Individuals with high working memory capacity (WMC) appear to be particularly good at focusing their attention (McCabe, Roediger, McDaniel, Balota, & Hambrick, 2010). Therefore, we studied the correlation between WMC and the ability to suppress neurological activity from a task-irrelevant stimulus. The research question tests the foundations of Lavie’s perceptual load theory; that early selection occurs, by testing if higher WMC enhances people’s ability to inhibit processing of task-irrelevant stimuli from low versus high load (i.e. the difference from low to high load should be smaller for high WMC than for low WMC). This was operationalised by measuring the correlation of WMC and auditory processing under low versus high visual load. Auditory processing was measured with auditory steady state responses (ASSR), and WMC was measured with an operation-letter span task. The results showed no significant correlation between WMC and ability to suppress task-irrelevant stimuli. Based on the data, it is not possible to conclude with certainty that effects of load on auditory processing are unaffected by WMC, because confidence intervals were large.

Objective: The primary purpose of this investigation was to determine the effect of multitalker babble on ASSRs in adult subjects with normal hearing (NH) and sensorineural hearing loss (HI). The secondary purpose was to investigate the relationships among ASSRs, word recognition in quiet, and word recognition in babble. Design: ASSRs were elicited by a complex mixed-modulation tonal stimulus (carrier frequencies of 500, 1500, 2500, and 4000 Hz; modulation rate of 40 or 90 Hz) presented in quiet and in babble. The level of each carrier frequency was adjusted to match the level of the multitalker babble spectrum, which was based on the long term speech spectrum average. Word recognition in noise (WIN) performance was measured and correlated to ASSR amplitude and ASSR detection rate. Study Sample: Nineteen normal-hearing adults and nineteen adults with sensorineural hearing loss were recruited. Results and Conclusions: The presence of babble significantly reduced the ASSR detection rate and ASSR amplitude for NH subjects, but had minimal effect on ASSRs for HI subjects. In addition, babble enhanced ASSR amplitude at high stimulus levels. ASSR detection rate and ASSR amplitude recorded in quiet and babble were significantly correlated with word recognition performance for NH and HI subjects. Sumario Objetivo: El objetivo fundamental de esta investigación fue determinar el efecto de balbuceo de hablantes múltiples en los ASSR de adultos jóvenes con audición normal (NH) y con pérdidas auditivas sensorineurales (HI). El objetivo secundario fue investigar las relaciones entre los ASSR, el reconocimiento de palabras en silencio y el reconocimiento de palabras con en medio de balbuceo. Diseño: Los ASSR fueron evocados por estímulo tonal de modulación mezclada compleja (frecuencias portadoras de 500, 1500, 2500 y 4000 Hz; tasa de modulación de 40 o 90 Hz) presentadas en silencio y con el balbuceo. Se ajustó el nivel de cada frecuencia portadora para emparejar el nivel del espectro del balbuceo de hablantes múltiples, el cual se basó en el promedio del espectro a largo plazo. Se midió el rendimiento para el reconocimiento de palabras en ruido (WIN) y se correlacionó con la amplitud de los ASSR y con la tasa de detección de los ASSR. Muestra Del Estudio: Se reclutaron diez y nueve adultos normoyentes y diez y nueve adultos con pérdida auditiva sensorineural. Resultados Y Conclusiones: La presencia del balbuceo reduce significativamente la tasa de detección de los ASSR y la amplitud de los ASSR en sujetos NH, pero tiene efectos mínimos en los ASSR de sujetos HI. Además, el balbuceo aumenta la amplitud de los ASSR con estímulos de niveles altos. La tasa de detección de los ASSR y la amplitud de los ASSR registrada en silencio y con balbuceo, fueron significativamente correlacionadas con el rendimiento para reconocer palabras en sujetos NH y HI.

In individuals claiming compensation for occupational noise induced hearing loss, a population with a high incidence of nonorganic hearing loss, a reliable and valid behavioural pure tone (PT) threshold is not always achievable. Recent studies have compared the accuracy of behavioural PT threshold estimation using the slow cortical auditory evoked potentials (SCAEP) and auditory steady-state responses (ASSR) but there is no consensus regarding recommended technique. A review of the literature indicated that no comparison has been completed on the use of SCAEP and a single frequency ASSR technique. A research project was therefore initiated with the aim of comparing the clinical effectiveness (accuracy) and clinical efficiency (time required) of SCAEP and ASSR for behavioural PT threshold estimation in adults exposed to occupational noise. Adult participants were divided into a group with normal hearing (behavioural PT thresholds < 20 dBHL; n = 15) and a group of participants with hearing loss (n = 16 adults), the latter of which were recruited from individuals referred for audiometric screening, as part of hearing conservation programs, and who were, therefore, exposed to occupational noise. The GSI Audera electrophysiological system was used for both SCAEP and ASSR threshold measurement at 0.5, 1, 2 and 4 kHz. Use was made of tone burst stimuli for the SCAEP (rise and fall of 10 ms with 80 ms plateau), while amplitude and frequency modulated (AM/FM) stimuli was used during ASSR testing. The system’s 40 Hz protocol was chosen for use during ASSR recording while participants slept because this led to lparticipants. ASSR thresholds could not be measured in two of the three sleeping participants in the preliminary study using an 80 Hz modulation rate due to excessive noise. The mean SCAEP difference scores (SCAEP threshold minus behavioural PT threshold) for both participant groups were -0.2+10.2, 2.8+10.1,5.8+9.7, 0.5+10.4 at 0.5, 1, 2, and 4 kHz respectively, while ASSR difference scores were 25.3+12.8, 21.7+11.3,32.3+12.2, 27.1+13.8. The SCAEP correlations with behavioural PT thresholds across frequencies (r = 0.85) were also stronger than ASSR correlations (r = 0.75). Therefore, with regard to proximity of auditory evoked potentials (AEP) to behavioural PT thresholds and consistency of this relationship, the SCAEP, rather than ASSR, is the AEP of choice. However, the SCAEP took on average 10.1 minutes longer to complete than the ASSR. Clinical effectiveness was given comparably more weight than the clinical efficiency of the AEP technique to estimate behavioural PT thresholds due to the impact on overcompensation for occupational noise induced hearing loss. As such, the study acknowledged the SCAEP as the AEP of choice for the purpose of behavioural PT thresholds in adults exposed to occupational noise. It is important to note that the conclusion reached in the current study arose from the comparison of the SCAEP with a specific ASSR technique. Accuracy of ASSR estimation of behavioural PT thresholds is strongly influenced by stimulus and recording parameters of the system used, and by the participant variables. Copyright / Dissertation (MCommunication Pathology)--University of Pretoria, 2010. / Speech-Language Pathology and Audiology / Unrestricted