Value Transfer in Discriminative Conditioning with Pigeons

The existence of a direct value transfer between stimuli in the context of instrumental discrimination learning is demonstrated. In a first experiment pigeons learned to discriminate instrumentally four successively presented target stimuli. Pecks to them were reinforced with graded amounts of reward and penalty (A++, B+, C-, D- -). These stimuli were accompanied by four different neutral stimuli (Na, Nb, Nc, Nd) but responses to these had no consequences. After discrimination of the target stimuli had been established the neutral stimuli were presented in pairs and in the absence of the target stimuli. These tests revealed a graded preference in accordance with the value transfer hypothesis. In a second experiment pigeons were taught to discriminate two target stimuli A+ and B-. Each of these was again accompanied by a neutral stimulus (Na, Nb). Pigeons developed a strong preference for Na. A discrimination reversal affecting the target stimuli (B+, A-) led to a strong reversed preference for Nb. A third experiment employed a similar design but in it one group of pigeons, unlike the control group, was prevented from pecking the neutral stimuli by transparent barriers. As both groups preferred the reward-related neutral stimulus with approximately equal strength it is concluded that classical conditioning, rather than pseudo-operant conditioning was responsible for the value transfer observed. A modification of an algebraic instrumental conditioning model incorporating an adventitious classical conditioning element is shown to emulate the value transfer obtained. The role of classical conditioning in instrumental discrimination learning is discussed.