A comparison of auditory brain stem responses elicited by click and chirp stimuli in adults with normal hearing and sensory hearing loss.

OBJECTIVES: The aim of this study was to compare the human auditory brain stem response (ABR) elicited by clicks and chirps with overall behavioral hearing thresholds in participants with normal hearing and with sensory hearing loss. The authors hypothesized that ABRs to chirps would be more robust and that thresholds would be more similar to overall behavioral hearing thresholds compared with ABRs to clicks. DESIGN: Twenty-five adults with normal hearing and 25 adults with sensory hearing loss were recruited. Subjects were without middle ear or neurological pathologies at the time of testing. Subjects with sensory hearing loss were separated into mild to moderate hearing loss and mild to severe hearing loss groups. Behavioral hearing thresholds for pure tones were obtained at nine octave and interoctave frequencies ranging from 250 to 8000 Hz; an average of these nine frequencies was calculated for each participant. Evoked potential thresholds were measured by ABRs to click and chirp stimuli. Analyses included wave V absolute latencies and wave V peak-to-peak amplitudes. Thresholds for ABRs to clicks and chirps were compared with each other and with overall behavioral hearing thresholds. RESULTS: ABR thresholds to chirp and click stimuli did not differ significantly for either the normal-hearing or the hearing loss groups. Wave V peak-to-peak amplitude was higher for chirps than clicks, particularly at lower intensities, for all groups. ABR thresholds to chirps were closer to overall behavioral thresholds than clicks in all groups. Moreover, ABR thresholds to chirps did not differ significantly from behavioral thresholds in the two hearing loss groups. CONCLUSIONS: ABRs obtained with chirp stimuli provide an efficient method for estimating hearing thresholds in individuals with normal hearing and sensory hearing loss where broadband signals are selected for testing. ABRs to chirps display higher peak-to-peak amplitudes than those obtained with clicks and may provide responses closer to behavioral thresholds. This information could result in improved accuracy in identifying hearing loss and estimating hearing sensitivity for broadband signals in infants, children, and difficult-to-test older populations.

Human sensitivity to differences in the rate of auditory cue change.

Measurement of sensitivity to differences in the rate of change of auditory signal parameters is complicated by confounds among duration, extent, and velocity of the changing signal. Dooley and Moore [(1988) J. Acoust. Soc. Am. 84(4), 1332-1337] proposed a method for measuring sensitivity to rate of change using a duration discrimination task. They reported improved duration discrimination when an additional intensity or frequency change cue was present. The current experiments were an attempt to use this method to measure sensitivity to the rate of change in intensity and spatial position. Experiment 1 investigated whether duration discrimination was enhanced when additional cues of rate of intensity change, rate of spatial position change, or both were provided. Experiment 2 determined whether participant listening experience or the testing environment influenced duration discrimination task performance. Experiment 3 assessed whether duration discrimination could be used to measure sensitivity to rates of changes in intensity and spatial position for stimuli with lower rates of change, as well as emphasizing the constancy of the velocity cue. Results of these experiments showed that duration discrimination was impaired rather than enhanced by the additional velocity cues. The findings are discussed in terms of the demands of listening to concurrent changes along multiple auditory dimensions.

Auditory perception of motor vehicle travel paths.

OBJECTIVE: These experiments address concerns that motor vehicles in electric engine mode are so quiet that they pose a risk to pedestrians, especially those with visual impairments. BACKGROUND: The "quiet car" issue has focused on hybrid and electric vehicles, although it also applies to internal combustion engine vehicles. Previous research has focused on detectability of vehicles, mostly in quiet settings. Instead, we focused on the functional ability to perceive vehicle motion paths. METHOD: Participants judged whether simulated vehicles were traveling straight or turning, with emphasis on the impact of background traffic sound. RESULTS: In quiet, listeners made the straight-or-turn judgment soon enough in the vehicle's path to be useful for deciding whether to start crossing the street. This judgment is based largely on sound level cues rather than the spatial direction of the vehicle. With even moderate background traffic sound, the ability to tell straight from turn paths is severely compromised. The signal-to-noise ratio needed for the straight-or-turn judgment is much higher than that needed to detect a vehicle. CONCLUSION: Although a requirement for a minimum vehicle sound level might enhance detection of vehicles in quiet settings, it is unlikely that this requirement would contribute to pedestrian awareness of vehicle movements in typical traffic settings with many vehicles present. APPLICATION: The findings are relevant to deliberations by government agencies and automobile manufacturers about standards for minimum automobile sounds and, more generally, for solutions to pedestrians' needs for information about traffic, especially for pedestrians with sensory impairments.