Biology subjects

Maddox, R. K.

Publications and source records attributed to Maddox, R. K..

3 recordsLinked to original sources

bioRxiv2019

The parallel auditory brainstem response

The frequency-specific tone-evoked auditory brainstem response (ABR) is an indispensable tool in both the audiology clinic and research laboratory. Most frequently the toneburst ABR is used to estimate hearing thresholds in infants, toddlers and other patients for whom behavioral testing is not feasible. Therefore, results of the ABR exam form the basis for decisions regarding interventions and hearing habilitation with implications extending far into the childs future. Currently, responses are elicited by periodic sequences of toneburst stimuli presented serially to one ear at a time, which take a long time to measure multiple frequencies and intensities, and provide incomplete information if the infant wakes up early. Here we describe a new method, the parallel ABR (pABR), which uses randomly timed toneburst stimuli to simultaneously acquire ABR waveforms to 5 frequencies in both ears. Here we describe the pABR and quantify its effectiveness in addressing the greatest drawback of current methods: test duration. We show that in adults with normal hearing the pABR yields high-quality waveforms over a range of intensities, with similar morphology to the standard ABR in a fraction of the recording time. Furthermore, longer latencies and smaller amplitudes for low frequencies at a high intensity evoked by the pABR versus serial ABR suggest that responses may have better place specificity due to the masking provided by the other simultaneous toneburst sequences. Thus, the pABR has substantial potential for facilitating faster accumulation of more diagnostic information that is important for timely identification and treatment of hearing loss.

neuroscience↗

bioRxiv2019

Improvement in auditory spatial discrimination from ambiguous visual stimuli is not explained by ideal observer causal inference

In order to survive and function in the world, we must understand the content of our environment. This requires us to gather and parse complex, sometimes conflicting, information. Yet, the brain is capable of translating sensory stimuli from disparate modalities into a cohesive and accurate percept with little conscious effort. Previous studies of multisensory integration have suggested that the brains integration of cues is well-approximated by an ideal observer implementing Bayesian causal inference. However, behavioral data from tasks that include only one stimulus in each modality fail to capture what is in nature a complex process. Here we employed an auditory spatial discrimination task in which listeners were asked to determine on which side they heard one of two concurrently presented sounds. We compared two visual conditions in which task-uninformative shapes were presented in the center of the screen, or spatially aligned with the auditory stimuli. We found that performance on the auditory task improved when the visual stimuli were spatially aligned with the auditory stimuli--even though the shapes provided no information about which side the auditory target was on. We also demonstrate that a model of a Bayesian ideal observer performing causal inference cannot explain this improvement, demonstrating that humans deviate systematically from the ideal observer model.

animal behavior and cognition↗

bioRxiv2017

Auditory brainstem responses to continuous natural speech in human listeners

Speech is an ecologically essential signal whose processing begins in the subcortical nuclei of the auditory brainstem, but there are few experimental options for studying these early responses under natural conditions. While encoding of continuous natural speech has been successfully probed in the cortex with neurophysiological tools such as electro- and magnetoencephalography, the rapidity of subcortical response components combined with unfavorable signal to noise ratios has prevented application of those methods to the brainstem. Instead, experiments have used thousands of repetitions of simple stimuli such as clicks, tonebursts, or brief spoken syllables, with deviations from those paradigms leading to ambiguity in the neural origins of measured responses. In this study we developed and tested a new way to measure the auditory brainstem response to ongoing, naturally uttered speech. We found a high degree of morphological similarity between the speech-evoked auditory brainstem responses (ABR) and the standard click-evoked ABR, notably a preserved wave V, the most prominent voltage peak in the standard click-evoked ABR. Because this method yields distinct peaks at latencies too short to originate from the cortex, the responses measured can be unambiguously determined to be subcortical in origin. The use of naturally uttered speech to evoke the ABR allows the design of engaging behavioral tasks, facilitating new investigations of the effects of cognitive processes like language processing and attention on brainstem processing.\n\nSIGNIFICANCE STATEMENTSpeech processing is usually studied in the cortex, but it starts in the auditory brainstem. However, a paradigm for studying brainstem processing of continuous natural speech in human listeners has been elusive due to practical limitations. Here we adapt methods that have been employed for studying cortical activity to the auditory brainstem. We measure the response to continuous natural speech and show that it is highly similar to the click-evoked response. The method also allows simultaneous investigation of cortical activity with no added recording time. This discovery paves the way for studies of speech processing in the human brainstem, including its interactions with higher order cognitive processes originating in the cortex.

neuroscience↗