Though Weber conjectured about temperature affecting touch sensation, he never pursued the idea. Stevens and Hooper (1982) found that temperature does affect touch sensation; however, they did not use the two-point method to find this out. Therefore, our experiment measured subjects' two-point thresholds at room temperature and a specified colder temperature on the back of the dominant hand and the tip of the dominant middle finger.
Methods
Subjects were eleven Alma College students. Each subject placed his or her dominant hand on a table, through a cut hole in a board that sat on top of the table. This prevented them from seeing if they were being touched with one point or two. In actuality, the subject was always touched with two points.
An alternating double staircase was used to measure data, with the distance between the two points ranging from two to thirty-five millimeters for the back of the hand and two to ten millimeters for the tip of the finger, increasing or decreasing in one-millimeter increments. Once the subject reversed on each staircase three times, that part of the experiment was concluded.
The experiment was run with the subject's hand and fingertip at room temperature (approximately 28-32 degrees Celsius) and cooled to a cold temperature of 20 degrees Celsius.
Results
All subjects' average two-point thresholds for each condition (room temperature back of hand, room temperature fingertip, cold back of hand and cold fingertip) were averaged together. The average threshold for the back of the hand at room temperature was 14.235 millimeters; at the cold temperature it was 13.016 millimeters. (See Figure 1.) The average threshold for the tip of the finger at room temperature was 2.332 millimeters; at the cold temperature it was 2.430 millimeters. (See Figure 2.)
Figure 1.Average difference in two-point thresholds on the back of the dominant hand when the tested area is at room temperature vs. when cooled to 20 degrees Celsius. The average threshold was 14.235 mm at room temperature, vs. 13.016 mm when cooled.
Figure 2.Average difference in two-point thresholds on the tip of the dominant middle finger when the tested area is at room temperature vs. when cooled to 20 degrees Celsius. The average threshold was 2.332 mm at room temperature, vs. 2.430 mm when cooled.
Conclusions
The results on the back of the hand were expected. This was in part due to a study by Stevens, Green, and Krimsley (1977) that showed that a decrease in skin temperature reduced subjects' punctuate pressure sensitivity. However, the results for the tip of the finger were unexpected. The tip of the finger is already more sensitive than the back of the hand; in addition, Stevens and Hooper (1982) suggested that perception of pressure could be impaired by cooling the skin. Our subjects reported that after being poked on the fingertip, they could still feel the sensation even after the device was moved. It is possible that, because the subject was still feeling the poke from the previous trial, his or her ability to detect whether the new poke was one or two points was decreased. Kenshalo and Nafe (1962) found that presenting a stimulus on the skin triggered the tissues to move quickly to accommodate the stimulus. After the stimulus was removed, however, the tissues were relatively slow to "rebound" back to their normal state. This could explain why the subjects still felt the sensation of the stimulus even after it was removed. The tissues had not "rebounded" yet, thus the finger was not able to detect the new point(s) on the fingertip.
As well, it is possible that since the fingertips are more sensitive to begin with, the cold had more of an effect on the tested fingertip, numbing it and making it more difficult to detect pressure. The back of the hand is less sensitive to begin with; therefore the cold temperature possibly had a relatively smaller numbing effect on it.
This experiment provides a basis for further investigation into two-point threshold combined with temperature control; it raises the question of how high the correlation is between the two. Though our experiment suggests that at least a small correlation exists, much more investigation is needed to formulate a more rounded theory about it.
References
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