Thomas F. Sawyer

Chemosensory and hormonal mediation of social memory in male rats

The persistence with which adult male rats investigated a juvenile conspecific was significantly reduced following preexposure to either the juvenile or chemosensory stimuli (soiled bedding or urine) from that juvenile. The reduced persistence did not occur when the chemosensory stimulus came from a juvenile different from the one with which the subject was subsequently tested, which suggests the presence of a chemosensorily mediated social memory. It is suggested that any such memory may have adaptive value in that it permits a male rat to more readily identify a novel conspecific. Also, the lack of reduced persistence of social investigatory behavior in castrated subjects demonstrates the importance of male gonadal hormones in the formation, storage, and/or retrieval of the proposed chemosensorily mediated social memory.

Contrasting task demands alter the perceived duration of brief time intervals

Four experiments were performed to assess the effects of task differences on duration judgments. Experiments 1 and 2 used the method of reproduction in prospective, within-subjects designs; their results supported previous research on the effects of task difficulty. Both experiments, using tasks that varied along somewhat different dimensions, found that subjects provided reproduction values that varied inversely with task difficulty. That is, while subjects tended to underreproduce across all tasks, the more difficult the task performed during the target interval, the greater the extent of the under-reproduction. Experiments 3 and 4 used a modification of the reproduction method by placing demands upon the subjects during both the target interval and the reproduction phase of each trial; they demonstrated that the greater the degree of contrast between demands made by the task performed during the target interval and those made during reproduction, the less accurate the duration reproduction. The results are discussed in terms of the contextual and resource allocation models of duration estimation.

Estrous cycle fluctuations in aggressiveness of house mice.

Abstract The purpose of this study was to determine whether interfemale, isolationinduced aggression in house mice varies over the phases of the estrous cycle. The results indicated that there were significant variations, with aggression being higher at proestrus and metestrus and lower at estrus and diestrus. Activity level showed fluctuations across the cycle similar to the pattern established by previous research. The results were interpreted in terms of possible adaptiveness.

Selection for agonistic behavior in wild female mice

This article reports the results of 11 generations of selective breeding for isolation-induced, interfemale aggression inMus musculus. Within-family selection was used to form two high, two low, and two unselected control lines, beginning with a population of wild-trapped mice. Selection was successful in establishing the divergent lines, so that in recent generations about 50% of high-line animals attack, as do 25% of controls and 5% of lows. Realized heritabilities for eight generations of selection were 0.12 for H1, 0.14 for H2 0.34 for L1, and 0.46 for L2. Male aggression has apparently not shown a correlated response to selection for female aggression. Group housing reduces the aggression of female mice, but the order of the lines is maintained under either isolation or group housing. Practical problems encountered in this selection program are discussed.

Androgen effects on responsiveness to aggression and stress-related odors of male mice

Abstract The effect of male gonadal hormones on responsiveness to the aggression and stress-related odors of male mice was examined. The initial experiment indicated that intact male mice would avoid an area of an open field that had been spotted with the urine of aggressive male donors, while castration of the subjects eliminated the response. Hormone replacement was effective in reinstating the aversion, clearly demonstrating the androgen-dependent nature of the response. A second experiment determined that the effects of castration do not generalize to another type of aversive odor, namely the alarm odors of castrate donors. That is, both intact and castrate males exhibited a pronounced aversion to the urine odors of castrates that had been subjected to a prolonged period of stress. These results suggest that gonadal hormone effects on olfactory responsivity are somewhat specific, and more interestingly, that the mechanism behind the effects of gonadal hormones on rodent aggression may lie in their influence on the nature of the response to the relevant olfactory stimuli.

Correlated characters in selection for aggressiveness in female mice. II. maternal aggressiveness

The present study investigated whether maternal aggression has shown a correlated response in a program of artificial selection for isolation-induced interfemale aggression in housemice. Females from the first replicate of lines (H1, C1, L1) and the second replicate of lines (H2, C2, L2) from generation S5 were given daily aggression tests for 20 consecutive days following the birth of their first litter. Evidence of a correlated response was found for replicate 2, but results for replicate 1 provided no evidence of a correlated response. In generation S10, when better separation of the lines on isolation-induced aggression had occurred, the study was repeated. In S10 there was clear evidence of a correlated response in both of the replicates.

Allocation of Attention and Practice in the Production of Time Intervals

During a baseline trial, participants attempted to produce a 60-sec. interval while working at either a simple tracing task or others that involved mirror-tracing. Subsequent practice with the assigned task, expected to reduce the need for allocation of attention to mirror-tracing for those groups, produced predictable effects on a second trial of duration producing. Those performing mirror-tracing reduced production rimes on the postpractice trial, while those performing simple tracing showed no change after practice. These results are interpreted within the attentional allocation model of estimation of prospective duration.

Allocation of attention and production of time intervals

14 students enrolled in introductory psychology classes engaged in several trials of card sorting to acquire the rule for correct sorting They also were instructed to keep track of time simultaneously and to continue sorting for what they believed was 20 sec. The duration of card sorting was significantly greater for the first sorting trial, during which the rule was unknown, relative to the second consecutive trial of errorless sorting when the rule had been learned. After a shift in the rule mean sorting duration was reduced from the second errorless trial but returned to a value comparable to that on the first sorting trial. Results are interpreted in terms of the attention-allocation model of time estimation.

Anchoring effects on judgement, estimation, and discrimination of numerosity

Three experiments (N = 234) examined anchoring effects on judgement, estimation, and discrimination of numerosity. Subjects were anchored by preexposing them to random dot patterns with a mean quantity of 25, 50, or 75 dots. Subsequent testing with patterns having greater or less numerosity than the anchoring point resulted in predictable effects, including positive or negative contrast effects for numerosity judgements (Exp. 1), positive or negative contrast for the numerical estimation of quantity (Exp. 2), and a larger number of errors when subjects attempted simultaneous discrimination between two dot patterns (Exp. 3). The results extend previous findings for anchoring effects to the stimulus dimension of numerosity.