Measuring the effects of spectral smearing and enhancement on speech recognition in noise for adults and children

Abstract

Broadened auditory filters associated with sensorineural hearing loss have clearly been shown to diminish speech recognition in noise for adults, but far less is known about potential effects for children. This study examined speech recognition in noise for adults and children using simulated auditory filters of different widths. Specifically, 5 groups (20 listeners each) of adults or children (5 and 7 yrs), were asked to recognize sentences in speech-shaped noise. Seven-year-olds listened at 0 dB signal-to-noise ratio (SNR) only; 5-yr-olds listened at þ3 or 0 dB SNR; and adults listened at 0 or À3 dB SNR. Sentence materials were processed both to smear the speech spectrum (i.e., simulate broadened filters), and to enhance the spectrum (i.e., simulate narrowed filters). Results showed: (1) Spectral smearing diminished recognition for listeners of all ages; (2) spectral enhancement did not improve recognition, and in fact diminished it somewhat; and (3) interactions were observed between smearing and SNR, but only for adults. That interaction made age effects difficult to gauge. Nonetheless, it was concluded that efforts to diagnose the extent of broadening of auditory filters and to develop techniques to correct this condition could benefit patients with hearing loss, especially children.

Spectral Ripple Discrimination in Normal-Hearing Infants

“…Measures of frequency resolution, including critical bandwidth and psychophysical tuning curve width, mature by 6 months of age (Olsho et al 1987, Schneider et al 1990, Spetner and Olsho 1990). Despite the fact that infants and young children are particularly reliant on spectral detail for speech discrimination in studies using CI simulations (Warner-Czyz et al 2014, Nittrouer et al 2015), spectral resolution remains immature in NH listeners through 7–10 years of age (Blagosklonova et al 1989, Allen and Wightman 1994, Peter et al 2014). One possible explanation for this is that development of spectral resolution in NH listeners is mainly due to maturation of across-channel intensity resolution.…”

“…For instance, young listeners have been shown to rely more than adults on spectral speech discrimination cues (Nittrouer et al 2015). Furthermore, based on their susceptibility to informational masking, (Allen and Wightman 1995, Oh et al 2001, Leibold and Neff 2011), young listeners might be less likely to focus on available within-channel temporal or intensity cues than adults.…”

Speech Recognition in Noise by Children with and without Dyslexia: How is it Related to Reading?

“…Stimuli for the sentence recognition task consisted of 54 four-word sentences that have been used previously (Nittrouer et al, 2015). All words in these sentences are monosyllabic, and were selected to be within the vocabularies of school-aged children.…”

“…The spectra of the voiced portions of all sentences were smeared so that the peaks and valleys of all spectra were only half as distant from the source spectrum as in the original signals. This goal was accomplished using procedures developed earlier (Nittrouer et al, 2015), which involved manipulating the amplitude of individual harmonics. That meant that only voiced portions of the sentences could be manipulated.…”

“…In order to assess the hypothesis that this recognition for children with dyslexia is impaired due to the presence of poor spectral processing, the speech spectrum was also smeared, and those stimuli presented in noise. Earlier work (Nittrouer, Tarr, Wucinich, Moberly, & Lowenstein, 2015) showed that the masking effects of noise were exacerbated with these smeared speech signals for listeners with normal auditory thresholds and typical language abilities, in spite of the fact that recognition in quiet for the smeared signals was near perfect. Applying the principles of experiments such as those of Gordon-Salant and Fitzgibbons (1993) and McAnally et al (1997), speech recognition in noise should be even further diminished for children with dyslexia when these smeared spectral signals are presented, if they have spectral processing disorders.…”