Background:
Effects of Hearing Loss
Gallaudet University
Department of Hearing Speech and Language Sciences
Matthew H. Bakke, Ph.D.
With compliments to Arthur Boothroyd, Ph.D.

Factors relating to effects of hearing loss
•	Age of onset
•	Degree/Configuration of Hearing Loss
•	Fluctuating, mild to moderate, unilateral often go undetected
•	Etiology – location of “lesion”
•	Psychological factors
•	Social/cultural factors

Hearing loss as a culture
•	Congenitally Deaf people may have a very different reaction to hearing than those who have grown up with hearing
•	May have different attitudes about
•	Amplification
•	Cochlear implantation 
•	Language and communication (vision vs. audition)
•	Disability vs. being Deaf

Speech Perception
•	The effects of hearing loss on phoneme perception is largely predictable on the basis of the audibility of acoustic cues
•	However, there are large individual differences
•	Hearing loss may involve 
•	Loss of sensitivity to sound
•	Reductions of auditory resolution

Arthur Boothroyd’s Hearing Loss “Groups”
•	Boothroyd developed a useful grouping system for children with sensory hearing loss
•	Useful in rehabilitation
•	Useful in understanding outcomes with hearing aids and cochlear implants
•	Based upon audibility as well as auditory resolution
•	Cochlear implant perception to be discussed later…

Group I - Mild
•	15 to 30 dB – described as “mild”
•	Retain much audibility of speech, unaided
•	Hearing aids restore full audibility of speech 
•	Auditory resolution is good
•	BUT susceptible to noise/reverberation interference
•	Children can develop oral language spontaneously
•	However, educational and communicative effects may be significant

Group I  Mild Hearing Loss (15-30 dB)
[Chart showing unaided hearing loss based on sound level in dBHL and Frequency in Hertz for those with mild hearing loss.  Also, an audible example is provided.]
Note:  This child with a mild hearing loss, unaided, lacks audibility of the higher frequencies in conversational speech.

Group I  Mild Hearing Loss (15-30 dB)
[Chart showing hearing loss with hearing aid based on sound level in dBHL and Frequency in Hertz for those with mild hearing loss.  Also, an audible example is provided.]
Note:  With appropriate amplification some of this audibility can be restored – at least up to the high-frequency limit of the hearing aid. Auditory resolution is relatively unimpaired in cases of mild hearing loss.

Group II - Moderate
•	30 to 60 dB – described as “moderate”
•	Partial audibility of conversational speech
•	Children can develop oral language spontaneously, but with differences
•	Hearing aids can restore full audibility of speech
•	Auditory resolution tends to be “good”
•	noise/reverberation susceptibility

Group II:  Moderate Hearing Loss (30-60 dB)
[Chart showing unaided hearing loss based on sound level in dBHL and Frequency in Hertz for those with moderate hearing loss.  Also, an audible example is provided.]
Note:  For the child with moderate hearing loss, audibility of conversational speech is reduced over a wide frequency range, but not eliminated.

Group II:  Moderate Hearing Loss (30-60 dB)
[Chart showing hearing loss with hearing aid based on sound level in dBHL and Frequency in Hertz for those with moderate hearing loss.  Also, an audible example is provided.]
Note:  Once again, a properly fitted hearing aid can restore almost full audibility and auditory resolution is usually good. 

Group III - Severe
•	60 to 90 dB 
•	Do not hear conversational speech without aids
•	Do not develop oral language spontaneously
•	Hearing aids can provide full audibility
•	But, auditory resolution can vary from good to poor
•	Noise/reverberation susceptibility
•	Speech production/perception problems
•	Voice quality
•	Place of articulation

Group III:  Severe Hearing Loss (60-90 dB)
[Chart showing unaided hearing loss based on sound level in dBHL and Frequency in Hertz for those with severe hearing loss.  Also, an audible example is provided.]
Note:  Without a hearing aid, the child with a severe hearing loss has no audibility of conversational speech.

Group III:  Severe Hearing Loss (60-90 dB)
[Chart showing hearing loss with hearing aid based on sound level in dBHL and Frequency in Hertz for those with severe hearing loss.  Also, an audible example is provided.]
Note:  With well fitted amplification, however, audibility of conversational speech can be restored and there is still an adequate range between threshold and the upper limit of comfort.  The critical issue now becomes auditory resolution, which can vary from *good to *poor in children with severe hearing loss. 

Group IV - Profound
•	90 to 110 dB – described as “profound”
•	Do not hear conversational speech
•	Do not develop oral language spontaneously
•	With amplification, only partial audibility of speech can be restored
•	Little speech discrimination capacity
•	Limited to prosodic features of speech plus speechreading
•	Visual Language likely to be primary

Group IV.  Profound Hearing Loss (90-110 dB)
[Chart showing unaided hearing loss based on sound level in dBHL and Frequency in Hertz for those with profound hearing loss.  Also, an audible example is provided.]
Note:  Without amplification, the child with a profound hearing loss is effectively totally deaf. 

Group IV.  Profound Hearing Loss (90-110 dB)
[Chart showing hearing loss with hearing aid based on sound level in dBHL and Frequency in Hertz for those with profound hearing loss.  Also, an audible example is provided.]
Note:  Even with amplification, it is not possible to provide good audibility of speech over a wide frequency range and to make matters worse auditory resolution is typically  very poor. 

Group V - Total
•	110 dB or more – described as “total”
•	Do not hear conversational speech with our without hearing aids
•	Perceive sound via sense of touch
•	Acquisition of oral language based on visual input and intensive habilitation
•	Cochlear Implant candidacy
•	Visual Language likely to be primary

Group V.  Total Hearing Loss (>110 dB)
[Chart showing unaided hearing loss based on sound level in dBHL and Frequency in Hertz for those with total hearing loss.  Also, an audible example is provided.]
Note:  And some profoundly deaf children are, in fact, totally deaf, their bottom left hand corner audiograms indicating tactile responses around the ear.

Group V.  Total Hearing Loss (>110 dB)
[Chart showing hearing loss with hearing aid based on sound level in dBHL and Frequency in Hertz for those with total hearing loss.  Also, an audible example is provided.]
Note:  Powerful hearing aids can provide some detection of sound – but only via the sense of touch. 

How do hearing aids impact on the hearing loss groups?
•	As hearing loss increases, aided auditory capacity decreases
•	Pure tone sensitivity and auditory resolution both decrease with increased cochlear damage
•	Person with hearing loss ~90 dB can still retain considerable auditory capacity when aided
•	However, when unaided, such a person will function as deaf

How do cochlear implants impact on the groups?
•	Implant now provides greater levels of audibility by bypassing the damaged cochlea
•	Ability to use the information from the implant depends upon many factors, but particularly time of implantation
•	Audibility is not enough
•	Audibility AND Resolution – (Processing & Mapping AND Neural Capacity)
•	Children with implants may “shift groups” and function similarly to Groups I, II or III

Simulations of Cochlear Implant-like Processed Speech

[Picture showing Filtered 0 to 6,000 Hz.]
[Picture showing 1-channel simulation.]
Note:  The following are simulations of processing with different numbers of effective channels of stimulation. The simulations are based on the work if Bob Shannon. The speech spectrum, between 250 and 6000 Hz is divided in to n channels, logarithmically spaced. The amplitude envelope is extracted from the speech signal and applied to noise bands - in this case having the same bandwidth and center frequency as the speech band from which the envelope was taken. In each case, the original spectrogram is shown above and spectrum of the simulation is shown below.  The first example uses only a single channel. In other words, all spectral information has been lost and only the overall temporal envelope remains.  

[Picture showing Filtered 0 to 6,000 Hz.]
[Picture showing 2-channel simulation.]
Note:  With just 2 channels we both see and hear crude spectral resolution leading to rudimentary auditory capacity. 

[Picture showing Filtered 0 to 6,000 Hz.]
[Picture showing 4-channel simulation.]
Note:  And with 4 channels there are the beginnings of phoneme and word recognition.

[Picture showing Filtered 0 to 6,000 Hz.]
[Picture showing 8-channel simulation.]
Note:  As the number of channels increases the spectrum of the simulated signal begins to match the original more closely – with clearer separation of first and second formants and transitions in both. Moreover the fricative sounds begin to look more like the originals. These similarities are paralleled by increases in intelligibility.

[Picture showing Filtered 0 to 6,000 Hz.]
[Picture showing 16-channel simulation.]
Note:  With just 16 channels, the details in the original spectrogram are replicated well – with a corresponding increase, not only in intelligibility but also in sound quality.

Emergency Siren demonstration

Full Spectrum Siren
[Picture of spectrum of siren.  Also, an audible example is provided.]

3000 Hz Low Pass Filtered Siren
[Picture of spectrum of 3000 Hz low pass filtered siren.  Also, an audible example is provided.]

2000 Hz Low Pass Filtered Siren
[Picture of spectrum of 2000 Hz low pass filtered siren.  Also, an audible example is provided.]

1500 Hz Low Pass Filtered Siren
[Picture of spectrum of 1500 Hz low pass filtered siren.  Also, an audible example is provided.]

1000 Hz Low Pass Filtered Siren
[Picture of spectrum of 1000 Hz low pass filtered siren.  Also, an audible example is provided.]

750 Hz Low Pass Filtered Siren
[Picture of spectrum of 750 Hz low pass filtered siren.  Also, an audible example is provided.]

500 Hz Low Pass Filtered Siren
[Picture of spectrum of 500 Hz low pass filtered siren.  Also, an audible example is provided.]

500 Hz Square Wave Signal
[Picture of spectrum of 500 Hz square wave signal.  Also, an audible example is provided.]

500 Hz Square Wave Signal
2000 Hz LP Filtered
[Picture of spectrum of 500 Hz square wave signal and 2000 Hz LP filtered signal.  Also, an audible example is provided.]

500 Hz Square Wave Signal
1500 Hz LP Filtered
[Picture of spectrum of 500 Hz square wave signal and 1500 Hz LP filtered signal.  Also, an audible example is provided.]

500 Hz Square Wave Signal
1000 Hz LP Filtered
[Picture of spectrum of 500 Hz square wave signal and 1000 Hz LP filtered signal.  Also, an audible example is provided.]

500 Hz Square Wave Signal
750 Hz LP Filtered
[Picture of spectrum of 500 Hz square wave signal and 750 Hz LP filtered signal.  Also, an audible example is provided.]

500 Hz Square Wave Signal
500 Hz LP Filtered
[Picture of spectrum of 500 Hz square wave signal and 500 Hz LP filtered signal.  Also, an audible example is provided.]

Take home lesson
•	People with hearing loss are a very diverse group with a wide range of communication and alerting needs
•	There is no one solution to emergency alerting that will work for all
•	Very wide band alerting signals are probably desirable
•	Redundancy in alerting within and across modalities (vision/hearing/touch) will likely be necessary to ensure that no one is excluded