Contrast and assimilation in categorization and exemplar production

Abstract

We studied contrast and assimilation in three tasks: an exemplar-production task, a categorization task, and a combined categorization-then-production task. On each trial of the first task, subjects produced a circle when prompted with a category label. In the second task, they classified lines that differed in length into one of four categories. On each trial of the combined task, they classified two lines and then produced a line when prompted by a category label. All three tasks converged on the same conclusion: subjects' representation of the categories (measured in pixels in the production tasks and by the direction of errors in classification) shifted systematically from trial to trial. When successive stimuli were from the same category, the representation of that category was pulled toward the exemplar from the previous trial. When successive stimuli were from different categories, the representations of the neighbouring categories were pushed from the category of the initial stimulus. We conclude that accounts of categorization and identification must accommodate both assimilation and contrast as a function of trial-to-trial shifts in representation.

Relative judgment in facial identity perception as revealed by sequential effects

“…We probed this issue by using sequential effects. Recently, there has been a resurgence of interest in sequential effects, particularly during binary categorization processing (Hampton, Estes, & Simmons, 2005;Stewart, Brown, & Chater, 2002;Zotov, Jones, & Mewhort, 2011). In these studies, when a sequence of stimuli is presented, the categorization responses to the stimuli in current trials have been found to vary according to the local sequential context shaped by the immediately preceding stimuli presented one trial back.…”

“…One interpretation suggests that sequential effects involve the computation of similarity/dissimilarity between preceding and current stimuli to guide perceptual judgments (Stewart & Brown, 2005;Stewart, et al, 2002). An alternative interpretation argues that sequential effects reflect the consequences regarding how the local sequential context shifts participants' internal criteria to the current category representation (Hampton, et al, 2005;Zotov, et al, 2011).…”

Decision contamination in the wild: Sequential dependencies in online review ratings

“…Contrast is the opposite effect, when the judgment of stimulus n moves farther away on the measurement scale from the judgment of stimulus nk. In this sense, assimilation can be thought of as an attracting force from the preceding stimulus, whereas contrast can be thought of as a repelling force (Zotov, Jones, & Mewhort, 2011).…”

User-experience in design and use: enhancing the experience of media content with programmable surround lighting

“…A contrast effect occurs when the difference in perception between, for example, two stimulus categories is increased rather than decreased when they are presented closely in time or simultaneously. Both contrast effects and assimilation effects have been observed, for example, in judgements of physical attractiveness [12], categorization and exemplar production [47], and the visual perception of natural scenes [28].…”