Earlier studies have found that priming a resident female hamster by allowing it to attack a conspecific intruder transiently reduced the latency of its attack on a second (probe) intruder. The present series of experiments showed that the time the subject spent in contact with each intruder prior to attack revealed this priming effect more clearly than did the conventional total elapsed time measure. The influence that stimuli encountered during the first few minutes of intruder exploration would heighten the subject’s aggressive arousal was confirmed in experiments showing that increasing exposure to an anaesthetized intruder from 0 to 90 s systematically reduced subsequent attack latency. Ninety seconds of contact with an anaesthetized intruder just prior to testing on a pair of priming and probe trials significantly reduced the priming effect. However, such exposure may not reproduce the full reduction in latency that follows an overt attack. Consecutive priming and probe attack latencies were uncorrelated even though the latter is routinely shorter than the former. Attacks were therefore modelled as stochastic events. Standard log survivor analysis suggests that attack probabilities increase to an asymptote during both priming and probe trials. A novel θ(t) transformation of the data showed more clearly that the priming effect results from a probability of attack which starts at a higher level on probe trials and rise to asymptote faster.
Bibliographical noteFunding Information:
We thank James Porter and Paul Mackenzie for their assistance in testing the animals and Annabelle Wright and Pat Stroy for their expert help in preparing the figures. The first stages of this work were supported by grants from the Harry Frank Guggenheim Foundation to M.P. Later stages were supported by a Senior Resident Research Associateship awarded to M.P. by the National Research Council. This research was conducted in compliance with the Animal Welfare Act and other Federal statutes and regulations relating to animals and experiments involving animals, and adheres to principles stated in the Guide for the Care and Use of Laboratory Animals, NIH Publication 85-23. The views of the authors do not purport to reflect the position of the Department of the Army or the Department of Defense (Para 4-3, AR 360-5).