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Effects of Sensorineural Hearing Loss on Cortical Event-Related Potential and Behavioral Measures of Speech-Sound Processing

Oates, Peggy A.; Kurtzberg, Diane; Stapells, David R.

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Objective To investigate systematically the effects of sensorineural hearing loss on cortical event-related potentials (ERPs) N1, MMN, N2 and P3 and their associated behavioral measures (d′ sensitivity and reaction time) to the speech sounds /ba/ and /da/ presented at 65 and 80 dB ppe SPL.

Design Cortical ERPs were recorded to /ba/ and /da/ speech stimuli presented at 65 and 80 dB ppe SPL from 20 normal-hearing adults and 20 adults who are hearing impaired. The degree of sensorineural impairments at 1000 to 2000 Hz ranged from mild losses (defined as 25 to 49 dB HL) to severe/profound losses (75 to 120 dB HL). The speech stimuli were presented in an oddball paradigm and the cortical ERPs were recorded in both active and passive listening conditions for each stimulus intensity.

Results Both ERP amplitudes and behavioral discrimination (d′) scores were lower for listeners with sensorineural hearing loss than for those with normal hearing. However, these differences in response strength were evident only for those listeners whose average hearing loss at 1000 to 2000 Hz exceeded 60 dB HL for the lower intensity stimuli and exceeded 75 dB HL for the higher intensity stimuli. In contrast, prolongations in the ERP and behavioral latencies, relative to responses from normal-hearing subjects, began with even mild (25 to 49 dB HL) threshold elevations. The amplitude and latency response changes that occurred with sensorineural hearing loss were significantly greater for the later ERP peaks (N2/P3) and behavioral discrimination measures (d′ and RT) in comparison with earlier (N1, MMN) responses.

Conclusions The results indicate that latency measures are more sensitive indicators of the early effects of decreased audibility than are response strength (amplitude, d′ or percent correct) measures. Sensorineural hearing loss has a greater impact on higher level or “nonsensory” cortical processing in comparison with lower level or “sensory” cortical processing. Possible physiologic mechanisms within the cortex that may be responsible for these response changes are presented. Lastly, the possible clinical significance of these ERP and behavioral findings is discussed.

There is considerable interest in the use of cortical event-related potentials (ERPs), especially MMN, for assessing populations where behavioral measures of speech detection and discrimination are difficult to obtain (e.g., infants, young children, and difficult-to-test patients). These potentials have shown promising, though preliminary, results in assessing benefit from sensory aids and monitoring of an individual's progress with auditory training. This study aimed to investigate systematically the effects of sensorineural hearing loss on cortical event-related potentials and their associated behavioral measures (d sensitivity and reaction-time) to the speech sounds /ba/ and /da/. Both ERP amplitudes and behavioral discrimination (d) scores were lower for listeners with sensorineural hearing loss than for those with normal hearing, but this effect was evident only for listeners with more pronounced hearing impairment. In contrast, prolongations in the ERP and behavioral latencies, relative to responses from normal-hearing subjects, began with even mild threshold elevations. The results indicate that latency measures are more sensitive indicators of the early effects of decreased audibility than are response strength (amplitude, d, or percent correct) measures.

Department of Communication Sciences and Disorders (P.A.O.), Towson University, Towson, Maryland; Department of Neuroscience and Neurology (D.K.), Albert Einstein College of Medicine, Bronx, New York; and School of Audiology and Speech Sciences (D.R.S.), University of British Columbia, Vancouver, B.C., Canada.

Address for correspondence: Peggy Oates, Ph.D., Department of Communication Sciences and Disorders, Towson University, 8000 York Road, Towson, Maryland 21252-0001. E-mail: poates@towson.edu.

Received June 11, 2001 accepted June 7 2002

Portions of this paper were presented at the XV Biennial International Symposium of the International Evoked Response Audiology Study Group, August, 1997.

© 2002 Lippincott Williams & Wilkins, Inc.