Roughness rendering by sinusoidal friction modulation: Perceived intensity and gradient discrimination*

Four experiments used a programmable ultrasonic friction-modulation device to explore parameters that might be candidates for roughness modulation and to assess whether spatially modulated texture gradients could be discriminated by their direction of change. Candidate roughness parameters included frequency, amplitude and two implementations of local friction variation (noise). Amplitude, frequency, and noise all moderated roughness. Observed interactions between parameters could reflect peripheral or attentional effects. Directional discrimination of graded frictional changes was well above chance, but did not indicate accessible and reliable differentiation that could readily be exploited in use contexts.