An investigation into the malleability of implicit food-related approach and avoidance inclinations in people high and low in reward sensitivity

[Truncated abstract] According to the revised Reinforcement Sensitivity Theory (RST), the behavioural activation system is thought to mediate reward sensitivity, and the fight-flight-freeze system is thought to mediate punishment sensitivity. There is theoretical debate whether these two systems are orthogonal (separate systems hypothesis; SSH) or can interact (joint systems hypothesis; JHS). The aim of this thesis was to test these competing hypotheses. Specifically, this thesis investigated the effect of individual differences in reward sensitivity on the automatic processing of food cues using priming procedures, and unipolar variants of the Implicit Association Test (IAT). Study 1 developed a unipolar IAT that could yield reliable estimates of separate implicit food-related approach and avoid inclinations. Studies 2 to 5 examined if people who were either high or low in reward sensitivity (RS) differentially reacted to being primed with either positive (e.g., taste) or negative (e.g., weight-gain) aspects of high-fat foods. Based on RST, it was hypothesised that implicit approach inclinations would be more facilitated for people high in RS than for people low in RS in the positive priming condition. In the negative priming condition, the SSH predicts that responses to food stimuli following negative priming of the negative aspects of those foods should be the same regardless of individual differences in level of RS. In contrast, the JSH postulates that each subsystem can exert joint effects, such that high RS not only facilitates responses to appetitive stimuli, but also antagonizes responses to aversive stimuli. That is people high in RS would show less facilitation of implicit avoidance inclinations following negative priming of appetitive food stimuli than people low in RS. In Study 2 participants were primed with positive aspects of eating chocolate or negative aspects of eating potato chips.