Position reversal training in the Virginia opossum: evidence for the acquisition of a learning set

Size and reversal learning in the beagle dog as a measure of executive function and inhibitory control in aging

Several studies converge on the idea that executive processes age earlier than other cognitive processes. As part of a larger effort to investigate age-related changes in executive processes in the dog, inhibitory control was measured in young, middle-aged, old, and senior dogs using size discrimination learning and reversal procedures. Compared to young and middle-aged dogs, old and senior dogs were impaired on both the initial learning of the size task and the reversal of original reward contingencies. Impaired performance in the two aged groups was characterized as a delay in learning the correct stimulus-reward contingencies and, among the senior dogs in particular, an increase in perseverative responding. These separate patterns of reversal impairments in the old and senior dogs may reflect different rates of aging in subregions of the frontal cortex.

Quokkas (Setonix brachyurus) demonstrate tactile discrimination learning and serial-reversal learning

Two male quokkas (Setonix brachyurus: a herbivorous macropod marsupial) were trained to discriminate pairs of stimuli in the laboratory. Quokkas indicated their choice by pulling on 1 of 2 simultaneously presented cords. The quokkas' discrimination abilities were tested on 6 tactile and 6 visual discrimination tasks. Correct responses were rewarded with food. For both quokkas, all tactile tasks were learned to a criterion of 75% correct in up to 4 20-trial sessions. No visual task maintained criterion performance in 4 sessions. One tactile discrimination was reversed 10 times. After the 1st reversal, the error rate declined sharply and fell to a level well below the initial discrimination.

Spatial learning in South American opossums and armadillos

This experiment compares spatial learning in the South American opossum (Didelphis albiventris) and armadillo (Chaetophractus villosus) in a Y-maze. Ss learned to turn to one arm of the maze for food reinforcement. To earn further reinforcements, they had to return to the start-box (after consuming the food) where they were restrained for a fixed intertrial interval. The number of entries to the unbaited arm en route to the goal-box (Ri errors), and in the way back to the start-box (Rf errors) were the dependent measures. Opossums and armadillos did not differ in Ri errors. However, only armadillos mastered the task of returning directly to the start-box after each reinforcement. Moreover, a significant within-session improvement in Rf errors was observed in armadillos, but failed to appear in opossums. Results are discussed in terms of species differences in sensitivity to temporal delays.

The Virginia opossum in psychological research

The Virginia opossum ( Didelphis virginiana) has certain characteristics by which it can make unique contributions to psychological research, namely, an exposed embryological development suitable for developmental studies, and a characteristic marsupial brain suitable for “split-brain” studies of relationships between the two cerebral hemispheres and comparative learning. Disadvantages to using opossums, such as their low resistance to parasites and disease, viciousness, and nocturnal habits, have largely been overcome as the result of recent interdisciplinary efforts.