Enhancement of short-term retention by appetitive-reinforcer reminder treatment

Abstract

Choice accuracy by rats in a delayed-alternation paradigm was shown to decrease over a 120-sec retention interval. The decrement in choice accuracy was reversed by presentation of the appetitive reinforcer outside ofthe apparatus during the retention interval. This suggests that the reinforcer served to reactivate the target spatial memory and that the short-term retention deficit in the absence of such memory reactivation was not due to a loss of information. The results are discussed with respect to recent criticisms of memory-reactivation treatments in short-term retention tasks.In principle, associative deficits can be caused by failure of information storage at the time of acquisition, irreversible decay of information during the retention interval, or failure of information retrieval at the time of retention testing. Although it is clear that processes that occur in temporal proximity to the learning event and during the retention interval are important for later retention (e.g., McGaugh, 1966), several memory theorists have emphasized the importance of retrieval processes (e. g., Lewis, 1979;Miller, Kasprow, & Schachtman, 1986;Spear, 1971Spear, , 1973Spear, , 1978.A critical observation in support of retrieval-based models of memory has been the reversal of a variety of associative performance deficits through memory reactivation, that is, "reminder" treatments. A reminder treatment re-presents, prior to testing, some subset of the stimuli present during the original learning episode. It has been hypothesized that such exposure serves to stimulate further processing of the learning event so that future retrieval is facilitated (Spear, 1978). Most studies that have demonstrated the reversal of associative performance deficits have included conditions to preclude nonassociative interpretations of reminder-induced behavioral change (see Miller et al., 1986, for a recent review).The vast majority of successful restorations of associative performance by reminder treatments have used longterm retention tasks. Few studies using animals as subjects have investigated the effect of reminder treatments on short-term retention, but those directed toward the problem have obtained positive results. Feldman and Gordon (1979) alleviated forgetting over a 9O-sec retention interval in aT-maze delayed-alternation preparation using rats. In delayed alternation, an animal is initially forced

Retroactive interference effects of surprising reward omission on serial spatial memory.

“…One starting point for the present experiments was the apparently inconsistent effect of delay-interval rewards on short-term retention (e.g., Harper et al, 1993;Jans & Catania, 1980;Kasprow, 1987;Terry, 1987; and the present Experiment 1). The varying results may be due to the different training histories used across the several studies, leading to differing expectancies for reward or omission in the delay interval.…”

“…Alternatively, one could suggest the results are due to a retrieval deficit. Both Kasprow (1987) and Medin et al (1980) argued that a postsample reward could reinstate or refresh the memory of a rewarded target stimulus, thus making it more retrievable at the time of test. A different form of retrieval failure could be due to contextual stimulus change induced by the interfering events (Kendrick & Rilling, 1984).…”

“…They attributed this to the disruptive effect of consummatory activity during the delay interval on memory. In contrast, Kasprow (1987) found that retentioninterval reward enhanced performance of rats in a delayed-alternation task, which he attributed to a reminder effect. Terry (1987), who also studied delayed alternation, did not note any difference between reward and omission presented during the retention interval.…”

“…The theoretical assumptions guiding the present experiments were derived from Wagner's rehearsal theory, which states that surprising stimuli are better rehearsed in short-term memory than are expected stimuli (e.g., Terry & Wagner, 1975); therefore, surprising stimuli may displace from, or compete with, rehearsal of other stimuli (e.g., Wagner et al, 1973). Rehearsal theory offers a reconciliation of the results found by Harper et al (1993) and Kasprow (1987), depending on whether the surprising delay-interval event is reward or omission. Rehearsal theory also suggests that a surprising omission should enhance memory for the maze in which it occurs (Terry & McSwain, 1984).…”