Hungry rats performed four different tasks which all required responding to be withheld for food reinforcement to be obtained. The tasks were the following: an omission schedule, a go/no-go procedure, a differential reinforcement of low rate schedule, and a choice task in which the subject could respond for a small immediate reward or a large delayed reward. Each rat experienced each task twice. For each task, the rank ordering of the subjects' performance on the test and retest was highly consistent, indicating the reliability of the task for measuring a particular "ability." However, there were no consistencies in the performance of individual rats between tasks. This suggests that claims regarding consistent individual differences in brain-lesioned nonhumans across a range of such tasks are not supported in intact subjects.Approaches to analyzing personality may be divided into two broad categories. One approach suggests that individuals may possess one out of a number of personality traits that are stable across different situations (e.g., Eysenck & Eysenck, 1985;Gray, 1987). This might be termed a trait approach. In contrast, the state approach suggests that behavior is more consistent in the same situation than across different situations (see Mischel, 1990;Shoda, Mischel, & Wright, 1993). Nonhumans as well as humans have been used to explore the mechanisms that might underlie personality (e.g., Mather & Anderson, 1993;Wanchisen, Tatham, & Mooney, 1989). In fact, some models of personality in humans draw extensively on work involving nonhuman performance in conditioning tasks (see, e.g., Gray, 1987). However, little work has been done to establish whether data collected from nonhuman subjects may be best characterized as supporting the state or trait view of personality.An example of a model of personality based on data from studies with nonhumans (especially rats) is that of Gray (1987). These data suggested a three-factor model of personality, involving an activation system that deals with behavior elicited by rewards; an inhibition system that deals with responses to punishment and the inhibition of ongoing behavior; and a flight/fight system which mediates the behavioral effects of unconditioned aversive events. Since damage to the septum and to the hippocampus has been found to produce impairments on a variety of tasks (see Gray, Rawlins, & Feldon, 1979, for a review), it Part of this work formed a thesis submitted in partial fulfillment of a Master of Science degree for the second author. Thanks are due Celia Heyes and Lisa Osborne and two anonymous reviewers for comments on an earlier version of this paper. Requests for reprints should be sent to: P. Reed, Department of Psychology, University College London, Gower Street, London WClE 6BT, England (e-mail:ucjtspr@ucl.ac.uk).
-Accepted by previous editor, Vincent M. LoLordohas been assumed that performance on those tasks was mediated by this common substrate, and that this may underlie the expression of a personality trait. If this point is accepted, ...