Effects of passive and active movement on vibrotactile detection thresholds of the Pacinian channel and forward masking

Abstract

We investigated the gating effect of passive and active movement on the vibrotactile detection thresholds of the Pacinian (P) psychophysical channel and forward masking. Previous work on gating mostly used electrocutaneous stimulation and did not allow focusing on tactile submodalities. Ten healthy adults participated in our study. Passive movement was achieved by swinging a platform, on which the participant's stimulated hand was attached, manually by a trained operator. The root-mean-square value of the movement speed was kept in a narrow range (slow: 10-20 cm/s, fast: 50-60 cm/s). Active movement was performed by the participant him-/herself using the same apparatus. The tactile stimuli consisted of 250-Hz sinusoidal mechanical vibrations, which were generated by a shaker mounted on the movement platform and applied to the middle fingertip. In the forward-masking experiments, a high-level masking stimulus preceded the test stimulus. Each movement condition was tested separately in a two-interval forced-choice detection task. Both passive and active movement caused a robust gating effect, that is, elevation of thresholds, in the fast speed range. Statistically significant change of thresholds was not found in slow movement conditions. Passive movement yielded higher thresholds than those measured during active movement, but this could not be confirmed statistically. On the other hand, the effect of forward masking was approximately constant as the movement condition varied. These results imply that gating depends on both peripheral and central factors in the P channel. Active movement may have some facilitatory role and produce less gating. Additionally, the results support the hypothesis regarding a critical speed for gating, which may be relevant for daily situations involving vibrations transmitted through grasped objects and for manual exploration.

A Tactile Virtual Reality for the Study of Active Somatosensation

“…However, the waveform frequency of each pulse was around 150 Hz, which typically activates the Pacinian receptor class. Nevertheless, estimated detection thresholds in the current study (approximately 70 µm) are considerably higher compared to the thresholds reported for the Pacinian receptor system, which are typically around 1 µm or less (Gescheider et al, 2009;Yildiz and Güçlü, 2013;Yıldız et al, 2015).…”

“…In the current experiment, we did not find any significant effect of the scanning speed on the detection thresholds; the exploratory speed of the hand during active exploration was on average 87 mm/s. It appears that the detrimental effect of movements on the detection threshold is dependent on the speed of the sensing hand (Cybulska-Klosowicz et al, 2011;Yıldız et al, 2015) and that the speed observed in the current study was much lower than the critical speed (approximately 200 mm/s) at which tactile sensitivity decreases. Moreover, fine texture perception requires movement and sensory gating would impede the whole process of perception.…”

Tactile Masking by Electrovibration

“…Although both passive and active movements elevated detection thresholds at higher speeds, the effect of forward masking was constant as the movement condition varied. The finger speeds used in the electrovibration study reported here were lower than the fast speed range used in the gating study [54]. Therefore, there was probably not much gating effect in our study, and the masking functions were similar to those reported previously.…”

“…If the normal force and or scan speed of a participant were not in the desired range (0.1-0.6 N, and ± 25% of 50 mm/s), the trial was repeated until a measurement within the range was obtained. We selected this range based on the normal forces and speeds reported in the literature as relevant to tactile exploration [53], [54]. Figs.…”

“…The similarity in the slopes of masking functions obtained by electrovibration and vibrotactile stimulation suggest that similar psychophysical channels were recruited for detection. However, in [54], Yıldız et al showed that movement produces a gating effect in detection, especially at high speeds. Although both passive and active movements elevated detection thresholds at higher speeds, the effect of forward masking was constant as the movement condition varied.…”