Asymmetry of temporal processing in listeners with normal hearing and unilaterally deaf subjects.
OBJECTIVE
In general, auditory cortex on the left side of the brain is specialized for processing of acoustic stimuli with complex temporal structure including speech, and the right hemisphere is primary for spectral processing and favors tonal stimuli and music. This asymmetry in processing is further emphasized when hemisphere-favored stimuli are presented to the contralateral ear. The purpose of the first experiment is to further investigate the properties that dictate lateralized processing of auditory stimuli by ear and the relationship between auditory task and stimulus type. Next, it is not clear what compensation may exist for the loss of function of one ear and consequently, reduced access to functions primary performed in the opposite hemisphere, in the case of early unilateral profound hearing loss. The purpose of experiment 2 is to determine if any compensation for loss of function is seen in persons with early unilateral deafness.


METHODS
Experiment 1: Gap detection thresholds were determined in 30 right-handed listeners with normal hearing using wide-band noise markers (temporally complex), 400 and 4000 Hz pure tones presented individually to the left and right ears. Experiment 2: The same procedure was administered to listeners with early-onset, severe-to-profound unilateral deafness (seven left ear deaf and five right ear deaf) in the hearing ear alone.


RESULTS
A significant right ear advantage was found for gap detection threshold using noise markers and a smaller left ear advantage was found for tonal stimuli. Listeners with unilateral deafness demonstrated that the hearing ear, left or right, performed in a manner similar to listeners with normal hearing.


CONCLUSIONS
Results indicate that (1) gap marker, more than task, was the salient feature in determining laterality of processing in this experiment, (2) the two ears have distinct processing capacity based on stimulus type, and (3) compensation for loss is not apparent in persons with congenital unilateral deafness.
Sininger
Yvonne S
YS
Division of Head and Neck Surgery, University of California Los Angeles, David Geffen School of Medicine, 62-132 Center for the Health Sciences, Los Angeles 90095-1624, USA. ysininger@mednet.ucla.edu
de Bode
Stella
S
D000293:Adolescent; D000328:Adult; D001303:Auditory Cortex / Q000502:physiology*; D001309:Auditory Threshold / Q000502:physiology; D003638:Deafness / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006309:Hearing / Q000502:physiology*; D046088:Hearing Loss, Unilateral / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010468:Perceptual Disorders / Q000175:diagnosis* / Q000453:epidemiology*; D012720:Severity of Illness Index; D013998:Time Perception