As one can imagine, food and our psychological mindset have a very interesting relationship. It has been proposed that seeing, smelling, or even thinking about food can elicit affective or hedonic responses, which affect our moods and emotions. These reactions have been thought to then modulate eating behaviours. A group of scientists in Japan recently demonstrated that the sight of food stimulated unconscious affective responses. This could explain some of the unhealthy eating behaviours, like excessive eating, which contribute to obesity, hypertension, and type II diabetes.
Food has a profound impact on our psychological states. The sight, smell, or even thought of food have been proposed to elicit affective or hedonic responses, affecting our moods and emotions. These responses have been advantageous in providing our ancestors with adaptive signals, and triggering behavioural responses necessary for seeking and acquiring valuable food from the environment. Unfortunately, in the modern world, high-calorie foods are readily available, and these affective responses may be one of the reasons for overeating and obesity. In fact, there is accumulating evidence suggesting that the mere observation and consumption of food elicits positive affective responses, which in turn stimulate further food intake. Researchers are interested in determining whether these responses occur unconsciously, and whether they can translate into excessive and unhealthy eating habits.
A group of researchers in Kyoto, Japan, investigated the unconscious, and conscious affective responses to food and non-food stimuli in a Japanese cohort consisting of thirty-four healthy non-obese volunteers (eighteen males and sixteen females). To test unconscious affective responses, researchers used a subliminal presentation condition, where participants were briefly (milliseconds) shown an image of a food item or a mosaic image (the food image rearranged such that it was unrecognisable). Following this, they were shown a mask image (random scrambled image) in the same location, followed by a picture of a neutral face. The participants were then asked to rate the face in terms of preference using a 9-point scale ranging from “dislike extremely” to “like extremely”. Previous studies have demonstrated that evaluation of a target (e.g. the neutral face) is positively biased when the individual is primed unconsciously with a positive stimulus (e.g. images of food). Similarly, to test conscious affective responses, supraliminal presentation conditions were used. In these conditions, the participants were shown pictures of either food or a mosaic image, and then asked to rate the image for preference. Following these procedures, participants were asked to fill out a questionnaire to measure eating tendencies, and were asked to assess their body-mass index (a measure of body fat). The researchers used the data to further investigate whether there is a relationship between these affective responses and eating behaviours.
The results demonstrated a significant increase in preference for the neutral face after the participants were primed with images of food, as opposed to a mosaic. Similarly, when studying conscious affective responses, participants had an increased preference for the food as opposed to the mosaic. Interestingly, preference was higher for stimuli that were presented in the right visual field (on the right side of the screen). This can be explained by the fact that the left hemisphere processes visual information from the right visual field and also is involved in processing positive affective responses. Furthermore, those that gave higher preference scores to the neutral faces following food priming were associated with higher external eating tendency scores. In contrast, under supraliminal conditions, there was no significant correlation between preference scores and external eating tendency. This result leads to the speculation that perhaps eating behaviours are more profoundly impacted by unconscious affective behaviours instead of conscious affective behaviours.
In conclusion, the study demonstrated that under supraliminal conditions, merely observing food induced affectively positive responses. More importantly, subliminal conditions demonstrated that unconsciously perceived food also increased participant’s preference. This appears to be the first evidence indicating that food can elicit unconscious affective responses. Furthermore, it showed that unconscious preference for food was positively related to external eating tendency. This is an important proposition and suggests that affective responses without conscious awareness may trigger activities that lead to unhealthy eating habits. This in turn, could increase the risk of complications including obesity, hypertension, and diabetes. The study sheds light on the importance of the role of unconscious affective responses and the need for controlling our environment in order to prevent unhealthy eating behaviours.
Written By: Haisam Shah, BSc