVS). Motivated by the law of closure of Gestalt psychology's theory, which states that humans perceive objects as a whole even when they are not complete, we take long and important edges of the object into account, and divide these edges into shorter edges and remove some of them.…”