Food attention bias and Delboeuf illusion: Joint effect of calorie content and plate size on visual attention

Plate size causes the Delboeuf illusion, and impacts food craving and food consumption. However, the underlying cognitive mechanism of the Delboeuf illusion remains unknown. This research adopted the food attention processing theory to gain an in-depth understanding of how the Delboeuf illusion impacts attention orientation, and to examine whether this effect varies between high- and low-calorie foods. Forty women completed a food-house task with eye-tracking, and evaluated the palatability and healthiness attributes of each food. The results showed that high-calorie (versus low-calorie) foods and small (versus large) plates were more capable of capturing attention. Notably, there was a joint effect of calorie content and plate size on food attention bias, suggesting that the Delboeuf illusion’s effect on food attentional bias differs according to calorie content. Interestingly, there was a moderated mediation effect of plate size, with the mediating effect of perceived healthiness on the relationship between calorie content and food attention bias when foods were placed on a small plate, but not on a large plate. However, we observed an attention bias towards high- versus low-calorie foods through the mediating effect of perceived palatability, irrespective of plate size. Our findings suggest that high-calorie foods, whether placed on a small or large plate, automatically attract attention due to their palatability. However, low-calorie foods are more capable of attracting attention when placed on a small plate, indicating that the Delboeuf illusion caused by plate size enhances the perceived healthiness of low-calorie foods.