When Oliver Twist thrust forth his gruel bowl to request, “Please, sir, I want some more,” the master’s ladle served up a blow to the head of the extraverted urchin.

Today’s extraverted schoolchildren serve more cereal to themselves – while youthful introverts take less – according to a study from the laboratory of Brian Wansink, professor of marketing and director of the Cornell Food and Brand Lab in the Dyson School of Applied Economics and Management.

“With increasing concerns about childhood obesity, knowing what types of children are most at risk from external cues could sharpen the focus of caregiver interventions,” said Wansink.

Previous experiments found adults serving themselves more when plate sizes are larger – an “external cue” that leads to what Wansink terms “mindless eating” – so the professor and his research colleagues treated elementary schoolchildren to four breakfasts at school.

In one scenario, children were given standard-size bowls and told to ask the server (a obliging cafeteria worker, not the grumpy cook in Charles Dickens’ “Oliver Twist”) for as much cereal and milk as they desired. The same experiment was repeated with much larger bowls.

Who you calling 'introvert?'

Psychologists differ on the personality traits of extraverts vs. introverts, but the Cornell food lab researchers noted some distinguishing characteristics, especially at mealtime. Extraverted children, they said, exhibit lower self-consciousness and have faster movement times; introverted children tend toward reflection and consideration and are more cautious in their actions. Although introverted children may have more internal control when serving their own food, the presence of a second person – the cafeteria server, for example – leads young introverts to relinquish their control of the situation:  “Please, I want more than I would take were I serving myself.”

At least one Jungian psychologist has branded the fictional Oliver Twist as an extravert.

Then the children got to serve themselves, using smaller and larger bowls. A special dining table from the food lab featured hidden scales with remote readouts at each place setting to weigh breakfast bowls, before and after eating. Unbeknownst to the visiting scientists, teachers and school counselors were evaluating each child and labeling them “extraverted” or “introverted.”

The differences were dramatic, Cornell scientists reported in the online journal, PLOS One (“Extraverted Children Are More Biased by Bowl Sizes Than Introverts,” Oct. 30). Extraverted children served themselves and consumed 28.9 percent more cereal than their introverted classmates; they also took 33.1 percent more in large bowls than they did in small bowls. Additionally, when all children served themselves, they served 23.2 percent more than when an adult served them.

Having to ask adults to serve them (“Please, cafeteria lady, I want more!”) seemed to make a difference, too. Suddenly, the introverted kids were eating 79.5 percent more in large bowls, compared with amounts of cereal ladled into small bowls. Extraverted kids asked for and consumed only 36.1 percent more in their big bowls.

Then the researchers packed up their tricky table, asked teachers for the extravert/introvert assessments of each child, returned to the Cornell campus to analyze results, and issued this advice for adults: “It might be best for caregivers to do the serving whenever possible – especially for extraverted children.”

A separate report Wansink’s group in the Nov. 18 Journal of Pediatrics examined children’s eating behavior at summer camp as well as elementary school. Campers with large cereal bowls consumed 52 percent more and wasted 26 percent more, compared with kids with small bowls. Schoolchildren with large bowls requested twice as much cereal, according to the journal report titled, “Bowl Size Increases the Amount of Cereal Children Request, Consume, and Waste.”