Differential outcome expectancies and directed forgetting effects in pigeons

Abstract

Pigeons were trained in a two-choice delayed matching-to-sample task with red and green hues. A brief postsample cue (a vertical or horizontal line) signaled whether the comparison stimuli would be presented or omitted on each trial. Comparison stimuli were always presented following the remember (R) cue, but never following the forget (F) cue or no-cue trials. One group of birds, the differential outcome (DO) group, received reinforcement with a probability of 1.0 for correct responses following one sample stimulus and a probability of 0.2 for correct responses following the other sample stimulus. The nondifferential outcome (NDO) group received reinforcement with a probability of 0.6 for correct responses to either stimulus. The effect of postsample cues was greater for the DO group than for the NDO group. Relative to the NDO group, the DO group displayed higher accuracy on R-cue trials and lower accuracy on F-and no-cue trials. Both tendencies contributed to the enhanced cue effectiveness obtained in the DO group. The results indicate that outcome expectancies are subject to maintenance rehearsal, which comes under the control of postsample Rand F cues. They also suggest that maintenance rehearsal may be easier to sustain under DO conditions than under NDO conditions when a memory test is anticipated, but that it may be easier to terminate maintenance rehearsal under DO conditions when a memory test is not anticipated. The results are inconsistent with the assumption that the rehearsal of outcome expectancies is automatic.

Directed forgetting in animals.

“…This has been done by comparing performance on R-cue trials and F-cue probe trials with performance on trials with no cue. It has generally been found that performance on R-cue trials is not different from that on uncued trials (Grant, 1981;Maki et al, 1981, Experiment 1;Santi, 1989;Santi & Savich, 1985). As Grant (1981) noted, however, baseline delayed matching training is typically carried out without a cue.…”

A postsample cue to forget does initiate an active forgetting process in pigeons.

“…On F-cued test trials, in contrast to F-cued training trials, a standard test for sample retention is presented. Lower accuracy on F-cued test trials than on R-cued training trials has been reported in both the choice (e.g., Grant, 1988;Maki & Hegvik, 1980;Maki, Olson, & Rego, 1981;Santi, 1989;Santi & Savich, 1985) and successive (e.g., Grant, 1981b;Grant & Barnet, 1991;Kendrick & Newman, 1984; versions of DMTS.…”

“…Reduced accuracy on F-cued test trials is typically referred to as the directed-forgetting effect, reflecting the widely held view that presentation of R and F cues affect the extent to which the code activated by the sample stimulus is processed or rehearsed during the delay interval (e.g., Grant, 1981aGrant, , 1981bGrant, , 1984Maki, 1981;Rilling, Kendrick, & Stonebraker, 1984;Santi, 1989;Santi & Savich, 1985). In a recent review article, however, Roper and Zentall (1993) questioned this view.…”

“…Roper and Zentall's (1993) nonmemorial accounts of specific instances of the F-cue effect were based, in large part, on an analysis of the training conditions that resulted in reduced accuracy on F-cued test trials. One training condition that reliably resulted in the F-cue effect, implemented in the omission procedure, involved terminating the trial immediately after presentation of the F cue on F-cued training trials (e.g., Grant, 1981b; Kendrick et al, 1981; Maki & Hegvik, 1980; Roper & Zentall, 1994; Santi, 1989; Santi & Savich, 1985). Several authors (e.g., Grant, 1981a, 1981b; Maki, 1981; Santi, 1989) have argued that the F-cue effect obtained following training in the omission procedure was a product of an active forgetting process in which, for example, presentation of the F cue reduced processing of the code that was activated by the previously presented sample stimulus.…”

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

“…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 (Brodigan & Peterson, 1976;Delong & Wasserman, 1981;Edwards, Jagielo, Zentall, & Hogan, 1982;Honig, Matheson, & Dodd, 1984;Nevin & Grosch, 1990;Peterson, 1984;Peterson, Wheeler, & Armstrong, 1978;Peterson, Wheeler, & Trapo1d, 1980;Santi, 1989; This research was supported by Grant A6378 from the Natural Sciences and Engineering Research Council of Canada to A.S. This article is based on a master's thesis submitted by the first author to Wilfrid Laurier University.…”