Frequency Analysis of the Detectability of Virtual Haptic Gratings

The tactile detectability of sinusoidal and square-wave virtual texture gratings were measured and analyzed. Using a three-interval one-up three-down adaptive tracking procedure, detection thresholds for virtual gratings were estimated using a custom-designed high position-resolution 3-degrees-of-freedom force-feedback haptic device. Two types of gratings were used, defined by sinusoidal and square waveforms, with spatial wavelengths of 0.2 to 25.6 mm. The results indicated that the participants demonstrated a higher sensitivity (i.e., lower detection threshold) to square-wave gratings than to sinusoidal ones at all the wavelengths tested. When the square-wave gratings were represented by the explicative Fourier series, it became apparent that the detectability of the square-wave gratings could be determined by that of the sinusoidal gratings at the corresponding fundamental frequencies. This was true for any square-wave grating as long as the detection threshold for the fundamental component was below those of the harmonic components