Much research in food psychology has examined the influence of perceptual features - color, texture, packaging - on preference for that food. Here, we addressed the reverse question of the influence of food preference on the perception of its quantity. Does a portion of a loved food appear different than the same portion of a hated food? We probed this question by employing state-of-the-art tools of psychophysics, which allowed us the parallel examination of several long-standing issues of psychophysics. The latter included the difference between symbolic and non-symbolic number, the difference between the methods of Magnitude Estimation and Magnitude Production, the difference between under- or over-estimation and rate of growth measured by the (slope of) psychophysical function as well as the derivation of the Difference Threshold by the method of Constant Stimuli. We addressed the question of an effect on perception of food valence with four distinct experiments. Presenting real food items, we found that perceived quantity is a compressive function of objective quantity regardless of valence
both loved- and hated-food dynamics are governed by Stevens' power function with an exponent of 0.8. In absolute terms, applying Magnitude Estimation, we witnessed a gross underestimation for loved and hated food alike. In contrast, applying Magnitude Production, participants underproduced loved food, but overproduced hated food. For discrimination of food quantity, we found better resolving power for hated food. Collectively, our results show that, across diverse psychophysical evaluations, food valence affects its perception, especially when people actively regulate the to-be-consumed portion.