Human echolocation: Basic mechanisms and neuroplasticity

The human brain has many amazing perceptual abilities. One of these is the ability to echolocate. To echolocate, an organism makes a sound, and listens to the returning echoes. Echolocation is best known from bats. In people it has received comparably little research attention, even though investigations in the 1940s already established the reality of this skill.

Recent studies suggest that echolocation may be related to vision. For example, blind echolocation experts can sense their environment through echolocation in a way that seems uncannily similar to vision, and neuroimaging research has shown that blind echo experts use 'visual' brain areas to process echoes. Interestingly, and relatedly, even though echolocation is mediated through hearing, recent research suggests that there might be different processes involved. Recent echolocation research has also confirmed that young people can learn echolocation. Yet, even though there are increasing numbers of people with age related vision loss for whom echolocation might be useful, it has not been investigated how older people might learn it.

Following up on these recent developments, the proposed research will investigate how echolocation is related to vision, and 'regular' spatial hearing, and it will investigate this in young and old people. The overarching goal is to advance our understanding of information processing in the human brain. The research has the potential to improve well-being of people with vision loss.

The proposed research will make us of behavioural experiments and brain imaging techniques (magnetic resonance imaging, MRI). We will train blind and sighted, and young and old people to echolocate, and we will measure their echolocation behaviour and their brain activity and structure with MRI. Furthermore, we will measure how echolocation is related to people's 'regular' spatial hearing. We will do this by investigating if echolocation improves people's abilities to localize sound sources, and if people's echolocation accuracy is influenced by their expectations about the echolocation sounds.

The impact strategy for the proposed research is based on communicating our scientific results to academics, professionals, and the general public. We propose to do this via presentation at scientific conferences, publication of articles in scientific and professional journals, public lectures, and working with the media to publicize our research, and through the creation of a website showcasing our findings. Furthermore, even though the research is focused on human brain and behaviour, our findings are expected to benefit research in engineering (remote sensing, signal acquisition and processing, development of assistive devices for blind people). In addition, the research is expected to inform echolocation research in non-human animals, and in this way it may lead to reduction of use of animals for research.

Within the UK approx. 360,000 people are registered partially sighted / blind, and approx. 300,000 of these are older than 50 years. There is already scientific evidence that echolocation offers functional advantages to blind people, for example to detect and avoid obstacles during walking, or to navigate unfamiliar environments. Yet, within the UK (but also worldwide) echolocation is not endorsed for mobility and orientation training for blind people. The proposed research will advance scientific understanding of echolocation and add to existing scientific evidence demonstrating usefulness of echolocation for blind people. In combination with the proposed impact strategy the proposed research has the potential to increase acceptance of echolocation as part of mobility and orientation training for blind people and in this way to improve well-being of people with visual impairments.

The scientific objectives of the proposed work are (1) Investigate which areas in the human brain are associated with echolocation (2) Measure how the ageing human brain learns to echolocate (3) Measure how echolocation is related to people's 'regular' spatial hearing. The proposed work will achieve these objectives using behavioural training, psychophysical testing, and magnetic resonance imaging (MRI), and by recruiting young and old sighted and blind participants.

Behavioural training will be implemented using tasks developed in past research, that require participants to determine location (azimuth, distance) and sizes of surfaces, or to approach an object placed within an enclosed area.

Psychophysical testing will measure people's echo-perception of location and size. We will also use psychophysical tests to measure participants' spatial source hearing abilities (i.e. not echolocation).

Magnetic resonance imaging will use functional MRI (fMRI) and anatomical scans (MRI). Data will be analysed using standard MRI analysis software packages (Brain Voyager, Free Surfer, SPM) and custom written analysis routines (Matlab). To minimize MR artefacts due to head movements, participants will not actively echolocate during scanning, but passively listen to echolocation recordings, an approach we developed in past research. Auditory fMRI scans will use sparse sampling, an acquisition technique commonly used for fMRI involving auditory stimulation.

*Participants* Experiments will be conducted with people who are either sighted (normal or corrected to normal vision) or blind (total blindness & ability to detect bright light), and who are either young (<35 yrs) or old (>55 yrs). Participants must have no history of neurological disease and audiometric thresholds within age specific reference norms (ISO 7029). Blind participants will be recruited regardless of age at onset of vision loss, but we will match onset of vision loss across age groups.

The research will lead to new insights regarding usefulness of echolocation for young and old blind people. Of primary relevance in this context are the behavioural data, but neuroimaging data as well, because they (a) corroborate behavioural results and (b) lead to identification of brain areas involved in echolocation. This may also foster development of neural stimulation protocols to facilitate learning (e.g. Cohen Kadosh et al (2010). Current Biol 20: 2016-2020).

Primary impact of the work will be in regard to vision loss with respect to organizations, professionals, individuals, society. Furthermore, the research will have positive impact on project staff, science education and women in science.

Benefits with respect to Vision Loss
Within the UK there are about 360k people with vision loss, and about 80% of these are older than 50 years. In the UK individuals with vision loss receive assistance through organizations and professionals. For example, upon diagnosis, NHS providers refer individuals to local authority professionals and organizations (e.g. Royal National Institute for the Blind, Action for Blind People). Currently, echolocation is not widely endorsed. The proposed research will contribute to knowledge about echolocation, which will be communicated to professionals and organizations. In this way, the project will lead to wider endorsement of echolocation as part of mobility and orientation training. Furthermore, the research will increase quality of life of individuals with vision loss and their relatives mediated through organizations (see above) and directly. For example, via public engagement the research will increase knowledge about echolocation and vision loss in the general public. In this way it is expected that blind people are more likely to learn about echolocation, and to consider acquiring this skill, which would have positive impact on their mobility. Furthermore, as a result of the project sighted people will be more aware of echolocation and issues related to vision loss, which will have positive impact on how blind people (echolocating or not) are treated in society. Improvements in blind people's mobility will have positive impact on relatives who will feel more confident about the well-being of their blind child/ parent/etc. It is expected that benefits to individuals add up to socio-economic benefits. For example, consider that a blind person who echolocates uses the bus for a monthly 10 mile (20 minute) trip, instead of being driven by a relative. If we consider this at a scale of 1000 people, the use of echolocation would result in 120,000 miles/year not driven or 240,000 minutes/year that relatives could spend on other activities. We realize that these numbers are unlikely the direct consequence of our 3-year project, but the project has potential to lead up to numbers such as these.

Impact will also be achieved by informing development of assistive technology for blind people.

The PI has a good track record of public engagement, relevant connections to professionals, and collaborations, making these plans feasible.

Staff working on the project
PDRA working on the project will gain research expertise, author science papers, present on conferences, be involved in outreach. These skills will make them competitive on the job market. For the PI the project will enable her to further develop her reputation as an internationally leading expert in human echolocation, put her into excellent position to attract international funding into UK.

Science education / Women in science
Echolocation is a skill that intrigues people. Thus, it is an ideal vehicle to foster science education, because outreach events are likely to attract a good response from the general public. In my work to date I have also found that in particular female students are attracted to echolocation research. Thus, the project is likely to encourage female students to consider a career in science.