Interactions of numerical and temporal stimulus characteristics on the control of response location by brief flashes of light

Assessing the performance of brushtail possums (Trichosurus vulpecula) on the Mechner counting procedure

This study assessed brushtail possums' performance on the Mechner counting procedure. Six brushtail possums were required to produce different Fixed-Ratio (FR) response targets by lever pressing. Their responses provided access to food reinforcement delivered either upon completing the target FR response requirement on a single lever or, in different conditions, on completing the target FR before producing an additional response on a second lever. The mean number of responses on the first lever before switching to the second lever typically occurred just above the target FR response requirement (FR: 4, 8, 16, 32 and 64). The variability in the number of switches between the levers around the target FR decreased from the first 10 days to the last 10 days, indicating an improvement in counting accuracy over sessions. The time to switch between the first and second lever was consistently variable across response requirements suggesting that it is unlikely the possums were using time to predict when to switch levers. This research further supports the use of the Mechner procedure as a method for measuring counting ability in animals and confirms the possibility of numerical competence in a marsupial species.

Generalization of response patterns in a multiple peak procedure

Stimulus generalization is typically assessed by analyzing overall response rates. Studies of generalization of response-rate patterns across time are less common, despite the ubiquitous nature of time and the strong temporal control over behavior in the natural world. Thus, we investigated generalization of response-rate patterns across time using a multiple peak procedure in pigeons. The frequency (fast or slow) at which the color of a keylight changed signaled a fixed-interval (FI) 5-s or 20-s schedule, counterbalanced across subjects. In peak trials, the frequency of keylight-color changes was varied. For the fast and slow training stimuli, response rates in peak trials were controlled by the arranged FI schedule value; they increased as the arranged reinforcer time approached, and decreased thereafter. Response-rate patterns to all test stimuli were similar to response-rate patterns to the slow training stimulus for all subjects. Thus, overall, strong generalization from the slow training stimulus to all test stimuli was evident, whereas there was little to no generalization from the fast training stimulus. These findings extend past research examining generalization of temporally controlled response-rate patterns, and provide a useful starting point for future investigations of generalization of fixed-interval responding. A thorough understanding of generalization processes requires analysis of dependent variables other than overall response rates, especially when responding is likely to be temporally controlled.

Flash rate discrimination in rats: rate bisection and generalization peak shift

Two experiments were conducted to determine whether responding by albino rats can be brought under the stimulus control of different flash rates. In the first experiment, a conditional discrimination procedure was employed whereby two different flash rates (fast or slow) signaled the availability of reinforcement on one of two levers (left or right). Stimulus control emerged rapidly and improved with continued training. When intermediate flash rates were presented during probe sessions, the bisection point of the fast and slow flash rates was near their geometric mean, consistent with research employing other stimulus types. In the second experiment, a successive discrimination procedure was employed whereby responding in the presence of one flash rate (S(+) ) was reinforced while responding in the presence of another flash rate (S(-) ) was not reinforced. Again, stimulus control emerged quickly and improved with continued training. Test sessions in which many different flash rates were presented for brief periods in extinction revealed the peak shift phenomenon, in which peak response rates are shifted from the S(+) in a direction away from the S(-) . Flash rate is endorsed as a continuous stimulus dimension that is useful for differentially signaling schedule components.