Douglas Noffsinger

Masking Level Differences Encountered in Clinical Populations

Methods for measuring masking level differences (MLDs) at 500 Hz and for spondees were used with 290 subjects: 50 persons with normal hearing and 240 patients with various diseases. Of particular interest was whether techniques currently in clinical use could be used with ease, dispatch, and profit in determining MLD size. The methods selected, which were variations of Békésy audiometry and speech reception threshold procedures, proved clinically feasible. Results revealed differences in behavior from one group of subjects to another. Although MLDs were not affected by cortical lesions, they were very often abnormally small for patients with eight-nerve tumor, Meniéres disease, or multiple sclerosis. The high incidence of abnormally small MLDs in populations with normal sensitivity to pure tones and speech but with evidence of subcortical central lesions, such as patients with multiple sclerosis, suggests that the MLD tasks can be of diagnostic value in detecting retrocochlear lesions. However, in persons with hearing loss or significant interaural differences in threshold sensitivity, or both, the MLD tests are not always reliable in differentiating cochlear from retrocochlear disease.

Aging, memory, and the cholinergic system: A study of dichotic listening☆

Impairment of cholinergic neural function has been proposed as a cause of memory and cognitive (M/C) disorders of the aged since with cholinergic blockade young subjects show the M/C pattern of the elderly. To validate this hypothesis, we compared the performance of young normal subjects, young scopolamine-treated subjects, and aged subjects, using a different type of behavioral task, a dichotic listening test, which primarily measures neural channel capacity. With simultaneous dichotic presentation, undrugged young subjects reported both messages correctly in 35% of trials. Aged subjects scored double-correct responses in only 19% of trials, a highly significant difference (p less than 0.001). Following treatment with 1.0 mg scopolamine, young subjects also scored double correct responses in only 19% of trials, a highly significant reduction from their undrugged performance (p less than 0.01), but virtually the same as that of normal aged subjects. Similar findings were obtained with a staggered dichotic presentation. These results extend the observation that cholinergic blockade in young subjects reproduces the pattern of M/C decline of the aged; thus providing further for the hypothesis that this decline may result from impaired function in cholinergic neurons. The neurobiologic implications of cholinergic impairment are discussed.

Speech Discrimination In Quiet And In White Noise By Patients With Peripheral And Central Lesions

Speech-discrimination scores in quiet and in white noise (O dB S/N ratio) were obtained from six groups of subjects. Differences of 40% or more between scores in quiet and in white noise were observed for less than 1% of the normal ears tested but were found for 8.0% of ears with noise trauma, 48% of ears with Menieres disease, 62% of ears with subsequently surgically confirmed 8th-nerve tumors, 14% of ears of patients with multiple sclerosis, and 42% of ears contralateral to the lesion in patients with temporal-lobe damage.

Masking Level Differences for Cochlear and Brain Stem Lesions

Masking level differences (MLD) for 500 Hz pure tones and for spondees were obtained from 48 subjects. Twelve were without otologic or neurologic complaints (normal), 12 had high frequency, noise-induced hearing losses, 12 were diagnosed otologically as having Ménières disorder, and 12 had neurologically diagnosed central nervous system (CNS) disorders. Results indicated that high frequency, noise-induced hearing losses do not affect MLD for 500 Hz stimuli, but do diminish the size of MLD for speech. Masking level differences for both 500 Hz and spondees were decreased for the Ménières disorder group. The group of patients having CNS disorders attributed to multiple sclerosis, to inflammatory lesion of the pons, to degenerative processes of the cerebellum and adjacent nervous tissue, or to brain stem cerebrovascular accident had normal hearing according to conventional pure tone and speech testing, but attained smaller than normal MLD for 500 Hz and spondees. These findings agree closely with results obtained in an earlier study and continue to suggest that, given normal peripheral auditory function, MLD tests may have unique value in detection of subtle lesions of the central auditory nervous system.

Value of Special Auditory Tests in the Latero-Medial Inferior Pontine Syndrome

Results from a special battery of auditory tests are used to document, for the first time, recovery from a total unilateral hearing loss occurring as part of a latero-medial inferior pontine syndrome. Although sensitivity for pure tones and speech was regained within two months of onset, definite retrocochlear signs persisted for nine months. The tests which best demonstrated the lingering retrocochlear abnormality were binaural masking level difference procedures for 500 Hz pure tones and speech and examination of the amplitude of the acoustic reflex over a ten second time period. The relative sensitivity of other speech and pure tone tasks in detecting the retrocochlear problem is detailed.

Identification of Synthetic, Voiced Stop-Consonants by Hearing-Impaired Listeners

The identification of synthetic, voiced stop consonants changing in place of articulation was investigated in 26 normal-hearing listeners and 16 hearing-impaired listeners who reported difficulties in speech understanding, but attained high speech discrimination scores on standard test materials. Two place continua (each containing 13 stimuli changing from /ba/ to /da/ and /ga/) were employed: a continuum in which place was cued by an initial noise burst and formant transitions, and a continuum in which place was cued by formant transitions alone. All normal listeners exhibited categorical and highly consistent identification for both stimulus continua. For the hearing-impaired listeners, identification was somewhat less consistent for the burst-and-transition stimuli, and much poorer for the transition-only stimuli. Similar differences were observed when comparing the responses of 4 subjects with a unilateral hearing loss when the stimuli were presented to their normal and impaired ears, and 2 subjects with a unilateral, sudden-onset hearing loss with recovered pure-tone sensitivity.