Providing Effective Communication Access 2 nd International Hearing Loop Conference June 19 th, 2011 Matthew H. Bakke, Ph.D., CCC A Gallaudet University
Outline of the Presentation Factors Affecting Communication Access Listener Talker Auditory Visual Practical recommendations for effective communication access Future directions Hearing technology Universal design Public Policy
Listener Factors FACTORS AFFECTING COMMUNICATION ACCESS
a) Hearing Acuity Great diversity among deaf and hard of hearing people Degree Configuration Type Laterality Symmetry
a) Hearing Acuity Degree of Hearing Loss Mild 15 to 30 db threshold Retains much speech audibility Susceptible to interference from noise/reverberation Moderate 30 to 60 db threshold Partial audibility Hearing aids can restore full audibility Increased susceptibility to interference
a) Hearing Acuity Degree of Hearing Loss Severe 60 to 90 db threshold No audibility of speech without hearing aids Hearing aids can provide full audibility Auditory resolution can range from good to poor Profound 90+ db threshold Partial audibility of speech with hearing aids Little speech discrimination without visual cues Dependence on visual communication (ASL, Cue)
Configuration a) Hearing Acuity Flat Rising (low frequency hearing loss) Sloping (high frequency hearing loss) Sharply sloping Precipitously sloping Type Sensory, Neural, Conductive Laterality Unilateral vs. Bilateral Symmetry Symmetrical vs. Asymmetrical
b) Auditory Processing Ability Frequency Resolution Discriminating sounds of different pitch in speech (e.g., consonants vs. vowels). Amplitude Resolution Discriminating the dynamic changes in level of the speech signal. Temporal Resolution Discriminating the rapidly changing temporal patterns of speech. Binaural Factors using two ears vs. one ear
Hearing Aids c) Hearing Technology Audibility of speech can range from full to very limited Can provide increased amplitude (gain) Gain can vary across frequency, improving speech audibility Cannot provide improved auditory resolution Head worn microphones susceptible to noise/reverberation Noise reduction technologies helpful but limited
c) Hearing Technology Cochlear Implants Increasingly used for severe profound HL Full audibility of speech is possible Auditory Resolution ranges from good to poor Head worn microphones susceptible to interference from noise/reverberation Wide range of outcomes Dependence on visual cues (e.g., speechreading, captions, ASL) is variable
c) Hearing Technology Coupling Direct Audio Input Product specific May require different plugs for connection Telecoil/Neckloop/Silhouette Low tech with high yield Hearing aid/ci requires effective T coil programming Bluetooth and future wireless More stuff to lug around complexity?
Age d) Other Listener Factors People 60 or older without hearing loss perform less well than younger in noise and under cognitive load (Mazevski Dissertation 2011, as yet unpublished) Cognitive Load Visual acuity Attention Context Knowledge of Content
Talker factors FACTORS AFFECTING COMMUNICATION ACCESS
a) Speech Habits Articulation of speech Speech rate Foreign or Regional Accent Suprasegmental features of speech Word stress Conveys meaning Sentence stress Can or interest, + or color to speech Dropping of amplitude at the end of utterance
b) Other Communicative Habits Eye contact with audience Head turning, movement around the stage/podium Use of visual media Sequential use of visual media Text/Image size Use of captioning or interpretation Pre preparation of captioner/interpreter Control of speech rate (i.e., not rushing through)
Auditory factors FACTORS AFFECTING COMMUNICATION ACCESS
a) Signal to Noise Ratio (SNR) For SNR, size matters; bigger is better What SNR is necessary? Wilson, et al (2007) 50% recognition for sentences (QuickSIN) and words (WIN) HL Group: 11.3 and 12.9 db (mild moderate HL) Bakke, et al (1999) minimally acceptable SNRs for loop generated (i.e., ~white) noise in people with wide range of HL was 18 db (75 th percentile)
a) Signal to Noise Ratio (SNR) Interestingly, ratings were similar for different degrees/configurations of hearing loss Clearly, SNRs greater than 18 db would result in higher numbers of good to excellent ratings Thus, 18 db is minimally acceptable and not a goal Goal: achieve the highest possible SNR while maintaining comfortable sound pressure levels
b) Reverberation Reverberation = echo within a room or space Each room has a characteristic reverberation that can be characterized by RT 60 in units of time Negative effect increases with distance between a microphone and mouth of the talker As the microphone moves away from the mouth, the intensity of the signal drops, reducing the signal to reverberation ratio
b) Reverberation How much reverberation is tolerable? Gordon Salant and Fitzgibbons (1995) used a method of Equivalent SNR to study effects of RT 60 with Low Predictability SPIN sentences. Equivalent SNR is a method of equating signal to noise ratio to the effects of reverberation As RT 60 increased, Equivalent SNR dropped for all groups (Older and Younger with NH and HL) The results are charted on the next slide. Take home lesson: this one good reason that we need loop systems (or FM / IR)
b) Reverberation Bakke, et al. (1999) obtained ratings in three rooms at multiple distances from a microphone from 3 to 180 inches (15 feet) They used a measure known as the Speech Transmission Index (STI) STI is a method for predicting speech recognition performance in Noise and Reverberation Minimally acceptable STI for in people with wide range of HL was 0.84 (75 th percentile) The microphone could not be more than 3 feet from the talker; but this was unacceptable in one room.
c) Frequency Response Byrne, et al (1994) published international data on the long term average speech spectrum (figure on next slide) Covers a frequency range of 63 to 16000 Hz Most speech energy is between ~100 to ~8000 Hz Early telephone research established the telephone frequencies: 300 3000 Hz
c) Frequency Response Cochlear Implants generally include the frequencies from ~200 Hz to ~ 8000 Hz Hearing aids tend to provide gain up to 4000 or 6000 Hz I am not aware of acceptability rating research on frequency response, but Assistive Listening Systems should provide no less than 4000 Hz, and more if achievable (Based on the limits of the hearing technology people now wear)
d) Microphone Use Microphone placement As shown in a previous slide, proximity of the microphone to the talker is critical. Placement of lapel microphones is a source of variability. If too close to the mouth, air turbulence will be picked up introducing noise Microphone directionality (omni vs. directional) Auto on microphones sometimes have delays that introduce silences in the speech
e) Dynamic Range for Audio More typically a problem for cinematic productions. The range between quiet speech, loud speech and loud sound effects can be great. Amplitude compression may be of some value in the ALS to reduce the overall dynamic range Mixing of sound effects with the message can be a problem for people with hearing loss Independent control of dialogue gain vs. sound effects gain?
Visual factors FACTORS AFFECTING COMMUNICATION ACCESS
Distance a) Speechreading Cues If too distant from the talker, speechreading cues are not usable. Video is often used to enhance these cues in large assemblies. Lighting Appropriate lighting on the talker enhances speechreading cues Lighting that enhances contrast is supportive Visual distracters Facial Expression and Body Language
b) Captioning CART or Communication Access Real time Translation Preparing of CART Provider with vocabulary Number one source of frustration with CART Rate of speech vs. capacity of CART Provider Placement of text Size of text Number of lines visible
c) Use of Visual Media Visual Media like PowerPoint can support communication access or frustrate it Similar to captioning, placement and size of text/images are factors Density of information on a slide Pausing for the audience to view a slide before speaking about it
PRACTICAL RECOMMENDATIONS FOR EFFECTIVE COMMUNICATION ACCESS
a) Consider Multiple Factors For any given venue and event, identify specific needs related to Listener Talker Auditory Channel Visual Channel People with special needs in the audience must be considered, including people with hearing loss and/or limited vision
a) Consider Multiple Factors Listener who is the audience? Consider the diverse needs of the audience of people with hearing loss. Can the technology interface with ALL hearing technologies? Is auditory content provided at good SNR and at an appropriate rate for the audience? Are there visual supports available? PowerPoint, Captioning, ASL or other Interpreting? Is the level of content revealed in advance? (introductory, intermediate, advanced)
a) Consider Multiple Factors Talker have you provided training, or at least guidelines? Written guidelines for presenting to audiences with hearing loss can include guidance on: Clear Speech Speech Rate Visual contact with the audience Microphone use Use of visual media Use of captioning / interpreters
a) Consider Multiple Factors Auditory Maximize signal to noise (SNR) also consider reducing background sounds like music tracks or sound effects Ensure system has full frequency response (as wide a bandwidth as possible but minimum 4 khz) Microphone placement as close to ALL talkers mouths as practicable using multiple microphones For interactive sessions: provide an audience microphone
Visual a) Consider Multiple Factors Provide appropriate lighting on the talker clearly lit with good contrast for speechreading Consider a large video screen for large venues Support spoken message with visual media (e.g., PowerPoint) providing time for audience to read If low vision people, read all information on slides aloud For those with low vision, provide large type handouts Always provide CART / Interpreters when required
b) US Access Board Guidelines A good start in planning for access technology Based on research conducted at the Lexington School/Center for the Deaf in 1999 Guidelines address the communication access technology elements and features Report available at the Access Board Website, www.access board.gov and the RERC on Hearing Enhancement Website www.hearingresearch.org
b) US Access Board Guidelines Recommendations: Receiver jacks ability to couple ALS to a system Receiver hearing aid compatibility neckloops vs. earbuds Output level capability 110 db minimum and 118 maximum (protection of hearing) Dynamic Range minimum 50 db Signal to noise ratio 18dB minimum SNR Distortion maximum 18dB peak clipping
RECOMMENDATIONS FOR FUTURE RESEARCH
Future Research Needs for Providing Communication Access Listener acceptability of signals in noise under various conditions (babble, HVAC, traffic, and so on) Listener acceptability of signals with different levels of background music or sound tracks Listener acceptability of various RT 60 levels Ratings of signals with systematically varied dynamic ranges (e.g., movie tracks) Audience ideas for research needs?
Acknowledgement The contents of this presentation were developed under a grant from the Department of Education, NIDRR grant number HI33E080003. However, those contents do not necessarily represent the policy of the Department of Education, and you should not assume endorsement by the Federal Government.
Questions / Discussion