Semantic context effects on color categorization

Semantic Context Effects on Color Categorization Rony Kubat (kubat@media.mit.edu) MIT Media Lab, 20 Ames Street Cambridge, MA 02139 USA and Daniel Mirman (mirmand@einstein.edu) Moss Rehabilitation Research Institute, Albert Einstein Healthcare Network 1200 W. Tabor Rd. Philadelphia, PA 19141 and Deb Roy (dkroy@media.mit.edu) MIT Media Lab, 20 Ames Street Cambridge, MA 02139 USA Abstract were asked to adjust the color of a fruit object until it ap- peared achromatic, their judgments were consistently shifted away from gray in a direction opposite to the typical color of the fruit (Hansen, Olkkonen, Sebastian, & Gegenfurtner, 2006). That is, the participants’ perception of the color of a displayed fruit was biased by the conceptual knowledge of the typical color of that fruit. It has long been known that color perception is not merely a matter of the wavelengths of light hitting the retina—if it were, changes in illumination would radically alter the per- ceived colors in the environment. There is now direct ev- idence that top-down knowledge is used to improve color constancy (Mitterer & de Ruiter, 2008), much like context and word knowledge can be used to adjust speech sound cat- egories (Norris, McClelland, & Cutler, 2003; Mirman, Mc- Clelland, & Holt, 2006). The use of context-dependent ex- pectations gives the perceptual system robustness in the face of changing environments, which is a central principle of in- teractive (McClelland, 1993) and Bayesian (Geisler & Diehl, 2003) theories. The paradigm for studying the effects of conceptual knowl- edge on color perception presented here is closely related to the Stroop (1935) paradigm. In the Stroop paradigm, two sources of information (traditionally, printed word and ink color) may be congruent or conflicting, and the interference caused by conflicting information reveals the interactions be- tween processing of these different sources of information. In other words, the traditional Stroop paradigm tests the in- teraction of conceptual information from lexical context and perceptual information from color perception. The present experiment uses a Stroop-like paradigm to test the interac- tion of conceptual information (i.e., iconic or lexical contexts) with color information. Thus, the critical principles of infor- mation integration that are at work in the Stroop paradigm are the same as those at work in the present experiment. We extend previous studies of the effect of context on color perception by testing whether in addition to iconic con- text, lexical context influences perception of ambiguous col- ors (i.e., ones that fall half-way between two basic color cat- egories (Berlin & Kay, 1969)). If color perception is part of an interactive and/or a single integrated perceptual-cognitive system, simple color categorization will be influenced by high A number of recent theories of semantic representation pro- pose two-way interaction of semantic and perceptual informa- tion. These theories are supported by a growing body of ex- periments that show widespread interactivity of semantic and perceptual levels of processing. In the current experiment, par- ticipants classified ambiguous colors into one of two color cat- egories. The ambiguous colors were presented either as a color patch (no semantic context), as an icon representing an object that is strongly associated with one of the color options, or as a word referring to such an object. Although the iconic and lexi- cal contexts were incidental and irrelevant to the color catego- rization task, participants’ responses were consistently biased toward the context color. These results extend previous find- ings by showing that lexical contexts, as well as iconic contexts influence color categorization. Keywords: Color perception; Semantics; Interactive process- ing; A number of current theories of the representation of word meanings propose that these representations are composed of perceptual and motor representations relevant for the word meaning. Such theories may be called grounded because they “ground” concepts in sensory/perceptual-motor/action rep- resentations (Barsalou, Simmons, Barbey, & Wilson, 2003; Roy, 2005); they may also be called distributed (McClelland & Rogers, 2003) because they propose that semantic knowl- edge is distributed throughout the perceptual-motor systems. Under such views, semantic knowledge of, for example, the meaning of color names involves precisely the same brain regions and representations as perception of color. In other words, the mechanisms of color perception are an intrinsic part of semantic knowledge. Conversely, this view also sug- gests that semantic knowledge is an intrinsic part of color per- ception. This latter point is consistent with interactive (McClelland, 1993) and Bayesian (Geisler & Diehl, 2003) theories of per- ception and cognition, which propose that top-down informa- tion (such as semantic knowledge) directly influences lower- level perceptual processes. Visual perception, in particular, is a highly interactive process. The perception of illusory con- tours is guided by top-down expectations (Lee & Nguyen, 2001) and recognition of objects is influenced by scene con- texts (Bar, 2004). Similarly, color perception appears to be influenced by memory of an object’s color: when participants