A recent research award from the Pennsylvania Lions Hearing Research Foundation to Paul Nealen of the Department of Biology will fund research aimed at improving hearing assist devices for the hearing impaired.
Humans are among the relatively rare animal taxa that perform ‘vocal learning’, in that we are born being unable to produce adult speech. Infants progress through stages of ‘babbling’ and vocal ‘practice’, and must hear their own vocal sounds in order to gradually shape them to match those in use by others around them. This dependence upon auditory feedback of vocalizations makes vocal learning difficult or impossible for persons of impaired hearing.
Cochlear implants can be used to provide rudimentary hearing in some young children with profound hearing loss, but the ability of cochlear implants to facilitate language learning and development remains poor. It is hypothesized that this weakness stems from the fact that cochlear implants do not provide all available vocal feedback to the inner ear.
When we speak, we normally hear the sound of own voice via two feedback pathways: from sound transmitted externally (aurally; through the air and to our ears) as well as cranially (via direct vibration of tissues between the 'voicebox' [larynx] and the cochlea of the inner ear). Cochlear implants capture and model the external (aural) sounds, but do not provide any of the cranial vocal feedback. The difference between these feedback pathways is apparent to anyone who has listened to a recording of their own voice – most persons report that their recorded voice sounds "odd”, or “funny”, because our recorded voices provided only aural, but not cranial, feedback (the so-called ‘answering machine effect’).
Nealen has devised a method to estimate cranial vocal feedback, via a combination of digital recordings/playback, perceptual discrimination, and signal spectral processing. The goal of this research is to describe the relative differences between aural and cranial vocal feedback, in order to inform the engineering of the next generation of cochlear implants. Research facility support for this project will be provided by the Speech, Language, and Hearing Clinic of the Department of Communication Disorders, Special Education, and Disability Services.
The Pennsylvania Lions Hearing Research Foundation is a private, non-profit organization that supports hearing research. This is the third research award that Nealen has received from their organization.