The form of the psychophysical function near threshold

Psychophysical functions typically depart from a simple power law in the vicinity of the absolute threshold. Five versions of the psychophysical power law have been proposed to describe the function near threshold. An account is given of some of the difficulties encountered in attempts to decide among the various versions by means of empirical tests.     

Empirical evaluation of a model of global psychophysical judgments: III. A form for the psychophysical function and intensity filtering

In part I, a concept of ratio estimation is defined and it is shown that if such estimates depend only upon the physical ratio of the signal to the reference signal, the psychophysical function must be a power function. Assuming the same exponents for each component, an invariance condition, equivalent to a sum of power functions, is studied empirically for binaural loudness. It is fully or partially sustained for 19 of 22 respondents. Since failures may be attributable to different exponents in the two ears, the ratio of the two exponents is estimated but that fails to explain the failures. Other possible explanations are suggested. In part II, an intensity filtering model is presented, accounting for the phenomenon where monaural loudness matches show a bias depending on the matching ear. We show (a) that the existence of such a bias does not alter the prior experimental results; and (b) assuming the power function, that five respondents attenuate the opposite ear and two enhance it.     

Multidimensional scaling of form: A psychophysical analysis

Both metric and nonmetric multidimensional scaling methods were used to analyze similarity estimates when random polygons were used as stimulus patterns. Three dimensions, dispersion, jaggedness, and elongation were obtained with both analyses and were related to physical measures of the patterns.     

Decision rules in the perception and categorization of multidimensional stimuli

This article examines decision processes in the perception and categorization of stimuli constructed from one or more components. First, a general perceptual theory is used to formally characterize large classes of existing decision models according to the type of decision boundary they predict in a multidimensional perceptual space. A new experimental paradigm is developed that makes it possible to accurately estimate a subject's decision boundary in a categorization task. Three experiments using this paradigm are reported. Three conclusions stand out: (a) Subjects adopted deterministic decision rules, that is, for a given location in the perceptual space, most subjects always gave the same response; (b) subjects used decision rules that were nearly optimal; and (c) the only constraint on the type of decision bound that subjects used was the amount of cognitive capacity it required to implement. Subjects were not constrained to make independent decisions on each component or to attend to the distance to each prototype.     

Effects of cognition on the psychophysical function

Previous investigation of the deterministic-sensory and the probability-sensory-learning models of psychophysical relationships have featured the manipulation of a single cognitive cue. The present study sought to expand these findings through the manipulation of multiple cognitive cues. Subjects made magnitude estimations of skin-area contact for each of two sets which varied identically in surface area but differed in that one set also varied in accelerative force. Within sets, three treatments featured systematic variation in the presentation of cognitive cues. Power functions were obtained for all treatments and the results supported the deterministic-sensory model. It was suggested, however, that resolution of the perception versus cognition issue must await the identification of innate and conditioned correlates of the subjective response to specific sensory stimuli.     

Considering multiple criteria for social categorization can reduce intergroup bias

Two experiments tested the notion that considering multiple criteria for social categorization can reduce intergroup bias. In both experiments, participants were required to consider alternative ways in which people could be classified, other than an initially salient intergroup dichotomy. In Experiment 1, the authors found that generating alternative social classifications that were unrelated to an initial target dichotomy reduced intergroup bias compared to a control condition. In Experiment 2, this effect was replicated and the authors found that unrelated, but not related, categorizations were necessary to reduce bias. This article adds support to the view that increasing categorical complexity is a useful tool in bias reduction. These findings are discussed in the context of a developing model of multiple categorization effects.     

Odor intensity: Differences in the exponent of the psychophysical function

A series of five experiments showed that there are reliable differences among the exponents of the psychophysical power functions for odorants. There was virtually a perfect rank-order correlation between the size of the exponent and the water-solubility of the odorants. The exponents for odorants that are completely soluble in water (n-propanol and acetone) were approximately 2.5 times the size of the exponents for odorants that are insoluble in water (n-octanol and geraniol). For n-aliphatic alcohols, the size of the exponent and solubility in water decrease as a function of carbon chain-length. Although the exponents were higher when the stimuli were delivered with an air-dilution olfactometer than when they were sniffed from cotton swabs, the relative values among odorants were independent of the method of stimulus presentation.     

Mechanisms of developmental change in infant categorization

Computational models are tools for testing mechanistic theories of learning and development. Formal models allow us to instantiate theories of cognitive development in computer simulations. Model behavior can then be compared to real performance. Connectionist models, loosely based on neural information processing, have been successful in capturing a range of developmental phenomena, in particular on-line within-task category learning by young infants. Here we describe two new models. One demonstrates how age dependent changes in neural receptive field sizes can explain observed changes in on-line category learning between 3 and 10 months of age. The other aims to reconcile two conflicting views of infant categorization by focusing on the different task requirements of preferential looking and manual exploration studies. A dual-memory hypothesis posits that within-task category learning that drives looking time behaviors is based on a fast-learning memory system, whereas categorization based on background experience and assessed by paradigms requiring complex motor behavior relies on a second, slow-learning system. The models demonstrate how emphasizing the mechanistic causes of behaviors leads to discovery of deeper, more explanatory accounts of learning and development.     

Visual and tactual form complexity:A psychophysical approach to perceptual equivalence

Equivalence of two modalities for processing form-complexity information was investigated by obtaining category judgments of the complexity of 100 random forms from 40 Ss who explored the forms visually and 40 Ss who explored them tactually. Intercorrelations of judgments and multiple regression analyses with form measures indicate that information was used in the same fashion independent of input modality. Latencies were interpreted as reflecting information gaining and processing capabilities.     

Decision strategies in the ABX (matching-to-sample) psychophysical task

The ABX psychophysical task is very useful when the dimensions along which the stimulus varies cannot be readily described. However, there are a few problems associated with its use. First, the task has often been used with slight procedural variations, which hinders the extraction of a bias-free index of performance. Second, the most common index of sensitivity derived from this task is the ubiquitous proportion correct. Third, some researchers undervalue the importance that the decision strategy adopted by the observer has on estimates of sensitivity. We describe a standard methodology for the ABX task and outline models of performance based on two decision strategies. These models can be used to extract the detection-theoretic index of performance, d', from ABX data. The results of three ABX discrimination experiments, in which circle size, number value, and tone amplitude are used, are reported. Analysis of the decision spaces derived from observer responses indicates that these observers adopted a suboptimal difference decision strategy, even after they had received considerable practice with feedback. This suggests that, given no prior knowledge of the nature of the decision strategy adopted by an observer, the difference model of ABX discrimination could be a good choice when observer performance is estimated.     

Empirical evaluation of a model of global psychophysical judgments: IV. Forms for the weighting function

Understanding the psychological interpretation of numerals is of both practical and theoretical interest. In classical magnitude estimation, respondents match numerals to sensations and in magnitude production they select sensations that stand in a prescribed numerical ratio to a given standard. The present work focusses on evaluating several possible, and related, forms for the function W formulating the distortion of numerals. The main form, of which a power function is a special case, is the Prelec exponential/power representation. Behavioral equivalents to power and to Prelec functions are formulated, tested, and rejected. It is argued that either the mathematical form or the assumption W(1)=1 is wrong. Whereas, the axiomatic literature has focussed exclusively on the former inference, we explore the alternate that W(1)≠1. Behavioral axioms are formulated in each case and experimentally tested. We conclude that most respondents satisfy a general power function and that those who do not, satisfy the general Prelec function.     

Decision criteria do not shift: Reply to Treisman

Recently, we argued that the detection criterion representation of decision-making biases, embedded within the theory of signal detection, is empirically testable and has, in fact, been falsified by empirical results from visual discrimination experiments. Treisman (2002) attempts to show that there is an alternative interpretation of our results that could explain them without dropping the detection criterion construct. In lieu of attempting to fit the data with a model, however, he gives two kinds of theoretical examples, both involving manipulations of the spacing of criteria on a decision axis. The first example correctly predicts that the bias estimate we developed will be zero but does so by assuming zero spacing between some criteria (some rating responses are never used). We did not observe zero spacing between any criteria and did not perform any analyses on responses that never occurred. Moreover, this example does not explain why the upper-bound bias estimates that we obtained by combining results from two criteria placements were also trivially small. His second example predicts that the bias should have been detectable with sufficiently large sample sizes. In our experiments, the sample sizes were, in fact, quite large, large enough for the results to be consistent in 18 different experimental conditions. Finally, all of Treisman’s criteria placement examples also fail to explain the pronounced effects of base rates on the shapes of the rating ROC curves, and his suggestion that there are problems of logical interpretation with our proposed distribution model ignores the predictions of large classes of alternatives to detection theory, including the dynamic models of perception.     

Social categorization as a function of priming

The present study investigates the effect of priming on the use of social categorizations. Using sex and race as stimulus categorizations, previous studies failed to confirm the hypothesis that priming one of the two available categorizations would enhance the use of the primed categorization relation to the not-primed categorization. As suggested by Stangor, Lynch, Duan and Glass (1992). a momentary increase in accessibility may be insufficient to further enhance the use of highly accessible categorizations like race and sex, but it may be expected that priming will increase the use of categorizations which are less habitually used in daily life. The results of the present experiment support the hypothesis that, when the stimulus categorizations are weakly accessible (university major, university town), the relative use of the previously primed categorizations does indeed increase, compared to the alternative, not-primed, categorization.