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The effect of hearing aid microphone mode on performance in an auditory orienting task.

Brimijoin WO, Whitmer WM, McShefferty D, Akeroyd MA - Ear Hear (2014 Sep-Oct)

Bottom Line: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user.The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones.If hearing-aid users are to receive maximum directional benefit in noisy environments, both adaptive directionality in hearing aids and clinical advice on using directional microphones should take head movement and orientation behavior into account.

View Article: PubMed Central - PubMed

Affiliation: MRC Institute of Hearing Research (Scottish Section), Glasgow Royal Infirmary, Glasgow, Lanarkshire, United Kingdom.

ABSTRACT

Objectives: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user. It is assumed that when the signal of interest is off-axis, users can reorient themselves to the signal to make use of the directional microphones to improve signal-to-noise ratio. The present study tested this assumption by measuring the head-orienting behavior of bilaterally fit hearing-impaired individuals with their microphones set to omnidirectional and directional modes. The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones.

Design: The authors instructed hearing-impaired individuals to turn and face a female talker in simultaneous surrounding male-talker babble. Participants pressed a button when they felt they were accurately oriented in the direction of the female talker. Participants completed three blocks of trials with their hearing aids in omnidirectional mode and three blocks in directional mode, with mode order randomized. Using a Vicon motion tracking system, the authors measured head position and computed fixation error, fixation latency, trajectory complexity, and proportion of misorientations.

Results: Results showed that for larger off-axis target angles, listeners using directional microphones took longer to reach their targets than they did when using omnidirectional microphones, although they were just as accurate. They also used more complex movements and frequently made initial turns in the wrong direction. For smaller off-axis target angles, this pattern was reversed, and listeners using directional microphones oriented more quickly and smoothly to the targets than when using omnidirectional microphones.

Conclusions: The authors argue that an increase in movement complexity indicates a switch from a simple orienting movement to a search behavior. For the most off-axis target angles, listeners using directional microphones appear to not know which direction to turn, so they pick a direction at random and simply rotate their heads until the signal becomes more audible. The changes in fixation latency and head orientation trajectories suggest that the decrease in off-axis audibility is a primary concern in the use of directional microphones, and listeners could experience a loss of initial target speech while turning toward a new signal of interest. If hearing-aid users are to receive maximum directional benefit in noisy environments, both adaptive directionality in hearing aids and clinical advice on using directional microphones should take head movement and orientation behavior into account.

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Related in: MedlinePlus

Schematic of presentation method showing noise locations (N) and possible signal positions (black boxes). On each trial, six noises and a signal anywhere from ±45° to 150° were presented. All stimuli were positioned with respect to the head angle (azimuth) of the listener at the beginning of the trial.
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Figure 1: Schematic of presentation method showing noise locations (N) and possible signal positions (black boxes). On each trial, six noises and a signal anywhere from ±45° to 150° were presented. All stimuli were positioned with respect to the head angle (azimuth) of the listener at the beginning of the trial.

Mentions: The listeners were presented with a background babble of voices. This babble was composed of ongoing concatenated male-talker sentences from the IEEE corpus (Rothauser et al. 1969). Six different male talkers were used, one for each of the six noise locations; these locations were fixed at ±30°, ±90°, and ±150° relative to the participant’s head angle as measured at the start of each trial (Fig. 1). The reasons for the specification of these locations with respect to the head rather than with respect to the 0° loudspeaker, an arbitrary point to which the listeners were asked to reorient after each trial, were that (1) the time involved in reorienting would unnecessarily lengthen the experiment time and (2) listeners are never particularly accurate in orienting. By presenting targets relative to the head we ensured that we could measure the head movements associated with a particular (and repeatable) angular offset relative to their starting positions. To present sounds from angles that were between two loudspeakers, we used equal-power panning based on a sine/cosine crossfade between the two nearest loudspeakers. The signals consisted of concatenated female-talker sentences from the BKB corpus (Bench et al. 1979). Signal position on each trial was also specified relative to the participant’s head angle at the beginning of the trial: signals were presented from 45° to 150° relative to the listener’s acoustic midline in 15° increments. These locations were repeated eight times each, and the order of all trials was randomly shuffled. The first signal in a block began 5 sec after babble started; this was to ensure that any long-term (slow attack) compression in the hearing aids was engaged before the start of the signal. Signal duration was determined by the participant; a 50 ms cosine2 onset gate was applied to each signal, and when the participant pressed a button (see later) to signal when they were facing the target signal the corresponding offset gate was applied. The long-term average level of the babble measured at the center of the ring was 59 dB (A). The long-term average signal level was 65 dB (A), so the average SNR was +6 dB.


The effect of hearing aid microphone mode on performance in an auditory orienting task.

Brimijoin WO, Whitmer WM, McShefferty D, Akeroyd MA - Ear Hear (2014 Sep-Oct)

Schematic of presentation method showing noise locations (N) and possible signal positions (black boxes). On each trial, six noises and a signal anywhere from ±45° to 150° were presented. All stimuli were positioned with respect to the head angle (azimuth) of the listener at the beginning of the trial.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4232295&req=5

Figure 1: Schematic of presentation method showing noise locations (N) and possible signal positions (black boxes). On each trial, six noises and a signal anywhere from ±45° to 150° were presented. All stimuli were positioned with respect to the head angle (azimuth) of the listener at the beginning of the trial.
Mentions: The listeners were presented with a background babble of voices. This babble was composed of ongoing concatenated male-talker sentences from the IEEE corpus (Rothauser et al. 1969). Six different male talkers were used, one for each of the six noise locations; these locations were fixed at ±30°, ±90°, and ±150° relative to the participant’s head angle as measured at the start of each trial (Fig. 1). The reasons for the specification of these locations with respect to the head rather than with respect to the 0° loudspeaker, an arbitrary point to which the listeners were asked to reorient after each trial, were that (1) the time involved in reorienting would unnecessarily lengthen the experiment time and (2) listeners are never particularly accurate in orienting. By presenting targets relative to the head we ensured that we could measure the head movements associated with a particular (and repeatable) angular offset relative to their starting positions. To present sounds from angles that were between two loudspeakers, we used equal-power panning based on a sine/cosine crossfade between the two nearest loudspeakers. The signals consisted of concatenated female-talker sentences from the BKB corpus (Bench et al. 1979). Signal position on each trial was also specified relative to the participant’s head angle at the beginning of the trial: signals were presented from 45° to 150° relative to the listener’s acoustic midline in 15° increments. These locations were repeated eight times each, and the order of all trials was randomly shuffled. The first signal in a block began 5 sec after babble started; this was to ensure that any long-term (slow attack) compression in the hearing aids was engaged before the start of the signal. Signal duration was determined by the participant; a 50 ms cosine2 onset gate was applied to each signal, and when the participant pressed a button (see later) to signal when they were facing the target signal the corresponding offset gate was applied. The long-term average level of the babble measured at the center of the ring was 59 dB (A). The long-term average signal level was 65 dB (A), so the average SNR was +6 dB.

Bottom Line: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user.The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones.If hearing-aid users are to receive maximum directional benefit in noisy environments, both adaptive directionality in hearing aids and clinical advice on using directional microphones should take head movement and orientation behavior into account.

View Article: PubMed Central - PubMed

Affiliation: MRC Institute of Hearing Research (Scottish Section), Glasgow Royal Infirmary, Glasgow, Lanarkshire, United Kingdom.

ABSTRACT

Objectives: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user. It is assumed that when the signal of interest is off-axis, users can reorient themselves to the signal to make use of the directional microphones to improve signal-to-noise ratio. The present study tested this assumption by measuring the head-orienting behavior of bilaterally fit hearing-impaired individuals with their microphones set to omnidirectional and directional modes. The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones.

Design: The authors instructed hearing-impaired individuals to turn and face a female talker in simultaneous surrounding male-talker babble. Participants pressed a button when they felt they were accurately oriented in the direction of the female talker. Participants completed three blocks of trials with their hearing aids in omnidirectional mode and three blocks in directional mode, with mode order randomized. Using a Vicon motion tracking system, the authors measured head position and computed fixation error, fixation latency, trajectory complexity, and proportion of misorientations.

Results: Results showed that for larger off-axis target angles, listeners using directional microphones took longer to reach their targets than they did when using omnidirectional microphones, although they were just as accurate. They also used more complex movements and frequently made initial turns in the wrong direction. For smaller off-axis target angles, this pattern was reversed, and listeners using directional microphones oriented more quickly and smoothly to the targets than when using omnidirectional microphones.

Conclusions: The authors argue that an increase in movement complexity indicates a switch from a simple orienting movement to a search behavior. For the most off-axis target angles, listeners using directional microphones appear to not know which direction to turn, so they pick a direction at random and simply rotate their heads until the signal becomes more audible. The changes in fixation latency and head orientation trajectories suggest that the decrease in off-axis audibility is a primary concern in the use of directional microphones, and listeners could experience a loss of initial target speech while turning toward a new signal of interest. If hearing-aid users are to receive maximum directional benefit in noisy environments, both adaptive directionality in hearing aids and clinical advice on using directional microphones should take head movement and orientation behavior into account.

Show MeSH
Related in: MedlinePlus