Objective Assessment of Speech Intelligibility in Crowded Public Spaces.

The objective of this study was to obtain a normative database of speech intelligibility data for young normal-hearing listeners communicating in public spaces. A total of 174 listeners participated in an interactive speech intelligibility task that required four-person groups to conduct a live version of the Modified Rhyme Test in noisy public spaces. The public spaces tested included a college library, a college cafeteria, a casual dining restaurant during lunch hour, and a crowded bar during happy hour. At the start of each trial, one of the participants was randomly selected as the talker, and a tablet computer was used to prompt them to say a word aloud from the Modified Rhyme Test. Then, the other three participants were required to select this word from one of six rhyming alternatives displayed on three other tablet computers. The tablet computers were also used to record the SPL at each listener location during and after the interval where the target talker was speaking. These SPL measurements were used to estimate the signal-to-noise ratio (SNR) in each trial of the experiment. As expected, the results show that speech intelligibility decreases, response time increases, and perceived difficulty increases as the background noise level increases. There was also a systematic decrease in SNR with increasing background noise, with SNR decreasing 0.44 dB for every 1 dB increase in ambient noise level above 60 dB. Overall, the results of this study have demonstrated how low-cost tablet computer-based data collection systems can be used to collect live-talker speech intelligibility data in real-world environments. We believe these techniques could be adapted for use in future studies focused on obtaining ecologically valid assessments of the effects of age, hearing impairment, amplification, and other factors on speech intelligibility performance in real-world environments.

Effects of Amplification on Neural Phase Locking, Amplitude, and Latency to a Speech Syllable.

OBJECTIVE: Older adults often have trouble adjusting to hearing aids when they start wearing them for the first time. Probe microphone measurements verify appropriate levels of amplification up to the tympanic membrane. Little is known, however, about the effects of amplification on auditory-evoked responses to speech stimuli during initial hearing aid use. The present study assesses the effects of amplification on neural encoding of a speech signal in older adults using hearing aids for the first time. It was hypothesized that amplification results in improved stimulus encoding (higher amplitudes, improved phase locking, and earlier latencies), with greater effects for the regions of the signal that are less audible. DESIGN: Thirty-seven adults, aged 60 to 85 years with mild to severe sensorineural hearing loss and no prior hearing aid use, were bilaterally fit with Widex Dream 440 receiver-in-the-ear hearing aids. Probe microphone measures were used to adjust the gain of the hearing aids and verify the fitting. Unaided and aided frequency-following responses and cortical auditory-evoked potentials to the stimulus /ga/ were recorded in sound field over the course of 2 days for three conditions: 65 dB SPL and 80 dB SPL in quiet, and 80 dB SPL in six-talker babble (+10 signal to noise ratio). RESULTS: Responses from midbrain were analyzed in the time regions corresponding to the consonant transition (18 to 68 ms) and the steady state vowel (68 to 170 ms). Generally, amplification increased phase locking and amplitude and decreased latency for the region and presentation conditions that had lower stimulus amplitudes-the transition region and 65 dB SPL level. Responses from cortex showed decreased latency for P1, but an unexpected decrease in N1 amplitude. Previous studies have demonstrated an exaggerated cortical representation of speech in older adults compared to younger adults, possibly because of an increase in neural resources necessary to encode the signal. Therefore, a decrease in N1 amplitude with amplification and with increased presentation level may suggest that amplification decreases the neural resources necessary for cortical encoding. CONCLUSION: Increased phase locking and amplitude and decreased latency in midbrain suggest that amplification may improve neural representation of the speech signal in new hearing aid users. The improvement with amplification was also found in cortex, and, in particular, decreased P1 latencies and lower N1 amplitudes may indicate greater neural efficiency. Further investigations will evaluate changes in subcortical and cortical responses during the first 6 months of hearing aid use.