The effect of body temperature on the determination of pitch by an absolute pitch possessor

Abstract

Few people have absolute pitch (AP); that is, they can identify a pitch that they are hearing without any reference point. Factors affecting this discrimination are poorly understood. We investigated one of the fundamental features of AP: the effect of temperature on discrimination accuracy. A person with AP was asked to measure her own body temperature with a tympanic thermometer, and then to tune a variable frequency sound generator to A4 (440 Hz) without seeing the frequency display. The body temperatures and corresponding frequencies were recorded. The measurements were repeated twice a day for three months. Although the overall correlation between body temperature and estimated frequency was insignificant, during limited periods we observed higher correlations (R ² = 0.7, or higher) with a temperature coefficient of about −3 Hz/K near 440 Hz. The peak vibration amplitude position of the basilar membrane is known to shift about 5 mm per octave change in frequency. We estimated that a temperature change of 0.1 K causes a shift in peak amplitude position of about 4 μm. Good auditory ear holders (good AP subjects) can discriminate a change of about 0.1% in sound frequency, which corresponds to a shift in peak amplitude position on the basilar membrane of about 7 μm. It is therefore clear that cochlear temperature must be regulated to within 0.1 K to achieve the pitch discrimination observed in people with AP, since adjacent hair cells are separated by less than 10 μm. Our results provide a consistent explanation for the relationship between pitch discrimination in persons with AP, the accuracy of body temperature regulation, and the separation of hair cells.