Conjunction and linear non-separability effects in visual shape encoding

Abstract

Four visual search experiments are reported which used simple 2D shapes varying on the global dimensions of aspect ratio/curvature or aspect ratio/tapering. Results indicate serial self-terminating search in all conditions. Most importantly, search rates are markedly modulated by the particular forms of structural relations existing between the targets and their distractors. Thus, single-feature targets with shape properties that are linearly separable from those of their distractors yield markedly faster search rates than linearly separable targets made of a conjunction of distractor features. In addition, linearly separable single-feature targets are searched at a much faster rate than single-feature targets which are not linearly separable. Follow-up experiments demonstrate that these conjunction and linear non-separability effects cannot be attributed to pairwise target-distractor discriminability differences across conditions. The main conclusions are that the shapes used are parsed according to elementary features in visual encoding, and that a linear discrimination mechanism is available which permits fast visual search rates if a single-feature target is linearly separable from its distractors.

Categorization training increases the perceptual separability of novel dimensions

“…Notably, this includes any research testing the ''independent'' or ''holistic'' nature of perceptual processing and representations (e.g., Arguin & Saumier, 2000Blais, Arguin, & Marleau, 2009;Fitousi & Wenger, 2013;Ganel & GoshenGottstein, 2004;Mack et al, 2011;Mestry et al, 2012;Richler et al, 2008;Schweinberger & Soukup, 1998;Soto & Wasserman, 2011;Soto et al, 2015;Stankiewicz, 2002;Thomas, 2001). In most research directed to answer such questions, experimenters have assumed that separability is a fixed characteristic of stimulus dimensions, in some cases determined by processing through independent brain pathways and/or representations (e.g., Andrews & Ewbank, 2004;Bruce & Young, 1986;Haxby et al, 2000;Kayaert, Biederman, & Vogels, 2005;Vogels et al, 2001;Winston, Henson, Fine-Goulden, & Dolan, 2004).…”

“…For example, some shape properties might have a special status in object recognition, being processed ''independently'' (Arguin & Saumier, 2000Kayaert et al, 2005;Stankiewicz, 2002;Vogels et al, 2001), simply because they are diagnostic in object categorization tasks usually encountered in the environment, instead of being innately determined (Biederman, 2001). Whether dimensions of face stimuli are separable (Fitousi & Wenger, 2013;Schweinberger & Soukup, 1998;Soto et al, 2015) might not be the result of different brain representations that are hardwired in the brain (Andrews & Ewbank, 2004;Bruce & Young, 1986;Haxby et al, 2000;Winston et al, 2004).…”

Categorical effects in visual search for colour

“…Conversely, search is 'difficult' or inefficient', resulting in steeper search slopes, if the target falls inside the area defined by the distractors in stimulus space (linearly nonseparable). The effect has been demonstrated in CIE colour space (Bauer et al, 1996a(Bauer et al, , 1996b(Bauer et al, , 1998D'Zmura, 1991) but also in other feature spaces such as size (Hodsoll & Humphreys, 2001) or shape (Arguin & Saumier, 2000). Figure 1 shows the simple case where there are two types of distractor.…”

Simply shapely: Relative, not absolute shapes are primed in pop-out search

“…One complication is that it is impossible to vary the shape of an object without changing any other low-level visual properties (see, e.g., Arguin & Saumier, 2000). To address this problem, the present study tested priming effects in three experiments that used different shapes, thus ensuring that variations in shape were not confounded with the same low-level visual property (e.g., size).…”