The Effect of Cochlear Damage on the Sensitivity to Harmonicity.

Damien Bonnard, René Dauman, Catherine Semal, Laurent Demany
Ear and Hearing. 2017-01-01; 38(1): 85-93
DOI: 10.1097/aud.0000000000000356

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1. Ear Hear. 2017 Jan/Feb;38(1):85-93.

The Effect of Cochlear Damage on the Sensitivity to Harmonicity.

Bonnard D(1), Dauman R, Semal C, Demany L.

Author information:
(1)1Institut de Neurosciences Cognitives et Intégratives d’Aquitaine, CNRS and
Université de Bordeaux (UMR 5287), Bordeaux, France; 2Centre Hospitalier
Universitaire Pellegrin, Université de Bordeaux, Bordeaux, France; and 3Institut
Polytechnique de Bordeaux, Bordeaux, France.

OBJECTIVES: A sum of simultaneous pure tones with harmonic relationships (i.e.,
simple frequency ratios) is normally heard as a single sound, with a single
pitch, even when its components are fully resolved in the auditory periphery.
This perceptual phenomenon called « harmonic fusion » is thought to play an
important role in auditory scene analysis as listeners often have to segregate
simultaneous harmonic sounds with different fundamental frequencies. The present
study explored the consequences of mild or moderate cochlear hearing loss for the
sensitivity to harmonicity and the detection of inharmonicity.
DESIGN: The subjects were 12 normal-hearing (NH) listeners and 8 listeners with
cochlear hearing loss amounting to 30 to 50 dB (mean: 42 dB) from 0.25 to 3 kHz.
In each subject, thresholds for the detection of a change in the frequency ratio
of simultaneous pure tones were measured with an adaptive forced-choice
procedure. The standard frequency ratio was either harmonic (2:1, i.e., one
octave) or inharmonic (0.8 or 1.2 octaves). The tones were presented at a low
sensation level (at most 15 dB) within broadband noise, to minimize their
cochlear interactions. In the main experimental conditions, the frequency
register of the stimuli varied randomly within each trial, so that subjects were
forced to process frequency ratios to achieve good performance; frequency
discrimination was not sufficient. In other conditions, by contrast, frequency
discrimination was sufficient to perform the task optimally.
RESULTS: For both groups of subjects, thresholds in the main experimental
conditions were lower (i.e., better) when the standard frequency ratio was
harmonic than when it was inharmonic. This effect, revealing sensitivity to
harmonicity, was weak for some members of the hearing-impaired group, but could
be observed even in subjects showing a very poor frequency discrimination
ability. The two groups, however, differed from each other with respect to the
detection of inharmonicity: for the NH group, in agreement with previous results,
negative deviations from one octave (i.e., compressions of this frequency ratio)
were better detected than positive deviations (stretchings); for the
hearing-impaired group, on the other hand, the sign of the deviations had no
effect on performance.
CONCLUSIONS: Sensitivity to harmonicity appears to be remarkably robust. However,
it can be reduced in some listeners with mild or moderate cochlear damage.
Moreover, as inharmonicity detection is asymmetric for NH listeners but
apparently becomes symmetric in case of cochlear damage, it may be that listeners
with cochlear damage do not detect inharmonicity in the same manner as NH
listeners do. In some circumstances, inharmonicity can be detected on the basis
of « beat » cues available in single frequency channels; however, the subjects
tested here were unlikely to use cues of this type.

DOI: 10.1097/AUD.0000000000000356
PMID: 27992390 [Indexed for MEDLINE]

Auteurs Bordeaux Neurocampus