Proper research methods help scientists test phenomena in the real world. Scientists begin with an observation, make an educated guess (i.e., an hypothesis) about why the event occurs, and design an experiment to test the hypothesis. Once the experiment is underway, scientists collect information, interpret data, and then reach conclusions about whether the hypothesis is true.
Scientific Validity Depends on Accurate Testing
In order for conclusions to have scientific validity, the experimental method must duplicate the phenomena being tested. Suppose a scientist wanted to determine at what temperature a bottle of milk sours. The scientist might bring several identical bottles of milk into the laboratory, expose each bottle to a wide range of temperatures, and then observe the temperature at which the milk curdled.
Physical science experiments are generally straightforward because they involve easily quantifiable phenomena. But what happens when a scientist wants to test a hypothesis in psychology (or any of the social sciences) where the natural phenomena cannot be reproduced faithfully?
A case in point involves research on tickling and perceptions of the tickle sensation.
Experimental Tickling is Not Natural Tickling
Experimental tickling is not performed under the same conditions as natural tickling. In a research setting, tickling is induced not by the fingers but by a brush, a piece of cotton, or a mechanical machine.
Tickling in the laboratory also focuses on the lighter tickling associated with knismesis than the more intense tickling (gargalesis) observed in real-life situations. Due to the difficulty associated with touching strangers (and especially students), researchers have to simulate tickling for brief periods of time and trust that the results mirror reality.
Sometimes the conclusions reached seem plausible. Other times, flaws in the experimental method are apparent.
Is Tickle Sensitivity Asymmetric?
Smith and Cahusac (2001) noted that the human body displays asymmetry in physical stimuli. For example, tolerance for pain is lower on the left side of the body than on the right side. The researchers wanted to investigate whether tickle sensitivity displayed a similar neuropsychological asymmetry.
To test this hypothesis, 34 university students (21 female, 13 male) were recruited. Tickling was applied with a “pointed nylon rod . . . moved 10 cm lengthwise over the bare sole of the foot” three times at one-second intervals first on one foot, and then repeated on the other foot. Subjects were asked to evaluate the intensity of the tickling.
Overall, the right foot was found to be more ticklish than the left foot. The experimental findings did not depend if the subject was right-handed, left-handed, or ambidextrous. As the left brain hemisphere controls emotions as well as the right side of the body, the experimenters claimed that ticklishness is a natural right-sided phenomenon.
External Tickling vs. Self-Tickling
Pridmore et al. (2006) wanted to investigate if self-tickling was more ticklish than tickling done by an external source. The tickle response was studied in 42 subjects (23 female, 19 male). Tickling was applied either with a mechanical pointer (as in the Smith and Cahusac study) or with a painter's brush. In each case, an experimenter did 12 tickles on the palm of the hand, and the subject self-tickled in the same spot for another 12 times.
According to the researchers, the results showed that ticklishness was greater when applied by an experimenter using the mechanical pointer than through self-tickling. There was no difference in ticklishness when using a brush.
Facial Expressions During Tickling
Harris and Alvarado (2005) wondered if there were a difference between smiles induced by tickling and smiles caused by jokes or humor. Although involuntary laughter provokes smiling, no previous research had explored whether ticklish smiling really was connected with positive emotions, or simply a mask to disguise anxiety and pain.
The experimenters recruited 84 subjects (61 female, 23 male). The experimenter stood behind each subject and gave advance warning that the subject would be tickled somewhere on the sides, from the waist to the underarms. Facial expressions were recorded as each subject was tickled for 10 seconds.
Females rated the tickling as “more ticklish and unpleasant” than males. Laughter from tickling occurred in 70-75% of all students. No student asked the tickling to stop. Although students smiled while being tickled, the type of smiling resembled “automatic responses to a physical stimulus,” which seemed more like pain than happiness.
Evaluation of Three Experimental Methods
For an experimental method to be valid, several criteria have to be met. First, the results must be reproducible by other researchers. To date, right-sided ticklishness has not been duplicated in other research studies. Self-tickling is known to be blocked by the cerebellum, so the results from Pridmore et al. were expected. Harris and Alvarado were the first to study facial expressions; as stress arises during tickling, their results may be affected by other factors.
Second, the tools used must be those normally associated with the phenomena being tested. Smith and Cahusac used a nylon rod, which is not a natural tickle tool. Although Pridmore et al. used a more natural tickle tool (i.e., the brush) along with the mechanical pointer, results for the brush were inconclusive. Only Harris and Alvarado used a natural tickling method.
Third, the sample sizes should reflect a normal population. In all three cases, the sample sizes were too small (< 84 subjects) to make generalizations.
Fourth, the method should reflect the actual phenomena under study. In all three cases, the tickling was brief (< 12 seconds), performed by strangers, and assessed by subjective self-reporting.
As with all scientific research, the experimental methods must be examined critically before results are accepted at face value. Clearly, research on tickling is a ticklish problem.
References
Harris CR, Alvarado N. 2005. Facial expressions, smile types, and self-report during humour, tickle, and pain. Cognition and Emotion. 19(5):655-69.
Pridmore S, Garry M, Karst M, Rahe-Meyer N, Rybak M. 2006. Tickling healthy subjects. German Journal of Psychiatry. 9:107-10.
Smith JL, Cahusac PMB. 2001. Right-sided asymmetry in sensitivity to tickle. Laterality. 6 (3):233-38.
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