Categorization of Prototypical Stimulus Classes by Pigeons

Previous findings have demonstrated the pigeon's ability to categorize sets of schematic faces defined by a polymorphous feature rule. We present here an experiment that was conducted to evaluate the influence of the category structure determined by the distribution of features across stimulus classes. The task was a middle-value discrimination, involving a band of positive stimuli surrounded by a band of negative stimuli. Two large sets of Brunswik faces were conceptualized as variations of a standard stimulus (prototype) and occupied highly overlapping regions in the feature space. The classes could be separated in terms of a distance-from-prototype rule. Only three of five animals were successful in classification training. Analyses of both the transfer performance and of the effects of feature values on the variance of responding revealed the classical prototype effect-that is, performance determined by the overall similarity to the central tendency of the classes. A theoretical evaluation of the data examines the possibility that pigeons discriminated between the classes by virtue of a prototype-distance rule, although exemplar models offer more parsimonious accounts.     

Gambles vs. quasi-realistic scenarios: expectations to find probability and risk-defusing information

The paper investigates predecisional information search in risky decisions, specifically information concerning the probability of a negative outcome and whether a risk-defusing operator (RDO) is available. Experiment 1 (54 participants) tested the hypothesis that search for such information is triggered by expectations that it can be obtained in the situation. Cues for the availability of information were manipulated. It was predicted that cues mentioning possible information sources raise expectations and consequently increase search activity. Furthermore, gambles were expected to differ from other real world contexts, with lower expectations for RDOs and higher ones for probabilities. The Method of Active Information Search was employed. The number of questions asked about probability and RDOs in different conditions confirmed the hypotheses. Experiment 2 (36 participants) ruled out the alternative interpretation that the expectation to actually find favorable probabilities or applicable RDOs respectively, rather than the expectation to obtain information, determined information search.     

Hempel’s logic of confirmation

This paper presents a new analysis of C.G. Hempel’s conditions of adequacy for any relation of confirmation [Hempel C. G. (1945). Aspects of scientific explanation and other essays in the philosophy of science. New York: The Free Press, pp. 3–51.], differing from the one Carnap gave in §87 of his [1962. Logical foundations of probability (2nd ed.). Chicago: University of Chicago Press.]. Hempel, it is argued, felt the need for two concepts of confirmation: one aiming at true hypotheses and another aiming at informative hypotheses. However, he also realized that these two concepts are conflicting, and he gave up the concept of confirmation aiming at informative hypotheses. I then show that one can have Hempel’s cake and eat it too. There is a logic that takes into account both of these two conflicting aspects. According to this logic, a sentence H is an acceptable hypothesis for evidence E if and only if H is both sufficiently plausible given E and sufficiently informative about E. Finally, the logic sheds new light on Carnap’s analysis.     

Immediate priming and cognitive aftereffects

Three forced-choice perceptual word identification experiments tested the claim that transitions from positive to negative priming as a function of increasing prime duration are due to cognitive aftereffects. These aftereffects are similar in nature to perceptual aftereffects that produce a negative image due to overexposure and habituation to a stimulus. Each experiment tested critical predictions that come from including habituation in a dynamic neural network with multiple levels of processing. The success of this account in explaining the dynamics of repetition priming, associative-semantic priming, and forward masking effects suggests that habituation is a useful mechanism for reducing source confusion between successively presented stimuli. Implications are considered for visible persistence, repetition blindness, attention-based negative priming, attentional blink, inhibition of return, the negative compatibility effect, affect priming, and flanker preview effects.     

Context retrieval and context change in free recall: recalling from long-term memory drives list isolation

Three experiments used the "list-before-the-last" free recall paradigm (Shiffrin, 1970) to investigate retrieval for context and the manner in which context changes. This paradigm manipulates target and intervening list lengths to measure the interference from each list, providing a measure of list isolation. Correct target list recall was only affected by the target list length when participants engaged in recall between the lists, whereas there were effects of both list lengths with other activities. This suggests that the act of recalling drives context change, thus isolating the target list from interference. Correspondingly, incorrect recall of intervening list items was affected only by the length of the intervening list when recall occurred between the lists, but was otherwise affected by both list lengths. Concurrent with these changes in context similarity, there were apparent changes in context retrieval, as indicated by the overall levels of target retrieval versus intervening recall. A multinomial model of sampling and recovery was implemented to assess the adequacy of this account and to quantify context similarity and context retrieval.     

Judgment and action knowledge in speed adjustment tasks: experiments in a virtual environment

Two experiments were conducted to investigate children's and adults’ knowledge of time and speed in action and judgment tasks. Participants had to set the speed of a moving car to a new speed so that it would reach a target line at the same time as a reference car moving at a higher speed and disappearing in a tunnel at the midway point. In Experiment 1 (24 10‐year‐olds, 24 adults), children's and adults’ speed adjustments followed the normative pattern when responses had to be graded linearly as a function of the car's initial speed. In a non‐linear condition, only adults’ action responses corresponded with the normative function. Simplifying the task by shortening the tunnel systematically in Experiment 2 (24 10‐year‐olds, 24 adults) enabled children to grade the speeds adequately in the action conditions only. Adults now produced normative response patterns in both judgment and action. Whether people show linearization biases was thus shown to depend on the interaction of age, task demands and response mode.