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Ng KKW, So A, Fang JY, Birznieks I, Vickery RM. Multiplexing intensity and frequency sensations for artificial touch by modulating temporal features of electrical pulse trains. Front Neurosci 2024; 18:1125597. [PMID: 38894940 PMCID: PMC11183272 DOI: 10.3389/fnins.2024.1125597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Accepted: 05/20/2024] [Indexed: 06/21/2024] Open
Abstract
In neural prostheses, intensity modulation of a single channel (i.e., through a single stimulating electrode) has been achieved by increasing the magnitude or width of each stimulation pulse, which risks eliciting pain or paraesthesia; and by changing the stimulation rate, which leads to concurrent changes in perceived frequency. In this study, we sought to render a perception of tactile intensity and frequency independently, by means of temporal pulse train patterns of fixed magnitude, delivered non-invasively. Our psychophysical study exploits a previously discovered frequency coding mechanism, where the perceived frequency of stimulus pulses grouped into periodic bursts depends on the duration of the inter-burst interval, rather than the mean pulse rate or periodicity. When electrical stimulus pulses were organised into bursts, perceived intensity was influenced by the number of pulses within a burst, while perceived frequency was determined by the time between the end of one burst envelope and the start of the next. The perceived amplitude was modulated by 1.6× while perceived frequency was varied independently by 2× within the tested range (20-40 Hz). Thus, the sensation of intensity might be controlled independently from frequency through a single stimulation channel without having to vary the injected electrical current. This can form the basis for improving strategies in delivering more complex and natural sensations for prosthetic hand users.
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Affiliation(s)
- Kevin K. W. Ng
- Center for Social and Affective Neuroscience, Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
| | - Alwin So
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
| | - Jun Yi Fang
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
| | - Ingvars Birznieks
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
- Bionics and Bio-robotics, Tyree Foundation Institute of Health Engineering, UNSW Sydney, Sydney, NSW, Australia
| | - Richard M. Vickery
- School of Biomedical Sciences, UNSW Sydney, Sydney, NSW, Australia
- Neuroscience Research Australia, Sydney, NSW, Australia
- Bionics and Bio-robotics, Tyree Foundation Institute of Health Engineering, UNSW Sydney, Sydney, NSW, Australia
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Bhattacharjee A, Schwarz C. Temporally Local Tactile Codes Can Be Stored in Working Memory. Front Hum Neurosci 2022; 16:840108. [PMID: 35712533 PMCID: PMC9195853 DOI: 10.3389/fnhum.2022.840108] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 05/04/2022] [Indexed: 11/13/2022] Open
Abstract
Tactile exploration often involves sequential touches interspersed with stimulus-free durations (e.g., the time during which the hand moves from one textured surface to the other). Whereas it is obvious that texture-related perceptual variables, irrespective of the encoding strategy, must be stored in memory for comparison, it is rather unclear which of those variables are held in memory. There are two established variables—“intensity” and “frequency”, which are “temporally global” variables because of the long stimulus integration interval required to average the signal or derive spectral components, respectively; on the other hand, a recently established third contender is the “temporally local” variable that codes for kinematic profiles of very short, suprathreshold events in the vibrotactile signal. Here, we present the first psychophysical evidence that temporally local variables can be stored in memory. To that end, we asked participants to detect changes in pulsatile indentation stimuli at their fingertips with and without a gap of 1 s between stimulus presentations. The stimuli either contained global variables alone (change of pulse rate), or a mix of local and global variables (change of pulse shape). We found, first, that humans are much better at detecting a change in stimuli when local variables are available rather than global ones alone—as evident by the fact that 21 compared to only 6 participants out of 25 yielded a valid psychophysical curve, respectively. Second, this observation persists even when there is a gap between the stimuli, implying local variables must be stored in memory. Third, an extensive array of relevant intensity definitions failed to explain participants’ performance in any consistent manner, which implies that perceptual decisions were less likely to be driven by intensity coding. Taken together, our results suggest that humans perform pulsatile change detection utilizing local pulse shape, and to a lesser degree global pulse rate, and that both parameters can be stored in memory.
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Affiliation(s)
- Arindam Bhattacharjee
- Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Eberhard Karls University Tübingen, Tübingen, Germany
- Hertie Institute for Clinical Brain Research, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Cornelius Schwarz
- Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Eberhard Karls University Tübingen, Tübingen, Germany
- Hertie Institute for Clinical Brain Research, Eberhard Karls University Tübingen, Tübingen, Germany
- *Correspondence: Cornelius Schwarz
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