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    Size: It all comes down to hunger


    Does fasting heighten the senses? Does hunger influence perception? And if so, how? These questions have been examined experimentally by Würzburg social psychologists Sascha Topolinski and Philippe Türk Pereira. The findings of their study ought to please the supporters of fasting.

    People who fast wax lyrical that hunger increases your sensitivity to aromas and flavors. They say that even a piece of apple becomes a feast if you are hungry enough before you consume it. Whether this really is the case has been the subject of a study by social psychologists Dr. Sascha Topolinski and Dr. Philippe Türk Pereira.

    Topolinski is a Research Associate at the Department of Psychology II at the University of Würzburg; Türk Pereira is a former employee of the department who now works as a Forensic Therapist in Psychiatry at Schloss Werneck hospital. Using a total of four experiments, the pair tested whether hunger really can influence perception. The criterion here was the perception of size in the mouth.

    Contradictory theories

    “The question as to whether a hungry person appraises an object in the mouth differently from a full person may sound like a party gag. In fact, it is not as simple as all that,” says Topolinski. After all, various psychological theories and everyday life have produced different and contradictory predictions:

    A hypothesis based on greed would suggest that hungry people perceive objects in the mouth as smaller than full people, says Topolinski. “For someone who is hungry a bit of food may seem like the proverbial drop in the ocean.” This theory is backed by the everyday experience that people who are hungry tend to pile far too much on their plates at a buffet. Or, to use common parlance: “Their eyes were bigger than their stomachs.”

    A hypothesis based on sensitization, on the other hand, leads to the opposite outcome: “Like the conclusion propagated by the fasting movement, this theory says that because sensory experiences in the mouth are rare when a person goes without food, the mouth becomes more sensitive, making small objects seem larger than they actually are,” explains Türk Pereira. Which of these two hypotheses is actually correct has been examined experimentally by the two psychologists.

    The first experiment: Assessing drinking straws

    As a first experiment, 30 volunteers had to either deprive themselves of food for three hours prior to the experiment (hungry group) or eat a meal before it (full group). Then, in the laboratory, the experimentees received short pieces of conventional drinking straws, all cut into segments of three centimeters. The experimentees had to guess the length of these pieces using either just their mouths or their hands without looking at the piece concerned.

    The result was unequivocal: Hungry participants estimated the length of the piece of plastic at approximately 0.4 centimeters longer than full experimentees when “measuring” using their mouths. However, when measuring by hand there was no difference between the perceptions of the two groups. “0.4 centimeters does not sound like much, but it is still 13 percent of the actual length,” says Topolinski. What is more, the human mouth itself is only a few centimeters wide and long.

    The experiment also revealed a clear correlation between the perception of size and the feeling of hunger: the more hunger the experimentees felt, the larger they estimated the piece of plastic to be.

    The second experiment: Assessing chewy candy

    In a second study, the psychologists repeated the experiment on a further 50 volunteers – but this time with actually edible objects, namely small, elongated chewy candy measuring 3.8 centimeters in length. The participants knew that the objects were edible and were also allowed to eat them after estimating their size.

    The result: In this case as well, hungry experimentees estimated using their mouths that the chewy candy was longer compared to their full counterparts. This time the difference was 0.3 centimeters (eight percent of the actual size). With the length estimation by hand, hunger had no apparent effect once again.

    The third experiment: Different lengths

    In a third experiment on a further 60 volunteers, the participants, as a kind of control, had to assess several pieces of drinking straws of different lengths, namely one, two, and three centimeters. This again revealed that hungry participants overestimated the lengths when guessing at the size using their mouths.

    “Interestingly, however, it was revealed that this effect disappears after several rounds,” says Topolinski. Once the participants had felt and assessed a few pieces of plastic in their mouths, full and hungry participants became more alike in their length estimates. “This was our first clue that overestimation due to hunger primarily has to do with sensitivity because the mouth is desensitized by repeated size estimations,” explains the psychologist.

    The fourth experiment: After enjoying chewing gum

    To examine this effect more closely, Topolinski and Türk Pereira conducted a fourth experiment with 44 volunteers focusing on the sensitization hypothesis. Once again, it involved equal numbers of hungry and full experimentees. However, this time some of them were given gum to chew before the actual task of estimating size. “Chewing gum does not make people full. Quite the opposite, in fact. It even increases hunger. But chewing desensitizes the mouth, making it less sensitive,” explains Türk Pereira.

    The result: Hungry and full experimentees who had chewed gum beforehand were similar in their estimation of the size of the test objects. “This was due to the fact that while the oral mucosa had indeed become more sensitive in the hungry people as a result of fasting, this sensitivity was eliminated by chewing some gum, with the result that there was no longer any difference between these hungry people and those who were full,” conclude the psychologists. Consequently, the experiment revealed that with the participants who had not chewed any gum, the hungry ones still overestimated the size of an object in the mouth.

    Conclusion: The fasting movement is right

    The fasting movement has won this point – according to the two psychologists. Hunger does in fact make the mouth more sensitive to stimuli and therefore leads to an overestimation of size. This is a finding that they believe even explains our traditional dining culture: “Starters and soups tend to be gentler and more delicate than main courses. This is probably because at the start of a meal we are hungrier and our mouths cannot yet tolerate any coarse or intensive experiences, so we prefer gentle and delicate dishes,” says Topolinski. Only once the mouth has become accustomed to the intake of food is it possible to enjoy the main meal with its stronger sensory impressions. Had the greed hypothesis been correct, he added, the dishes would need to be the other way round: starters would have to be lavish and intense, and main dishes light and gentle.

    Topolinski, S., & Türk Pereira, P: Mapping the Tip of the Tongue - Deprivation, Sensory Sensitization, and Oral Haptics. Perception, doi:10.1068/p6903


    Dr. Sascha Topolinski, T: +49 (0)931 31-82285, e-mail: sascha.topolinski@psychologie.uni-wuerzburg.de

    By Gunnar Bartsch