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This study compared auditory behavioral and physiologic measures in normal control subjects and subjects prescribed with a selective serotonin reuptake inhibitor (SSRI) who were yet to take the drug and those currently taking an SSRI. Test measures used were pure tone averages (PTA), acoustic reflex thresholds, uncomfortable loudness levels (UCL), otoacoustic emissions, masking level difference, temporal integration, amplitude resolution, and Beck Depression Inventory-II (BDI-II) scores. Results indicated that there was a significant difference in the amplitude resolution of the unmedicated group when compared to the medicated and the control group. There was also a significant positive correlation between dynamic range (difference between UCL and PTA) and amplitude resolution. The BDI-II revealed a significant difference between the scores of the unmedicated and the control group as well as the medicated and the control group. Although other test measures indicated differences between the groups, the differences were not statistically significant.

The purpose of this thesis is to provide a review and discussion of the current literature on auditory processing, speech discrimination, word recognition, and early lexical representations in children with normal hearing and those with hearing impairment in addition to identifying areas in which current research is lacking. This information is needed to consider potential interactions between various factors affecting the development of spoken word recognition. This will also provide a starting point for identifying further research needs. Since children with hearing loss do not receive the same amount of exposure to speech and language as typically developing children, it can be expected that the development of speech and word recognition in this population may progress differently. If we can identify differences in auditory processing and phonological development in children with hearing impairment, we can modify speech and language therapy to focus on more specific and effective targets. The subsequent chapters will provide a critical review of the current literature on the aforementioned topics. In Chapters 2 and 3, studies assessing differences in processing, attention to sound, intersensory perception, and sound discrimination abilities in children with normal hearing and hearing impairment will be discussed. Chapters 4 and 5 focus on word recognition skills, and early lexical representations. Chapter 6 will synthesize results of available studies and suggest areas in which more research is needed. Together, these chapters will help us gain a better understanding of the complex interactions between auditory processing, executive functioning, phonological development and later word recognition outcomes. By identifying which avenues have the greatest effect on outcomes in cochlear implant users, we can modify speech and language therapy in order to address the unique needs of this special population. / text

Auditory Processing Disorder (APD) is an auditory-specific perceptual deficit in the processing of auditory stimuli that occurs in spite of normal peripheral hearing thresholds and normal intellectual capacity American Speech-Language-Hearing Association (ASHA, 2005). The diagnostic process of APD typically involves a test battery consisting of sub-tests designed to examine the integrity of various auditory processes of the central auditory nervous system (CANS). One category of these sub-tests is the low-pass filtered speech test (FST), whereby a speech signal is distorted by using filtering to modify its frequency content. One limitation of the various versions of the FST currently available is that they are administered using a constant level of low-pass filtering (e.g. a fixed 1 kHz corner frequency) which makes them prone to ceiling and floor effects (Farrer & Keith, 1981). As a consequence, the efficacy and accuracy of these tests is significantly compromised (Martin & Clark, 1977). The purpose of the present study was to counter these effects by utilising the University of Canterbury Adaptive Filtered Speech Test (UCAST) which uses a computer-based adaptive procedure intended to improve the efficiency and sensitivity of the test over its constant-level counterparts. A comprehensive APD test battery was carried out on 18 children aged 7-13 suspected of APD and on an aged-matched control group of 10 children. Fifteen of the APD suspected children were diagnosed with APD based on their performance on a traditional APD test battery, comprising the Compressed and Reverberated Words Test (CRWT), the Double Digits test (DDT), the Frequency Pattern test (FPT) and the Random Gap Detection test (RGDT). In addition, the UCAST was administered to examine whether the low-pass filter limit at which children score 62.5% of words correct i) differed significantly between children who either passed or failed the APD test battery; ii) correlated with their score on the traditional APD battery (TAPDB); and iii) correlated with their score on a commercially available low-pass filtered speech test, the Filtered Words Subtest of SCAN-C (Keith, 2000b). Results demonstrated a significant difference between the UCAST low-pass filter limit at which APD and control children scored 62.5% words correct (two-way repeated measures ANOVA, p < 0.01). Significant correlations were found between the UCAST and three of the four tests used in the TAPD - the DDT, the RGDT and the FPT (Pearson Correlation coefficient, p < 0.01). No correlation was found between the UCAST and the CRWT or between the UCAST and the SCAN-C (FW) test (p > 0.05). These findings provide evidence that an adaptive filtered speech test may discriminate between children with and without APD with greater sensitivity and specificity than its constant-level counterparts.

Aims: The aims of this study were to identify school-aged children who exhibit spatial stream segregation deficits by using the Listening in Spatialized Noise – Sentences (LiSN-S) test, and to determine the effectiveness of personal FM systems as an intervention for these children. Method: Participants consisted of 22 children between the age of 7;0 and 11;11 years with normal hearing thresholds. Based on their performance on the LiSN-S test, participants with normal and impaired spatial stream segregation ability were assigned to the control group (n=12) and the FM group (n=10) respectively. Participants from the latter group were provided with and required to use the personal ear-level FM devices during school time for a period of eight weeks. The impact of the FM systems was determined by both quantitative and qualitative data, which were gathered at three sampling points: (1) Before FM trial; (2) At the end of the FM trial (i.e. after eight weeks of use); and finally (3) At eight weeks following withdrawal of the FM systems. Results: Results revealed children with APD improved on their ability to segregate spatial streams following the use of personal FM devices, whereas control participants did not exhibit this change. The personal FM devices seemed to provide the greatest benefit to the younger participants. Qualitative measures, including individualised Goal Attainment Scales (GAS), indicated positive improvements in auditory behaviours following the use of FM devices in all participants. In addition, teachers anecdotally reported positive behavioural changes in the FM participants during the FM trial. Conclusion: Personal FM systems appear to be an effective management strategy for school age children who exhibit difficulty in spatial stream segregation.

Perceptual capacity and selection in attention have for long been an interest in cognitive science, with early theories of early selection to late selection. Hearing is an important subject to investigate when it comes to attention and early auditory processing can be investigated by using auditory steady state responses (ASSRs). Studies on ASSRs to irrelevant sounds have investigated the 40 Hz ASSR and concluded no effect of load. As studies on temporal activation of ASSRs indicate that lower and higher frequencies activate different stages of the auditory pathway, there is a need to investigate other frequencies than the 40 Hz. This study investigated the 20 Hz and 80 Hz amplitude modulations using EEG. The visual stimuli were a rapid stream of letters and varied between no load, low load, and high load. The auditory stimuli were an amplitude-modulated tone with a carrier frequency of 500 Hz, with three varying modulation frequencies: 20 Hz, 40 Hz, and 80 Hz. Load level and amplitude modulation alternated over 18 blocks. The statistical analysis was comprised of t tests and Bayes Factor. Results provided support for the null hypothesis for the 20 Hz frequency but were inconclusive for the 40 Hz and 80 Hz frequency. More data is needed to give a conclusion for effect of load for the 40 Hz and 80 Hz frequency. As we did not have enough data, we cannot say anything about the temporal activation of ASSRs in the brain.

Autistic people frequently experience sensory processing difficulties. For many on the autism spectrum, such difficulties can significantly impact important functions and quality of life. We are only beginning to understand the neural mechanisms of atypical sensory processing. However, one established way to measure certain levels of auditory processing is with auditory brainstem responses (ABR). While ABR has been primarily hypothesized in the current literature as a means of early detection/diagnosis in autism, additional research is needed to determine the ABR’s utility in examining sensory processing in this population. Thus, we evaluated ABR in 19 young children with autism during various stimulus (click and tone burst) and intensity conditions by comparing ABR waveform characteristics, such as absolute peak latencies and amplitudes, inter-peak latencies (IPL), inter-aural latency differences (IAD) between age-matched groups of autistic and typically developing children. We also examined within ear waveform cross correlations and inter-aural cross correlations (IACC) to assess replicability and synchrony of participants’ auditory brainstem responses. Though we observed longer peak latencies (esp. wave III and V) and IPLs in both the autism and typically developing groups in different conditions, there were no statistically significant results in cross correlation or IACC. These results indicate that at the level of the brainstem, auditory processing may differ slightly, but is mostly similar between autistic and typically developing children. In terms of sensory processing in autism, future studies should examine the connection between ABR responses and behavioral measures of sensory processing, as well as function at more central levels of the auditory system.

In order to further explore the nature of anesthesia-induced unconsciousness and its relationship to nociception, investigators attempted to determine whether mismatch negativity could be detected during general anesthesia and surgery. An auditory odd-ball paradigm designed to elicit mismatch negativity was presented to ten patients during general anesthesia and surgery. Five of the ten also underwent testing in the awake state prior to surgery. Multiple EEG recordings were obtained in each patient and each condition using the BioSemi ActiveTwo 64 EEG electrode system. The anesthetic regime required only that 0.7 MAC of an inhaled agent was administered. Several methods of analysis were utilized to determine whether an MMN response could be identified: visual inspection of ERP waveforms, targeted t-tests, cluster permutation tests, and multivariate pattern analysis. Whereas deviant-related negativity was readily detected in the awake state, deviant-related negativity was not detected during surgery and general anesthesia. Results demonstrate that essential components of the MMN response are abolished during typically conducted general anesthesia even with significant surgical stimulation. These results are consistent with previous research on ERPs and anesthesia. Results cast doubt on the possibility of sensory memory related to intraoperative events. / Thesis / Master of Science (MSc)

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