Contrast and assimilation in the Baldwin illusion

Four experiments were conducted to investigate the role of "large" squares on the occurrence of assimilation and contrast in the Baldwin illusion. In Exps. 1 and 2, in which subjects reproduced the length of the test line, large squares induced illusions of assimilation. In Exp. 3, reproduction of the entire length of the test line also resulted in illusions of assimilation but bisection of the test line and reproduction of one-half the length of the test line resulted in contrast. Exp. 4 replicated the findings involving judgments of one-half the length of the test line. Over-all, the results indicate that judgments of one-half the length of the test line result in contrast, whereas judgments of the entire extent result in assimilation.     

Contrast and assimilation in lightness judgments

Experiments studied how assimilation and contrast varied as a function of the reflectance of figures above and below the reflectance of a gray background. The results showed that for the experimental conditions investigated: (a) contrast always occurs when the reflectance of lines is above the reflectance of the background, (b) assimilation occurs when the reflectance is below that of the background, (c) circles produce the same degree of assimilation and contrast as lines of equal width, and (d) repeated judgments do not affect contrast but reduce assimilation; as line darkness and line width increase assimilation gives way to contrast following repeated judgments. The results are discussed in connection with the hypothesis that assimilation and contrast arise from opponent processes in the visual system.     

Contrast and assimilation in lightness judgments

Experiments studied how assimilation and contrast varied as a function of the reflectance of figures above and below the reflectance of a gray background. The results showed that for the experimental conditions investigated: (a) contrast always occurs when the reflectance of lines is above the reflectance of the background, (b) assimilation occurs when the reflectance is below that of the background, (c) circles produce the same degree of assimilation and contrast as lines of equal width, and (d) repeated judgments do not affect contrast but reduce assimilation; as line darkness and line width increase assimilation gives way to contrast following repeated judgments. The results are discussed in connection with the hypothesis that assimilation and contrast arise from opponent processes in the visual system,     

Contrast and assimilation in categorization and exemplar production

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.     

Ideals, central tendency, and frequency of instantiation as determinants of graded structure in categories

Three possible determinants of graded structure (typicality) were observed in common taxonomic categories and goal-derived categories: (1) an exemplar's similarity to ideals associated with goals its category serves; (2) an exemplar's similarity to the central tendency of its category (family resemblance); and (3) an exemplar's frequency of instantiation (people's subjective estimates of how often it is encountered as a category member). Experiment 1 found that central tendency did not predict graded structure in goal-derived categories, although it did predict graded structure in common taxonomic categories. Ideals and frequency of instantiation predicted graded structure in both category types to sizeable and equal extents. A fourth possible determinant--familiarity--did not predict typicality in either common taxonomic or goal-derived categories. Experiment 2 demonstrated that both central tendency and ideals causally determine graded structure, and work showing that frequency causally determines graded structure is discussed. Experiment 2 also demonstrated that the determinants of a particular category's graded structure can change with context. Whereas ideals may determine a category's graded structure in one context, central tendency may determine a different graded structure in another. It is proposed that graded structures do not reflect invariant structures associated with categories but instead reflect people's dynamic ability to construct concepts.     

"Perception" versus "Learning": The effect of different instructions upon the central tendency shift

Abstract.— Earlier studies of context effects in stimulus generalization, especially in the adaption-level tradition, have failed to take into account the subjective difference between a learning experiment and an experiment in perception. In the present study, 68 student subjects were trained to discriminate a 30 cm vertical line from shorter and longer lines, and were subsequently tested for generalization with asymmetrical test series (centering around 34 cm). Half of the subjects were told that they were participating in a perception experiment, the other half that they were participating in a learning experiment. Subjects in the latter condition were considerably more influenced by context and gave a greater number of equivalence responses than did the subjects in the perception condition. Amount of training and discriminability of training stimuli did also influence the central tendency shift, but to a lesser extent.     

Working memory and spatial judgments: Cognitive load increases the central tendency bias

Previous work demonstrates that memory for simple stimuli can be biased by information about the distribution of which the stimulus is a member. Specifically, people underestimate values greater than the distribution’s average and overestimate values smaller than the average. This is referred to as the central tendency bias. This bias has been explained as an optimal use of both noisy sensory information and category information. In largely separate literature, cognitive load (CL) experiments attempt to manipulate the available working memory of participants in order to observe the effect on choice or judgments. In two experiments, we demonstrate that participants under high cognitive load exhibit a stronger central tendency bias than when under a low cognitive load. Although not anticipated at the outset, we also find that judgments exhibit an anchoring bias not described previously.     

Word frequency, repetition, and lexicality effects in word recognition tasks: beyond measures of central tendency

Response time (RT) distributions obtained from 3 word recognition experiments were analyzed by fitting an ex-Gaussian function to the empirical data to determine the main effects and interactive influences of word frequency, repetition, and lexicality on the nature of the underlying distributions. The ex-Gaussian analysis allows one to determine if a manipulation simply shifts the response time (RT) distribution, produces a skewing of the RT distribution, or both. In contrast to naming performance, the lexical decision results indicated that the main effects and interactions of word frequency, repetition, and lexicality primarily reflect increased skewing of the RT distributions, as opposed to simple shifts of the RT distributions. The implications of the results were interpreted within a hybrid 2-stage model of lexical decision performance.     

Spatial dependence of color assimilation by the watercolor effect

Color assimilation with bichromatic contours was quantified for spatial extents ranging from von Bezold-type color assimilation to the watercolor effect. The magnitude and direction of assimilative hue change was measured as a function of the width of a rectangular stimulus. Assimilation was quantified by hue cancellation. Large hue shifts were required to null the color of stimuli < or = 9.3 min of arc in width, with an exponential decrease for stimuli increasing up to 7.4 deg. When stimuli were viewed through an achromatizing lens, the magnitude of the assimilation effect was reduced for narrow stimuli, but not for wide ones. These results demonstrate that chromatic aberration may account, in part, for color assimilation over small, but not large, surface areas.     

Ego involvement moderates the assimilation effect of affective expectations

Based on the affective expectations model and research on mental effort mobilization, two experiments manipulated affective expectations (no expectations versus positive expectations) and ego involvement (low versus high) and assessed participants’ affective reactions to hedonically neutral stimuli. In Experiment 1, evaluations were more positive when participants had positive expectations about neutral photos—but only when ego involvement was low. High ego involvement neutralized this affective expectation assimilation effect. Experiment 2 replicated these findings for experienced mood after reading a hedonically neutral short essay. Furthermore, high ego involvement led to longer response latencies in the affect ratings in Study 1. The findings support the idea that high ego involvement resulted in relatively high mental effort that was necessary to detect discrepancies between affective expectations and stimuli’s real affective potential and therefore moderated the assimilation effect to affective expectations.

Modern robust data analysis methods: measures of central tendency

Various statistical methods, developed after 1970, offer the opportunity to substantially improve upon the power and accuracy of the conventional t test and analysis of variance methods for a wide range of commonly occurring situations. The authors briefly review some of the more fundamental problems with conventional methods based on means; provide some indication of why recent advances, based on robust measures of location (or central tendency), have practical value; and describe why modern investigations dealing with nonnormality find practical problems when comparing means, in contrast to earlier studies. Some suggestions are made about how to proceed when using modern methods.     

The bimean: A measure of central tendency that accommodates outliers

Observations that depart considerably from the center of a distribution demand special consideration. They may be retained, trimmed, or weighted less than other data. This article provides a BASIC program that implements Mosteller and Tukey’s (1977) technique for weighting observations less as they depart from the middle of a distribution. Influence curves for this “bisquare-weighted mean,” or “bimean,” are displayed and compared with more traditional measures of central tendency.     

Reducing the tendency to self-handicap: The effect of self-affirmation

Self-handicapping, the creating or claiming of obstacles to one’s performance to influence explanations given for subsequent outcomes, has been shown to have a host of attitudinal and behavioral consequences. Given the wide ranging impact of self-handicapping, it is important to understand the conditions under which self-handicapping is more or less likely to occur. Accordingly, the present study tested the hypothesis that people will be less likely to engage in self-handicapping if they have previously engaged in self-affirmation. The results of this study found that self-affirmation was more effective in reducing self-handicapping behavior when individuals experienced non-contingent success than when they experience contingent success. Theoretical contributions to the self-handicapping and self-affirmation literatures are discussed, as are practical implications.