Revealing human inductive biases for category learning by simulating cultural transmission

We explored people’s inductive biases in category learning—that is, the factors that make learning category structures easy or hard—using iterated learning. This method uses the responses of one participant to train the next, simulating cultural transmission and converging on category structures that people find easy to learn. We applied this method to four different stimulus sets, varying in the identifiability of their underlying dimensions. The results of iterated learning provide an unusually clear picture of people’s inductive biases. The category structures that emerge often correspond to a linear boundary on a single dimension, when such a dimension can be identified. However, other kinds of category structures also appear, depending on the nature of the stimuli. The results from this single experiment are consistent with previous empirical findings that were gleaned from decades of research into human category learning.     

How to solve a mechanical problem: the relevance of visible and unobservable functionality for kea

Animals sometimes succeed quickly in solving a mechanical problem that is a modification of one they have previously learnt to solve. However, they may do so by attending to the visible features of the relevant physical dimension without knowing its causal functionality, if that is not directly perceivable. This kind of problem solving can be tested by simultaneously offering two mechanical devices with the same visual features but different inherent appropriateness for problem solving. Here, we provide data collected by following this procedure for the first time in a bird species. Captive kea, Nestor notabilis, a parrot species highly interested in the affordances of objects, were offered a mechanical problem in which they had to remove a baited tube from one of two upright poles where removal was blocked at the end of one pole but not the other. With extended but not with restricted exploration of a baseline apparatus, the kea immediately succeeded in removing the tube from an apparatus that had modified pole ends when they were able to visually observe (without touching) that one of these ends would block tube removal but the other would not. However, when the kea were allowed to explore two poles that had a removable and a fixed obstruction where the difference in function was not visible, they preferred the removable one during unbaited exploration but failed afterwards to push a tube to the end of the pole with the loose structure during subsequent baited test trials. Thus, in spite of the speed with which the kea learnt the tasks, there was no indication that they understood the underlying unobservable causal structure of the problem.     

BOOK REVIEWS

This paper deals with the traumatic departures of Jews from Morocco during the 1950s and 1960s. The issue is analyzed through a set of diverse oral narrations. The study is based on several interviews conducted both among Jews who left Morocco and Muslims still living in the city of Meknes. The repression of the memory by Muslims of two young Jews murdered in 1967 in Meknes is questioned. In fact, although the perceptions concerning the Jews' departure differs according to the interviewee's social class, a common feeling appears to be shared by different societal sectors regarding this specific issue, which still comes across as a sensitive one today. The representation of Jews traditionally depicted as “fearful” and “weak” turns into “courageous” and “strong” during the Six‐Day War. This new representation perturbed the Muslim population, which seemed to be unable to deal with the new status Jews were acquiring. In fact, emigration was commonly considered to betray a lack of virility. The paper argues that the unexpected departure of an historic component of Moroccan society has left an open wound in Morocco. Even the memory of the “events” by the Jewish population appears to be fragmented into ambiguous constructions, leading, on the one hand, to perceptions of fear and uncertainty and, on the other, to images of affectionate relationships and intense nostalgia.     

Developmental changes in effects of risk and valence on adolescent decision-making

Recent research on risky decision-making in adults has shown that both the risk in potential outcomes and their valence (i.e., whether those outcomes involve gains or losses) exert dissociable influences on decisions. We hypothesised that the influences of these two crucial decision variables (risk and valence) on decision-making would vary developmentally during adolescence. We adapted a risk-taking paradigm that provides precise metrics for the impacts of risk and valence. Decision-making in 11–16 year old female adolescents was influenced by both risk and valence. However, their influences assumed different developmental patterns: the impact of valence diminished with age, while there was no developmental change in the impact of risk. These different developmental patterns provide further evidence that risk and valence are fundamentally dissociable constructs and have different influences on decisions across adolescence.     

Geometric and featural representations in semantic concepts

We explore the adequacy of two types of similarity representation in the context of semantic concepts. To this end, we evaluate different categorization models, assuming either a geometric or a featural representation, using categorization decisions involving familiar and unfamiliar foods and animals. The study aims to assess the optimal stimulus representation as a function of the familiarity of the stimuli. For the unfamiliar stimuli, the geometric categorization models provide the best account of the categorization data, whereas for the familiar stimuli, the featural categorization models provide the best account. This pattern of results suggests that people rely on perceptual information to assign an unfamiliar stimulus to a category but rely on more elaborate conceptual knowledge when assigning a familiar stimulus.     

Interacting noradrenergic and corticosteroid systems shift human brain activation patterns during encoding

Emotionally arousing experiences are usually well retained, an effect that depends on the release of adrenal stress hormones. Animal studies have shown that corticosterone and noradrenaline – representing the two main stress hormone systems – act in concert to enhance memory formation by actions involving the amygdala, hippocampus and prefrontal cortex (PFC). Here we test whether interactions between these two stress hormone systems also affect human memory formation as well as the associated pattern of brain activation. To this end, forty-eight male human subjects received hydrocortisone, yohimbine or both before presentation of emotional and neutral pictures. Activity in the amygdala, hippocampus and PFC was monitored with functional Magnetic Resonance Imaging (fMRI) during encoding of these stimuli, when hormonal levels were elevated. Memory performance was tested 1 week later. We investigated whether an increased level of one of the two hormone systems would lead to differential effects compared to the combined application of the drugs on brain activation and memory performance. We report that the application of cortisol led to an overall enhancing effect on recognition memory, with no significant additional effect of yohimbine. However, during encoding the brain switched from amygdala/hippocampus activation with either hormone alone, to a strong deactivation of prefrontal areas under the influence of the combination of both exogenous hormones. Although we did not find evidence that exogenous stimulation of the noradrenergic and corticosteroid systems led to significant interaction effects on memory performance in this experiment, we conclude that stress hormone levels during encoding did differentially determine the activation pattern of the brain circuits here involved.     

An Experiment in Judging Personalities

Use of the semantic differential technique has largely been restricted to “paper and pencil” settings and student populations. In this study, adult respondents in an interview setting were asked to evaluate two concepts—use of lake (a) as a source of electric power and (b) as a recreational area—by means of eight seven-point scales. Results indicated considerable conceptscale interaction, suggesting that Osgood's interpretation of the semantic differential may be restricted by both technique of data collection and subpopulation. Respondent hostility might be an intervening variable. The semantic differential technique appeared to yield a preliminary evaluation of the two concepts, suggesting its use as an indicator of orientation.