Discrimination threshold for haptic volume perception of fingers and phalanges

Abstract

Humans exhibit a remarkable ability to discriminate variations in object volume based on natural haptic perception. The discrimination thresholds for the haptic volume perception of the whole hand are well known, but the discrimination thresholds for haptic volume perception of fingers and phalanges are still unknown. In the present study, two psychophysical experiments were performed to investigate haptic volume perception in various fingers and phalanges. The configurations of both experiments were completely dependent on haptic volume perception from the fingers and phalanges. The participants were asked to blindly discriminate the volume variation of regular solid objects in a random order by using the distal phalanx, medial phalanx, and proximal phalanx of their index finger, middle finger, ring finger, and little finger. The discrimination threshold of haptic volume perception gradually decreases from the little finger to the index finger as well as from the proximal phalanx to the distal phalanx. Overall, both the shape of the target and the part of the finger in contact with the target significantly influence the precision of haptic perception of volume. This substantial data set provides detailed and compelling perspectives on the haptic system, including for discrimination of the spatial size of objects and for performing more general perceptual processes.

A Systematic Comparison of Perceptual Performance in Softness Discrimination with Different Fingers

“…Furthermore, our assumptions are also in line with previous findings in volume perception (Zhang et al, 2018;Zhang et al, 2019), spatial acuity (Ducan & Boynton, 2007;Manser-Smith et al, 2018;Sathian & Zangaladze,1996;Schweizer et al, 2000;Vega-Bermudez & Johnson, 2001) and two-point discrimination (Louis et al, 1984). The previous findings in tactile sensitivity are not completely uniform concerning differences between the individual fingers, but the general pattern shows a decreasing sensitivity from the large index and middle fingers to the smallest little finger.…”

“…Additionally, results from Louis et al ( 1984 ), Manser-Smith et al ( 2018 ), and Schweizer et al ( 2000 ) indicate a declining spatial acuity from index and middle fingers to the ring finger and to the little finger. The results are also in line with Zhang et al ( 2018 , 2019 ), who found a better performance for index and middle fingers as compared to the ring and small fingers in volume perception. Both factors – the ability to produce force and sensory ability – potentially influence the performance in softness perception and might thus explain the higher frequency of usage.…”

“…The little finger seems to have the worst localization threshold (Louis et al, 1984 ; Schweizer et al, 2000 ). Similar patterns have also been found in active and passive volume perception (Zhang et al, 2018 ; Zhang et al, 2019 ). In contrast, Dellon, Mourey, and Dellon ( 1992 ) found better performance of the little finger in two-point discrimination as compared to the index finger.…”

Neonatal Assessment Manual Score: Is There a Role of a Novel, Structured Touch-Based Evaluation in Neonatal Intensive Care Unit?

“…Haptic perception is a delicate process: the human fingers-in particular, the index finger-can touch and discriminate surfaces with small wrinkles of various amplitudes (51). The fingertips also display low thresholds for discriminating objects with different volumes (52).…”

“…The sensitivity of the hand LTMs and the specialization of the haptic system together with the accumulated professional knowledge in the NICU setting will contribute to effective interaction between top-down predictions and bottom-incoming sensory signals processed and modulated at different levels of the nervous system hierarchy. It is therefore plausible that an operator may feel the changes in the newborn's body volume, evaluating the compliance of the newborn's tissues, that is, perceiving the resistance put up to the applied pressures and the changes in tissue softness (51,52,55).…”