Aggression in domesticated rats reared in a burrow-digging environment

Male and female rats were raised individually in either large boxes filled with soil (burrow environment) or laboratory cages of comparable size (cage environment). In a test of intruder-elicited aggression, intruders exposed to burrow-environment residents lost more body weight, were more likely to have empty stomachs, and received more wounds during a 24 hour aggression test. The results indicate that the physical environment during the period from weaning to maturity is an important determinant of aggression intensity in adult rats.     

The automatic evaluation of novel stimuli

From classic theory and research in psychology, we distill a broad theoretical statement that evaluative responding can be immediate, unintentional, implicit, stimulus based, and linked directly to approach and avoidance motives. This statement suggests that evaluative responses should be elicited by novel, nonrepresentational stimuli (e.g., abstract art, "foreign" words). We tested this hypothesis through combining the best features of relevant automatic–affect research paradigms. We first obtained explicit evaluative ratings of novel stimuli. From these, we selected normatively positive and negative stimuli to use as primes in a sequential priming paradigm. Two experiments using this paradigm demonstrated that briefly presented novel prime stimuli were evaluated automatically, as they facilitated responses to subsequently presented target stimuli of the same valence just as much as did pictures or names of real objects. A final experiment revealed that exposure to novel stimuli produces muscular predispositions to approach or avoid them.     

Categorization of novel stimuli in well-known natural concepts: a case study

In this study, we investigated to what extent exemplar-based and prototype predictors can be applied to predicting categorization in natural language concepts. Participants categorized novel tropical foods into two well-known natural language concepts:fruits and vegetables. The results indicate that both the prototype predictors and the exemplar predictors contribute significantly in accounting for the categorization choices but that the contribution of the prototype predictor comes from just a limited number of features.     

Priming a natural or human-made environment directs attention to context-congruent threatening stimuli

Research suggests that attention is attracted to evolutionary threats (e.g., snakes) due to an evolved "fear-module" that automatically detects biological threats to survival. However, recent evidence indicates that non-evolutionary threats (e.g., guns) capture and hold attention as well, suggesting a more general "threat-relevance" mechanism that directs attentional resources toward any potential danger in the environment. The current research measured how selective attentional resources were influenced both by the type of threat (e.g., snake vs. gun) and by the context in which the threat was encountered. Participants were primed with either natural or human-made environments to assess how these contexts influence attention to evolutionary and non-evolutionary threats, as measured by a spatial-cueing task. The results indicate that whether biological or non-biological threats receive greater attentional processing is determined by the context in which they are encountered.     

Priming a natural or human-made environment directs attention to context-congruent threatening stimuli

Research suggests that attention is attracted to evolutionary threats (e.g., snakes) due to an evolved “fear-module” that automatically detects biological threats to survival. However, recent evidence indicates that non-evolutionary threats (e.g., guns) capture and hold attention as well, suggesting a more general “threat-relevance” mechanism that directs attentional resources toward any potential danger in the environment. The current research measured how selective attentional resources were influenced both by the type of threat (e.g., snake vs. gun) and by the context in which the threat was encountered. Participants were primed with either natural or human-made environments to assess how these contexts influence attention to evolutionary and non-evolutionary threats, as measured by a spatial-cueing task. The results indicate that whether biological or non-biological threats receive greater attentional processing is determined by the context in which they are encountered.     

Effect of restraint on gastric acid secretion in cats

Experiments were carried out on cats fitted with a gastric fistula. In one group of 6 cats basal gastric secretion, and in another group of 7 cats pentagastrin induced gastric secretion was collected two or three times a week during a 2 hr session. The sessions were conducted either in a “harness” situation where the cat’s movements were restricted, or in a “cage” situation where the cat was unrestricted and could move freely. It was found that in four of 6 cats in the basal secretion group and in five of 7 cats in the pentagastrin induced secretion group, gastric acid output was significantly higher in sessions in harness than in sessions in cage. These differences in acid output were due to acidity rather than volume of secretion. It was hypothesized that restriction of the animal’s movements in the harness could evoke a “reflex of freedom” which, however, could not be accomplished because of the confinement. This could evoke a neural conflict eventually leading to functional disturbances in the autonomic system. This, in turn, resulted in changes in gastric acid secretion.     

Diversity during training enhances detection of novel stimuli

This research demonstrates that when individuals are expected to detect novel targets, they will be best prepared when trained with diverse categories. Participants were trained in a simulated luggage screening task in one of three conditions of diversity: high (participants searched for dangerous objects belonging to five different categories); low (participants searched for targets belonging to one of the five categories); and no training (control condition). After training, all participants were asked to look for the same novel dangerous objects in the bags. Results show that, during training, the low diversity condition resulted in highest hit rates and fastest response times. In contrast, after training, results were reversed: participants that trained in a high diversity condition were most effective at detecting novel targets. Those with no training at all were equally poor at detecting novel targets as those that trained in a low diversity condition.     

Adult learners in a novel environment use prestige-biased social learning

Social learning (learning from others) is evolutionarily adaptive under a wide range of conditions and is a long-standing area of interest across the social and biological sciences. One social-learning mechanism derived from cultural evolutionary theory is prestige bias, which allows a learner in a novel environment to quickly and inexpensively gather information as to the potentially best teachers, thus maximizing his or her chances of acquiring adaptive behavior. Learners provide deference to high-status individuals in order to ingratiate themselves with, and gain extended exposure to, that individual. We examined prestige-biased social transmission in a laboratory experiment in which participants designed arrowheads and attempted to maximize hunting success, measured in caloric return. Our main findings are that (1) participants preferentially learned from prestigious models (defined as those models at whom others spent longer times looking), and (2) prestige information and success-related information were used to the same degree, even though the former was less useful in this experiment than the latter. We also found that (3) participants were most likely to use social learning over individual (asocial) learning when they were performing poorly, in line with previous experiments, and (4) prestige information was not used more often following environmental shifts, contrary to predictions. These results support previous discussions of the key role that prestige-biased transmission plays in social learning.     

Effect of intermittent acoustic stimuli on mental processes

In a Sternberg experiment, the influence of rhythmic acoustic stimuli on the scanning rate of short-term memory was studied. During the experiment, 60 subjects heard rhythmic or arrhythmic impulse noises with different rates of repetition. Results showed that the scanning rate of short-term memory is lowest if the impulses are arrhythmic. With rhythmic impulses at high rate of repetition, an accelerated scanning rate was obtained. The results can be interpreted as consequences of interference processes and as adaptational effects of internal processing rhythms.     

Effect of posttrial episodes on conditioning in compound conditioned stimuli

The effect of signaled and nonsignaled posttrial episodes (PTEs) on conditioning to the target CS of a preceding compound CS-US trial was examined in two conditioned emotional response (CER) experiments with rats. Experiment 1 revealed that a nonsignaled PTE, a second shock US, interfered with conditioning to the preceding target CS and that the interference effect of the PTE was greater when it occurred 5 sec as opposed to 1,800 sec after the preceding compound CS-US trial. Experiment 2 revealed that if the shock PTE was signaled by a CS, its ability to interfere with conditioning was reduced. This second study also revealed that omission of an "expected" US interfered with conditioning to the target CS. The implications of these data for information processing models of Pavlovian conditioning are discussed.     

The effect of conspecifics on corticoadrenal response of rats to a novel environment

The effect of housing conditions and the presence of a conspecific on corticoadrenal response to a novel environment was studied in male Sprague-Dawley rats. The response to a novel environment was the same in rats housed in groups and rats housed alone for 20 days before testing, suggesting that isolation during adulthood did not affect corticoadrenal response to a novel environment. The presence of a nonfamiliar rat (proceeding from another home cage) did not modify corticoadrenal response to the novel environment but the presence of a rat proceeding from the same home cage induced a higher corticoadrenal response to this stressful stimuli. These results can be explained considering that rats exhibit greater emotional reactivity, as measured by adrenal function, in situations which combine familiar (the other rat) and novel (the box) elements than those completely unfamiliar.     

Hypotheses in perception: their development about unambiguous stimuli in the environment

A series of seven photographs which depict a real scene as it is approached by an observer were shown, in sequence, to ninety-six university students. The photographs were either projected colour transparencies or black-and-white prints. Two sixes of photographs were used in each set and the series was presented with or without the first photograph. In earlier studies in which blurred photographs were used as stimuli, observers were unsure about their hypotheses. That was not the case in this study. Although individual observers differed widely in their initial hypotheses, the initial photographs were not perceived as ambiguous. It required on average from 2.9 photographs (large, black-and-white, full series) to 4.5 photographs (small, colour, full series) for correct identification. In general, colour is a hindrance to correct identification. For the full series approximately three hypotheses are put forward before the scene is correctly identified.