Encoding and decoding of shape in tactile sensing

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 100-104).by Balasundara I. Raju.M.S

Encoding and decoding of shape in tactile sensing

Supervised by Dr. Mandayam A. Srinivasan.Also issued as Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 100-104).by Balasundara I. Raju

Encoding tactile frequency and intensity information in the temporal pattern of afferent nerve impulses

Using our hands to interact with the world around us produces complex vibrations travelling across the skin. These complex waves are transduced by tactile afferent neurons whose impulse patterns convey information about the external world. A major question in this field is how important the timing of these afferent impulses is in shaping perception. We have the means to investigate this question by artificially inducing impulse patterns using brief mechanical and electrical stimuli, allowing us to study the neural coding of vibrotactile sensory information. Our lab has used this to show that when mechanical pulses evoked impulse trains grouped into periodic bursts, perceived frequency corresponded to the duration of the silent inter-burst gap interval, rather than the periodicity or the mean impulse rate. In this thesis, we induced controlled impulse trains, while measuring the perceptual responses of human subjects using psychophysical methods to assess the dimensions of frequency and intensity. As electrical stimulation has broad utility in prosthetic applications, we first verified that the same perceived frequency as predicted by the burst gap was elicited with electrical pulses in subjects within the low frequency flutter range. We then tested whether this same coding mechanism also applied outside the flutter frequency range by conducting further experiments with higher pulse rates. We found that burst gap coding correctly predicted perceived frequencies above flutter, suggesting a generalised temporal processing strategy that operates on tactile afferent inputs spanning a broad range of frequencies. Next, we investigated perceived intensity where stimulus pulse rate was varied without changes in afferent population recruitment or in perceived frequency by using bursts of pulsatile stimuli. Increasing the number of pulses within a burst caused a significant increase in perceived intensity when electrical stimulation was used. Mechanical pulses with the same burst groupings did not produce a comparable intensity increase, possibly due to minimal variations in the population firing rate. These new insights into the encoding of tactile information through temporal patterning in peripheral impulse patterns may allow the multiplexing of frequency and intensity sensations with a fixed stimulation amplitude for use in neural interfaces to deliver sensory feedback information

Role of mechanics in tactile sensing of shape

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references (leaves 199-205).by Kiran Dandekar.Ph.D

Sensory Communication

Contains table of contents for Section 2 and reports on five research projects.National Institutes of Health Contract 2 R01 DC00117National Institutes of Health Contract 1 R01 DC02032National Institutes of Health Contract 2 P01 DC00361National Institutes of Health Contract N01 DC22402National Institutes of Health Grant R01-DC001001National Institutes of Health Grant R01-DC00270National Institutes of Health Grant 5 R01 DC00126National Institutes of Health Grant R29-DC00625U.S. Navy - Office of Naval Research Grant N00014-88-K-0604U.S. Navy - Office of Naval Research Grant N00014-91-J-1454U.S. Navy - Office of Naval Research Grant N00014-92-J-1814U.S. Navy - Naval Air Warfare Center Training Systems Division Contract N61339-94-C-0087U.S. Navy - Naval Air Warfare Center Training System Division Contract N61339-93-C-0055U.S. Navy - Office of Naval Research Grant N00014-93-1-1198National Aeronautics and Space Administration/Ames Research Center Grant NCC 2-77

Mechano-to-Neural Transduction of the Pacinian Corpuscle

University of Minnesota Ph.D. dissertation. October 2017. Major: Biomedical Engineering. Advisor: Victor Barocas. 1 computer file (PDF); xv, 207 pages.Cutaneous mechanoreceptors are responsible for our ability to distinguish between different touch modalities and experience the physical world around us. Mechanoreceptors are innervated by afferent mechanosensitive neurons that transduce mechanical stimuli into action potentials and terminate in specialized end organs. The Pacinian corpuscle (PC) has been studied more than any of our other mechanoreceptors due to its large size and ease of identification during dissection. The PC, which is found primarily within the dermis of glabrous skin, responds to low-amplitude, high-frequency vibrations in the 20-1000 Hz range. The PC functions as a bandpass filter to vibrations, an effect attributed to the structural and mechanical complexity of its end organ. The PC contains a central mechanosensitive nerve fiber (neurite) that is encapsulated by alternating layers of flat, epithelial-type cells (lamellae) and fluid. The overarching goal of this thesis was to unify the anatomical and electrophysiological observations of the PC via a detailed mechanistic model of PC response to mechanical stimulation, requiring a multiphysics, multiscale approach. First, we developed a multiscale finite-element mechanical model to simulate the equilibrium response of the PC to indentation while accounting for the layered, anisotropic structure of the PC and its deep location within the skin. Next, we developed a three-stage finite-element model of the PC’s mechanical and neural responses to a vibratory input that accounted for the lamellar mechanics and neurite electrochemistry. This mechano-neural model was able to simulate the PC’s band-pass filtration of vibratory stimuli and rapid adaptation to sustained mechanical stimuli. We then used this model to evaluate the relationship between the PC’s material and geometric parameters and its response to vibration and developed dimensionless expressions for the relationship between these parameters and peak frequency or bandwidth. We then embedded multiple mechano-neural PC models within a finite-element model of human skin to simulate the mechanical and neural behavior of a PC cluster in vivo. We then performed a literature search to compile the structural parameters of PCs from various species and used our mechano-neural model to simulate the frequency response across species. Finally, we isolated PCs from human cadaveric hands and performed micropipette aspiration experiments to determine an apparent Young’s modulus of the PC. The computational and experimental work performed in this thesis contribute to the understanding of the fundamental behavior of mechanoreceptors, which is a necessary first step towards the development of haptic feedback-enabled devices

Perception de la vitesse : les bases psychophysiques et neuronales

David Katz a fait l’observation que le mouvement entre la peau et l’objet est aussi important pour le sens du toucher que la lumière l’est pour la vision. Un stimulus tactile déplacé sur la peau active toutes les afférences cutanées. Les signaux résultants sont très complexes, covariant avec différents facteurs dont la vitesse, mais aussi la texture, la forme et la force. Cette thèse explore la capacité des humains à estimer la vitesse et la rugosité de surfaces en mouvements. Les bases neuronales de la vitesse tactile sont aussi étudiées en effectuant des enregistrements unitaires dans le cortex somatosensoriel primaire (S1) du singe éveillé. Dans la première expérience, nous avons montré que les sujets peuvent estimer la vitesse tactile (gamme de vitesses, 30 à 105 mm/s) de surfaces déplacées sous le doigt, et ceci sans indice de durée. Mais la structure des surfaces était essentielle (difficulté à estimer la vitesse d’une surface lisse). Les caractéristiques physiques des surfaces avaient une influence sur l’intensité subjective de la vitesse. La surface plus rugueuse (8 mm d’espacement entre les points en relief) semblait se déplacer 15% plus lentement que les surfaces moins rugueuses (de 2 et 3 mm d’espacement), pour les surfaces périodiques et non périodiques (rangées de points vs disposition aléatoire). L’effet de la texture sur la vitesse peut être réduit en un continuum monotonique quand les estimés sont normalisés avec l’espacement et présentés en fonction de la fréquence temporelle (vitesse/espacement). L'absence de changement des estimés de vitesse entre les surfaces périodiques et non périodiques suggère que les estimés de rugosité devraient aussi être indépendants de la disposition des points. Dans la deuxième expérience, et tel que prévu, une équivalence perceptuelle entre les deux séries de surfaces est obtenue quand les estimés de la rugosité sont exprimés en fonction de l'espacement moyen entre les points en relief, dans le sens de l'exploration. La troisième expérience consistait à rechercher des neurones du S1 qui pourraient expliquer l’intensité subjective de la vitesse tactile. L’hypothèse est que les neurones impliqués devraient être sensibles à la vitesse tactile (40 à 105 mm/s) et à l’espacement des points (2 à 8 mm) mais être indépendants de leur disposition (périodique vs non périodique). De plus, il est attendu que la fonction neurométrique (fréquence de décharge/espacement en fonction de la fréquence temporelle) montre une augmentation monotonique. Une grande proportion des cellules était sensible à la vitesse (76/119), et 82% d’entres elles étaient aussi sensibles à la texture. La sensibilité à la vitesse a été observée dans les trois aires du S1 (3b, 1 et 2). La grande majorité de cellules sensibles à la vitesse, 94%, avait une relation monotonique entre leur décharge et la fréquence temporelle, tel qu’attendu, et ce surtout dans les aires 1 et 2. Ces neurones pourraient donc expliquer la capacité des sujets à estimer la vitesse tactile de surfaces texturées.David Katz showed that movement between the skin and an object is as important for touch as light is to vision. Moving tactile stimuli activate all of the cutaneous afferents involved in discriminative touch. The resultant signals are complex, varying with multiple factors including speed and also texture, local shape, and force. This thesis explored the human ability to estimate the speed and roughness of moving tactile stimuli. The neuronal basis underlying tactile speed perception was investigated using single unit recordings from primary somatosensory cortex (S1) in awake monkeys. In the first psychophysical experiment, we showed that subjects (n=26) can scale tactile speed (range, 30-105 mm/s), and this, contrary to previous studies, in a situation in which the duration of each trial was constant across all speeds tested. Surface structure was, in contrast, essential since subjects had difficulty scaling the speed of a smooth surface. Moreover, the physical characteristics of the surfaces influenced tactile speed perception. The roughest surface (8 mm raised-dot spacing) seemed to move 15% slower than the smoother surfaces (2 and 3 mm spacing), and this independently of dot disposition (periodic: rectangular array of raised dots vs non periodic: random dots). The effects of surface texture on speed were reduced to a single continuum when the estimates were normalized by dot spacing and plotted as a function of temporal frequency (speed/dot spacing). The absence of any difference in speed scaling as a function of dot disposition (periodic vs non periodic) suggested that tactile roughness should also be independent of dot disposition. A second psychophysical experiment (n=15) confirmed our hypothesis, showing perceptual equivalence for the periodic and non periodic surfaces when these were matched for dot spacing in the direction of the scan. The third experiment investigated the neuronal mechanisms that underlie subjective tactile speed perception, by recording the responses of cutaneous neurones in the hand representation of S1 cortex to the displacement of textured surfaces under the finger tips of two awake rhesus monkeys. The hypothesis was that neurones implicated in tactile speed perception should be sensitive to tactile speed (similar range to that used in the human experiments) and dot spacing, but be independent of dot disposition (periodic vs non periodic). Furthermore, we predicted that the neurometric function (discharge frequency/dot spacing as a function of temporal frequency) would show a monotonic relation. A large proportion of S1 neurones were sensitive to speed (76/119); 82% of these were also sensitive to texture. Speed sensitivity was widely distributed across the three areas that comprise the cutaneous hand representation, areas 3b, 1, and 2. Of 94 neurons fully tested (periodic and nonperiodic surfaces), the large majority of speed-sensitive cells (60/64) showed a significant monotonic relation with temporal frequency for both surfaces when discharge frequency was normalized by dot spacing. The neurones with the strongest relation to temporal frequency were concentrated in caudal S1, areas 1 and 2, and likely contribute to the human ability to scale tactile speed

The temporal pattern of impulses in primary afferents analogously encodes touch and hearing information

An open question in neuroscience is the contribution of temporal relations between individual impulses in primary afferents in conveying sensory information. We investigated this question in touch and hearing, while looking for any shared coding scheme. In both systems, we artificially induced temporally diverse afferent impulse trains and probed the evoked perceptions in human subjects using psychophysical techniques. First, we investigated whether the temporal structure of a fixed number of impulses conveys information about the magnitude of tactile intensity. We found that clustering the impulses into periodic bursts elicited graded increases of intensity as a function of burst impulse count, even though fewer afferents were recruited throughout the longer bursts. The interval between successive bursts of peripheral neural activity (the burst-gap) has been demonstrated in our lab to be the most prominent temporal feature for coding skin vibration frequency, as opposed to either spike rate or periodicity. Given the similarities between tactile and auditory systems, second, we explored the auditory system for an equivalent neural coding strategy. By using brief acoustic pulses, we showed that the burst-gap is a shared temporal code for pitch perception between the modalities. Following this evidence of parallels in temporal frequency processing, we next assessed the perceptual frequency equivalence between the two modalities using auditory and tactile pulse stimuli of simple and complex temporal features in cross-sensory frequency discrimination experiments. Identical temporal stimulation patterns in tactile and auditory afferents produced equivalent perceived frequencies, suggesting an analogous temporal frequency computation mechanism. The new insights into encoding tactile intensity through clustering of fixed charge electric pulses into bursts suggest a novel approach to convey varying contact forces to neural interface users, requiring no modulation of either stimulation current or base pulse frequency. Increasing control of the temporal patterning of pulses in cochlear implant users might improve pitch perception and speech comprehension. The perceptual correspondence between touch and hearing not only suggests the possibility of establishing cross-modal comparison standards for robust psychophysical investigations, but also supports the plausibility of cross-sensory substitution devices

The Relationship of Somatosensory Perception and Fine-Force Control in the Adult Human Orofacial System

The orofacial area stands apart from other body systems in that it possesses a unique performance anatomy whereby oral musculature inserts directly into the underlying cutaneous skin, allowing for the generation of complex three-dimensional deformations of the orofacial system. This anatomical substrate provides for the tight temporal synchrony between self-generated cutaneous somatosensation and oromotor control during functional behaviors in this region and provides the necessary feedback needed to learn and maintain skilled orofacial behaviors. The Directions into Velocity of Articulators (DIVA) model highlights the importance of the bidirectional relationship between sensation and production in the orofacial region in children learning speech. This relationship has not been as well-established in the adult orofacial system. The purpose of this observational study was to begin assessing the perception-action relationship in healthy adults and to describe how this relationship may be altered as a function of healthy aging. This study was designed to determine the correspondence between orofacial cutaneous perception using vibrotactile detection thresholds (VDT) and low-level static and dynamic force control tasks in three representative age cohorts. Correlational relationships among measures of somatosensory capacity and low-level skilled orofacial force control were determined for 60 adults (19-84 years). Significant correlational relationships were identified using non-parametric Spearman’s correlations with an alpha at 0.1 between the 5 Hz test probe and several 0.5 N low-level force control assessments in the static and slow ramp-and-hold condition. These findings indicate that as vibrotactile detection thresholds increase (labial sensation decreases), ability to maintain a low-level force endpoint decreases. Group data was analyzed using non-parametric Kruskal-Wallis tests and identified significant differences between the 5 Hz test frequency probe and various 0.5 N skilled force assessments for group variables such as age, pure tone hearing assessments, sex, speech usage and smoking history. Future studies will begin the processing of modeling this complex multivariate relationship in healthy individuals before moving to a disordered population

Gamma Band Oscillation Response to Somatosensory Feedback Stimulation Schemes Constructed on Basis of Biphasic Neural Touch Representation

abstract: Prosthetic users abandon devices due to difficulties performing tasks without proper graded or interpretable feedback. The inability to adequately detect and correct error of the device leads to failure and frustration. In advanced prostheses, peripheral nerve stimulation can be used to deliver sensations, but standard schemes used in sensorized prosthetic systems induce percepts inconsistent with natural sensations, providing limited benefit. Recent uses of time varying stimulation strategies appear to produce more practical sensations, but without a clear path to pursue improvements. This dissertation examines the use of physiologically based stimulation strategies to elicit sensations that are more readily interpretable. A psychophysical experiment designed to investigate sensitivities to the discrimination of perturbation direction within precision grip suggests that perception is biomechanically referenced: increased sensitivities along the ulnar-radial axis align with potential anisotropic deformation of the finger pad, indicating somatosensation uses internal information rather than environmental. Contact-site and direction dependent deformation of the finger pad activates complimentary fast adapting and slow adapting mechanoreceptors, exhibiting parallel activity of the two associate temporal patterns: static and dynamic. The spectrum of temporal activity seen in somatosensory cortex can be explained by a combined representation of these distinct response dynamics, a phenomenon referred in this dissertation to “biphasic representation.” In a reach-to-precision-grasp task, neurons in somatosensory cortex were found to possess biphasic firing patterns in their responses to texture, orientation, and movement. Sensitivities seem to align with variable deformation and mechanoreceptor activity: movement and smooth texture responses align with potential fast adapting activation, non-movement and coarse texture responses align with potential increased slow adapting activation, and responses to orientation are conceptually consistent with coding of tangential load. Using evidence of biphasic representations’ association with perceptual priorities, gamma band phase locking is used to compare responses to peripheral nerve stimulation patterns and mechanical stimulation. Vibrotactile and punctate mechanical stimuli are used to represent the practical and impractical percepts commonly observed in peripheral nerve stimulation feedback. Standard patterns of constant parameters closely mimic impractical vibrotactile stimulation while biphasic patterns better mimic punctate stimulation and provide a platform to investigate intragrip dynamics representing contextual activation.Dissertation/ThesisDoctoral Dissertation Biomedical Engineering 201