Abstract
Reward-predictive stimuli augment instrumental reward-seeking in humans, an effect denoted Pavlovian-to-instrumental transfer (PIT), but the role of differential reward value of these stimuli and of emotional conditioned responses in PIT remains unknown.Fifty one participants experienced a Pavlovian phase that associated two stimuli with either 10p (CS10) or 50p (CS50). Next, participants underwent instrumental training for two responses reinforced with either 10p or 50p. Finally, the transfer phase continued as had instrumental training, now in the presence of the Pavlovian stimuli.Participants were dichotomised as aware/unaware according to their expectancy awareness of the CS→outcome associations. Only aware participants demonstrated PIT (increased choice and number of responses on the 10p and 50p response key in the presence of CS10 and CS50 respectively), yet both aware and unaware groups rated the 50p stimulus as more pleasant than the 10p stimulus.These findings suggest that expectancy of reward is necessary for PIT; however, emotional conditioned responses appear not sufficient to influence PIT. Future research should attempt to manipulate emotional conditioned responses in a PIT context, to test the sufficiency of reward expectancy in PIT.
Highlights
Multiple theories of reward-seeking converge on a causal role of stimuli paired with positive reward-induced states in activating behavioural processes [1]
Aware participants demonstrated PIT, yet both aware and unaware groups rated the 50p stimulus as more pleasant than the 10p stimulus. These findings suggest that expectancy of reward is necessary for PIT; emotional conditioned responses appear not sufficient to influence PIT
Expectancy ratings showed a discrimination over time between the trials predicting a 50p and the trials predicting a 10p win, but only in the group of aware participants (a group x block x awareness interaction was significant [F (7, 343 = 11.5, p < 0.001, Á2p = 0.190], explained in a further ANOVA for aware and unaware groups separately by a CS by block interaction [F(7,217) = 34.45, p < 0.001, Á2p = 0.526] in the aware group but not in the unaware group ([F(7,126) = 1.21, p = 0.303, Á2p = 0.063; see Fig. 2)
Summary
Multiple theories of reward-seeking converge on a causal role of stimuli paired with positive reward-induced states in activating behavioural processes [1] Such stimuli prime reward states in a similar manner to primary rewards themselves [2], elicit approach behaviour to reward-associated targets [3], and activate processes attributing incentive salience to reward procurement [4]. In order to ensure that any effect of a stimulus (S) on a response (R) is due to an outcome (O) representation, it is necessary to separate the training of S → O from R → O. Any influence of a stimulus on a response under such separated training conditions is termed Pavlovian-toinstrumental transfer [PIT, 6]
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