Temporal Processing In The Superior Olivary Complex: Impact Of Deafness And Peripheral Electrical Stimulation Strategies
Funder
National Health and Medical Research Council
Funding Amount
$225,500.00
Summary
The brain can use timing or temporal information to extract the frequency and location of sound. Timing information is coded by the pattern of responses of brain cells that match the period of the sound wave. These responses can be measured as small voltage spikes or action potentials. Integration of these responses from one brain-processing site to another relies on precise (temporally matched) firing among a population of cells that are activated in response to sound. Sound localisation relies ....The brain can use timing or temporal information to extract the frequency and location of sound. Timing information is coded by the pattern of responses of brain cells that match the period of the sound wave. These responses can be measured as small voltage spikes or action potentials. Integration of these responses from one brain-processing site to another relies on precise (temporally matched) firing among a population of cells that are activated in response to sound. Sound localisation relies on this temporal integration from information coming from both ears. Specifically, the integration of this information relies on the balance of incoming inputs from both ears, which maintains an appropriate time window depending on the location of sound in space. Recent evidence suggests that in deafness this process of integration is disrupted which may be possibly due to an inability to regulate the coherent activation of cells. This has implications for cochlear implant users whose ability to process temporal information is compromised by a loss of temporal coding ability resulting from prior deafness. In this project we will measure voltage changes occurring inside cells of the superior olivary complex, which contains a group of structures that integrate input from both ears. We will examine the ability of these cells to process temporal information in normal and deafened conditions. This study will lead not only to an understanding of basic mechanisms for auditory coding but also to improved electrical stimulation strategies for patients with cochlear implants.Read moreRead less
Improved Perception Of Temporal Information In Electrical Signals For Profoundly Deaf Users Of Cochlear Implants
Funder
National Health and Medical Research Council
Funding Amount
$170,440.00
Summary
The ultimate goal of this project is to improve the ability of cochlear implant users to understand speech. The way in which a speech signal varies in amplitude over time provides useful information to the listener about the content of the speech signal. Currently, the way that the acoustic signal amplitude is converted to electrical signal amplitude for cochlear implantees does not take into consideration the very significant loudness summation present in multiple-electrode electrical stimulati ....The ultimate goal of this project is to improve the ability of cochlear implant users to understand speech. The way in which a speech signal varies in amplitude over time provides useful information to the listener about the content of the speech signal. Currently, the way that the acoustic signal amplitude is converted to electrical signal amplitude for cochlear implantees does not take into consideration the very significant loudness summation present in multiple-electrode electrical stimulation. That is, when there are multiple sequential current pulses on different electrodes over a short time, the resultant loudness is greater than the loudness due to individual current pulses. The lack of consideration of loudness summation effects has led to the amplitude variations in the acoustic signal not being accurately represented in the loudness variation perceived by the cochlear implantee. This project aims to develop a practical way of more accurately representing speech signal amplitude fluctuations for cochlear implantees by studying the effects of loudness summation. A second aim of the project is to study the effects on perception of using differently-shaped current pulses from those currently used. There is evidence from physiology experiments that using different shapes might cause the electrical stimulation to activate a more narrowly-spaced set of auditory neurons for each electrode. The application of results of both these studies will lead directly to improved perception of speech and other sounds by cochlear implantees, thus improving their communication ability and quality of life.Read moreRead less
Using Contextual Effects To Test Theories Of Coding In Visual Cortex
Funder
National Health and Medical Research Council
Funding Amount
$200,500.00
Summary
The visual cortex is the main structure in the brain that processes the visual scene. Cells in the cortex respond selectively to features of the scene such as the orientation of objects, the direction they move and their brightness relative to the background. Cortical cells are arranged in a topographic map of visual space, so that nearby cells respond to light from nearby parts of the image. Recent advances have shown that cells talk to each other so a stimulus in one part of the visual field c ....The visual cortex is the main structure in the brain that processes the visual scene. Cells in the cortex respond selectively to features of the scene such as the orientation of objects, the direction they move and their brightness relative to the background. Cortical cells are arranged in a topographic map of visual space, so that nearby cells respond to light from nearby parts of the image. Recent advances have shown that cells talk to each other so a stimulus in one part of the visual field can influence the responses of cells looking at other regions. This communication between cells is important in guiding the brain to focus on areas of the visual scene that are most important, a process known as attention. An example would be that a mouse moving through the periphery of someone's vision would attract their attention away from objects elsewhere in the scene. This project is designed to study the way that cells in the visual cortex cooperate to guide attention. Attention is important because it reduces the need to process all the detail in the visual scene with the same level of accuracy, leaving more resources free to process what is important. Attention deficits are a problem for people with dyslexia, so understanding the physiological basis of attention is an important goal. As well as attention, the visual system has a range of other mechanisms to select important information from the visual scene. For example, visual adaptation tends to improve the ability to code changes in the visual scene at the expense of reducing the sensitivity of the system overall. This project will investigate the relationship between attentional and adaptive mechanisms in the visual cortex. We expect to establish the precise physiological mechanisms that drive adaptive and attentional mechanisms in the mammalian brain.Read moreRead less