Neural oscillator network modelling of auditory stream segregation

Imagine yourself at a dinner party. Five conversations are going on around the table, music hums in the background, cutlery rattles and glasses clink. Caught in a dull discussion about stock options, you're wishing you were with the people over your shoulder reminiscing about skiing in the Alps. No matter where you are, your brain is constantly buzzing in a world of sound. How are we able to choose what to tune in to?

Although individual sound sources (e.g. a voice, a humming fridge) change over time some features remain constant, like where they're coming from, whether they are high or low in pitch and how often they repeat. In a situation like the one described above we have some control over what we hear, we can focus on an individual voice or conversation whilst pushing other sounds into the background. There is evidence that the brain uses two strategies to differentiate sound sources:

1) by features (e.g. sources are high or low pitch, sources come from different locations), and

2) by timing and rhythm (people talk at different speeds and start/stop stop talking at different times).

The brain's sound processing pathways separate sounds by their features, resulting in, for example, different groups of neurons responding to high and low pitch sounds. Ongoing brain rhythms (oscillations in brain activity) can synchronise with specific sound sources in order to track them. Combined together this allows the brain to follow specific sound sources with groups of neurons tracking features and synchronisation of their activity tracking these features over time.

Dynamical systems is a field of mathematics describing processes (such as brain rhythms) that change over time. Amongst other types of dynamics, it has helped us understand oscillations and synchronisation across biology, physics, and chemistry to social networks and technological applications. Oscillations in the activity of neurons is important for lots of cognitive functions like making decisions, forming memories and enjoying music. The research here focuses on using mathematical theory about oscillations to develop a computer model of the brain regions involved in processing and segregating sound sources. The current state of the art in computer modelling has focused on the first strategy (separating by features). Here, the focus will be on integrating this with the second strategy, paying specific attention to how the brain uses timing and rhythm to segregate sounds. This is based on the hypothesis that synchronisation of oscillations is crucial for tracking sounds over time. Indeed, when we listen to repetitive sounds (like a simple musical rhythm) neurons in both auditory and motor regions of the brain start to fire in time to the beat, even when we aren't moving ourselves. The research aims to reveal how both of these regions working together enable us simultaneously keep track of both the sound source we're focusing on (stock options) and the one we'd like to really be paying attention to (skiing in the Alps).

The potential beneficiaries of this research are:

- Clinicians working on treatment of hearing disorders and their patients
- Companies and industry developing hearing technology
- Academics researching hearing disorders
- General public and students with an interest in brain research

The ability to segregate auditory objects is crucial for normal day to day communications (e.g. focusing on one voice in a noisy place), an ability that is compromised by hearing impairment and auditory system dysfunction. The proposed research will help to understand how auditory streaming functions with normal hearing, a necessary step for building a complete picture of the link between hearing impairment and comprised communication abilities. Therefore, future research stemming from this proposal could be used improve treatment decisions and treatment strategies, resulting in better outcomes for patients. Through links with a local hearing clinic, project staff will also seek to understand the experiences of patients with hearing disorders and discuss research with them. Project staff will attend and present findings at an industry conference attended by hearing healthcare professionals in order to identify opportunities for the research to be exploited in these ways.

The research could also be useful for companies that develop hearing technology such as cochlear implants and hearing aids. Again, a better understanding of auditory streaming will be informative for future improvements to the design and efficiency of such technology. Project staff will meet and discuss the research with a local company in order to better understand how the research could be applied in the hearing technology sector. The outcome of these discussions will feed in to interactions with healthcare professionals and the dissemination of research findings at an hearing technology industry conference.

Researchers working on understanding hearing loss and auditory dysfunction will benefit from the results of this research. A clearer understanding of both where and how auditory streams are encoded in the brain will feed into research in these areas. The principal investigator will benefit in this way, as they aim to develop future projects geared toward understanding how damage or dysfunction in the auditory system translates to difficulties with segregating auditory objects and communication. To achieve these aims the research will be disseminated in academic journals and at international conferences that are read and attended by a broad cross section of auditory scientists.

Members of the public and students with an interest in science will benefit from this project. Its staff will participate in public science events, giving interactive presentations on research both directly from the project and from related areas. The aim is to engage the public, and get them thinking about perception as an active process and how what you hear depends on computations in the brain, not just the sound waves arriving at the ear and cochlea. Many young adults who may be thinking about going to university or a career in science do not realise the breadth of opportunities available and are not aware of connections between subjects like mathematics and neuroscience. With the aim of inspiring the next generation of scientists and researchers, project staff will give talks on these topics at schools.