The tw o parameters manipulated in Experiment 1, were the amount o f magazine training given to observers in preparation for their demonstration and test sessions, and the presence o f a tone during food pellet delivery. In the conventional procedure, observer rats are magazine trained in each of 4 daily sessions. Also, throughout magazine training, demonstration, and test sessions, all occurrences of a food pellet delivery are accompanied by a tone. Two o f the eight groups of observers in Experiment 1 were subjected to this conventional procedure, one being exposed to a left pushing demonstrator and the other a right pushing demonstrator.
Extended magazine training might reduce the strength of imitative learning in the NDR procedure. During magazine training, food is delivered to the magazine tray independent of responses made by the observer. There is some evidence for both pigeons (Welker, 1976) and rats (Oakes, Rosenblum and Fox, 1982) that noncontingent delivery of food can retard subsequent instrumental conditioning for food reinforcement. If prior experience of non contingent arrival of food also inhibits learning that an observed response leads to the arrival of food, then a larger demonstrator-consistent responding bias might be expected to occur
in groups o f observers prepared with fewer magazine training sessions than is the case in the conventional procedure.
Similarly, presentation of a tone during each food pellet delivery, which occurs throughout the conventional procedure, may not provide the optimal conditions for imitative learning. The pairing of tones and food during observers' magazine training might be expected to disrupt their formation of an association between an observed response and food during a demonstration session because, throughout observers' experience, tones have had a perfectly predictive relationship with food delivery (c.f., Williams, Preston & de Kervor, 1990). However, it could also be argued that conventional magazine training might be expected to result in tones acquiring secondary reinforcing properties that might facilitate demonstrator- consistent responding. The effects of tone presentation during demonstration sessions for conventionally prepared observers has already been investigated in experiment that employed a NDR test (Heyes, Jaldow & Dawson, 1994, Experiment 1 and 2). In these experiments, observers magazine trained with a tone presented during the delivery of each food pellet were found to respond in the same direction as their demonstrator if their demonstrator's responses were followed by simultaneous presentation of tone and food, but not if they were followed by food alone, tone alone, or neither of these events. These findings suggest that tones may not acquire sufficient secondary reinforcing properties through conventional magazine training to result in a demonstrator-consistent responding effect. Although the same findings also suggest that food alone is not sufficient for demonstrator-consistent responding, this interpretation may not extend to observers magazine trained without tones. If tone presentation during demonstration sessions disrupts imitation, then a larger demonstrator- consistent responding effect might be expected to occur in groups of observers for which tones never accompany food delivery than groups trained and tested in the conventional manner.
All observers were tested the joystick-transfer test (Heyes, Dawson & Nokes, 1992) because it was thought to have the potential to yield a larger demonstrator-consistent responding effect than a standard test by reducing any influence of observational autoshaping, a non- imitative social learning process. During a demonstration session in either the joystick- transfer or standard procedures, observers have an opportunity to form a representation of the joystick moving, as it crosses the animal's visual field in one direction. Observational
autoshaping would be considered to have occurred if, during the test session, observers tended to reproduce the same direction in which the joystick travelled across its visual field (Denny et al, 1988; see Chapter 2, Section 3.3.2.). In the bidirectional control procedure, observational autoshaping would be expected to result in a tendency to respond in the opposite direction to that demonstrated. It is possible that observational autoshaping does occur in the bidirectional control procedure, but that its influence is overcome by a stronger influence to respond in the demonstrator-consistent direction due to imitation or some other process. A Joystick-transfer test is likely to reduce any demonstrator-inconsistent bias due to observational autoshaping because, unlike a standard test, a joystick-transfer test involves moving the joystick to a new location between the demonstration and test sessions. The context in which the joystick may be seen by a rat encountering it in a new location (side panel) would be less like its appearance during the demonstration session (wire mesh in front o f stick and open compartment behind it) than if it was encountered in the original location (wire mesh and open compartment behind it).
Method
Subjects
A total o f 48 male hooded Lister rats, obtained from Harlan Olac Ltd. (Bicester, Oxon.), were approximately 5 months old when they served as subjects. Of these, 16 had served as observers in an earlier study, and were assigned to the role of demonstrators in the present experiment. The other 32 were experimentally naïve, and served as observers. Throughout the duration of the experiment they were housed in groups of four (all demonstrators, or observers from the same cell of the design) in moulded plastic and metal hanging cages (54 X 32 X 21 cm). All animals had free access to water, and were maintained at 90% of their free-feeding body weights.