Contents lists available at ScienceDirect Appetite journal homepage: www.elsevier.com/locate/appet An investigation of variety effects during operant responding in the rat utilizing different reward flavors Brittany A. Halverstadt ∗ , Howard C. Cromwell Department of Psychology and the J.P. Scott Center for Neuroscience, Mind and Behavior at Bowling Green State University, Bowling Green, OH, 43403, USA ARTICLE INFO Keywords: Expectancy Habituation Incentive contrast Motivation Valuation ABSTRACT Humans and nonhuman animals respond to food diversity by increasing intake and appetitive behaviors, re- flecting 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 va- luation. 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 con- sumption (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 con- tinued 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 in- forming clinical approaches focusing on motivation and eating disorders. 1. Introduction The effect of variety is observed as an increase in food consumption and appetitive behaviors that occurs in response to a diverse array of foods being available (Sørensen, Møller, Flint, Martens, & Raben, 2003; Wilkinson, Hinton, Fay, Rogers, & Brunstrom, 2013; Keenan, Brunstrom, & Ferriday, 2015). Recent animal work suggests multiple psychological mechanisms working together to cause variety effects. Human and nonhuman animal work on these effects has focused on the impacts of predictability, familiarity, duration, and intensity of ex- posure on variety effects. Treit, Spetch, and Deutsch (1983) found in- creased food intake in rats when a meal consisted of food in a variety of flavors, compared to when all the food was the same flavor. The fact that differences in flavor alone and not differences in the composition of the foods influenced consumption suggests that food variety may lead to the observed effects on consumption by interfering with sensory- specific satiety (Brondel et al., 2009; Rolls et al., 1983, 1986). The sensory-specific satiety effect is observed as a selective decrease in food intake and taste pleasantness in items eaten to satiety (Rolls, 1995). Food items not consumed can reinvigorate consumption and be rated relatively more pleasant (Griffioen-Roose, Finlayson, Mars, Blundell, & de Graaf, 2010). This effect can be observed for both liking and wanting processes in affect and motivation (Havermans, Janssen, Giesen, Roefs, & Jansen, 2009). Using an animal model, satiety has been shown to only partially mediate variety effects; Lupfer-Johnson, Murphy, Blackwell, LaCasse, and Drummond (2010) used dwarf hamsters (Pho- dopus campbelli), which hoard food in their cheeks rather than consume it immediately, to demonstrate that post-oral satiation alone cannot account for the decreased responding to a repeatedly presented food reward. Habituation, or the reduction in responding to repeated experiences, may play a role in variety effects (Bouton, Todd, Miles, Leon, & Epstein, 2013; Lupfer-Johnson et al., 2010). When comparing the response patterns of rats given only one type of reward (grain or sucrose) during an operant task, the within-session decrease in responding was medi- ated primarily by habituation. Animals experiencing mixed reward types (grain alternated with sucrose) exhibited a significantly atte- nuated within-session decline in response rate (Bouton et al., 2013). In https://doi.org/10.1016/j.appet.2018.12.024 Received 26 April 2018; Received in revised form 17 December 2018; Accepted 17 December 2018 ∗ Corresponding author. 118 Psychology Building, Bowling Green State University, Bowling Green, OH, 43402, USA. E-mail address: bhalver@bgsu.edu (B.A. Halverstadt). Appetite 134 (2019) 50–58 Available online 20 December 2018 0195-6663/ © 2018 Elsevier Ltd. All rights reserved. T