Behavioral Perception and Neural Correlates of Categorical Perception in Cochlear Implant Users / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Although many cochlear implant (CI) recipients receive significant benefits from using the implants, speech perception ability is still known to vary among CI users, and the variability is closely related to the ability of users to process temporal information. As one of the important temporal cues for speech perception in CI users, voice onset time (VOT) can be used to examine behavioral perception and neural correlates of temporal processing. In this study, we measured categorical perception and N1-P2 cortical auditory evoked potentials (CAEPs) using a /ba/-/pa/ VOT continuum in CI users as well as in normal-hearing (NH) listeners. SUBJECTS AND METHOD: Ten CI subjects and 11 NH controls participated in syllable identification tasks and in electroencephalography recording. CI subjects were divided into two groups, which were ‘good’ and ‘poor’ performers based on their speech perception scores. The stimuli used in both experiments were a synthetic /ba/-/pa/ VOT continuum. The identification boundary and N1-P2 peak-to-peak amplitude were measured for each subject group. RESULTS: Behavioral results revealed that poor CI performers had a delayed identification boundary compared to NH listeners and good CI performers. However, N1-P2 peak-to-peak amplitudes in both good and poor CI performers were significantly smaller than those in NH group. CONCLUSION: N1-P2 amplitudes reflected decreased auditory cortical activity of temporal cues in CI users. The categorical perception of good CI performers was similar to that of NH listeners, whereas their cortical responses were decreased to the level similar to that of poor CI performers. This finding indicates that CAEPs would be more sensitive to altered temporal processing of CI users than to behavioral measures.

Cortical Auditory Event Related Potentials (P300) for Frequency Changing Dynamic Tones

BACKGROUND AND OBJECTIVES: P300 has been studied with a variety of stimuli. However, the nature of P300 has not been investigated for deviant stimuli which change its characteristics from standard stimuli after a period of time from onset. SUBJECTS AND METHODS: Nine young adults with normal hearing participated in the study. The P300 was elicited using an oddball paradigm, the probability of standard and deviant stimuli was 80% and 20% respectively. Six stimuli were used to elicit P300, it included two pure-tones (1,000 Hz and 2,000 Hz) and four tone-complexes (tones with frequency changes). Among these stimuli, 1,000 Hz tone served as standard while others served as deviant stimuli. The P300 was recorded in five separate blocks, with one of the deviant stimuli as target in each block. Electroencephalographic was recorded from electrode sites Fz, Cz, C3, C4, and Pz. Latency and amplitude of components of the cortical auditory evoked potentials were measured at Cz. RESULTS: Waveforms obtained in the present study shows that, all the deviant stimuli elicited obligatory P1-N1-P2 for stimulus onset. 2,000 Hz deviant tone elicited P300 at a latency of 300 ms. While, tone-complexes elicited acoustic change complex (ACC) for frequency changes and finally elicited P300 at a latency of 600 ms. In addition, the results showed shorter latency and larger amplitude ACC and P300 for rising tone-complexes compared to falling tone-complexes. CONCLUSIONS: Tone-complexes elicited distinct waveforms compared to 2,000 Hz deviant tone. Rising tone-complexes which had an increase in frequency elicited shorter latency and larger amplitude responses, which could be attributed to perceptual bias for frequency changes.

Potenciales evocados auditivos de corteza: complejo P1-N1-P2 y sus aplicaciones clínicas / Auditory cortex evoked potentials: P1-N1-P2 complex and clinical applications

Los potenciales evocados de corteza prometen ser una herramienta útil en la evaluación de las funciones auditivas, proporcionando información sobre la funcionalidad e integridad de estructuras auditivas centrales. Dentro de sus posibles usos encontramos: estimación del umbral auditivo en adultos permitiendo una mayor precisión en comparación a otras técnicas electrofisiológicas, como herramienta de evaluación y seguimiento del entrenamiento auditivo, evaluación de la amplificación (especialmente utilizando estímulos complejos como el habla) relacionado con la detección del estímulo auditivo amplificado a nivel de la corteza y de la plasticidad auditiva como lo podría ser la monitorización de los cambios producidos por la estimulación auditiva. Sin embargo aún presentan algunas limitaciones que deben ser resueltas antes de ser incorporados dentro de la batería de pruebas audiológicas de uso clínico habitual, factores propios del sujeto, de la técnica utilizada y condiciones de evaluación (ej. diferentes tipos de audífonos) pueden hacer que estas respuestas presenten una variabilidad que podría dificultar su uso rutinario.

Cortical auditory evoked potentials have the potential to be a tool for the assessment of auditory functions, providing information on the functionality and integrity of central auditory structures. Among its possible uses are: hearing threshold estimation on adults that are more accurate compared to other electrophysiological techniques; a tool for assessment and monitoring of auditory training; evaluation of amplification (especially using complex stimuli such as speech) related to the detection of an amplified sound at the level of the auditory cortex; and monitoring plasticity via the changes produced by an auditory stimulation. However there are still some limitations to be resolved before incorporating cortical auditory evoked potentials in to the battery of audiological tests used in clinics. Factors related to the subject and the technique and assessment conditions (e.g. different types of hearing aids), may vary these responses and hinder its reliability and use.