Use of ASSR in estimation of hearing thresholds for cochlear implant users

Sisäkorvaistute on osittain kirurgisella toimenpiteellä korvaan asetettu elektroninen laite. Sen avulla ohitetaan vahingoittunut sisäkorva ja voidaan tuottaa kuurolle tai vakavasti kuulovammaiselle henkilölle ääniaistimuksia. Se tuottaa sähköisen ärsykkeen, joka ohittaa vahingoittuneet tai puuttuvat simpukan karvasolut ja stimuloi suoraan kuulohermoja. Kuulon testaus perinteisillä menetelmillä perustuu potilaan antamaan subjektiiviseen palautteeseen. Lapsilta ja vaikeasti testattavilta potilailta tällaisen palautteen saaminen on mahdotonta. Kuulon mittaus ilman potilaan aktiivista osallistumista ja yhteistyötä on mahdollista objektiivisia kuulonmittausmenetelmiä käyttäen. Objektiivisten kuulonmittausmenetelmien tarve on kasvanut maailmanlaajuisen vastasyntyneiden kuulon tutkimuksen myötä. Auditory steady-state response (ASSR) on uusi tutkimusmenetelmä, jolla voidaan mitata ääniärsykkeen tuottamia aivorunko- tai kortikaalivasteita. Sen avulla on mahdollista objektiivisesti arvioida potilaan kuulokynnys taajuusspesifisti. ASSR:n avulla ärsykkeet voidaan antaa suoraan sisäkorvaistutteen kautta, joka mahdollistaa sisäkorvaistutepotilaiden objektiivisen kuulonmittauksen. Tämän tutkimuksen tarkoituksena oli tutkia ASSR-vasteita sisäkorvaistutepotilailta ja selvittää voiko näitä vasteita käyttää apuna lasten ja vaikeasti testattavien potilaiden istutteen säätämisessä. Tutkimuksen tulokset viittaavat vahvasti siihen, että sisäkorvaistutteen kautta stimuloituja ASSR-vasteiden parametreja voidaan käyttää potilaan audiogrammin estimointiin. Jatkotutkimuksien myötä voi olla mahdollista, että niitä voidaan käyttää hyväksi sisäkorvaistutteen prosessorin parametrien ohjelmoinnissa.A cochlear implant is a surgically implanted electronic device that bypasses damaged inner ear and provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. It produces an electrical stimulus, which bypasses the damaged or missing hair cells and stimulates the remaining auditory neurons directly. Hearing testing by traditional methods is subjective and is based on the sound perception that patient reports. From children or difficult-to-test patients this kind of feedback is not possible to receive. To define the patient's hearing ability without active participation or cooperation, objective hearing tests can be applied. Since the worldwide introduction of hearing screening in newborns, the need for objective audiometric techniques to quantify hearing thresholds has increased. Auditory steady state response (ASSR) is a new research method for determining brainstem or cortical responses caused by sound stimuli. With the ASSR method it may be possible to record responses elicited by sound stimuli given through the cochlear implant. This could offer an opportunity to objectively determine an implanted patient's hearing threshold. The purpose of this research was to study ASSR responses with cochlear implant patients and to determine how ASSR can help in programming implant processor with difficult-to-test patients and children who cannot report their auditory perception. The results of this study strongly suggest that ASSR parameters measured using stimulation through cochlear implant can be used in estimation of patient's audiogram. With further study it might be used in determining the parameters for the programming of the implant processor

LOUDNESS PERCEPTION AT AND NEAR ELEVATED THRESHOLD: IS SOFT STILL SOFT?

Background: Two differing models of loudness recruitment (abnormally fast growth of loudness above elevated thresholds) for individuals with sensory hearing loss have been described (Buus & Florentine, 2002; Moore & Glasberg, 2004). The two models provide conflicting data related to perceived loudness at elevated thresholds and loudness growth near threshold in listeners with sensory hearing loss compared to normally hearing listeners. The present study was conducted to gain insight into this discrepancy. Methods: 29 listeners with normal hearing and 29 listeners with hearing loss participated in a simple yes/no detection task for 4000 Hz tones presented at and near their hearing threshold (at -4, 0, 4, 10, and 16 SL) while their pupil dilation response was recorded. Participants also completed a subjective rating task to judge the loudness of the same tones and other at higher levels up to 28 dB SL. Results: A significant difference between groups was seen in the pupil dilation response at threshold (0 SL) and 10 SL conditions. At threshold, pupil dilation in normal hearing listeners initiated earlier and was sustained longer compared to listeners with hearing loss consistent with increased difficulty of sound detection at threshold. Similar response behavior was observed at -4 SL. At 10 SL, pupil dilation in listeners with hearing loss was sustained longer compared to normal hearing listeners. Pupil dilation to tones at other levels (4 and 16 SL conditions) was not different between groups. Both groups subjectively rated the loudness of tones at all levels similarly with similar loudness growth patterns. Conclusion: Results suggest that normal hearing listeners experienced more difficulty in the sound detection task at threshold, as well as more uncertainty in decision making. This observation may be consistent with a louder perception for tones at threshold in listeners with hearing loss, which supports the softness imperception loudness model put forth by Florentine et al. In general, caution should be exercised when interpreting pupillary responses to directly indicate perceived loudness or psychoacoustic sensation as task induced cognitive processing may more heavily contribute to the response

Decoding Electrophysiological Correlates of Selective Attention by Means of Circular Data

Sustaining our attention to a relevant sensory input in a complex listening environment, is of great importance for a successful auditory communication. To avoid the overload of the auditory system, the importance of the stimuli is estimated in the higher levels of the auditory system. Based on these information, the attention is drifted away from the irrelevant and unimportant stimuli. Long-term habituation, a gradual process independent from sensory adaptation, plays a major role in drifting away our attention from irrelevant stimuli. A better understanding of attention-modulated neural activity is important for shedding light on the encoding process of auditory streams. For instance, these information can have a direct impact on developing smarter hearing aid devices in which more accurate objective measures can be used to re ect the hearing capabilities of patients with hearing pathologies. As an example, an objective measures of long-term habituation with respect to di erent level of sound stimuli can be used more accurately for adjustment of hearing aid devices in comparison to verbal reports. The main goal of this thesis is to analyze the neural decoding signatures of long-term habituation and neural modulations of selective attention by exploiting circular regularities in electrophysiological (EEG) data, in which we can objectively measure the level of attentional-binding to di erent stimuli. We study, in particular, the modulations of the instantaneous phase (IP) in event related potentials (ERPs) over trials for di erent experimental settings. This is in contrast to the common approach where the ERP component of interest is computed through averaging a su ciently large number of ERP trials. It is hypothesized that a high attentional binding to a stimulus is related to a high level of IP cluster. As the attention binding reduces, IP is spread more uniformly on a unit circle. This work is divided into three main parts. In the initial part, we investigate the dynamics of long-term habituation with di erent acoustical stimuli (soft vs. loud) over ERP trials. The underlying temporal dynamics in IP and the level of phase cluster of the ERPs are assessed by tting circular probability functions (pdf) over data segments. To increase the temporal resolution of detecting times at which a signi cant change in IP occurs, an abrupt change point model at di erent pure-tone stimulations is used. In a second study, we improve upon the results and methodology by relaxing some of the constrains in order to integrate the gradual process of long-term habituation into the model. For this means, a Bayesian state-space model is proposed. In all of the aforementioned studies, we successfully classi ed between di erent stimulation levels, using solely the IP of ERPs over trials. In the second part of the thesis, the experimental setting is expanded to contain longer and more complex auditory stimuli as in real-world scenarios. Thereby, we study the neural-correlates of attention in spontaneous modulations of EEG (ongoing activity) which uses the complete temporal resolution of the signal. We show a mapping between the ERP results and the ongoing EEG activity based on IP. A Markov-based model is developed for removing spurious variations that can occur in ongoing signals. We believe the proposed method can be incorporated as an important preprocessing step for a more reliable estimation of objective measures of the level of selective attention. The proposed model is used to pre-process and classify between attending and un-attending states in a seminal dichotic tone detection experiment. In the last part of this thesis, we investigate the possibility of measuring a mapping between the neural activities of the cortical laminae with the auditory evoked potentials (AEP) in vitro. We show a strong correlation between the IP of AEPs and the neural activities at the granular layer, using mutual information.Die Aufmerksamkeit auf ein relevantes auditorisches Signal in einer komplexen H orumgebung zu lenken ist von gro er Bedeutung f ur eine erfolgreiche akustische Kommunikation. Um eine Uberlastung des H orsystems zu vermeiden, wird die Bedeutung der Reize in den h oheren Ebenen des auditorischen Systems bewertet. Basierend auf diesen Informationen wird die Aufmerksamkeit von den irrelevanten und unwichtigen Reizen abgelenkt. Dabei spielt die sog. Langzeit- Habituation, die einen graduellen Prozess darstellt der unabh angig von der sensorischen Adaptierung ist, eine wichtige Rolle. Ein besseres Verst andnis der aufmerksamkeits-modulierten neuronalen Aktivit at ist wichtig, um den Kodierungsprozess von sog. auditory streams zu beleuchten. Zum Beispiel k onnen diese Informationen einen direkten Ein uss auf die Entwicklung intelligenter H orsysteme haben bei denen genauere, objektive Messungen verwendet werden k onnen, um die H orf ahigkeiten von Patienten mit H orpathologien widerzuspiegeln. So kann beispielsweise ein objektives Ma f ur die Langzeit- Habituation an unterschiedliche Schallreize genutzt werden um - im Vergleich zu subjektiven Selbsteinsch atzungen - eine genauere Anpassung der H orsysteme zu erreichen. Das Hauptziel dieser Dissertation ist die Analyse neuronaler Dekodierungssignaturen der Langzeit- Habituation und neuronaler Modulationen der selektiver Aufmerksamkeit durch Nutzung zirkul arer Regularit aten in elektroenzephalogra schen Daten, in denen wir objektiv den Grad der Aufmerksamkeitsbindung an verschiedene Reize messen k onnen. Wir untersuchen insbesondere die Modulation der Momentanphase (engl. Instantaneous phase, IP) in ereigniskorrelierten Potenzialen (EKPs) in verschiedenen experimentellen Settings. Dies steht im Gegensatz zu dem traditionellen Ansatz, bei dem die interessierenden EKP-Komponenten durch Mittelung einer ausreichend gro en Anzahl von Einzelantworten im Zeitbereich ermittelt werden. Es wird vermutet, dass eine hohe Aufmerksamkeitsbindung an einen Stimulus mit einem hohen Grad an IP-Clustern verbunden ist. Nimmt die Aufmerksamkeitsbindung hingegen ab, so ist die Momentanphase uniform auf dem Einheitskreis verteilt. Diese Arbeit gliedert sich in drei Teile. Im ersten Teil untersuchen wir die Dynamik der Langzeit-Habituation mit verschiedenen akustischen Reizen (leise vs. laut) in EKP-Studien. Die zugrundeliegende zeitliche Dynamik der Momentanphase und die Ebene des Phasenclusters der EKPs werden durch die Anpassung von zirkul aren Wahrscheinlichkeitsfunktionen (engl. probability density function, pdf) uber Datensegmente bewertet. Mithilfe eines sog. abrupt change-point Modells wurde die zeitliche Au osung der Daten erh oht, sodass signi kante Anderungen in der Momentanphase bei verschiedenen Reintonstimulationen detektierbar sind. In einer zweiten Studie verbessern wir die Ergebnisse und die Methodik, indem wir einige der Einschr ankungen lockern, um den gradualen Prozess der Langzeit-Habituation in das abrupt changepoint Modell zu integrieren. Dazu wird ein bayes`sches Zustands-Raum-Modell vorgeschlagen. In den zuvor genannten Studien konnte erfolgreich mithilfe der Momentanphase zwischen verschiedenen Stimulationspegeln unterschieden werden. Im zweiten Teil der Arbeit wird der experimentelle Rahmen erweitert, um komplexere auditorische Reize wie in realen H orsituationen untersuchen zu k onnen. Dabei analysieren wir die neuronalen Korrelate der Aufmerksamkeit anhand spontaner Modulationen der kontinuierlichen EEG-Aktivit at, die eine zeitliche Au osung erm oglicht. Wir zeigen eine Abbildung zwischen den EKP-Ergebnissen und der kontinuierlichen EEG-Aktivit at auf Basis der Momentanphase. Ein Markov-basiertes Modell wird entwickelt, um st orende Variationen zu entfernen, die in kontinuierlichen EEG-Signalen auftreten k onnen. Wir glauben, dass die vorgeschlagene Methode als wichtiger Vorverarbeitungsschritt zur soliden objektiven Absch atzung des Aufmerksamkeitsgrades mithilfe von EEG-Daten verwendet werden kann. In einem dichotischen Tonerkennungsexperiment wird das vorgeschlagene Modell zur Vorverarbeitung der EEG-Daten und zur Klassi zierung zwischen gerichteten und ungerichteten Aufmerksamkeitszust anden erfolgreich verwendet. Im letzten Teil dieser Arbeit untersuchen wir den Zusammenhang zwischen den neuronalen Aktivit aten der kortikalen Laminae und auditorisch evozierten Potentialen (AEP) in vitro im Tiermodell. Wir zeigen eine starke Korrelation zwischen der Momentanphase der AEPs und den neuronalen Aktivit aten in der Granularschicht unter Verwendung der Transinformation

Determination and evaluation of clinically efficient stopping criteria for the multiple auditory steady-state response technique

Background: Although the auditory steady-state response (ASSR) technique utilizes objective statistical detection algorithms to estimate behavioural hearing thresholds, the audiologist still has to decide when to terminate ASSR recordings introducing once more a certain degree of subjectivity. Aims: The present study aimed at establishing clinically efficient stopping criteria for a multiple 80-Hz ASSR system. Methods: In Experiment 1, data of 31 normal hearing subjects were analyzed off-line to propose stopping rules. Consequently, ASSR recordings will be stopped when (1) all 8 responses reach significance and significance can be maintained for 8 consecutive sweeps; (2) the mean noise levels were ≤ 4 nV (if at this “≤ 4-nV” criterion, p-values were between 0.05 and 0.1, measurements were extended only once by 8 sweeps); and (3) a maximum amount of 48 sweeps was attained. In Experiment 2, these stopping criteria were applied on 10 normal hearing and 10 hearing-impaired adults to asses the efficiency. Results: The application of these stopping rules resulted in ASSR threshold values that were comparable to other multiple-ASSR research with normal hearing and hearing-impaired adults. Furthermore, in 80% of the cases, ASSR thresholds could be obtained within a time-frame of 1 hour. Investigating the significant response-amplitudes of the hearing-impaired adults through cumulative curves indicated that probably a higher noise-stop criterion than “≤ 4 nV” can be used. Conclusions: The proposed stopping rules can be used in adults to determine accurate ASSR thresholds within an acceptable time-frame of about 1 hour. However, additional research with infants and adults with varying degrees and configurations of hearing loss is needed to optimize these criteria

Transducer influence on Auditory Steady State Evoked Potentials

Preliminary studies have stirred the hope that sound-field stimulation through auditory steady state evoked potentials can be used to assess aided thresholds in the difficult-to-test population. Before the introduction of ASSEP into the clinical field, as a technique for the prediction of aided thresholds in the difficult-to-test population, a question arises concerning its clinical validation. The application of ASSEP through sound field stimulation, in the determination of aided thresholds and for the evaluation of amplification fittings, is dependent on the determination of unaided responses. Subsequently the estimation of unaided thresholds in the hearing impaired population is dependent on the establishment of normative data from the normal hearing population. The aim of this study was to determine the influence of insert earphones and sound field speaker presentation on threshold estimations using monotic auditory steady state evoked potentials, in a group of normal hearing adults. To achieve the aim of the study, a comparative, within-group experimental design was selected. The results of the current study indicated that the monotic single ASSEP technique under both insert earphone- and sound field conditions provided a reasonable estimation (25-35 dB HL for inset earphones; 20-33 dB HL for sound field speaker presentation) of the behavioural pure tone thresholds. The minimum response levels obtained under insert earphone conditions differed significantly from those obtained under sound field conditions for all the frequencies tested except 2 kHz (p < 0.01). Subsequently, the current study indicates that minimum response levels obtained using a specific transducer should serve as the basis of comparison with behavioural thresholds obtained under the same transducer. Therefore, behavioural pure tone thresholds obtained under insert earphone conditions will not suffice as a basis of comparison for minimum response levels obtained for the ASSEP technique under sound field conditions, and vice versa. This research endeavour concluded that the monotic ASSEP technique under both insert earphone and sound field conditions provide useful information for the estimation of frequency specific thresholds, but that the results are transducer specific and that comparison across transducers should be avoided.Dissertation (M (Communication Pathology))--University of Pretoria, 2006.Speech-Language Pathology and AudiologyUnrestricte

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

otorhinolaryngology; neurosciences; hearin

Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing

​The International Symposium on Hearing is a prestigious, triennial gathering where world-class scientists present and discuss the most recent advances in the field of human and animal hearing research. The 2015 edition will particularly focus on integrative approaches linking physiological, psychophysical and cognitive aspects of normal and impaired hearing. Like previous editions, the proceedings will contain about 50 chapters ranging from basic to applied research, and of interest to neuroscientists, psychologists, audiologists, engineers, otolaryngologists, and artificial intelligence researchers.