Starkey Research & Clinical Blog

Do Patients with Severe Hearing Loss Benefit from Directional Microphones?

Ricketts, T.A., & Hornsby, B.W.Y. (2006). Directional hearing aid benefit in listeners with severe hearing loss. International Journal of Audiology, 45, 190-197.

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Hearing Technologies. This editorial does not represent the opinions of the original authors.

The benefit of directional microphones for speech recognition in noise is well established for individuals with mild to moderate hearing loss (Madison & Hawkins, 1983; Killion et al., 1998; Ricketts 2000a; Ricketts & Henry, 2002).  The potential benefit of directional microphones for severely hearing-impaired individuals is less understood and few studies have examined directional benefit when hearing loss is greater than 65dB.

Killion and Christensen (1998) proposed that listeners with severe-to-profound hearing loss may experience reduced directional benefit because they are less able to make use of speech information across frequencies. Ricketts, Henry and Hornsby confirmed this hypothesis in a 2005 study. They found an approximately 7% increase in speech recognition score per 1dB increase in directivity for listeners with moderate hearing loss, whereas listeners with severe loss achieved only an approximately 3.5% increase per 1dB increase in directivity.

In their 2005 study, Ricketts and Hornsby used individually determined SNRs and auditory-visual stimuli that allowed testing at poorer SNRs without floor effects. The authors point out that visual cues usually offer a greater benefit at poor SNRs, especially for sentence materials (Erber, 1969; Sumby & Pollack, 1954; MacLeod & Summerfield, 1987).  Individuals rely more on visual cues in poorer SNRs, visual information that provides complementary, non-redundant cues is most beneficial (Grant, 1998; Walden et al., 1993).

The purpose of their study was to examine potential directional benefit for severely hearing-impaired listeners at multiple SNRs in auditory-only and auditory-visual conditions. Directional and omnidirectional performance in quiet conditions were also tested to rule out performance differences between microphone modes that could be attributed to reduction of environmental noise by the directional microphone. Finally, it was determined if performance in quiet conditions would significantly exceed performance in highly positive SNRs. Though significant improvement in SNRs more favorable than +15 dB is usually not expected, some research suggests that hearing-impaired individuals may experience additional benefit from more favorable SNRs (Studebaker et al, 1999).

Twenty adult participants with severe-to-profound sensorineural hearing loss participated in the study. All participants used oral communication, had at least nine years of experience with hearing aids and had pure tone average hearing thresholds greater than 65dB.  Participants were fitted with power behind-the-ear hearing aids with full shell, unvented earmolds. Digital noise reduction and feedback management was turned off. The directional program was equalized, so that gain matched the omnidirectional mode as closely as possible.

The Audio/Visual Connected Speech Test (CST; Cox et al, 1987), a speech recognition test with paired passages of connected speech, was presented to listeners on DVD. Speech was presented at a 0-degree azimuth angle and uncorrelated competing noise was presented via five loudspeakers surrounding the listener. Testing took place in a sound booth with reflective panels to approximate common levels of reverberation in everyday situations.

Baseline SNRs were obtained for each subject in auditory-only and auditory-visual conditions, at a level that was near, but not reaching floor performance. Speech recognition testing was conducted for omnidirectional and directional conditions at baseline SNR, baseline + 4dB and baseline + 8dB. Presentation SNRs ranged from 0dB to +24dB for auditory-only conditions and from -6dB to +18dB for auditory-visual conditions. Listeners were tested with auditory-only stimuli in quiet conditions, for omnidirectional and directional modes. Testing in quiet was not performed with auditory-visual stimuli, as performance was expected to approach ceiling performance levels.

The multiple SNR levels were achieved with two different methodologies. Half of the participants listened to a fixed noise level of 60dB SPL and speech levels were varied to achieve the desired SNRs. The remaining participants listened to a fixed speech level of 67dB SPL and the noise levels were adjusted to reach the desired SNR levels. Data analysis revealed no significant differences between these two test methodologies for any of the variables, so their data was pooled for subsequent analyses.

The results showed significant main effects for microphone mode (directional versus omni), SNR and presentation condition (auditory-only versus auditory-visual). There were significant interactions between microphone mode and SNR, as well as between presentation condition and SNR.  Each increase in SNR resulted in significantly better performance for both omnidirectional and directional modes. Performance in directional mode was significantly better than omnidirectional for all SNR levels. The authors pointed out that auditory-visual performance at all three SNRs was always better than auditory-only, despite the fact that the absolute SNRs for auditory-visual conditions were lower than the equivalent auditory-only conditions, by an average of 5dB.  The authors interpreted this finding as strong support for the benefit of visual cues for speech recognition in adverse conditions.

When the effects of directionality and SNR were analyzed separately for auditory-only and auditory-visual conditions, they found that directional performance was significantly better than omnidirectional performance for all auditory-visual conditions. In auditory-only conditions, directionality only had a significant effect at the baseline SNR, but not in the baseline +4dB, baseline +8dB or quiet conditions.

Perhaps not surprisingly, Ricketts and his colleagues found that the addition of visual cues offered their severely-impaired listeners a significant advantage for understanding connected speech. When they compared the auditory-only and auditory-visual scores at equivalent SNR levels, they determined that participants achieved an average improvement of 22% with the availability of visual cues. This finding is in agreement with previous research that found a visual advantage of 24% for listeners with moderate hearing loss (Henry & Ricketts, 2003).

Also not surprisingly, performance improved with increases in signal to noise ratio.  For the auditory-only condition, they found an average improvement of 1.6% per dB and 2.7% per dB for the omnidirectional and directional modes, respectively. For the auditory-visual condition, there was an improvement of 3.7% per dB for omnidirectional mode and 3.1% per dB for directional mode.  Furthermore, they found an additional performance increase of 8% for directional mode and 12% for omnidirectional mode when participants were tested in quiet conditions. This was somewhat surprising given previous research based on the articulation index (AI) that suggested maximal performance could be expected at SNRs of approximately +15dB.  The absolute SNR for the baseline +8dB condition was 14.7dB, so further improvements in quiet conditions support the suggestion that hearing-impaired listeners experience increased improvement for SNRs up to +20dB (Studebaker et al, 1999; Sherbecoe & Studebaker, 2002).

The benefit of visual cues was not specifically addressed by this study because it did not compare auditory-only and auditory-visual performance at the same SNR levels. However, the discovery that visual cues improved performance even when the SNRs were approximately 5dB poorer was strong support for the benefit of visual information for speech recognition in noisy environments. This underscores the recommendation that severely hearing-impaired listeners should always be counseled to take advantage of visual cues whenever possible, especially in adverse listening conditions. Although visual cues cannot completely counterbalance the auditory cues lost to hearing loss and competing noise, they supply additional information that can help the listener identify or differentiate phonemes, especially in connected speech containing semantic and syntactic context. In conversational situations, visual cues include not just lip-reading but also the speaker’s gestures, expressions and body language. All of these cues can aid speech recognition, so hearing-impaired individuals as well as their family members should be trained in strategies to maximize the availability of visual information.

Ricketts and Hornsby’s study supports the potential benefit of directional microphones for individuals with severe hearing loss. Many hearing aid users with severe-to-profound loss have become accustomed to the use of omnidirectional microphones and may be resistant to directional microphones, especially automatic directionality, if it is in the primary program of their hearing instruments. One strategy for addressing these cases is to program the hearing aid’s primary memory as full-time omnidirectional while programming a second, manually accessed, memory with a full-time directional microphone. This way the listener is able to choose when and how they use their directional program and may be less likely to experience unexpected and potentially disconcerting changes in perceived loudness and sound quality.

In addition to providing evidence for the benefit of visual cues and directionality, the findings of this study can be extrapolated to support the use of FM and wireless accessories. The fact that performance in quiet conditions was still significantly better than the next most favorable SNR (14.7dB) shows that improving SNR as much as possible provides demonstrable advantages for listeners with severe hearing loss. Even for individuals who do well with their hearing instruments overall, wireless accessories that stream audio directly to the listeners hearing instruments may further improve understanding. These accessories improve SNR by reducing the effect of room acoustics and reverberation, as well as reducing the effect of competing noise and distance between the sound source and the listener. Most modern hearing instruments are compatible with wireless accessories so hearing aid evaluations should always include discussion of their potential benefits. These devices work with a wide range of hearing aid styles, do not require the use of an adapter or receiver boot and are much less expensive than an FM system.

Ricketts and Hornsby’s study underscores the importance of visual information and directionality for speech recognition in noisy environments and illuminates ways in which clinicians can help patients with severe-to-profound loss achieve improved communication in everyday circumstances. Modern technologies such as directional processing and wireless audio streaming accessories can be effective tools for improving SNRs in everyday situations that may otherwise challenge or overwhelm the listener with severe to profound hearing loss.

References

Erber, N.P. (1969). Interaction of audition and vision in the reception of oral speech stimuli. Journal of Speech and Hearing Research 12, 423-425.

Grant, K.W., Walden, B.E. & Seitz, P.F. (1998). Auditory-visual speech recognition by hearing-impaired subjects: consonant recognition, sentence recognition and auditory-visual integration. Journal of the Acoustical Society of America 103, 2677-2690.

Henry, P. & Ricketts, T. A. (2003).  The effect of head angle on auditory and visual input for directional and omnidirectional hearing aids. American Journal of Audiology 12(1), 41-51.

Killion, M. C., Schulien, R., Christensen, L., Fabry, D. & Revit, L. (1998). Real world performance of an ITE directional microphone. Hearing Journal 51(4), 24-38.

Killion, M.C. & Christensen, L. (1998). The case of the missing dots: AI and SNR loss. Hearing Journal 51(5), 32-47.

MacLeod, A. & Summerfield, Q. (1987). Quantifying the contribution of vision to speech perception in noise. British Journal of Audiology 21, 131-141.

Madison, T.K. & Hawkins, D.B. (1983). The signal-to-noise ratio advantage of directional microphones. Hearing Instruments 34(2), 18, 49.

Pavlovic, C. (1984). Use of the articulation index for assessing residual auditory function in listeners with sensorineural hearing impairment. Journal of the Acoustical Society of America 75, 1253-1258.

Pavlovic, C., Studebaker, G. & Scherbecoe, R. (1986). An articulation index based procedure for predicting the speech recognition performance of hearing-impaired individuals. Journal of the Acoustical Society of America 80(1), 50-57.

Ricketts, T.A. (2000a). Impact of noise source configuration on dire3ctional hearing aid benefit and performance. Ear and Hearing 21(3), 194-205.

Ricketts, T.A. & Henry, P. (2002). Evaluation of an adaptive directional microphone hearing aid. International Journal of Audiology 41(2), 100-112.

Ricketts, T., Henry, P. & Hornsby, B. (2005). Application of frequency importance functions to directivity for prediction of benefit in uniform fields. Ear & Hearing 26(5), 473-86.

Studebaker, G., Sherbecoe, R., McDaniel, D. & Gwaltney, C. (1999). Monosyllabic word recognition at higher-than-normal speech and noise levels. Journal of the Acoustical Society of America 105(4), 2431-2444.

Sherbecoe, R.L., Studebaker, G.A. (2002). Audibility-index functions for the Connected Speech Test. Ear & Hearing 23(5), 385-398.

Sumby, W.H. & Pollack, I. (1954). Visual contribution to speech intelligibility in noise. Journal of the Acoustical Society of America 26, 212-215.

Walden, B.E., Busacco, D.A. & Montgomery, A.A. (1993). Benefit from visual cues in auditory-visual speech recognition by middle-aged and elderly persons. Journal of Speech and Hearing Research 36, 431-436.

Do hearing aid wearers benefit from visual cues?

Wu, Y-H. & Bentler, R.A. (2010) Impact of visual cues on directional benefit and preference: Part I – laboratory tests. Ear and Hearing 31(1), 22-34.

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors. 

The benefits of directional microphone use have been consistently supported by experimental data in the laboratory (Valente et al. 1995; Ricketts & Hornsby 2006; Gravel et al. 1999; Kuk et al. 1999). Similarly, hearing aid users have indicated a preference for directional microphones over omnidirectional processing in noise in controlled environments (Preves et al. 1999; Walden et al. 2005; Amlani et al. 2006). Despite the robust directional benefit reported in laboratory studies, field studies have yielded less impressive results; with some studies reporting perceived benefit (Preves et al. 1999; Ricketts et al. 2003) while others have not (Walden et al. 2000; Cord et al. 2002, 2004; Palmer et al. 2006).

One factor that could account for reduced directional benefit reported in field studies is the availability of visual cues. It is well established that visual cues, including lip-reading (Sumby & Pollack 1954) as well as eyebrow (Bernstein et al. 1989) and head movements (Munhall et al. 2004), can improve speech recognition ability in the presence of noise. In field studies, the availability of visual cues could result in a decreased directional benefit due to ceiling effects. In other words, the benefit of audio-visual (AV) speech cues might result in omnidirectional performance so close to a listener’s maximum ability that directionality may offer only limited additional improvement.  This could reduce both measured and perceived directional benefits.  It follows that ceiling effects from the availability of AV speech cues could also reduce the ability of auditory-only (AO) laboratory findings to accurately predict real-world performance.

Few studies have investigated the effect of visual cues on hearing aid performance or directional benefit. Wu and Bentler’s goal in the current study was to determine if visual cues could partially account for the discrepancy between laboratory and field studies of directional benefit. They outlined three experimental hypotheses:

1. Listeners would obtain less directional benefit and would prefer directional over omnidirectional microphone modes less frequently in auditory-visual (AV) conditions than in auditory-only (AO) conditions.

2. The AV directional benefit would not be predicted by the AO directional benefit.

3. Listeners with greater lip-reading skills would obtain less AV directional benefit than would listeners with lesser lip-reading skills.

Twenty-four adults with hearing loss participated in the study. Participants were between the ages of 20-79 years, had bilaterally symmetrical, downward-sloping, sensorineural hearing losses, normal or corrected normal vision and were native English speakers. Participants were fitted with bilateral, digital, in-the-ear hearing instruments with manually-accessible omnidirectional and directional microphone modes.

Directional benefit was assessed with two speech recognition measures:  the AV version of the Connected Speech Test (CST; Cox et al., 1987) and the Hearing in Noise Test (HINT; Nilsson et al., 1994). For the AV CST the talker was displayed on a 17” monitor. Participants listened to sets of CST sentences again in a second session to evaluate subjective preference for directional versus omnidirectional microphone modes. Speech stimuli were presented in six signal-to-noise (SNR) conditions ranging from -10dB to +10dB in 4db steps. Lip-reading ability was assessed with the Utley test (Utley, 1946), an inventory of 31 sentences recited without sound or facial exaggeration.

Analysis of the CST scores yielded significant main effects for SNR, microphone mode and presentation mode (AV vs. AO) as well as significant interactions among the variables. The benefit for visual cues was greater than the benefit afforded by directionality. As the authors expected, for most SNRs the directional benefit was smaller for AV conditions than AO conditions with the exception of the poorest SNR condition, -10dB.  Scores for all conditions (AV-DIR, AV-OMNI, AO-DIR, AO-OMNI) plateau at ceiling levels for the most favorable SNRs; meaning that both AV benefit and directional benefit decreased as SNR improved to +10dB.  HINT scores, which did not take into account ceiling effects, yielded a significant mean directional benefit of 3.9dB.

Participants preferred the directional microphone mode in the AO condition, especially at SNRs between -6dB to +2dB. At more favorable SNRs, there was essentially no preference. In the AV condition, participants were less likely to prefer the directional mode, except at the poorest SNR, -10dB. Further analysis revealed that the odds of preferring directional mode in AO condition were 1.37 times higher than in the AV condition. In other words, adding visual cues reduced overall preference for the directional microphone mode.

At intermediate and favorable SNRs there was no significant correlation between AV directional benefit and the Utley lip-reading scores. For unfavorable SNRs, the negative correlation between these variables was significant, indicating that in the most difficult listening conditions, listeners with better lip-reading skills obtained less AV directional benefit than those participants who were less adept at lip-reading.

The outcomes of these experiments generally support the authors’ hypotheses. Visual cues significantly improved speech recognition scores in omnidirectional trials close to ceiling levels, reducing directional benefit and subjective preference for directional microphone modes.  Auditory-only (AO) performance, typical of laboratory testing, was not predictive of auditory-visual (AV) performance. This is in agreement with prior indications that AO directional benefit as measured in laboratory conditions doesn’t match real-world directional benefit and suggests that the availability of visual cues can at least partially explain the discrepancy.  The authors suggested that directional benefit should theoretically allow a listener to rely less on visual cues. However, face-to-face conversation is natural and hearing-impaired listeners should leverage avoid visual cues when they are available.

The results of Wu and Bentler’s study suggest that directional microphones may provide only limited additional benefit when visual cues are available, for all but the most difficult listening environments. In the poorest SNRs, directional microphones may be leverages for greater benefit.  Still, the authors point out that mean speech recognition scores were best when both directionality and visual cues were available. It follows that directional microphones should be recommended for use in the presence of competing noise, especially in high noise conditions. Even if speech recognition ability is not significantly improved with the use of directional microphones in many typical SNRs, there may be other subjective benefits to directionality, such as reduced listening effort, distraction or annoyance that listeners respond favorably to.

It is important for clinicians to prepare new users of directional microphones to have realistic expectations. Clients should be advised that directionality can reduce competing noise but not eliminate it. Hearing aid users should be encouraged to consider their positioning relative to competing noise sources and always face the speech source that they wish to attend to.  Although visual cues appear to offer greater benefits to speech recognition than directional microphones alone; the availability of visual speech cues may be compromised by poor lighting, glare, crowded conditions or visual disabilities, making directional microphones all the more important for many everyday situations. Thus all efforts should be made to maximize directionality and the availability of visual cues in day-to-day situations, as both offer potential real-world benefits.

References

Amlani, A.M., Rakerd, B. & Punch, J.L. (2006). Speech-clarity judgments of hearing aid processed speech in noise: differing polar patterns and acoustic environments. International Journal of Audiology 12, 202-214.

Bernstein, L.E., Eberhardt, S.P. & Demorest, M.E. (1989). Single-channel vibrotactile supplements to visual perception of intonation and stress. Journal of the Acoustical Society of America 85, 397-405.

Cord, M.T., Surr, R.K., Walden, B.E., et al. (2002). Performance of directional microphone hearing aids in everyday life. Journal of the American Academy of Audiology 13, 295-307.

Cord, M.T., Surr, R.K., Walden, B.E., et al. (2004). Relationship between laboratory measures of directional advantage and everyday success with directional microphone hearing aids. Journal of the American Academy of Audiology 15, 353-364.

Cox, R.M., Alexander, G.C. & Gilmore, C. (1987). Development of the Connected Speech Test (CST). Ear and Hearing 8, 119S-126S.

Gravel, J.S., Fausel, N., Liskow, C., et al. (1999). Children’s speech recognition in noise using omnidirectional and dual-microphone hearing aid technology. Ear and Hearing 20, 1-11.

Kuk, F., Kollofski, C., Brown, S., et al. (1999). Use of a digital hearing aid with directional microphones in school-aged children. Journal of the American Academy of Audiology 10, 535-548.

Lee L., Lau, C. & Sullivan, D. (1998). The advantage of a low compression threshold in directional microphones. Hearing Review 5, 30-32.

Leeuw, A.R. & Dreschler, W.A. (1991). Advantages of directional hearing aid microphones related to room acoustics. Audiology 30, 330-344.

Munhall, K.G., Jones, J.A., Callan, D.E., et al. (2004). Visual prosody and speech intelligibility: head movement improves auditory speech perception. Psychological Science 15, 133-137.

Nilsson, M., Soli, S. & Sullivan, J.A. (1994). Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America 95, 1085-1099.

Palmer, C., Bentler, R., & Mueller, H.G. (2006). Evaluation of a second order directional microphone hearing aid: Part II – Self-report outcomes. Journal of the American Academy of Audiology 17, 190-201.

Preves, D.A., Sammeth, C.A. & Wynne, M.K. (1999). Field trial evaluations of a switched directional/omnidirectional in-the-ear hearing instrument.  Journal of the American Academy of Audiology 10, 273-284.

Ricketts, T. (2000b). Impact of noise source configuration on directional hearing aid benefit and performance. Ear and Hearing 21, 194-205.

Ricketts, T. & Hornsby, B.W. (2003). Distance and reverberation effects on directional benefit. Ear and Hearing 24, 472-484.

Ricketts, T. & Hornsby, B.W. (2006). Directional hearing aid benefit in listeners with severe hearing loss. International Journal of Audiology 45, 190-197.

Ricketts, T., Henry, P. & Gnewikow, D. (2003). Full time directional versus user selectable microphone modes in hearing aids. Ear and Hearing 24, 424-439.

Sumby, W.H. & Pollack, I. (1954). Visual contribution to speech intelligibility in noise. Journal of the Acoustical Society of America 26, 212-215.

Valente, M., Fabry, D.A. & Potts, L.G. (1995). Recognition of speech in noise with hearing aids using dual microphones. Journal of the American Academy of Audiology 6, 440-449.

Walden, B.E., Surr, R.K., Cord, M.T., et al. (2000). Comparison of benefits provided by different hearing aid technologies. Journal of the American Academy of Audiology 11, 540-560.

Walden, B.E., Surr, R.K . Grant, K.W., et al. (2005). Effect of signal-to-noise ratio on directional microphone benefit and preference. Journal of the American Academy of Audiology 16, 662-676.

Wu, Y-H. & Bentler, R.A. (2010) Impact of visual cues on directional benefit and preference: Part I – laboratory tests. Ear and Hearing 31(1), 22-34.

Differences Between Directional Benefit in the Lab and Real-World

Relationship Between Laboratory Measures of Directional Advantage and Everyday Success with Directional Microphone Hearing Aids

Cord, M., Surr, R., Walden, B. & Dyrlund, O. (2004). Relationship between laboratory measures of directional advantage and everyday success with directional microphone hearing aids.Journal of the American Academy of Audiology 15, 353-364.

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

People with hearing loss require a better signal-to-noise ratio (SNR) than individuals with normal hearing (Dubno et al, 1984; Gelfand et al, 1988; Bronkhorst and Plomp, 1990).  Among many technological improvements, a directional microphone is arguably the only effective hearing aid feature for improving SNR and subsequently, improving speech understanding in noise. A wide range of studies support the benefit of directionality for speech perception in competing noise (Agnew & Block, 1997; Nilsson et al, 1994; Ricketts and Henry, 2002; Valente, 1995) Directional benefit is defined as the difference in speech recognition ability between omnidirectional and directional microphone modes. In laboratory conditions, directional benefit averages around 7-8dB but varies considerably and has ranged from 2-3dB up to 14-16dB (Valente et al, 1995; Agnew & Block, 1997).

An individual’s perception of directional benefit varies considerably among hearing aid users. Cord et al (2002) interviewed individuals who wore hearing aids with switchable directional microphones and 23% reported that they did not use the directional feature. Many respondents said they had initially tried the directional mode but did not notice adequate improvement in their ability to understand speech and therefore stopped using the directional mode. This discrepancy between measured and perceived benefit has prompted exploration of the variables that affect performance with directional hearing aids. Under laboratory conditions, Ricketts and Mueller (2000) examined the effect of audiometric configuration, degree of high frequency hearing loss and aided omnidirectional performance on directional benefit, but found no significant interactions among any of these variables.

The current study by Cord and her colleagues examined the relationship between measured directional advantage in the laboratory and success with directional microphones in everyday life. The authors studied a number of demographic and audiological variables, including audiometric configuration, unaided SRT, hours of daily hearing aid use and length of experience with current hearing aids, in an effort to determine their value for predicting everyday success with directional microphones.

Twenty hearing-impaired individuals were selected to participate in one of two subject groups. The “successful” group consisted of individuals who reported regular use of omnidirectional and directional microphone modes. The “unsuccessful” group of individuals reported not using their directional mode and using their omnidirectional mode all the time. Analysis of audiological and demographic information showed that the only significant differences in audiometric threshold between the successful and unsuccessful group were at 6-8 kHz, otherwise the two groups had very similar audiometric configurations, on average. There were no significant differences between the two groups for age, unaided SRT, unaided word recognition scores, hours of daily use or length of experience with hearing aids.

Subjects were fitted with a variety of styles – some BTE and some custom – but all had manually accessible omnidirectional and directional settings. The Hearing in Noise Test (HINT; Nilsson et al, 1994) was administered to subjects with their hearing aids in directional and omnidirectional modes. Sentence stimuli were presented in front of the subject and correlated competing noise was presented through three speakers: directly behind the subject and on each side. Following the HINT participants completed the Listening Situations Survey (LSS), a questionnaire developed specifically for this study. The LSS was designed to assess how likely participants were to encounter disruptive background noise in everyday situations, to determine if unsuccessful and successful directional microphone users were equally likely to encounter noisy situations in everyday life.  The survey consisted of four questions:

1) On average, how often are you in listening situations in which bothersome background noise is present?

2) How often are you in social situations in which at least 3 other people are present?

3) How often are you in meetings (e.g. community, religious, work, classroom, etc.)?

4) How often are you talking with someone in a restaurant or dining hall setting?

The HINT results suggest average directional benefit of 3.2dB for successful users and 2.1dB for unsuccessful users. Although directional benefit was slightly greater for the successful users, the difference between the groups was not statistically significant.  There was a broad range of directional benefit for both groups: from -0.8 to 6.0dB for successful users and from -3.4 to 10.5dB for the unsuccessful users. Interestingly, three of the ten successful users obtained little or no directional benefit, whereas seven of the ten unsuccessful users obtained positive directional benefit.

Analysis of the LSS results showed that successful users of directional microphones were somewhat more likely than unsuccessful users to encounter listening situations with bothersome background noise and to encounter social situations with more than three other people present. However, statistical analysis showed no significant differences between the two groups for any items on the LSS survey, indicating that users who perceived directional benefit and used their directional microphones were not significantly more likely to encounter noisy situations in everyday life.

These observations led the authors to conclude that directional benefit as measured in the laboratory did not predict success with directional microphones in everyday life. Some participants with positive directional advantage scores were unsuccessful directional microphone users and conversely, some successful users showed little or no directional advantage. There are a number of potential explanations for their findings. First, despite the LSS results, it is possible that unsuccessful users did not encounter real-life listening situations in which directional microphones would be likely to help. Directional microphone benefit is dependent on specific characteristics of the listening environment (Cord et al, 2002; Surr et al, 2002; Walden et al, 2004), and is most likely to help when the speech source is in front of and relatively close to the listener, with spatial separation between the speech and noise sources. Individuals who rarely encounter this specific listening situation would have limited opportunity to evaluate directional microphones and may therefore perceive only limited benefit from them.

Unsuccessful directional microphone users may have also had unrealistically high expectations about directional benefits. Directionality can be a subtle but effective way of improving speech understanding in noise. Reduction of sound from the back and sides helps the listener focus attention on the speaker and ignore competing noise. Directional benefit is based on the concept of face-to-face communication, if users expect their hearing aids to reduce all background noise from all angles they are likely to be disappointed. Similarly, if they expect the aids to completely eliminate background noise, rather than slightly reduce it, they will be unimpressed. It is helpful for hearing aid users, especially those new to directional microphones, to be counseled about realistic expectations as well as proper positioning in noisy environments. If listeners know what to expect and are able to position themselves for maximum directional effect they are more likely to perceive benefit from their hearing aids in noisy conditions.

To date, it has been difficult to correlate directional benefit under laboratory conditions with perceived directional benefit. It is clear that directionality offers performance benefits in noise, but directional benefit measured in a sound booth does not seem to predict everyday success with directional microphones. There are many factors that are likely affect real-life performance with directional microphone hearing aids, including audiometric variables, the frequency response and gain equalization of the directional mode, the venting of the hearing aid and the contribution of visual cues to speech understanding (Ricketts, 2000a; 2000b). Further investigation is still needed to elucidate the impact of these variables on the everyday experiences of hearing aid users.

As is true for all hearing aid features, directional microphones must be prescribed appropriately and hearing aid users should be counseled about realistic expectations and appropriate circumstances in which they are beneficial. Although most modern hearing instruments have the ability to adjust automatically to changing environments, manually accessed directional modes offer hearing aid wearers increased flexibility and may increase use by allowing the individual to make decisions regarding their improved comfort and performance in noisy places. Routine reinforcement of techniques for proper directional microphone use are encouraged. Hearing aid users should be encouraged to experiment with their directional programs to determine where and when they are most helpful. For the patient, proper identification of and positioning in noisy environments is essential step toward meeting their specific listening needs and preferences.

References

Agnew, J. & Block, M. (1997). HINT thresholds for a dual-microphone BTE. Hearing Review 4, 26-30.

Bronkhorst, A. & Plomp, R. (1990). A clinical test for the assessment of binaural speech perception in noise. Audiology 29, 275-285.

Cord, M.T., Surr, R.K., Walden, B.E. & Olson, L. (2002). Performance of directional microphone hearing aids in everyday life. Journal of the American Academy of Audiology 13, 295-307.

Cord, M., Surr, R., Walden, B. & Dyrlund, O. (2004). Relationship between laboratory measures of directional advantage and everyday success with directional microphone hearing aids. Journal of the American Academy of Audiology 15, 353-364.

Dubno, J.R., Dirks, D.D. & Morgan, D.E. (1984).  Effects of age and mild hearing loss on speech recognition in noise. Journal of the Acoustical Society of America 76, 87-96.

Gelfand, S.A., Ross, L. & Miller, S. (1988). Sentence reception in noise from one versus two sources: effects of aging and hearing loss. Journal of the Acoustical Society of America 83, 248-256.

Kochkin, S. (1993). MarkeTrak III identifies key factors in determining customer satisfaction. Hearing Journal 46, 39-44.

Nilsson, M., Soli, S.D. & Sullivan, J.A. (1994). Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America 95, 1085-1099.

Ricketts, T. (2000a). Directivity quantification in hearing aids: fitting and measurement effects. Ear and Hearing 21, 44-58.

Ricketts, T. (2000b). Impact of noise source configuration on directional hearing aid benefit and performance. Ear and Hearing 21, 194-205.

Ricketts, T. (2001). Directional hearing aids. Trends in Amplification 5, 139-175.

Ricketts, T.  & Henry, P. (2002). Evaluation of an adaptive, directional microphone hearing aid. International Journal of Audiology 41, 100-112.

Ricketts, T. & Henry, P. (2003). Low-frequency gain compensation in directional hearing aids. American Journal of Audiology 11, 1-13.

Ricketts, T. & Mueller, H.G. (2000). Predicting directional hearing aid benefit for individual listeners. Journal the American Academy of Audiology 11, 561-569.

Surr, R.K., Walden, B.E. Cord, M.T. & Olson, L. (2002). Influence of environmental factors on hearing aid microphone preference. Journal of the American Academy of Audiology 13, 308-322.

Valente, M., Fabry, D.A. & Potts, L.G. (1995). Recognition of speech in noise with hearing aids using dual microphones. Journal of the American Academy of Audiology 6, 440-449.

Walden, B.E., Surr, R.K., Cord, M.T. & Dyrlund, O. (2004). Predicting microphone preference in everyday living. Journal of the American Academy of Audiology 15, 365-396.

Considerations for Directional Microphone Use in the Classroom

Directional Benefit in Simulated Classroom Environments

Ricketts, T., Galster, J. and Tharpe, A.M. (2007)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Classroom acoustic environments vary widely and are affected by a number of factors including reverberation and noise from within the classroom and adjacent areas. Signal-to-noise ratio (SNR) is known to affect speech perception for children with normal hearing and those with hearing loss (Crandell, 1993; Finitzo-Hieber & Tillman, 1978). Because listeners with hearing loss typically require more favorable SNRs to achieve the same performance as normal hearing listeners, hearing-impaired students are particularly challenged by high levels of classroom noise.

FM systems are often recommended as a method for improving SNR in the classroom. However, they may not effectively convey voices other than the teacher’s, so children may be less able to hear comments or questions from other students.  The additional bulk of ear level FM systems may prompt reluctance to wear the FM system, as the student may perceive this as calling attention to their hearing loss.  Because of these and other potential limitations of FM systems, the use of hearing aids with directional microphones is an opportunity to improve SNR for hearing-impaired children.

The benefits of directional microphones for speech perception in the presence of background noise are well known for adults (Bentler, 2005; Ricketts & Dittberner, 2002; Ricketts, Henry & Gnewikow, 2003). Research has shown that children also benefit from directionality in laboratory conditions (Gravel, Fausel, Liskow & Chobot, 1999; Hawkins, 1984; Kuk, et al., 1999), but more information is needed on the effect of directional microphone use in classroom environments.  The study summarized in this post evaluated directional microphone use in simulated classroom situations and the subjective reaction to omnidirectional and directional modes by children and parents.

The authors recruited twenty-six hearing-impaired subjects ranging in age from 10-17 years participated in the experiment.  All but two had prior experience with hearing aids.  Subjects were fitted bilaterally with behind-the-ear hearing instruments that were programmed with omnidirectional and directional modes.  Digital noise reduction and feedback suppression features were disabled and all participants were fitted with unvented, vinyl, full-shell earmolds.

This study consisted of three individual experiments. The first investigated directional versus omnidirectional performance in noise in five simulated classroom scenarios:

1) Teacher Front – speech stimuli presented in front of the listener.

2) Teacher Back – speech presented behind the listener.

3) Desk Work – speech presented in front of the listener, the listener’s head oriented down toward desk

4) Discussion – three speech sources at 0 and 50-degree azimuth (left and right), simulating a round table discussion

5) Bench Seating – speech presented at 90-degree azimuth (left and right)

Speech recognition performance was evaluated in each of these scenarios using a modified version of the Hearing in Noise Test for Children (HINT-C, Nilsson, Soli & Sullivan, 1994). Speech stimuli were initially presented at 65dB SPL for the five test conditions. Noise was presented from four loudspeakers positioned 2 meters from each corner of the room. For conditions 1-3, the noise level was 55dB. For conditions 4 and 5, noise levels were fixed at 65dB.

A second experiment examined the performance of omnidirectional versus directional modes in the presence of multiple talkers. Monosyllabic words from the NU-6 lists (Tillman & Carhart, 1966) were randomly presented at 63dB SPL from speakers positioned 1.5 meters, surrounding the listener at three angles: 0 degrees (in front of listener), 135 degrees (back right) and 225 degrees (back left). Noise was presented at 57dB SPL, which again yielded an SNR of 6dB.

Not surprisingly, the results of the first experiment showed that directional performance was significantly better than omnidirectional performance for Teacher Front, Desk Work and Discussion conditions, but was significantly worse for the Teacher Back condition.  There was no significant difference between omnidirectional and directional modes for the Bench Seating condition.  In the Bench Seating condition, however, subjects were not specifically instructed to look at the speaker. If some subjects did look at the speaker and others did not, individual differences between omnidirectional and directional modes may have been obscured on average.  Improved performance was generally noted as the distance between speaker and listener decreased. This is consistent with previous studies with adult listeners, which showed increased directional benefit with decreasing distance (Ricketts & Hornsby, 2003, 2007).

The second experiment yielded no significant difference in performance between omnidirectional and directional modes when speech was in front of the listener. When speech was presented behind the listener, omnidirectional mode was significantly better than directional in both the back-right and back-left conditions.  The authors surmised that the directional benefit may have been reduced because subjects were told that all of the talkers were important and because 2/3 of the talkers were behind them, they may have been more focused on speech coming from the back.

The current study offers insight into the potential benefit of directional microphones for classroom environments. An FM system remains the primary recommendation for improving signal-to-noise ratio of a teacher’s voice, but overhearing other students and multiple talkers can be compromised by FM technology.  Additionally, because of social, cosmetic or financial concerns FM use may not be feasible for many students. Therefore, directional hearing instruments will likely continue to be widely recommended for hearing-impaired schoolchildren. This study reported a directional benefit ranging from 2.2 to 3.3 dB, which is consistent with studies of adult listeners (Ricketts, 2001).  Therefore, directional microphone use in classrooms may indeed be beneficial, as long as the teacher or speaker of interest is in front of the listener. However, for round table or small group arrangements, directionality could be detrimental, especially when talkers are behind the listener.  The authors point out that many school scenarios involve multiple talkers or speech from the sides and back, so directional microphone benefit may be limited overall.

The results of these experiments underscore the importance of counseling for school-age hearing aid users, as well as their parents and teachers. It is common practice to recommend preferential seating close to the teacher in the front of the classroom. Improved performance with decreases in distance from the speech source, in this and other studies, shows that this recommendation is particularly important for hearing aid users, whether or not they are in a directional mode. Furthermore, hearing-impaired students should be instructed to face the teacher so they can benefit from directional processing as well as visual cues. This should also be discussed in detail with teachers so that efforts can be made to arrange classroom seating accordingly.

An incidental finding of the first experiment showed that performance for the Desk Work condition was better than the Teacher Front condition, even though the distance between speaker and listener was comparable.  In the Desk Work condition, subjects were instructed to work on an assignment on the desk as they listened. Therefore, the listener’s head position was pointed slightly downward, which may have resulted in more optimal, horizontal positioning of the microphone ports, increasing directional effect. This finding demonstrates the importance of selecting the proper tubing or wire length, to position the hearing aid near the top of the pinna and align the microphone ports along the intended plane.

Overall, directional processing improved performance for speech sources in front of the listener and reduced performance for speech sources behind the listener. The instruments in this study were full-time omnidirectional or directional instruments, so it is unknown how automatic, adaptive directional instruments would perform under similar conditions. Because of the prevalence of automatic directionality in current hearing instruments, this is a question with important implications for school-age hearing aid users.  Perhaps automatic directionality could provide better overall access to speech in many classroom environments, but controlled study is needed before specific recommendations can be made.

References

Anderson, K.L. & Smaldino, J.J. (2000). The Children’s Home Inventory of Listening Difficulties. Retrieved from http://www.edaud.org.

Bentler, R.A. (2005). Effectiveness of directional microphones and noise reduction schemes in hearing aids: A systematic review of the evidence. Journal of the American Academy of Audiology, 16, 473-484.

Crandell, C. (1993). Speech recognition in noise by children with minimal degrees of sensorineural hearing loss. Ear and Hearing 14, 210-216.

Finitzo-Hieber, T. & Tillman, T. (1978). Room acoustics effects on monosyllabic word discrimination ability for normal and hearing-impaired children. Journal of Speech and Hearing Research, 21, 440-458.

Gravel, J., Fausel, N., Liskow, C. & Chobot, J. (1999). Children’s speech recognition in noise using omnidirectional and dual-microphone hearing aid technology. Ear and Hearing, 20, 1-11.

Hawkins, D.B. (1984). Comparisons of speech recognition in noise by mildly-to-moderately hearing-impaired children using hearing aids and FM systems. Journal of Speech and Hearing Disorders, 49, 409-418.

Kuk, F.K., Kollofski, C., Brown, S., Melum, A. & Rosenthal, A. (1999). Use of a digital hearing aid with directional microphones in school-aged children. Journal of the American Academy of Audiology, 10, 535-548.

Nilsson, M., Soli, S.D.  & Sullivan, J. (1994). Development of the Hearing in Noise Test for the measurement of speech reception thresholds in quiet and in noise. The Journal of the Acoustical Society of America, 95, 1085-1099.

Resnick, S.B., Dubno, J.R., Hoffnung, S. & Levitt, H. (1975). Phoneme errors on a nonsense syllable test. The Journal of the Acoustical Society of America, 58, 114.

Ricketts, T., Lindley, G., & Henry, P (2001). Impact of compression and hearing aid style on directional hearing aid benefit and performance. Ear and Hearing, 22, 348-361.

Ricketts, T. & Dittberner, A.B. (2002). Directional amplification for improved signal-to-noise ratio: Strategies, measurement and limitations. In M. Valente (Ed.), Hearing aids: Standards, options and limitations (2nd ed., pp. 274-346). New York: Thieme Medical.

Ricketts, T., Galster, J. & Tharpe, A.M. (2007). Directional benefit in simulated classroom environments. American Journal of Audiology, 16, 130-144.

Ricketts, T., Henry, P. & Gnewikow, D. (2003). Full time directional versus user selectable microphone modes in hearing aids. Ear and Hearing, 24, 424-439.

Ricketts, T. & Hornsby, B.( 2003). Distance and reverberation effects on directional benefit. Ear and Hearing, 24, 472-484.

Ricketts, T. & Hornsby, B.(2007). Estimation of directional benefit in real rooms: A clinically viable method. In R.C. Seewald (Ed.), Hearing care for adults: Proceedings of the First International Conference (pp 195-206). Chicago: Phonak.

Tillman, T. & Carhart, R. (1966). An expanded test for speech discrimination using CNC monosyllables (Northwestern University Auditory Test No. 6) SAM-TB-66-55. Evanston, IL: Northwestern University Press.

A comparison of Receiver-In-Canal (RIC) and Receiver-In-The-Aid (RITA) hearing aids

Article of interest:

The Effects of Receiver Placement on Probe Microphone, Performance and Subjective Measures with Open Canal Hearing Instruments

Alworth, L., Plyler, P., Bertges-Reber, M. & Johnstone, P. (2010)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors.

Open-fit behind-the-ear hearing instruments are favored by audiologists and patients alike, because of their small size and discreet appearance, as well as their ability to minimize occlusion. The performance of open-fit instruments with the Receiver-In-The-Aid (RITA) and Receiver-In-Canal (RIC) has been compared to unaided conditions and to traditional, custom-molded instruments. However, few studies have examined the effect of receiver location on performance by comparing RITA and RIC instruments to each other. In the current paper, Alworth and her associates were interested in the effect of receiver location on:

– occlusion

– maximum gain before feedback

– speech perception in quiet and noise

– subjective performance and listener preferences

Theoretically, RIC instruments should outperform RITA instruments for a number of reasons. Delivery of sound through the thin tube on a RITA instrument can cause peaks in the frequency response, resulting in upward spread of masking (Hoen & Fabry, 2007). Such masking effects are of particular concern for typical open-fit hearing aid users; individuals with high-frequency hearing loss. RIC instruments are also capable of a broader bandwidth than RITA aids (Kuk & Baekgaard, 2008) and may present lowered feedback risk because of the distance between the microphone and receiver (Ross & Cirmo, 1980), and increased maximum gain before feedback (Hoen & Fabry, 2007; Hallenbeck & Groth, 2008).

The authors recruited twenty-five subjects with mild to moderate, high frequency, sensorineural hearing loss participated in the study. Fifteen had no prior experience with open-canal hearing instruments, whereas 10 had some prior experience. Each subject was fitted bilaterally with RIC and RITA instruments with identical signal processing characteristics, programmed to match NAL-NAL1 targets. Directional microphones and digital noise reduction features were deactivated. Subjects used one instrument type (RIC or RITA) for six weeks before testing and then wore the other type for six weeks before being tested again. The instrument style was counterbalanced among the subjects.

Probe microphone measures were conducted to evaluate occlusion and maximum gain before feedback. Speech perception was evaluated with the Connected Speech Test -CST (Cox et al, 1987), the Hearing in Noise test -HINT (Nilsson, et al, 1994), the High Frequency Word List – HFWL (Pascoe, 1975) and the Acceptable Noise Level – ANL test (Nabelek et al, 2004). Subjective responses were evaluated with the Abbreviated Profile of Hearing Aid Benefit – APHAB (Cox & Alexander, 1995), overall listener preferences for quiet and noise, and satisfaction ratings for five criteria: sound quality, appearance, retention and comfort, speech clarity and ease of use and care.

Real-Ear Occluded Response measurements showed minimal occlusion for both types of instruments in this study. Although there was more occlusion overall for RIC instruments, the difference between RIC and RITA hearing instruments was not significant. Overall maximum gain before feedback did not differ between RIC and RITA instruments. However, when analyzed by frequency, the authors found significantly greater maximum gain in the 4000-6000Hz range for RIC hearing instruments.

On the four speech tests, there were no significant differences between RITA versus RIC instruments. Furthermore, there were no significant improvements for aided listening over unaided, except for experienced users with RIC instruments on the Connected Speech Test (CST). It appears that amplification did not significantly improve scores in quiet conditions, for either instrument type, because of ceiling effects. The high unaided speech scores indicated that the subjects in this study, because of their audiometric configurations, already had broad enough access to high frequency speech cues, even in the unaided conditions. Aided performance in noise was significantly poorer than unaided on the HINT test, but no other significant differences were found for aided versus unaided conditions. This finding was in agreement with previous studies that also found degraded HINT scores for aided versus unaided conditions (Klemp & Dhar, 2008; Valente & Mispagel, 2008).

APHAB responses indicated better aided performance for both instrument types than for unaided conditions on all APHAB categories except aversiveness, in which aided performance was worse than unaided. There were no significant differences between RIC and RITA instruments. However, satisfaction ratings were significantly higher for RIC hearing instruments. New users reported more satisfaction with the appearance of RIC instruments; experienced users indicated more satisfaction with appearance, retention, comfort and speech clarity. Overall listener preferences were similar, with 80% of experienced users and 74% of new users preferring RIC instruments over RITA instruments.

The findings of Alworth and colleages are useful information for clinicians and their open-fit hearing aid candidates. Because they provided significantly more high frequency gain before feedback than RITA instruments, RIC instruments may be more appropriate for patients with significant high-frequency hearing loss. Indeed, this result may suggest that RIC instruments should be the preferred recommendation for open-fit candidates. The results of this study also underscore the importance of using subjective measures with hearing aid patients. Objective speech discrimination testing did not yield significant performance differences between RIC and RITA instruments, but participants showed significant preference for RIC instruments.

Further information is needed to compare performance in noise with RIC and RITA instruments. In this study and others, some objective scores and subjective ratings were poorer for aided conditions than unaided conditions. It is important to note that in the current study, all noise and speech was presented at a 0° azimuth angle, with directional microphones disabled. In real-life environments, it is likely that users would have directional microphones and would participate in conversations with various noise sources surrounding them. Previous work has shown significant improvements with directionality in open-fit instruments (Valente & Mispagel, 2008; Klemp & Dhar, 2008). Future work comparing directional RIC and RITA instruments, in a variety of listening environments, would be helpful for clinical decision making.

Although the performance effects and preference ratings reported here support recommendation of RIC instruments clinicians should still consider other factors when discussing options with individual patients. For instance, small ear canals may preclude the use of RIC instruments because of retention, comfort or occlusion concerns. Patients with excessive cerumen may prefer RITA instruments because of easier maintenance and care, or those with cosmetic concerns may prefer the smaller size of RIC instruments. Every patient’s individual characteristics and concerns must be considered, but the potential benefits of RIC instruments warrant further examination and may indicate that this receiver configuration should be recommended over slim-tube fittings.

References

Alworth, L.N., Plyler, P.N., Rebert, M.N., & Johstone, P.M. (2010). The effects of receiver placement on probe microphone, performance, and subjective measrues with open canal hearing instruments. Journal of the American Academy of Audiology, 21, 249-266.

Cox, R.M., & Alexander, G.C. (1995). The Abbreviated Profile of Hearing Aid Benefit. Ear and Hearing, 16, 176-186.

Cox, R.M., Alexander, G.C. & Gilmore, C. (1987). Development of the Connected Speech Test (CST). Ear and Hearing, 8, 119-126.

Hallenbeck, S.A., & Groth, J. (2008). Thin-tube and receiver-in-canal devices: there is positive feedback on both! Hearing Journal, 61(1), 28-34.

Hoen, M. & Fabry, D. (2007). Hearing aids with external receivers: can they offer power and cosmetics? Hearing Journal, 60(1), 28-34.

Klemp, E.J. & Dhar, S. (2008). Speech perception in noise using directional microphones in open-canal hearing aids. Journal of the American Academy of Audiology, 19(7), 571-578.

Kuk, F. & Baekgaard, L. (2008). Hearing aid selection and BTEs: choosing among various “open ear” and “receiver in canal” options. Hearing Review, 15(3), 22-36.

Nabelek, A.K., Tampas, J.W. & Burchfield, S.B. (2004). Comparison of speech perception in background noise with acceptance of background noise in aided and unaided conditions. Journal of Speech and Hearing Research, 47, 1001-1011.

Nilsson, M., Soli, S. & Sullivan, J. (1994). Development of the Hearing in Noise Test for the measurement of speech reception threshold in quiet and in noise. Journal of the Acoustical Society of America, 95, 1085-1099.

Pascoe, D. (1975). Frequency responses of hearing aids and their effects on the speech perception of hearing impaired subjects. Annals of Otology, Rhinology and Laryngology suppl. 23, 84: #5, part 2.

Valente, M. & Mispagel, K. (2008). Unaided and aided performance with a directional open-fit hearing aid. International Journal of Audiology, 47, 329-336.

Reviewing the benefits of open-fit hearing aids

Article of interest:

Unaided and Aided Performance with a Directional Open-Fit Hearing Aid

Valente, M., and Mispagel, K.M. (2008)

This editorial discusses the clinical implications of an independent research study. The original work was not associated with Starkey Laboratories and does not reflect the opinions of the authors. 

With the continued popularity of directional microphone use in open-fit and receiver-in-canal (RIC) hearing aids, there has been increasing interest in evaluating their performance in noisy environments. A number of studies have investigated the performance of directional, open-fit BTEs in laboratory conditions. (Valente et al., 1995; Ricketts, 2000a; Ricketts, 2000b). Some have evaluated directional microphone performance in real-life or simulated real-life noise environments (Ching et al, 2009). In the current study, the authors compared performance in omnidirectional, directional and unaided conditions using RIC instruments in R-SpaceTM (Revitt et al, 2000) recorded restaurant noise. Their goal was to obtain more externally valid results by using real-life noise in a controlled, laboratory setting.

The R-SpaceTM method involved recordings of real restaurant noise from an 8-microphone, circular array. For the test conditions, these recordings were presented through an 8-speaker, circular array to simulate the conditions in the busy restaurant. One important factor that distinguishes this study from most others is that the subjects listened to speech stimuli in the presence of noise from all directions, including the front. At the time of this study only a few other studies had tested directional microphone performance in the presence of multiple noise sources, including frontal (Ricketts, 2000a; Ricketts, 2001; Bentler et al., 2004).

The authors recruited 26 adults with no prior hearing aid experience for the study. They were fitted with binaural receiver-in-canal (RIC) instruments. The instruments were programmed without noise reduction processing and with independent omnidirectional and directional settings. Subjects were counseled on use and care of the instruments, including proper use of omnidirectional and directional programs. They returned for follow-up adjustments one week after their fitting then used their instruments for four weeks before returning for testing. Subjects were given the opportunity to either purchase the hearing aids after the study at a 50% discount or receive a $200 payment for participation.

Hearing in Noise Test (HINT) (Nilsson et al., 1994) sentence reception thresholds were obtained to evaluate sentence perception in the uncorrelated R-Space noise. The Abbreviated Profile of Hearing Aid Benefit (APHAB) (Cox & Alexander, 1995) was also administered to evaluate perceived benefit from the instruments in the study. Four APHAB subscales were evaluated independently:

– Ease of communication (EC)
– Reverberation (RV)
– Background noise (BN)
– Aversiveness to loud sounds (AV)

The authors found that subjects’ performance in the directional condition was significantly better than both omnidirectional and unaided conditions. The omnidirectional condition was not significantly better than unaided; in fact results were slightly worse than those obtained in the unaided condition.

For the APHAB results, the authors found that on the EC, RV and BV subscales, aided scores were significantly better than unaided scores. Perhaps not surprisingly, the AV score, which evaluates “aversiveness to noise” was worse in the aided conditions. The aided results combined omnidirectional and directional conditions, so it is possible that aversion to noise in omnidirectional conditions was greater than the directional conditions. However, this was not specifically evaluated in the current study.

The authors pointed out that their directional benefit, which on average was 1.7dB, was lower than those found in other studies of open-fit or RIC hearing instruments (Ricketts, 2000b; Ricketts, 2001; Bentler, 2004; Pumford et al., 2000). However, they mention that most of those studies did not use frontal noise sources in their arrays. Frontal noise sources should have obvious detrimental effects on directional microphone performance, so it is likely that the speaker arrangement in the current study affected the measured directional improvement. At the time of this publication one other study had been conducted using the R-SpaceTM restaurant noise (Compton-Conley et al 2004). They found mean directional benefits of 3.6 to 5.8 dB, but their subjects had normal hearing and the hearing aids they used were not an open-fit design and were very different from the ones in the current study..

Clinicians can gain a number of important insights from Valente and Mispagel’s study. First and foremost, directional microphones are likely to provide significant benefits for users of RIC hearing aids. At the time of publication, the authors noted that directional improvement should be studied in order to warrant the extra expense of adding directional microphones to an open-fit hearing aid order. However, most of today’s open-fit and RIC instruments already come standard with directional microphones, many of which are automatically adjustable. So there is no need to justify the use of directional microphones on a cost basis, as they usually add nothing to the hearing aid purchase price.

This study provided more evidence for directional benefit in noise, but further work is needed to determine performance differences between directional and omnidirectional microphones in quiet conditions. Dispensing clinicians should always order instruments that have omnidirectional and directional modes, whether manually or automatically adjustable. This helps ensure that the instruments will perform optimally in most situations. Even instruments with automatically adjustable directional microphones often have push-buttons that allow us to give patients additional programs. For example, a manually accessible, directional program, perhaps with more aggressive noise reduction, offers the user another option for excessively noisy situations.

The current study obtained slightly reduced directional effects compared to other studies that tested subjects in speaker arrays without frontal noise sources. This underscores the importance of counseling patients about proper positioning when using directional settings. In general, patients should understand that they will be better off when they can put as much noise behind them as possible. But, it is also important to ensure that patients have reasonable expectations about directional microphones. They must understand that the directional microphone will help them focus on conversation in front of them, but will not completely remove competing noise behind them. Patients must also understand that omnidirectional settings are likely to offer no improvement in noise and might even be a detriment to speech perception in some noisy environments.

Subjects in Valente and Mispagel’s study were offered the opportunity to purchase their hearing instruments at a 50% discount after the study’s completion. Only 8 of the 26 subjects opted to do so. Of the remaining subjects, 3 reported that the perceived benefit was not enough to justify the purchase, whereas 15 subjects did not report any significant perceived benefit. This leads to another important point about patient counseling.

The subjects in this study, like most candidates for open-fit or RIC instruments, had normal low-frequency hearing. Therefore, they may have had less of a perceived need for hearing aids in the first place. It is important for audiologists to discuss realistic expectations and likely hearing aid benefits with patients in detail at the hearing aid selection appointment, before hearing aids are ordered. Patients who are unmotivated or do not perceive enough need for hearing assistance will ultimately be less likely to perceive significant benefit from their hearing aids. This is particularly true in everyday clinical situations, in which patients are not typically offered a 50% discount and will have to factor financial constraints into their decisions. For most open-fit or RIC candidates, their motivation and perceived handicap will be related to their lifestyle: their social activities, employment situation, hobbies, etc. Because a patient who has a less than satisfying experience with hearing aids may be reluctant to pursue them again in the future, it is critical for the clinician to help them establish realistic goals early on, before hearing aid options are discussed.

References
Bentler, R., Egge, J., Tubbs, J., Dittberner, A., and Flamme, G. (2004). Quantification of directional benefit across different polar response patterns. Journal of the American Academy of Audiology 15(9), 649-659.

Ching, T.C., O’Brien, A., Dillon, H., Chalupper, J., Hartley, L., Hartley, D., Raicevich, G., and Hain, J. (2009). Journal of Speech, Language and Hearing Research 52, 1241-1254.

Compton-Conley, C., Neuman, A., Killion, M., and Levitt, H. (2004). Performance of directional microphones for hearing aids: real world versus simulation. Journal of the American Academy of Audiology 15, 440-455.

Cox, R.M. and Alexander, G.C. (1995). The abbreviated profile of hearing-aid benefit. Ear and Hearing 16, 176-183.

Nilsson, M., Soli, S. and Sullivan, J. (1994). Development of the hearing in noise test for the measurement of speech reception thresholds in quiet and in noise. Journal of the Acoustical Society of America 95, 1085-1099.

Pumford, J., Seewald, R,. Scollie, S. and Jenstad, L. (2000). Speech recognition with in-the-ear and behind-the-ear dual microphone hearing instruments. Journal of the American Academy of Audiology 11, 23-35.

Revit, L., Schulein, R., and Julstrom, S. (2002). Toward accurate assessment of real-world hearing aid benefit. Hearing Review 9, 34-38, 51.

Ricketts, T. (2000a). The impact of head angle on monaural and bilateral performance with directional and omnidirectional hearing aids. Ear and Hearing 21, 318-329.

Ricketts, T. (2000b). Impact of noise source configuration on directional hearing aid benefit and performance. Ear and Hearing 21, 194-205.

Ricketts, T., Lindley, G., and Henry, P. (2001). Impact of compression and hearing aid style on directional hearing aid benefit and performance. Ear and Hearing 22, 348-360.

Valente, M., Fabry, D., and Potts, L. (1995). Recognition of speech in noise with hearing aids using a dual microphone. Journal of the American Academy of Audiology 6, 440-449.

Valente, M., & Mispagel, K.M. (2008). Unaided and aided performance with a directional open-fit hearing aid. International Journal of Audiology, 47, 329-336.