Effects of self movement on absolute and masked thresholds in the pacinian channel

In this thesis, we simulated active touch by measuring absolute and masked thresholds in the Pacinian channel during cyclic self-movement. Based on previous work we hypothesized improvement in the absolute thresholds and increase of masking e ciency compared to passive touch condition. An aluminum contactor (r=0.685 cm) was used for the stimulation of the left middle ngertip of the subjects. The measurements of the psychophysical thresholds were repeated for three conditions: no movement, slow self-movement (0.1-0.2 m/s), and fast self-movement (0.5-0.6 m/s). The slow movement condition (-20.8 dB) and the fast movement condition (-21.8 dB) yielded on average lower thresholds than the passive condition (-17.9 dB). Paired t-tests showed that the di erences between the movement conditions and the passive condition were signi cant (p=0.023 for passive vs. slow; p=0.024 passive vs. fast). Interestingly the threshold shift due to masking increased with self-movement (2.9 dB for passive; 7.9 dB for slow; 9.2 dB for fast). The di erences between the threshold shift due to masking for passive and individual movement conditions were signi cant. According to these results, self-movement signi cantly enhanced sensation in the Pacinian channel. However the speed of the self-movement did not matter. Forward- masking e ciency also increased due to self-movement. Therefore this enhancement seems to operate at both threshold and suprathreshold levels. Since self-movement involves both proprioceptive and motor signals, the exact source of this enhancement currently cannot be identi ed. Keywords: Psychophysics, somatosensation, vibratory stimulus, Pacinian, human, active touch.