Seminario INCyL – Sónia Luísa Coelho De Sousa

Understanding speech in noisy environments is challenging but essential for human
verbal communication. Fortunately, the auditory system can adapt to background noise,
which facilitates speech intelligibility in noisy environments. Behavioral adaptation to noise,
however, varies across individuals for reasons that are unclear. The aim of the work
presented in this thesis was to investigate whether behavioral adaptation to noise is
affected by ‘hidden’ hearing loss (HHL), a reduced ability to inhibit cognitive interference,
or aging.
Eighty-nine adult speakers of Castilian Spanish (19–86 years old) with clinically normal
hearing participated in the experiments. Speech reception thresholds (SRTs), the signal-to-
noise ratio at 50 % recognition, were measured for disyllabic words embedded in noise.
SRTs were measured for words delayed 50 ms and 800 ms in the noise, for various noises
and levels. Adaptation to noise was calculated as the improvement in the long-delay
relative to the short-delay condition. Because adaptation is greater for vocoded than for
natural words, words were processed through a tone vocoder. The risk of HHL was
assessed using the amplitude and the rate of growth (slope) of wave I of the auditory
brainstem response (ABR). The ability to inhibit cognitive interference was assessed using
the Stroop color and word test.
The data revealed that participants exhibited significant adaptation to noise, and that
adaptation was greater at higher noise levels and for steady than for fluctuating noises.
However, adaptation was not significantly associated with ABR wave I amplitude or slope,
age, or Stroop test score, even after controlling for the potential confounding effect of
audiometric threshold.
Findings suggest that behavioral adaptation to noise is preserved across the adult lifespan
and is independent of subclinical auditory deficits or inhibitory control abilities. Findings
further suggest that speech-in-noise difficulties experienced by older adults or individuals
at risk of suffering from HHL should be attributed to factors other than impaired adaptation
to noise.

Keywords: adaptation to noise, age, auditory brainstem response, inhibition of cognitive interference, dynamic range adaptation, hidden hearing loss, Stroop test.