Somatosensory Precision in Speech Production

SummarySpeech production is dependent on both auditory and somatosensory feedback [1–3]. Although audition may appear to be the dominant sensory modality in speech production, somatosensory information plays a role that extends from brainstem responses to cortical control [4–6]. Accordingly, the motor commands that underlie speech movements may have somatosensory as well as auditory goals [7]. Here we provide evidence that, independent of the acoustics, somatosensory information is central to achieving the precision requirements of speech movements. We were able to dissociate auditory and somatosensory feedback by using a robotic device that altered the jaw's motion path, and hence proprioception, without affecting speech acoustics. The loads were designed to target either the consonant- or vowel-related portion of an utterance because these are the major sound categories in speech. We found that, even in the absence of any effect on the acoustics, with learning subjects corrected to an equal extent for both kinds of loads. This finding suggests that there are comparable somatosensory precision requirements for both kinds of speech sounds. We provide experimental evidence that the neural control of stiffness or impedance—the resistance to displacement—provides for somatosensory precision in speech production [8–10]

Speech motor learning in profoundly deaf adults,”

Speech production, like other sensorimotor behaviors, relies on multiple sensory inputs-audition, proprioceptive inputs from muscle spindles and cutaneous inputs from mechanoreceptors in the skin and soft tissues of the vocal tract. However, the capacity for intelligible speech by deaf speakers suggests that somatosensory input alone may contribute to speech motor control and perhaps even to speech learning. We assessed speech motor learning in cochlear implant recipients who were tested with their implants turned off. A robotic device was used to alter somatosensory feedback by displacing the jaw during speech. We found that implant subjects progressively adapted to the mechanical perturbation with training. Moreover, the corrections that we observed were for movement deviations that were exceedingly small, on the order of millimeters, indicating that speakers have precise somatosensory expectations. Speech motor learning is substantially dependent on somatosensory input. One of the puzzles of human language is that individuals who become deaf as adults remain capable of producing quite intelligible speech for many years in the absence of auditory input 1-3 . This ability suggests that speech production is substantially dependent on nonauditory sensory information and particularly on afferent input from the somatosensory system. Previous studies that have sought to identify a somatosensory basis for speech motor function have done so in the presence of auditory inputs 4-12 and therefore any effects that were observed may have resulted from the presence of the auditory signal. Here we found that somatosensory input on its own may underlie speech production and speech motor learning. We studied speech learning in cochlear implant recipients, who we tested with their implants turned off. We assessed speech learning by using a robotic device that applied forces that displaced the jaw and altered somatosensory feedback during speech. We found that implant subjects progressively corrected their speech movements to offset errors in the motion path of the jaw even in the absence of auditory input. Indeed, the levels of adaptation that we observed were comparable for implant subjects and normal-hearing control subjects. This indicates that speech learning is substantially dependent on somatosensory feedback. Speech production must be understood both as an auditory 13-15 and a somatosensory task RESULTS Five post-lingually deaf adults participated in the study We plotted jaw trajectories in speech for a representative implant subject and a normal-hearing control subject Kinematic and acoustical tests of adaptation were conducted quantitatively on a per subject basis using analysis of variance (ANOVA) followed by Tukey's honestly significantly different (HSD) post hoc tests. Subjects showed similar kinematic patterns in both the implant and control groups. In the implant group, adaptation was observed in all five subjects, as indicated by a significant decrease in curvature over the training period (P o 0.01 for all subjects

Mechanical and tribological performance of a hybrid MMC coating deposited on Al–17Si piston alloy by laser composite surfacing technique

Laser composite surfacing (LCS) is a photon driven manufacturing technology that can be utilized for depositing hybrid metal matrix composite coatings (HMMC) on softer Ti/Al/Mg alloys to enhance their tribo-mechanical properties. LCS offers the advantages of higher directionality, localized microstructural refinement and higher metallurgical bonding between coating and substrate. The current research presents the tribo-mechanical evaluation and characterization of solid lubricant based Ni–WC coatings deposited by LCS on Al–Si piston alloy by varying the concentration of graphite between 5-to-15-weight percentage. The tribological behavior of LCS samples was investigated using a ball-on-plate tribometer. Results indicate that the surface hardness, wear rate and friction coefficient of the Al–Si hypereutectic piston alloy were improved after LCS of graphite based HMMC coatings. The maximum surface hardness of 781Hv was acquired for the Ni–WC coating containing 5 wt% graphite. The friction coefficient of Al–Si under dry sliding conditions was reduced from 0.47 to 0.21. The reduction in the friction coefficient was attributed to the formation of a shearable transfer layer, which prevented delamination and reduced adhesion, abrasion and fatigue cracking