Appetitive state and Attentional processing

The central assumption of the thesis was that attention is drawn towards food, particularly in a state of extremis or need. Attention given to food should depend on the motivational state of individuals, with the salience of food stimuli caused by ‘wanting’ increasing attention towards food. The first experiment (Chapter Three) of the thesis, attempted to extend and build on the groundwork laid out by Piech et al (Piech et al., 2010). As previously mentioned, the EBA design had been found to detect changes in attentional processing of food depending on hunger state, with greater levels of hunger increasing attention toward food-related stimuli. Our study utilised this method for two reasons. Firstly, to track changes in attention to food over

the time leading up to and following a meal, relative to changes in motivation, with a reliable method. Secondly, to investigate, the

phenomenon known as sensory specific satiety (SSS), and its role in implicit processing, by measuring differences in attention to different food types: savoury foods (sandwiches) that had been consumed compared to similar and dissimilar foods that were not consumed. Confirming previous literature on implicit processing, Experiment 1 (Chapter 3) found that attention to food was greater than to neutral stimuli, and that attentional blindness increased in the time leading up to meal consumption. The results demonstrated that attention to food increased with increases in hunger, regardless of food type. In addition, as predicted, after food consumption and the onset of satiety, attention was specifically reduced to images representing foods that were similar to those the participant had consumed (both

sandwich-specific and sandwich-general), but not to images of dissimilar foods such as desserts. Importantly, these differences were maintained for up to an hour after consumption. The demonstration that attention to food increases in line with hunger supports comparable research investigating attentional processing of food relative to motivational state (Castellanos et al., 2009; di Pellegrino et al., 2011; Mengarelli, 2012; I. Nijs, 2010; Piech et al., 2010; Tapper et al., 2010), but provides the first report of real-time changes in attention related to spontaneous changes in appetite associated with normal meal patterns – rather than after the imposition of fasting.

In addition explicit ratings of food pleasantness displayed similar declines to attentional processing, following the expectations of sensory-specific satiety (SSS). In particular, SSS devaluations in food pleasantness ratings were observed between the immediate pre- and post-consumption experimental sessions. With the food-type that was consumed (sandwiches) showing larger devaluations than unconsumed food stimuli (dessert). Remarkably the

findings of chapter 3 and 4 (experiment 1) demonstrate that attentional bias follows the same direction and specificity of change. Essentially the results

from Chapter 3 suggest pleasantness/desirability and attentional capture all decline for food that has been consumed, as predicted by incentive salience. Moreover, the fact that the consumed food is devalued hedonically and its attention capturing power is simultaneously reduced demonstrates a mechanism whereby varying incentive salience can modify motivation- specific behaviour.

The results of this investigation, considered along with research on explicit processes by Cameron et al (Cameron et al., 2014), Weenen et al (Weenen et al., 2005) and Rolls (E. T. Rolls, 2006), and implicit research by di Pellegrino (di Pellegrino et al., 2011), Piech et al (Piech et al., 2010) and Castellanos et al (Castellanos et al., 2009) serve to highlight the underlying neurocognitive processes thought to be responsible for motivational

processes, and the similarities between explicit and implicit processes. In particular, they provide further support for the theoretical framework of incentive salience process relative to eating motivation, which suggests that processing motivational stimuli depends on drive/’wanting’ and liking. Specifically, the consumption of food has been found to alter neural processing of consumed foods relative to unconsumed food (Berridge & Kringelbach, 2015; Gottfried, O'Doherty, & Dolan, 2003; Kringelbach, O'Doherty, Rolls, & Andrews, 2003). However, an important distinction between Experiment 1 (Chapter 3) and those previous studies is that the present experiment tracked changes over time for both implicit and explicit processing. A key finding of the present study was that changes in attention to food in the pre-prandial stage where not reflected in explicit pleasantness ratings. Suggesting that attentional processing may be more sensitive than explicit processing in gauging ‘wanting’ food.

The findings of Chapter 3 raised a number of questions. Firstly there were differences in the relative degree of distraction by sandwich images after

consumption. These results indicated that images of consumed sandwiches were more affected by changes in appetite caused by their consumption than images of non-consumed sandwiches. Secondly attention to dessert related stimuli appeared to be resistant to changes in appetitive state following food consumption. This ultimately led to us to question of whether this was a reflection of sensory specific satiety (i.e., desserts had not been consumed), or whether sweet or dessert foods in general were resistant to the changes in appetitive state due to their high palatability.

In the second experiment (chapter 4), we attempted to examine this question in more detail, to investigate the degree to which specific types of food vary in their ability to capture attention relative to both motivational state and the consumption of the particular food types. In addition, the experiments of Chapter 4 were also designed to explore the impact of hedonic value on attentional capture by using highly palatable foods. In order to investigate these factors, the stimuli and food consumed were changed and investigated across two experiments. In Chapter 4, participants were provided with one of two sweet foods. In the first experiment (4A) participants were provided with fruit, while in the second experiment (4B) participants were given cheesecake. The findings of both studies showed differing variations in attention to food, relative to changes in motivational state. Essentially attention to fruit, which was rated at approximately the same level of pleasantness as neutral images in an explicit rating task, was influenced by changes in appetitive state as a result of consuming fruit. However, attention to very palatable cheesecake remained high in both experiments. Cheesecake images continued to cause attentional blindness regardless of appetitive state or the type of food consumed.