Academic journal article The Psychological Record

Motivation Level and Memory for Motivational Events

Academic journal article The Psychological Record

Motivation Level and Memory for Motivational Events

Article excerpt

When faced with a series of differing reward events, rats seem to be capable of employing a variety of strategies to anticipate the forthcoming events in the series. Animals may derive relational rules such as "increasing" or "decreasing" if the series themselves obey such formal structure (Hulse & Dorsky, 1979). They also may count the rewards (e.g. Burns & Gordon, 1988; Capaldi & Miller, 1988) and use that numerical information as a predictive cue. Another possibility is that associations between trial-to-trial stimulus changes and behavior may come to control approach (e.g., Burns, Wiley, & Payne, 1986; D'Amato & Colombo, 1990). Often emphasized as a mechanism for anticipation are interitem associations based upon memorial representations of the characteristics of reward on Trial N which come to cue reward on Trial N+1 (e.g., Capaldi, 1985; Capaldi & Molina, 1979; Haggbloom & Brooks, 1985).

The view that interitem associations control anticipation in animals is a derivative of an early theory of sequential learning (Capaldi, 1967) designed to accommodate results from a few key experiments that bore on the concern with the role of reward in instrumental learning shared by the Neobehaviorists (Amsel, 1989). The partial reinforcement effect and the successive negative contrast effect were among these results. From the point of view of the sequential theory, the successive negative contrast effect (SuNCE), a precipitous behavioral change following reduced reward, was the consequence of generalization decrement caused by the change in reward value. What were then conceptualized only as stimulus carryovers or aftereffects, as opposed to memories, from reward on Trial N were conditioned by reward to behavior on Trial N+1 and became a portion of the S that formed the S-R connection. Changes in S brought about generalization decrement in that theory (Capaldi & Lynch, 1967).

Often the SuNCE does not occur, and the failures are predictable. One of the most intensely investigated failures happens when sucrose solutions, as opposed to ordinary food-pellet rewards, are used as the reward values in successive contrast experiments (Flaherty, 1982). However, a single experiment (Burns, Ziropadja, Djuric, 1984), using sated rats, gave the only good evidence of SuNCE in rats rewarded with sucrose. Following interitem theory, that success in the context of many failures implies that motivation influences the salience of interitem information, specifically, food deprivation decreases interitem salience of sucrose rewards.

Experiments which examine the single alternation of rewards and nonrewards (or large and small rewards) have produced some of the clearest indications that interitem associations guide anticipation in instrumental learning situations (e.g., Tyler, Wortz, & Bitterman, 1953). In single-alternation experiments using ordinary food-pellet rewards, rats typically come to approach rewards (or large rewards) more vigorously than they do nonrewards (or smaller rewards), the apparent cue being a memory of the preceding reward event. Here again, sucrose rewards have produced an exception (Burns, 1976; Burns, Lorig, Carr, & Worthy, 1984). Hungry rats given alternating high and low concentrations of sucrose in solution did not pattern their approaches by responding more vigorously to the high concentrations than to the low concentrations. Here again, there is an implication that reduced motivation may enhance the interitem salience of sucrose rewards because a recent study (Burns & Griner, 1993) has shown single-alternation patterning in sated, sucrose-rewarded rats.

Yet another technique for studying interitem associations in animals is one that is probably most similar to the original methods used by Ebbinghaus (1885) to study these associations in people. In this technique a series of rewards differing in some characteristic such as amount, number, or quality is arranged and presented repeatedly to the animal (e. …

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