A Common Mechanism Is Possibly Underlying the Shift in Perceptual and Conceptual Judgment Produced by Irrelevant Information

A Common Mechanism Is Possibly Underlying the Shift in Perceptual and Conceptual Judgment Produced by Irrelevant Information Penka Hristova (phristova@cogs.nbu.bg) Boicho Kokinov (bkokinov@nbu.bg) Central and East European Center for Cognitive Science, Department of Cognitive Science and Psychology, New Bulgarian University, 21 Montevideo Street Sofia 1618, Bulgaria Abstract This paper presents two experiments exploring context effects on human judgment and testing JUDGEMAP’s predictions that irrelevant information such as the color of the stimulus can produce a contrast effect with respect to skewed stimuli set to be judged. The first experiment demonstrates the effect on a perceptual judgment task (judging the length of lines which are colored in red and green), while the second experiment demonstrates exactly the same effect on a conceptual judgment task (judging the age of a person when the absolute age is presented by numbers with colored digits – red and green). These results rule out the “recalibration” of the perceptual system explanation. The fact that the same effects were obtained in both cases prompts for a common explanation. JUDGEMAP provides such an explanation: the color is used in retrieving past instances in WM based on the spreading activation mechanism and thus the comparison set becomes biased. The biased comparison set which is then mapped on the scale elements produces a shift in the mean ratings. Introduction Suppose someone claims that your judgment of her tallness on a scale may depend on the color of her eyes. Most probably you would consider this to be a strange statement. The color of someone’s eyes is certainly not a relevant dimension in the judgment of tallness. Under certain circumstances, however, the irrelevant information, like the color of the eyes, may actually become critical for the subsequent judgment. This strange statement is to be explored in the current paper. This paper focuses on the mechanism that may underlie such strange prediction, namely: how irrelevant stimulus dimension may influence judgment. The research aims to discriminate between two possible explanations of the effect of the irrelevant stimulus dimension: (1) low level perceptual recalibration of the sensory system (see Arieh and Marks, 2002 for a review) and (2) contextually sensitive memory retrieval (Kokinov, Hristova, Petkov, 2004). In fact, the experimental work presented in the current paper was inspired by the predictions of the JUDGEMAP Model (Kokinov, Hristova, Petkov, 2004) for contextually sensitive retrieval, which may result in systematic shift in judgments due to the irrelevant information. Evidence for the effect of irrelevant information Marks (1988) demonstrates that judgment of loudness may depend on the irrelevant to the task tone frequencies. Participants were asked to judge the loudness of a series of tones between 30 and 85 dB. If relatively low sounds were of 500Hz and relatively high ones, of 2500 Hz, participants judged the loudness of the same sound differently depending on its frequency. 500Hz tones were judged to be louder than the tones of the same sound pressure level but of 2500 Hz frequency. These loudness shifts were called differential context effects (DCEs), since loudness judgment depends differentially on the two contextual (irrelevant) frequencies (Marks, 1988). Evidence for DCEs is reported also in the judgments of length of vertical and horizontal lines (Arieh and Marks, 2002), taste (Rankin and Marks, 1991, 1992), haptic touch (Marks and Armstrong, 1996), olfaction (Rankin and Marks, 2000). This line of research demonstrates a contrast effect in the judgment of a stimulus depending on its irrelevant dimension, i.e. a stimulus judgment is displaced away from the context of the stimuli that share the same irrelevant information. Arieh and Marks (2002) argue that DCEs originate relatively early in the perceptual stream and are possibly a result of the “recalibration of the supra-threshold responsiveness of the perceptual systems”. It was shown that DCEs are spatially specific, i.e. were evident only in locations at which they were induced (Arieh and Marks, 2002; Marks, 1996). For example, visual length perception appeared to be specific to the eye and to the retinal region in which the context was induced (Arieh and Marks, 2002). Thus, according to Arieh and Marks (2002) DCEs reflect a relatively early and local change in perceptual sensitivity. Goldstone (1995, 1998) also assumes that irrelevant information influences the judgment process relatively early in the information processing and discusses the possibility for context effects to result from perceptually grounded on-line categorization of the stimuli to be judged, i.e. learning/forming categories of stimuli produce a change in the perception of these stimuli. Goldstone (1995) reports a shift in color perception toward the color of similar figures although the shape of figures was an irrelevant-to-the-task characteristic. In general, the effect found in these studies was opposite in direction to the one found by Marks and his colleagues and is essentially an assimilation towards the prototype of the category of stimuli sharing the same irrelevant characteristics. Goldstone (1995, 1998) addresses the possibility that this effect might be a form of perceptual learning. In sum, both contrast and assimilation effects were demonstrated due to the irrelevant-to-the-task dimension. Marks and colleges (Marks, 1988, 1992, 1994, Marks and Warner, 1991, Arieh and Marks, 2002) always report a