Tactual Frequency and Amplitude Discrimination with Fixed and Roving Background

The authors present frequency and amplitude discrimination thresholds for motional and vibrational stimuli presented with and without the presence of roving background signals. Participants received on their left index fingertip sinusoidal displacement waveforms over a range of 2-200 Hz in frequency and 20-35 dB sensation level in amplitude. When the target stimulus was presented in isolation, the average Weber fraction for frequency was 0.18−0.25, and the average amplitude discrimination threshold was 2.2−2.5 dB. When roving background signals were presented with the targets and the participants were instructed to ignore the interfering backgrounds, the discrimination thresholds for both frequency and amplitude increased. The amount of increase depended on the nature of the background signals. The results are discussed in terms of their implications for tactual displays of speech in communication aids for the deaf.