Speech Recognition and Noise Adaptation in Realistic Noises.

The recognition of isolated words in noise improves as words are delayed from the noise onset. This phenomenon, known as adaptation to noise, has been mostly investigated using synthetic noises. The aim here was to investigate whether adaptation occurs for realistic noises and to what extent it depends on the spectrum and level fluctuations of the noise. Forty-nine different realistic and synthetic noises were analyzed and classified according to how much they fluctuated in level over time and how much their spectra differed from the speech spectrum. Six representative noises were chosen that covered the observed range of level fluctuations and spectral differences but could still mask speech. For the six noises, speech reception thresholds (SRTs) were measured for natural and tone-vocoded words delayed 50 (early condition) and 800 ms (late condition) from the noise onset. Adaptation was calculated as the SRT improvement in the late relative to the early condition. Twenty-two adults with normal hearing participated in the experiments. For natural words, adaptation was small overall (mean = 0.5 dB) and similar across the six noises. For vocoded words, significant adaptation occurred for all six noises (mean = 1.3 dB) and was not statistically different across noises. For the tested noises, the amount of adaptation was independent of the spectrum and level fluctuations of the noise. The results suggest that adaptation in speech recognition can occur in realistic noisy environments.