Figure 4
Electric and normal sensation thresholds (a) Comparison of the present result (symbols) with previous studies (dashed lines). The Kanai et al. study used two rubber electrodes with one being placed on the back of the head (inion, 3 × 4 cm) and another on the vertex (6 × 9 cm)32. The Stevens study used a copper wire immersed in saline solution that filled the ear canal and an aluminum disk strapped on the forearm8. The Hawkes study used a ring electrode on the finger and a round electrode on the palm48. All amplitude data were converted into dB referring to 1 mA except for electric hearing data from Stevens 1937, in which dB values were referred to 10 μW. (b) Comparison with normal auditory sensation thresholds (dB RE: 20 μPa) evoked by sound98 and normal tactile sensation thresholds evoked by vibration (dB RE: 1 μm)99.
