An investigation of variety effects during operant responding in the rat utilizing different reward flavors

Humans and nonhuman animals respond to food diversity by increasing intake and appetitive behaviors, reflecting enhanced valuation for items presented in the context of variety. Previous work on food variety effects has posited two main explanatory mechanisms. Variety could slow habituation processes by decreasing exposure to a single food item or could elicit contrast effects in which comparisons between items impact relative valuation. This study used three flavors of sucrose rewards to investigate rats' responses to qualitative reward variety in different variety contexts: low (2 flavors) and high (3 flavors) conditions. Control sessions used only a single flavored pellet (no variety). Animals were tested in low (10 trials), moderate (20 trials) and high consumption (30 trials) sessions. A trial within each session was defined as completion of the operant response and acquisition of the reward pellet. Cues associated with flavors were used to examine predictability and between-trial ('micro') variety. Indicators of a variety effect were found including faster responding for rewards during the variety context compared to an initial control (no variety) context. This decrease in response latency continued to be observed for some measures in post-variety control contexts. The most robust statistical finding of variety effects was found using trial-by-trial analysis, with shorter response latencies obtained for trials with outcomes differing from the preceding trial compared to successive trials with identical outcomes. These results have implications for understanding how a general reward context like variety impacts behavior, and for informing clinical approaches focusing on motivation and eating disorders.