Does the presence of food act merely to allow individuals to satisfy their preexisting hunger, or might the sight of food actually stimulate the appetitive drive, which would not have existed in the absence of food? One experiment found that normal-weight individuals ate the same amount (just under two sandwiches) regardless of whether they were initially presented with one sandwich (and had to obtain additional sandwiches from a refrigerator) or three sandwiches (29). This study suggests that the visual salience of food has a minimal impact on consumption. Obese subjects in this study, however, ate considerably more when presented with three sandwiches than when presented with only one, suggesting that visual cues have a strong effect on them. This finding was interpreted as support for the externality theory of obesity, with the visual salience of food representing an external cue par excellence. (One important implication of this study is that in the absence of excitatory external cues, obese people should eat less than do normal-weight people.) Another experiment found that normal-weight subjects ate the same amount of cashews regardless of whether the cashews were brightly illuminated or difficult to see (and regardless of whether they were instructed to think about the cashews or about something else), whereas obese subjects ate above-normal amounts of the visually salient cashews and below-normal amounts of the dimly illuminated cashews (30). Obese subjects also ate more when instructed to think about the cashews, reinforcing the point that it is awareness of food that matters and not simply optical effects. It should be noted that some researchers interpret these findings to mean that obese subjects eat in direct response to external cues and not because such cues stimulate hunger, which in turn drives eating. However, it has been suggested that exposure to food cues may trigger anticipatory (cephalic phase) reflexes at the physiological level, such that the sight or smell of palatable food may literally make the fat person hungry (18). Recently, we have shown that directing people's attention toward or away from food-related stimuli can increase or decrease their reported hunger (C. R Herman, J. Ostovich, and J. Polivy, unpublished data, 1998); this effect was obtained in normal-weight nondieters, suggesting that the effects of food stimuli are not confined to the obese. Our study did not measure eating, however, so we cannot conclude that attentional or perceptual manipulations will affect intake.
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