<b>Top</b>: Illustrations of the sinusoidal vibrations used in Experiment 1.

<p>Subjects compared the frequency of two vibrations that differed in amplitude (ΔA); the difference between the higher and lower frequency vibrations was either −20%, −13.3%, −6.6%, 0%, +6.6%, +13.3%, or +20%. The examples illustrated are for a 32 Hz and a 40 Hz vibration, with ΔA = −6.6% and +20%. <b>Below</b>: The six graphs plot the frequency discrimination thresholds (in Hz) for 6 different subjects as a function of ΔA. Each black point is the average threshold measured by two independently run adaptive staircases. Each graph includes the line-of-best-fit and the R² for that regression line.