Browsing by Subject "Neural prosthesis"

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Open Access
An information-theoretic analysis of spike processing in a neuroprosthetic model
(2007-05-03T18:53:57Z) Won, Deborah S.
Neural prostheses are being developed to provide motor capabilities to patients who suffer from motor-debilitating diseases and conditions. These brain-computer interfaces (BCI) will be controlled by activity from the brain and bypass damaged parts of the spinal cord or peripheral nervous system to re-establish volitional control of motor output. Spike sorting is a technologically expensive component of the signal processing chain required to interpret population spike activity acquired in a BCI. No systematic analysis of the need for spike sorting has been carried out and little is known about the effects of spike sorting error on the ability of a BCI to decode intended motor commands. We developed a theoretical framework and a modelling environment to examine the effects of spike processing on the information available to a BCI decoder. Shannon information theory was applied to simulated neural data. Results demonstrated that reported amounts of spike sorting error reduce mutual information (MI) significantly in single-unit spike trains. These results prompted investigation into how much information is available in a cluster of pooled signals. Indirect information analysis revealed the conditions under which pooled multi-unit signals can maintain the MI that is available in the corresponding sorted signals and how the information loss grows with dissimilarity of MI among the pooled responses. To reveal the differences in non-sorted spike activity within the context of a BCI, we simulated responses of 4 neurons with the commonly observed and exploited cosine-tuning property and with varying levels of sorting error. Tolerances of angular tuning differences and spike sorting error were given for MI loss due to pooling under various conditions, such as cases of inter- and/or intra-electrode differences and combinations of various mean firing rates and tuning depths. These analyses revealed the degree to which mutual information loss due to pooling spike activity depended upon differences in tuning between pooled neurons and the amount of spike error introduced by sorting. The theoretical framework and computational tools presented in this dissertation will BCI system designers to make decisions with an understanding of the tradeoffs between a system with and without spike sorting.
Open Access
The cochlear implant and possibilities for narrowing the remaining gaps between prosthetic and normal hearing.
(World journal of otorhinolaryngology - head and neck surgery, 2017-12) Wilson, Blake S
The cochlear implant has become the standard of care for severe or worse losses in hearing and indeed has produced the first substantial restoration of a lost or absent human sense using a medical intervention. However, the devices are not perfect and many efforts to narrow the remaining gaps between prosthetic and normal hearing are underway.To assess the present status of cochlear implants and to describe possibilities for improving them.The present-day devices work well in quiet conditions for the great majority of users. However, not all users have high levels of speech reception in quiet and nearly all users struggle with speech reception in typically noisy acoustic environments. In addition, perception of sounds more complex than speech, such as most music, is generally poor unless residual hearing at low frequencies can be stimulated acoustically in conjunction with the electrical stimuli provided by the implant. Possibilities for improving the present devices include increasing the spatial specificity of neural excitation by reducing masking effects or with new stimulus modes; prudent pruning of interfering or otherwise detrimental electrodes from the stimulation map; a further relaxation in the criteria for implant candidacy, based on recent evidence from persons with high levels of residual hearing and to allow many more people to benefit from cochlear implants; and "top down" or "brain centric" approaches to implant designs and applications.Progress in the development of the cochlear implant and related treatments has been remarkable but room remains for improvements. The future looks bright as there are multiple promising possibilities for improvements and many talented teams are pursuing them.
Open Access
Toward Better Representations of Sound with Cochlear Implants
(2015) Wilson, Blake Shaw
This dissertation is about the first substantial restoration of human sense using a medical intervention. In particular, the development of the modern cochlear implant (CI) is described, with a focus on sound processors for CIs. As of October 2015, more than 460 thousand persons had each received a single CI on one side or bilateral CIs for both sides. More than 75 percent of users of the present-day devices use the telephone routinely, including conversations with previously unknown persons and with varying and unpredictable topics. That ability is a long trip indeed from severe or worse losses in hearing. The sound processors, in conjunction with multiple sites of highly-controlled electrical stimulation in the cochlea, made the trip possible.
Many methods and techniques were used in the described research, including but not limited to those of signal processing, electrical engineering, neuroscience, speech science, and hearing science. In addition, the results were the products of collaborative efforts, beginning in the late 1970s. For example, our teams at the Duke University Medical Center and the Research Triangle Institute worked closely with investigators at 27 other universities worldwide.
The most important outcome from the research was unprecedented levels of speech reception for users of CIs, which moved a previously experimental treatment into the mainstream of clinical practice.