Subject: Auditory illusions (Imran Dhamani )


Subject: Subject: Auditory illusions
From:    Imran Dhamani  <imrandhamani@xxxxxxxx>
Date:    Tue, 2 Aug 2011 11:02:31 +0530
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Dear Nedra,                       Although I am not an expert in this area, but I have done some preliminary (unpublished) work on the use of the McGurk effect for the evaluation of current day multichannel digital hearing aids. Few of the basic assumptions for the rationale and implications were as follows: 1)      One of the main benefits of audio visual integration is in difficult listening situations when either the speech is degraded or there is background noise 2)      The visual cue in an auditory visual integration task is relatively unaffected by noise. 3)      Hearing impaired listeners especially those with relatively larger auditory deprivation periods rely more on visual cues (the AV balance is slightly tilted towards visual dominance) in speech perception than normal hearing listeners, thus making them better speech readers and also relatively poor AV integrators. 4)      The psycho-acoustical aspects of sensori-neural hearing loss suggests a reduction in the possibility of perceiving certain classes of speech sounds especially in presence of noise. 5)      Moreover some of the speech sounds may not be heard in noisy environments no matter how intensely they are amplified by the hearing aids 6)      The Digital multichannel hearing aids may also have some amount of internal distortion and delay due to digital processing and filtering 7)      In such scenarios the hearing aid user may benefit from the visual cues provided by a speakers facial and lip movements which should relatively be unaffected by noise and thus boost speech perception for energetic masking at poor signal to noise ratios as well as in informational masking. 8)      We presented hearing aid users (relatively homogenous group in terms of hearing aid used) the Mc Gurk stimuli in both congruent and incongruent conditions in quiet and in noise (three different SNRs) at comfortable level at which the subjects scored > 70% on a screening test using PB words. 9)      A criterion of 3/4th fusion responses was kept to determine the presence of Mc Gurk effect 10)   The results indicated that subjects with normal hearing performed better than the subjects using HA’s in all conditions. The presence of auditory and visual information simultaneously in the congruent condition was beneficial for speech perception in quiet and in noise. Noise reduced the subjects ability to perceive speech at poor SNR and had a more severe impact on the performance of the HA users than in normal subjects. The McGurk effect was absent in the HA users at the poorer SNRs compared to normal listeners and in these conditions the HA users responses to the McGurk stimuli were mainly visually dominated. 11)   Background noise and increased listening effort are significant factors influencing hearing-aidsatisfaction and one of the major reason for rejection of HA’s. 12)   Testing McGurk effect in a noisy environment may be a useful way to understand auditory visual speech perception in HA users and verify the benefits of aided AV speech perception in noise in HA users. 13)   Some of the implications in terms of hearing aid rehabilitation for the same may be in terms of enhancing optimal HA fitting to achieve not only good auditory perception in noise but also optimum auditory visual perception in noise and the emphasis on auditory training and the use of speech reading skills. 14)   The study that I have mentioned above was in no way devoid of limitations like lesser sample size and the hearing aids were used at the same programs that the HA users were using in their everyday listening environments and thus all the user had different program settings. May be the rationale and implications might be of some interest to you though. regards, Imran Dhamani


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