Thresholds for the perception of rotation: variability, psychometric curves, and comparison with hearing thresholds.

Psychometric curves were determined for the perception of rotation about a vertical axis. If a logarithmic scale is used, an integrated Gaussian curve gives a reasonable description of the psychometric curve. This curve is characterized by two values: the 50% point, which is defined as the threshold, and the s.d. The s.d. of the vestibular psychometric curve is about 10 dB which is 4 times larger than the s.d. found for the auditory system. The distribution of vestibular thresholds in healthy subjects obtained by Clark and Stewart (1969) is plotted on a logarithmic acceleration scale; it can fitted by a Gaussian function. The s.d. of this function is 5.5 dB, a value which is similar to that found for auditory thresholds. From this it is concluded that the inter-individual variability of the detection threshold for the vestibular system is the same as the inter-individual variability of the detection for the auditory system.