Who Hates Fingernails on a Chalkboard?

Research Questions:

• Which test subjects react adversely to the sound of fingernails on a chalkboard?
• Are their reactions physiologically measurable?
• Do subjects who do not self-report a negative reaction to the sound of fingernails on a chalkboard still have a physiological reaction?
• Do subjects who do not react negatively to fingernails on a chalkboard report other sounds that trigger a similar negative response?
• Do sounds identified in the question above trigger a physiological response?
• Do sounds identified above affect other test subjects?

Most people, but NOT everyone, cringe at the sound of fingernails on a chalkboard. In studies, physiological responses such as increased heart rate and blood pressure are consistently measured in response to this sound, even when the sound is mitigated so that test subjects don’t consciously perceive it as negative. There is no consensus as to exactly why this sound evokes such a response, but the most popular theory is that human ear canals are shaped so as to amplify the certain pitches made by this phenomenon.

Materials:

• Blood pressure/heart rate monitor (this should be available at a drug store for a reasonable cost)
• Chalkboard
• A quiet room
• An assistant (preferably one who does not mind fingernails on a chalkboard)
• 40 or more test subjects
• Paper and pencil for recording and analyzing data

Experimental Procedure:

1. Familiarize yourself with the use of the blood pressure/heart rate monitor.
2. Sit each test subject in a quiet room and attach the blood pressure/heart rate monitor to her.
3. Measure and record the subject’s blood pressure and heart rate.
4. Have your assistant stand behind the test subject (so that the subject can’t see him) and scrape his fingernails repeatedly across the chalkboard.
5. Observe the subject’s reaction and ask her how the sound makes her feel.
6. Measure and record the subject’s heart rate and blood pressure as well as their observed and self-reported reactions.
7. With test subjects who do not self-report negative reactions to the sound, ask whether there are other sounds that for them evoke responses similar to that evoked for most people by fingernails on a chalkboard.
8. If the answer to the above question is yes for any of these subjects, retest the other subjects who did NOT self-report a negative reaction to nails on the board, this time using the sound(s) reported as disturbing by other subjects.
9. Record subjects’ observed, self-reported, and physiological reactions to this new sound(s).
10. Analyze your data addressing the research questions above and any others that occur to you in the course of your research.

Terms/Concepts: self-report, physiological response, blood pressure, heart rate

References: "Why Fingernails on Blackboards Sound So Horrible," by Duncan Geere, Wired Science, http://www.wired.com/wiredscience/2011/11/chalk-board-fingernail-sound/.