The body as a tattletale : Physiological responses to food stimuli perception within the context of expectations

The interaction with food involves a series of unexplored reactions that may help understand how individuals perceive the food in their environment. Among these reactions, the responses of the autonomic nervous system (ANS) are believed to reveal affective states, motivation, and preferences that people may not be able to articulate when experiencing food. An individual’s experience with food can be affected when expectations are disconfirmed. Expectations provide an idea (based on previous experiences, pre-set ideas, beliefs or even the context of consumption) of what the food product should look, smell, feel, and taste like. The novelty, valence, and relevance of the food product along with how arousing it is for the individual can also contribute in the responses related to expectations. The present thesis aimed to assess if ANS responses (particularly heart rate and skin conductance) capture the processes related to the (dis)confirmation of expectations when individuals are presented to food products and the effect that novelty, arousal, valence, relevance, and attention might have in these responses. This thesis addressed four topics in order to achieve this objective: I) ANS responses elicited by food stimuli of different valence when expectations are created and (dis)confirmed and when food stimuli are presented in situations of different relevance, II) ANS responses related to novelty (first experience with a stimulus), valence (pleasant or unpleasant stimulus) and (dis)confirmations of expectations, III) ANS responses related to the degree of the expectation disconfirmation, IV) Influence of attention and arousal in ANS responses to expectation (dis)confirmation. The comparison of ANS responses obtained when expectations were created and when they were (dis)confirmed showed that ANS responses captured more than the effect of expectations (Chapter 2). The creation and (dis)confirmation of expectations led to similar ANS response patterns. The responses obtained (heart rate decrease from baseline and skin conductance increase from baseline) seemed to be related to enhanced attention for the positive and negative stimuli and to defense reactions for the negative stimulus. Relevance was found to intensify all the ANS responses to stimuli. Looking separately at the patterns of ANS responses related to novelty, valence and disconfirmations showed that novelty evokes changes in heart rate (small increase followed by a decrease from baseline) and skin conductance (increase from baseline) that could be a combination of arousal and attentional responses related to an initial orientation response (Chapter 3). Skin conductance changed according to valence, with negative stimuli leading to larger increases in skin conductance than positive or neutral stimuli. The effect of disconfirmations seemed to only be captured by heart rate and may be related attention processes to the change/disconfirmation. ANS responses were not affected by the degree of the disconfirmations (Chapter 4). A study design in which expectations were manipulated to create small and large disconfirmations only found ANS responses that could be again reflecting the orientation response and attention (heart rate decrease from baseline) related to the novelty of the design and heightened arousal and attention (increase in skin conductance) related to the processing of the manipulation of expectations. Evaluating whether the ANS responses obtained in all studies indeed reflected attention and arousal showed that skin conductance was a stable measure for arousal (Chapter 5). However, it could only differentiate between the most arousing stimuli. It was not possible to confirm whether ANS responses reflect attention due to the lack of replicability of heart rate responses. Overall, the chapters of this thesis show that disconfirmations lead to ANS responses (particularly heart rate decreases and skin conductance increases from baseline) that could be reflecting changes in orientation and attention. Novelty and valence (particularly negative) lead to large increases in skin conductance but these responses are linked to the arousal of the stimuli. Relevance influences the intensity of these ANS responses by making them stronger when the stimuli are deemed important or significant by individuals. The findings of this thesis show that the components captured by ANS responses may not be helpful for studying the reactions to food. Research areas such as food research could only use ANS responses in study designs that include highly relevant, novel, arousing or contrasting disconfirmations or stimuli. However, the characteristics that would be captured by ANS would already be noticeable and could be better measured by cheaper methods.