The Effect of Body Weight on Concurrent Schedule Performance and the Pecking Response With Hens

Motivating Operations (MOs) are frequently manipulated (by changing access to commodities and manipulating other variables such as body weight) in order to change responding. Manipulations of body weight have been found to alter behaviour, for example obese and lean rats display differential sensitivity to reinforcers on concurrent schedules of reinforcement. What is not known is the effect that altering MOs may have on the topography of the response related to obtaining the reinforcer. This study has two aims, to investigate the effect of altering body weight on concurrent schedule performance and to investigate the effect that altering body weight may have on the time durations of each component of the hens peck response. Three hens held at 85%--5% were shaped via the method of successive approximations and three via autoshaping to respond for food reinforcers on a touch screen. Analysis of video footage of pecks into individual components (head fixation to beak contact to no movement) showed that the time duration of each component remained stable across both groups. Hens then worked for the same reinforcer under concurrent VI VI schedules with a range of reinforcer ratios with body weight held at 85%--5%, then 95--5%.