Matt’s research is preoccupied with auditory evoked potentials, and biomedical instrumentation.
Auditory evoked potentials (aka the Auditory Brainstem Response, ‘ABR’) are scalp-recorded electrical responses of the brain elicited by acoustic stimuli. They are composed of several waves (peaks), which relate to the synchronous electrical activity of the auditory nerve, caudal, and rostral auditory brainstem structures. ABRs are used for hearing threshold estimation, especially for neonatal screening, long term monitoring of intensive care unit patients with traumatic brain injury (TBI), and intraoperative monitoring (IOM) for any skull base surgery.
Australia is currently in the process of implementing Universal Hearing Screening for all newborns. Universal Hearing Screening will require testing of upwards of 240,000 neonates each year. Using current methods, ABR neonatal hearing tests can take upwards of 20 minutes. The motivation for Matt’s research is to investigate the possibility of reducing the time required to complete the ABR hearing screening test, and to improve the quality of diagnostic information available from the test.
To reduce screening times, and to improve the quality of hearing diagnostics, Matt has been experimenting with different stimuli and protocols, such as:
Chirps
Chirp stimuli compensate for travelling wave delays along the basilar membrane – the vibrating partition that stimulates hair cells in the cochlea. These travelling wave delays are frequency dependent, so the rising frequency chirp attempts to synchronise the arrival time of each frequency component. This results in maximal basilar membrane displacement and a larger evoked response.
Toneburst
Sequences
Audiologists are always interested in the hearing threshold at different frequencies, but the lower frequencies are notoriously difficult to record an evoked response from. Tone burst sequences assist with this, by keeping the high frequency portions of the cochlea ‘occupied’ when the low frequency response is being recorded. This is a form of ‘high-frequency masking’, but the additional benefit is that the response from the high and mid frequencies is recorded within the same protocol. Ultimately, this leads to a higher quality of diagnostic information within clinical time constraints.
Maximal
Length Sequences
Maximal Length Sequences (MLS) are a pseudorandom sequence of clicks (or tones, or chirps) that offer a drastically reduced test time when acquiring the ABR. The evoked response from each click overlaps with the next, but a sophisticated method of deconvolution allows the true ABR to be extracted from ‘the mess’. When used in conjunction with binaural interleaving, MLS protocols can acquire a full gamut of diagnostic data within a very short amount of time.