Understanding the structural determinants of object confusion in memory: An assessment of psychophysical approaches to estimating visual similarity

Abstract

Computer-generated shapes varying on visual dimensions such as curvature, tapering, and thickness have been used to investigate identification deficits in the category-specific visual agnosia (CSVA) Patient E.L.M.. However, whether the implemented variations on each of these dimensions were perceived by novice observers as "similar amounts of change" is unknown. To estimate distance in psychophysical shape space, sets of shapes were developed using two different scaling methods-an objective method based on visual search, and a subjective method based on judgments of similarity-and a third approach that did not involve scaling. How well each method estimated psychophysical shape space was assessed by measuring the confusions within memory among the shapes. The results suggested that, although neither of the approaches perfectly reflected psychophysical shape space, subjective scaling was a better estimator of distance in psychophysical shape space than were other approaches. The number of confusions produced on each set of shapes was used to develop a new set of shapes that accurately estimated distance in psychophysical shape space. These results suggest that a combination of approaches is preferable in order to accurately estimate distance in psychophysical shape space.

A role for action knowledge in visual object identification

“…The goal of Experiment 1 was to look individually at action space and 3-D object space to demonstrate that the similarity relationship demonstrated by Desmarais and Dixon (2005) also exists for the visual identification of 3-D objects and actions. Participants learned to identify novel objects and novel actions with pronounceable nonwords.…”

“…), similarity was either intuitively determined or determined by participants' subjective similarity ratings (Dixon et al, 1997;Dixon et al, 1999;Dixon et al, 2002;Schweizer, Dixon, Desmarais, & Smith, 2002). Dixon et al (1997) and Desmarais and Dixon (2005) have shown that participants' subjective ratings of visual similarity do not adequately reflect similarity in memory space. In the current experiments, the consistent main effect of similarity attests to the importance of visual similarity in visual object identification.…”

“…Desmarais and Dixon (2005) have developed a set of psychophysically scaled shapes. This set consists of eight novel shapes formed using various combinations of curvature, tapering and thickness (see Figure 1).…”

“…Shapes 0,0,0 and 0,0,1 are one CB apart, whereas shapes 0,0,0 and 1,0,1 are two CBs apart, and shapes 0,0,0 and 1,1,1 are three CBs apart. Desmarais and Dixon (2005) psychophysically scaled these shapes to ensure that changes on each of the three dimensions were equally salient. By using this shape set, one knows, and can therefore control the visual similarity relations among the exemplars that make up this collection of objects.…”

“…In order to circumvent this problem some researchers have favored the use of novel objects. Desmarais and Dixon (2005) trained healthy undergraduates to identify eight novel shapes (see Figure 1) using nonword labels (e.g., baiv, jorl, yoot). When participants object often involves how an object is used.…”