Central Auditory Processing Disorders : Effects of Age and Hearing Loss to Electrophysiological and Behavioral Responses

Abstract

Introduction. Central auditory processing involve normal sound perception, speech recognition, ability of cognition and memory. Accordingly speech recognition difficulties may manifest due to changes at any segment of auditory processing. Cortical auditory evoked potentials (CAEPs) and behavioral measures provide insight into the neural mechanisms underlying speech recognition. These disorders are observed both in young and elderly population. Aim of the study. To evaluate central auditory processing for subjects of different age and hearing level through the presentation of noise using CAEPs and behavioral measures of speech discrimination. However due to complicated connectivity in auditory pathway it is difficult to identify the central auditory processing damage. Behavioral tests in conjunction with electrophysiological examination will reveal more complicated information for differenciation between peripheral and central auditory processing disorders. Materials and methods. Three groups of subjects participated: young normal hearing, young hearing-impaired and elderly hearing– impaired subjects. To minimaze subject variables, the CAEPs (wave peaks P1,N1,P2,N2,P3,N3 in miliseconds) was investigated using passive listening paradigme. The CAEPs were elicited by 1,1s change in frequency 1000 Hz and 2000 Hz in pure tones presented at 65, 70 and 75 dB SPL. Sentence recognition tests in quite and noise, Digit Pairs (DP) and Word Pairs (WP) were developed in Latvian language prior to investigation. They were presented to all subjects. Results. The most prominent finding was the increased latency of P3, N3 in elderly and also in younger hearing impaired adults groups and highly differed within groups. More prolonged latencies were find of N1, P2 in elderly hearing impaired group than in younger hearing impaired group adults. Conclusions. During this investigation the CAEPs are performed for the first time in our clinic therefore the main standarts are determined for our laboratory. The speech recognition tests (Sentence recognition test, DD, DW) are developed in Latvian. The present findings suggest patterns of CAEP are variable within individuals however shows that auditory perception and cognitive function is not only a result of aging and must be associated with a general slowing of neuronal processing or decreased neuronal synchrony within the central auditory nervous system. Determination of central auditory processing capacity level is of crucial significance to prognose and evaluate the hearing result after hearing prosthetics and to appraise indications for hearing prosthetics, cochlear and middle ear implantation including.