Allen Parducci

The Category Effect With Rating Scales: Number of Categories, Number of Stimuli, and Method of Presentation

Squares receive higher category ratings when the smaller sizes are presented more frequently than the larger sizes. This shift in the rating scale is greater when there are either fewer categories (the Category Effect) or more stimuli. Similar shifts were obtained whether the stimuli were presented successively for judgment or simultaneously. The Category Effect also occurred when subjects were not told how many categories to use until after the contextual stimuli had been presented. A simple range-frequency model describes most of the shifts in scale by variations in a single weighting parameter. However, these shifts are predicted by an elaborated model in which the number of representations of any stimulus in working memory is limited by a principle of consistent assignment of each stimulus to a single category. This elaborated model correctly predicts the disappearance of the Category Effect when contexts are manipulated by varying the spacing of stimulus values rather than by varying their relative frequencies.

Effects of context in judgments of sweetness and pleasantness

Dramatic effects of the immediate stimulus context were demonstrated for ratings of sweetness and also for ratings of pleasantness of soft drinks containing different concentrations of sucrose. The same drinks were rated sweeter when the lower concentrations were presented more frequently, less sweet when the higher concentrations were presented more frequently. A quasi-normal distribution of frequencies yielded ratings falling between the two skewed distributions. Ratings of sweetness were accurately predicted by Parducci’s (1974) range-frequency model of judgment, which was originally developed to explain contextual effects in other psychophysical dimensions. Ratings of pleasantness were also affected by context; the highest ratings were assigned to concentrations of intermediate sweetness in their respective contexts.

A formal analysis of ratings of physical attractiveness: Successive contrast and simultaneous assimilation

Photographs of faces were presented in a series, either singly or in pairs, for ratings of physical attractiveness. In Experiment 1, faces were presented singly, and both the range and relative frequencies of physical attractiveness (on baseline scaling) were manipulated experimentally. The same face elicited higher ratings when less attractive faces predominated in the experimental series, successive contrast. Increasing the number of available categories resulted in higher ratings but did not reduce the amount of successive contrast. Both range and skewing effects were in accordance with a range-frequency model that permits the subjective range to vary with number of categories. In Experiment 2, faces were presented in pairs. The same face now elicited lower ratings when presented simultaneously with a less attractive face, simultaneous assimilation. Successive contrast was again observed between pairs and was greater for 5- than for 101-point rating scales. A model that uses the judgments resulting from a range-frequency compromise as the stimulus values for integration within pairs provides the best account of how both contrast and assimilation occur within the same experimental session. Alternative interpretations of the observed contrast and assimilation were discussed.

Nocebo: the psychologic induction of pain

More than two-thirds of an unselected sample of 34 college students reported mild headaches when told that a (nonexistent) electric current was passing through their heads. These reports appeared independent of whether the instructions emphasized the headache-producing effect of the current or whether the emphasis was on a perceptual task, with headache as only a possible side effect. The results are consistent with a view of pain as localized stress. They provide additional grounds for the suspicion that clinical focusing on pain may itself be a cause of pain.

Category Ratings and the Relational Character of Judgment

Abstract Category ratings express the relational character of judgment, communicating the place of each stimulus in a context of related stimuli. Rating scales reflect two basic tendencies of judgment: (1) categories divide the subjective rang into equal subranges, and (2) the same number of contextual stimuli are repre-sented by each category. The rating scale can be predicted from a simple weighted average of range and frequence values, and the overall mean of the ratings can be predicted from the skewing of the contextual values. However, even in psychophysical experiments, the subjective range may extend beyond the end values of the stimulus series. Various rating-scale phenomena provide examples of the relational character of judgment.

Reducing the Dependence of Clinical Judgment on the Immediate Context: Effects of Number of Categories and Type of Anchors

Two experiments explored methods for standardizing ratings of the psychopathology of clinical case histories. In both experiments, the same case histories were rated as more pathological when mostly mild rather than severe cases were presented as the immediate context. Psychometric analyses demonstrated that this type of contextual effect is a potentially important source of unreliability in clinical judgment. In Experiment 1, increasing the number of points in the rating scale from 3 to either 7 or 100 significantly reduced the effects of the immediate context. Ratings were parsimoniously modeled by Parduccis (1983) range-frequency theory. In Experiment 2, providing verbal anchors in the form of either detailed DSM descriptions for each rating category or sample case histories for the two end-categories increased the reliability of the ratings by reducing the effects of the immediate contexts; however, these reductions occurred only when the ranges of the immediate contexts had been severely restricted. According to the range-frequency analysis, verbal anchors served to equate the endpoints of the subjective range for the different contextual conditions. Comparison with previous research suggests that the anchors also reduced the effects of the sequential position in which clinical cases appear. We therefore recommend that studies of the reliability of behavioral assessment techniques take into account the effects of differences in context.

Independent contexts for category ratings: A range-frequency analysis

Subjects were instructed to rate with a single set of categories an intermingled series of smaller squares and larger circles, establishing a separate scale of size for each domain. The major finding was that the scale established for one domain was independent of the skewing of sizes in the other domain. However, subjects were also able to combine the two domains into a single context when instructed to do so, particularly when the smallest circle was only slightly larger than the largest square. A range-frequency analysis of the rating suggests that under certain conditions the endpoints defining the subjective range depend upon the stimulus frequencies: the subjective endpoint is more extreme when the closest stimuli are presented with greater relative frequency.

Stimulus averaging and the context for judgment

Loudness judgments of stimulus sets composed of four bursts of noise were analyzed for two types of contextual effects: between-set and within-set. Experiment I demonstrated between-set effects for these four-component stimuli; they were shown to be similar to those found in previous work with single stimuli. Experiment 2 tested an averaging model for within-set contextual effects. The results were inconsistent with the model. One interpretation is that there are within-set effects and that these are caused by shifts in the effective range of stimuli. Alternative interpretations attribute the apparent contextual effects either to an averaging of physical values or to an inappropriate scale of judgment.

Limits on the applicability of signal detection theories

Two auditory signals were presented in random sequences in which the more intense signal came on.2, .5, or.8a/the trials. Each trial began with an intermediate tone which was identified in the instructions as either the standard for comparison or simply as a warning tone. Half the Os were instructed to discriminate whether the signal was “louder” or “softer” than the standard, the other half to recognize which signal had been presented. For both discrimination and recognition tasks, the total proportion of ldlouder” judgments was independent of the presentation probabilities, accuracy for each signal varying inversely with its probability of presentation. These results suggest strict limitations on the response optimization posited by theories of signal detection.

Natural anchoring at the neutral point of category rating scales

Contextual theories of judgment assume that the rating of any stimulus depends on its relationship to a context of similar stimuli. For example, any specific act of behavior would be rated less favorably when considered in the context of good behaviors then when considered in the context of bad ones. However, two experiments suggest an absolute anchoring of the natural neutral point, an exception to this generalization. In Experiment 1, morally indifferent acts remained “neutral,” regardless of context; and in Experiment 2 the break-even or zero-point in a simulated game of chance was always rated “neutral.” In both experiments, contextual manipulations had powerful effects upon ratings of other stimuli, though never shifting them across the neutral point. Furthermore, both experiments suggest that neutral-point anchoring also affects the use of the most extreme categories in a manner that is unique to this phenomena. In Experiment 2 for example, the introduction of extremely positive “wins” not only made other wins seem less favorable while leaving ratings of the zero-point unchanged, but also made the most negative losses seem more favorable. It is as if the introduction of an extremely positive “win” also introduces the possibility of an extremely negative “loss.” Taken together these findings contradict the basic adaptation-level premise that the entire scale is determined by the neutral point; they are also inconsistent with the assumption of range theories that the scale is anchored by the endpoints of the range of stimuli actually experienced.