Cortical potentials evoked by tone frequency changes can predict speech perception in noise.

Accurate and objective assessment of higher order auditory processing is challenging and mainly relies on evaluations that require a subjects' active participation in tests such as frequency discrimination or speech perception in noise. This study investigates the value of cortical auditory evoked potentials (CAEPs) evoked in response to auditory change stimuli, known as acoustic change complexes (ACCs), as an objective measurement of auditory performance in hearing impairment. Secondary objectives were to assess the effect of hearing loss and non-professional musical experience on the ACC, and compare the ACC to the 'conventional' CAEP evoked in response to stimulus onset. In 24 normal-hearing subjects, consisting of 12 musicians and 12 non-musicians, and 13 age-matched hearing-impaired subjects ACCs were recorded in response to 12% frequency increases at four base frequencies (0.5, 1, 2 and 4 kHz). ACC amplitudes and latencies were compared to frequency discrimination thresholds at each base frequency, and to speech perception in noise. Frequency discrimination and speech perception in noise were significantly better for larger ACC N1-P2 amplitudes and shorter N1 latencies, whereas both frequency discrimination and speech perception did not correlate with onset CAEP amplitude or latency. Multiple regression analysis for prediction of speech perception in noise revealed that the strongest model was obtained by averaging over three frequencies (1, 2 and 4 kHz) with two significant predictors: hearing loss (R2 = 0.52) and ACC latency (R2 = 0.35). Thus, explaining 87% of the variance, this model indicates that subjects with longer ACC latencies have worse speech perception in noise than subjects with comparable hearing thresholds and shorter ACC latencies. If hearing loss was removed from this model, the combination of ACC amplitude and latency over those three frequencies explained 74% of the total variance in speech perception in noise. There were no differences in frequency discrimination, speech perception, CAEP, or ACC between recreational musicians and non-musicians. We conclude that the objective ACC N1 latency is a good predictor of speech perception in noise. When confirmed in validation studies with larger numbers of subjects, it can aid clinicians in their evaluation of auditory performance and higher order processing, in particular when behavioral testing is unreliable.

Cortical potentials evoked by tone frequency changes compared to frequency discrimination and speech perception: Thresholds in normal-hearing and hearing-impaired subjects.

Frequency discrimination ability varies within the normal hearing population, partially explained by factors such as musical training and age, and it deteriorates with hearing loss. Frequency discrimination, while essential for several auditory tasks, is not routinely measured in clinical setting. This study investigates cortical auditory evoked potentials in response to frequency changes, known as acoustic change complexes (ACCs), and explores their value as a clinically applicable objective measurement of frequency discrimination. In 12 normal-hearing and 13 age-matched hearing-impaired subjects, ACC thresholds were recorded at 4 base frequencies (0.5, 1, 2, 4 kHz) and compared to psychophysically assessed frequency discrimination thresholds. ACC thresholds had a moderate to strong correlation to psychophysical frequency discrimination thresholds. In addition, ACC thresholds increased with hearing loss and higher ACC thresholds were associated with poorer speech perception in noise. The ACC threshold in response to a frequency change therefore holds promise as an objective clinical measurement in hearing impairment, indicative of frequency discrimination ability and related to speech perception. However, recordings as conducted in the current study are relatively time consuming. The current clinical application would be most relevant in cases where behavioral testing is unreliable.