Figure 1

Experimental setup. The subjects sit and place their right-hand finger tips on the sensors while wearing headphones (a). The subject is asked to produce 20 N with four fingers while the reference and tracking forces produced are provided as auditory feedback tones. The reference tone (i.e. auditory feedback for reference force) in red (c) is a sinusoid signal with a constant frequency of 1000 Hz and intensity of 70 dB played in the left ear, while the tracking tone (i.e. auditory feedback for the tracking force) in blue (c) is a sinusoid signal determined by three feedback conditions; Frequency condition (F): the frequency of the tracking tone changed depending on the sum of finger forces, with a constant intensity of 70 dB, 2) Intensity condition (I): the intensity of the tracking tone changed depending on the sum of finger forces (b), with a constant frequency of 1000 Hz, and 3) Frequency & Intensity condition (FI): both the frequency and intensity of the tracking tone changed depending on the sum of finger forces.