Overview of the perceptual data, showing the relation between physical and perceived force magnitude, measured using free magnitude estimation.
(a) Typical example of force magnitude perception data of one participant, for all directions together. The small grey dots show individual measurements, while the thick black dots with error bars show the mean per physical force magnitude ± standard deviation. The black line shows the fit of the power function, which describes the relation between physical force magnitude (F) and mean perceived force magnitude (ψ). The fit was used to normalize the data. (b) Exponents of the fitted power functions, per participant and mean ± standard error over participants. Note that on average, the power function exponents differ from 1, indicating a non-linear relationship between physical and perceived force magnitude.