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Somatosensory Modulation during Speech Planning

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Previous studies have found that the detection of near-threshold stimuli is decreased immediately before movement and throughout movement production. This has been suggested to occur through the use of the internal forward model processing an efferent copy of the motor

Previous studies have found that the detection of near-threshold stimuli is decreased immediately before movement and throughout movement production. This has been suggested to occur through the use of the internal forward model processing an efferent copy of the motor command and creating a prediction that is used to cancel out the resulting sensory feedback. Currently, there are no published accounts of the perception of tactile signals for motor tasks and contexts related to the lips during both speech planning and production. In this study, we measured the responsiveness of the somatosensory system during speech planning using light electrical stimulation below the lower lip by comparing perception during mixed speaking and silent reading conditions. Participants were asked to judge whether a constant near-threshold electrical stimulation (subject-specific intensity, 85% detected at rest) was present during different time points relative to an initial visual cue. In the speaking condition, participants overtly produced target words shown on a computer monitor. In the reading condition, participants read the same target words silently to themselves without any movement or sound. We found that detection of the stimulus was attenuated during speaking conditions while remaining at a constant level close to the perceptual threshold throughout the silent reading condition. Perceptual modulation was most intense during speech production and showed some attenuation just prior to speech production during the planning period of speech. This demonstrates that there is a significant decrease in the responsiveness of the somatosensory system during speech production as well as milliseconds before speech is even produced which has implications for speech disorders such as stuttering and schizophrenia with pronounced deficits in the somatosensory system.

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2019-05

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The Influence of Walking Speed on Gaze Behaviors

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In this experiment, three cats walked freely in four different conditions (walking on a flat surface in the dark, walking on a flat surface in the light, along a horizontal ladder, and a stone-cluttered pathway) while gaze was recorded. Four

In this experiment, three cats walked freely in four different conditions (walking on a flat surface in the dark, walking on a flat surface in the light, along a horizontal ladder, and a stone-cluttered pathway) while gaze was recorded. Four gaze behaviors were identified based upon head and eye velocity parameters relative to the walking velocity of the cat: constant gaze, fixation, gaze shift away, and gaze shift toward (see Methods). The objective of the study was to determine whether speed influences the phase that these gaze behaviors occur, where phase is defined as the degree from 0-360 of the step cycle. In the step cycle, 0 degrees is defined as the start of swing of the right forelimb. Additionally, speed’s influence on the uniformity of gaze behaviors to the step cycle was investigated in the three cats. The cats performed complex walking tasks, or conditions, as well as simple tasks to determine if speed has a greater effect on gaze behavior timing when walking terrain was difficult. I hypothesized that 1) gaze-stride coordination would be influenced by speed, 2) faster steps would show improved gaze behavior uniformity between subjects, and 3) fast steps during complex walking tasks would show further improvement of gaze behavior uniformity between subjects. To, this end, recorded steps were first split into fast and slow steps based upon step duration parameters (see Methods). These fast and slow steps were confirmed as significantly different from one another using a one-way ANOVA test on a linear mixed effects model (Table 3). Then, a linear mixed effects model was made per walking condition to account for subject effects, and a two-way ANOVA test was performed on the model to compare the phases of gaze behaviors to the speed when they occurred. It was found that speed does not influence the phase that gaze behaviors occur, except for walking on a flat surface in the dark. However, post-hoc tests could not be run to determine which behaviors were affected by speed. (see Discussion). The insignificance of speed suggests that speed is accounted for by the visual center responsible for the control of gaze behavior (see Discussion). Aside from speed’s influence on phase, uniformity was examined using standard deviation (Figure 3 ). It was found that faster steps tend to adopt a “gaze stepping” behavior described in a previous paper (Rivers et al. 2014). In future studies, it would be useful to increase the number of subjects for a similar experiment to improve the robustness of the results to determine if the relationship between speed and gaze behaviors reported in this paper is accurately depicted.

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2019-05

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Startle-evoked movement in multi-jointed, two-dimensional reaching tasks

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Previous research has shown that a loud acoustic stimulus can trigger an individual's prepared movement plan. This movement response is referred to as a startle-evoked movement (SEM). SEM has been observed in the stroke survivor population where results have shown

Previous research has shown that a loud acoustic stimulus can trigger an individual's prepared movement plan. This movement response is referred to as a startle-evoked movement (SEM). SEM has been observed in the stroke survivor population where results have shown that SEM enhances single joint movements that are usually performed with difficulty. While the presence of SEM in the stroke survivor population advances scientific understanding of movement capabilities following a stroke, published studies using the SEM phenomenon only examined one joint. The ability of SEM to generate multi-jointed movements is understudied and consequently limits SEM as a potential therapy tool. In order to apply SEM as a therapy tool however, the biomechanics of the arm in multi-jointed movement planning and execution must be better understood. Thus, the objective of our study was to evaluate if SEM could elicit multi-joint reaching movements that were accurate in an unrestrained, two-dimensional workspace. Data was collected from ten subjects with no previous neck, arm, or brain injury. Each subject performed a reaching task to five Targets that were equally spaced in a semi-circle to create a two-dimensional workspace. The subject reached to each Target following a sequence of two non-startling acoustic stimuli cues: "Get Ready" and "Go". A loud acoustic stimuli was randomly substituted for the "Go" cue. We hypothesized that SEM is accessible and accurate for unrestricted multi-jointed reaching tasks in a functional workspace and is therefore independent of movement direction. Our results found that SEM is possible in all five Target directions. The probability of evoking SEM and the movement kinematics (i.e. total movement time, linear deviation, average velocity) to each Target are not statistically different. Thus, we conclude that SEM is possible in a functional workspace and is not dependent on where arm stability is maximized. Moreover, coordinated preparation and storage of a multi-jointed movement is indeed possible.

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2016-12