Alterations in the memory code for temporal events induced by differential outcome expectancies in pigeons

Abstract

The effect of differential outcome expectancies on memory for temporal and nontemporal information was examined. Pigeons were trained to match short (2-sec) and long (8-sec) sample durations to red and green comparison stimuli, and vertical and horizontal lines to vertical and horizontal comparison stimuli. In Experiment 1, one differential outcome (DO) group received food for correct choices on short-sample trials, whereas another received food for correct choices on long-sample trials. On line-orientation trials, half of each DO group received food for correct responses following vertical samples, whereas the other half received food for correct responses following horizontal samples. Overall retention was greater in the DO groups than in a nondifferential (NDO) group that received either food or no food for correct responses on a random half of all trials. Furthermore, although the NDO group displayed a choose-short bias for temporal samples, both DO groups displayed equivalent biases to select the comparison stimulus associated with food. In Experiment 2, differential outcome expectancies were extinguished off-baseline. Subsequently, in the first nondifferential outcome test session, the DO groups performed less accurately than the NDO group. These findings indicate that temporal samples are not retrospectively and analogically coded when they are differentially associated with food and no food. Instead, they are remembered in terms of the corresponding outcome expectancies.The delayed matching-to-sample (DMTS) procedure has been used extensively to study working memory processes in animals. After a delay interval, subjects are required to match one of two comparison stimuli to a previously presented sample stimulus in order to receive the reinforcer. As the delay between the sample stimulus and the comparison stimuli is increased, matching accuracy declines. However, when different types of reinforcers are associated with correct matching responses to each sample stimulus, retention over the delay interval is better than when the same type of reinforcer is used after each sample stimulus. This differential outcome effect (DOE) has also been manifested as increased rates of acquisition, higher levels of overall accuracy, and a bias to choose the comparison stimulus associated with the more favorable outcome

Memory codes for temporal and nontemporal samples in many-to-one matching by pigeons

“…It is unlikely that the failure to obtain a significant chooseshort effect was due to a floor effect at delay intervals greater than zero. The delays used in the present experiment were similar to those which in other studies have consistently resulted in significant choose-short effects (Ducharme & Santi, 1993;Spetch, 1987;Spetch & Rusak, 1989;Spetch & Wilkie, 1983). In other studies, with similar delay intervals, accuracy on short -sample trials has been much higher than it was in the present experiment.…”

“…In contrast to previous evidence that temporal information is coded in a retrospective and analogical fashion (Spetch & Sinha, 1989;Wilkie & Willson, 1990), the present research has identified an additional condition under which temporal information does not appear to be coded in this way. There are now three experimental procedures in which temporal samples are not retrospectively and analogically coded: the present MTO mapping conditions, successive MTS , and choice MTS in which temporal samples are associated with differential outcomes of food and no food (Ducharme & Santi, 1993). In addition, the present interference test results indicate that temporal summation effects are observed even when a choose-short effect has not been observed and most importantly even when the temporal target samples are preceded by color presampIes.…”

“…Recently, Ducharme and Santi (1993) have shown that pigeons do not code temporal samples retrospectively and analogically when they are differentially associated with food and no-food outcomes in a choice MTS task. Instead, event durations are remembered in terms of the corresponding outcome expectancies.…”