Body Weight as a Motivating Operation: The Effect of Body Weight on Demand for Food in Hens.

Abstract

Demand for wheat and puffed wheat was examined in six hens, using an ascending geometric progression of fixed-ratio schedules of reinforcement. Hens responded by pecking a key for 2-s access to food in 40-min sessions. The body weight criterion used to decide if a hen was to be placed in an experimental session differed across conditions, to determine if this would affect performance, using wheat and puffed wheat as reinforcers in different conditions. In the first experiment the hens were maintained by post-session feeding at 80 ± 5% of their free-feeding body weights. In Conditions 1 and 2 the hens were placed in a session even when they were more than 5 % above the target weight. In Conditions 3 and 4 they were placed in a session if their body weight was within the specified range, meaning there could be several days between sessions. There were clear differences resulting from food type, both in behaviour under the fixed ratio schedules, and in the resulting demand functions (with consumption measured as either number of reinforcers or weight of food obtained). Wheat resulted in lower overall response rates than puffed wheat at low fixed ratio values. The body weight criterion did not result in large effects on performance, however, the more relaxed body weight criterion gave a higher essential value for puffed wheat than for wheat (replicating Foster et al., 2009), whereas, the strict body weight criterion gave a lower essential value for puffed wheat than for wheat under the analysis proposed by Hursh and Silberberg (2008) and using number of reinforcers as the consumption measure. A second experiment replicated Jackson (2011), using the same two foods, strict body weight criteria and sessions which terminated after 40 reinforcers or 40-min. The resulting data were similar to Jackson (2011), who found similar performance for both foods. The difference between the demand functions for the two foods, with reinforcer rate as the consumption measure, were greatly reduced in comparison to Experiment 1. The essential value of the two foods was not consistently different across hens. These results suggest that the session termination criterion did affect demand.