Robert Luke

Source Analysis Of Auditory Steady-State Responses In Acoustic And Electric Hearing

ABSTRACT Speech is a complex signal containing a broad variety of acoustic information. For accurate speech reception, the listener must perceive modulations over a range of envelope frequencies. Perception of these modulations is particularly important for cochlear implant (CI) users, as all commercial devices use envelope coding strategies. Prolonged deafness affects the auditory pathway. However, little is known of how cochlear implantation affects the neural processing of modulated stimuli. This study investigates and contrasts the neural processing of envelope rate modulated signals in acoustic and CI listeners. Auditory steady‐state responses (ASSRs) are used to study the neural processing of amplitude modulated (AM) signals. A beamforming technique is applied to determine the increase in neural activity relative to a control condition, with particular attention paid to defining the accuracy and precision of this technique relative to other tomographies. In a cohort of 44 acoustic listeners, the location, activity and hemispheric lateralisation of ASSRs is characterised while systematically varying the modulation rate (4, 10, 20, 40 and 80 Hz) and stimulation ear (right, left and bilateral). We demonstrate a complex pattern of laterality depending on both modulation rate and stimulation ear that is consistent with, and extends, existing literature. We present a novel extension to the beamforming method which facilitates source analysis of electrically evoked auditory steady‐state responses (EASSRs). In a cohort of 5 right implanted unilateral CI users, the neural activity is determined for the 40 Hz rate and compared to the acoustic cohort. Results indicate that CI users activate typical thalamic locations for 40 Hz stimuli. However, complementary to studies of transient stimuli, the CI population has atypical hemispheric laterality, preferentially activating the contralateral hemisphere. HIGHLIGHTSBeamforming analysis of auditory steady state responses to a range of modulation rates.Accuracy and precision of beamforming method is investigated.Source analysis of electrically evoked auditory steady‐state responses.Cochlear implant population shows atypical hemispheric laterality of steady state responses.

Kalman Filter Based Estimation of Auditory Steady State Response Parameters

Auditory steady state responses (ASSRs) are brain responses to modulated or repetitive stimuli that can be captured in the EEG recording. ASSRs can be used as an objective measure to clinically determine frequency specific hearing thresholds, to quantify the sensitivity of the auditory system to modulation, and have been related to speech intelligibility. However, the detection of ASSRs is difficult due to the low signal to noise ratio of the responses. Moreover, minimizing measurement time is important for clinical applications. Traditionally ASSRs are analyzed using discrete Fourier transform (DFT) based methods. We present a Kalman filter based ASSR analysis procedure and illustrate several benefits over traditional DFT based methods. We show on a data set of 320 measurements that the proposed method reaches valid amplitude estimates significantly faster than the state of the art DFT method. Further, we provide two extensions to the proposed method. First, we demonstrate information can be incorporated from multiple recording electrodes by extending the system model. Secondly, we extend the model to incorporate artifacts from cochlear implant (CI) stimulation and demonstrate electrically evoked auditory steady state responses (EASSRs) can be accurately measured.