The long-term goal of this research is to create a prosthetic hand capable of restoring a sense of touch to users. In the United States alone, 1.2 million people suffer from limb loss [1], [2]. The current standard of care for individuals with limb loss is unsatisfactory; upwards of 50% of individuals abandon their prostheses citing a lack of sensory feedback from the prosthetic hand as a principal reason [3]. Electrocutaneous stimulation of the residual arm nerves can be used to provide sensory feedback to individuals with limb loss. A higher stimulation frequency results in a more intense sensation. We measured the Weber fraction -- the minimum percent change in stimulation frequency that can be identified correctly 75% of the time -- to describe how well electrocutaneous stimulation can convey the magnitude of tactile stimuli. We previously showed that the Weber fraction is much smaller at lower stimulation frequencies (17% change needed at 50 Hz vs 42% change needed at 100 Hz), which means that electrocutaneous stimulation is more discriminable at lower stimulation frequencies [4]. Here, we show that this enhanced discriminability is due to supplemental temporal cues present at lower frequencies only. When stimulation intensity is decoupled from stimulation frequency, participants were still able to discriminate stimulation frequency at 50 Hz (when there is at least a 30% change) but were not able to discriminate stimulation frequency at 100 Hz. The ability to discriminate stimulation frequency based strictly on temporal cues only at 50 Hz implies that these tactile cues enhance discriminability selectively at lower frequencies. These results help deepen the understanding of the neural basis of tactile perception and can aid the development of sensitized prosthetic hands. [1] M. P. Fahrenkopf, N. S. Adams, J. P. Kelpin, and V. H. Do, "Hand Amputations," Eplasty, vol. 18, p. ic21, Sep. 2018.
[2] B. Peerdeman et al., "Myoelectric forearm prostheses: State of the art from a user-centered perspective," J. Rehabil. Res. Dev., vol. 48, pp. 719-37, Jul. 2011, doi: 10.1682/JRRD.2010.08.0161.
[3] L. Jabban, S. Dupan, D. Zhang, B. Ainsworth, K. Nazarpour, and B. W. Metcalfe, "Sensory Feedback for Upper-Limb Prostheses: Opportunities and Barriers," IEEE Trans. Neural Syst. Rehabil. Eng., vol. 30, pp. 738-747, 2022, doi: 10.1109/TNSRE.2022.3159186.
[4] A. Citterman, M. Brinton, and J. George, Low Frequencies Improve Intensity Discrimination for Electrocutaneous Artificial Sensory Feedback. 2021. doi: 10.13140/RG.2.2.23554.81602.