Neural coding in the Non-Pacinian I tactile channel: A psychophysical and simulation study of magnitude estimation

Abstract

Psychophysical experiments and model simulations were performed to identify plausible neural codes representing stimulus magnitude in the Non-Pacinian I (NP I) tactile channel associated with rapidly adapting fibers. Sinusoidal mechanical displacements were applied on the fingertips of eight human subjects. The NP I channel was isolated by elevating the thresholds of the Pacinian (P) channel during forward masking. Psychophysical magnitude estimates were obtained at 40 Hz for the NP I channel and at 250 Hz for the P channel by using a small contactor (radius: 2 mm). The P channel was additionally tested with a larger contactor (radius: 4.3 mm) to compensate for the lower innervation density of the Pacinian fibers. The magnitude estimates were fitted by power functions. The exponent (1.02) obtained with the large contactor for the P channel was higher than the exponent (0.68) obtained with the small contactor, but it was not statistically different from the exponent (1.21) obtained with the small contactor for the NP I channel. This suggests that the exponent increases when more fibers are recruited in the P channel. Six hypothetical neural codes were tested by using a computational population model for the rapidly adapting afferents. The validity of each code was evaluated by comparing psychophysical and simulation exponents, by finding the correlations between the magnitude estimates and the neural code results, and by a novel distance metric for measuring the proximity between the data sets. The codes based on the number of active fibers, the total spike count, the mean and the standard deviation of the spike count distribution yielded the best results, while the codes based on the interspike intervals were not related with the magnitude estimates.

Reproducibility of flutter-range vibrotactile detection and discrimination thresholds

“…Moreover, the intersubject variability of the various thresholds falls in line with previous findings in adults 13,[27][28][29] , with reaction times having around 20-30% variation, detection and frequency discrimination thresholds having 20-40% variation, and amplitude discrimination thresholds having 40-60% variation. The intrasubject variability of detection thresholds has been shown to be around ~25-30% 55,56 , which also falls in line with the present findings.…”

Tactile Masking by Electrovibration

“…The results generally show that tactile detection is enabled by one of four independent psychophysical channels (P, NPI, NPII, NPIII) mediated by four mechanoreceptor systems (PC, RA, SA II, SA I). Most of these findings were validated by subsequent works in different laboratories [10], [25], [26], [27] and used in computational modelling of the sense of touch [28], [29], [30], [31]. The concept of investigating human perception through psychophysical channels has been widely established for sensory modalities such as vision, hearing, and touch [32], [33], [34], [35], [36], [37].…”

“…see [38]). However, without an accurate population model for all mechanoreceptive fibers, it is still not easy to predict response to a complex stimuli, especially at suprathreshold levels (for NPI channel, see [30], [62])…”

Effect of Remote Masking on Tactile Perception of Electrovibration

“…Different tactile masking types are usually defined based on their temporal order (see Vardar et al for a short review [7]). As one of the most frequently applied techniques, forward masking has been shown to increase detection levels for both low and high frequency stimuli, and can be used to selectively mask psychophysical channels [8], [9], [10], [11]. Forward masking can be explained by two alternative theories: persistence and neural adaption [12].…”