Executives who thought they were consuming medium-size cookies ate, on average, 0.4 ounces (12.02 grams) more of the cookies than executives who thought they were eating large cookies.

However, those who munched on the medium cookies later said they had eaten less than those who ate large cookies…

And when subjects were given a task to do while eating, the distortions were exacerbated. For instance, participants (who made their judgments when the plate was not in front of them) said a bowl that actually held 10 mini sandwiches held only eight when it was labeled as small. But when participants had a task to do while they lunched, they said it had around seven sandwiches.