Vestibular attenuation to random-waveform galvanic vestibular stimulation during standing and treadmill walking.

The ability to move and maintain posture is critically dependent on motion and orientation information provided by the vestibular system. When this system delivers noisy or erred information it can, in some cases, be attenuated through habituation. Here we investigate whether multiple mechanisms of attenuation act to decrease vestibular gain due to noise added using supra-threshold random-waveform galvanic vestibular stimulation (GVS). Forty-five participants completed one of three conditions. Each condition consisted of two 4-min standing periods with stimulation surrounding a 1-h period of either walking with stimulation, walking without stimulation, or sitting quietly. An instrumented treadmill recorded horizontal forces at the feet during standing and walking. We quantified response attenuation to GVS by comparing vestibular stimulus-horizontal force gain between conditions. First stimulus exposure caused an 18% decrease in gain during the first 40 s of standing. Attenuation recommenced only when subjects walked with stimulation, resulting in a 38% decrease in gain over 60 min that did not transfer to standing following walking. The disparity in attenuation dynamics and absent carry over between standing and walking suggests that two mechanisms of attenuation, one associated with first exposure to the stimulus and another that is task specific, may act to decrease vestibulomotor gain.

Absence of Nonlinear Coupling Between Electric Vestibular Stimulation and Evoked Forces During Standing Balance.

The vestibular system encodes motion and orientation of the head in space and is essential for negotiating in and interacting with the world. Recently, random waveform electric vestibular stimulation has become an increasingly common means of probing the vestibular system. However, many of the methods used to analyze the behavioral response to this type of stimulation assume a linear relationship between frequencies in the stimulus and its associated response. Here we examine this stimulus-response frequency linearity to determine the validity of this assumption. Forty-five university-aged subjects stood on a force-plate for 4 min while receiving vestibular stimulation. To determine the linearity of the stimulus-response relationship we calculated the cross-frequency power coupling between a 0 and 25 Hz bandwidth limited white noise stimulus and induced postural responses, as measured using the horizontal forces acting at the feet. Ultimately, we found that, on average, the postural response to a random stimulus is linear across stimulation frequencies. This result supports the use of analysis methods that depend on the assumption of stimulus-response frequency linearity, such as coherence and gain, which are commonly used to analyze the body's response to random waveform electric stimuli.

Hearing care and management priority among parents of children with Down syndrome: a grounded theory.

OBJECTIVE: This study qualitatively explored the factors that influence how parents of children who are Deaf or hard-of-hearing with Down syndrome prioritise hearing care and management and developed an associated theory to explain that priority. DESIGN: Grounded theory was used for the purposes of this qualitative study. Data were collected using in-depth interviews which were analysed using a three-tiered qualitative coding process. STUDY SAMPLE: Eighteen mothers of children who are Deaf or hard-of-hearing with Down syndrome participated in this study. RESULTS: The higher the extent of engaged professional support, perception of benefit for child, parent activation, and family engagement, the higher the priority for hearing care and management will likely be among parents of children who are Deaf or hard-of-hearing with Down syndrome. CONCLUSIONS: Understanding how parents of children who are Deaf or hard-of-hearing with Down syndrome decide to prioritise hearing care and management has implications for how hearing health providers and others provide care to parents to enhance priority for hearing-related needs.