The interference of different background noises on speech processing

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The interference of different background noises
on speech processing

• Birgitta Larsby, Mathias Hällgren, Björn Lyxell
• Technical Audiology and The Swedish Institute
  for Disabillity Research
• Linköping University, Linköping, Sweden

FROM SIGNAL TO DIALOUGE Dynamic Aspects of
Hearing, Language and Cognition September 7-8,
2007, Linköping, Sweden
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The speech process assumes detection of isolated
acoustic sounds or words as well as integration
of sounds, words and sentences into meaningful
units. This process can easily be disturbed by
competing sounds.
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Purpose of research

• to generate knowledge that will allow for
  identification and understanding of the factors
  that are critical for creating an optimum sound
  environment where speech understanding is
  optimized and the degree of perceived effort is
  minimized.

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Speech comprehension

• PERIPHERAL HEARING
• COGNITIVE ABILITIES
• Working memory capacity
• Selective attention
• Speed of information processing
• Knowledge

Picasso 1946
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Speech comprehension

• Includes both audition and cognition.

Evaluation of speech comprehension

• Tests of hearing
• Cognitive tests

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• Stimulus-driven, bottom-up processes work in
  parallel with controlling top-down processes in
  every information-processing stage.

• Bottom-up (signal-based) processing
• Automatic
• Effortless
• Fast
• Highly accurate
• Top-down (knowledge-based) processing
• Controlled
• Effortful
• Slower
• Less accurate

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Hearing Impairment

• The auditory signal is limited and/or distorted
• The speech process becomes more cognitively
  demanding than normally and the individual has to
  depend more on effortful top-down processing

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Speech processing in noise

• Limited and distorted auditory signal
• Cognitive skills are important to compensate for
  reduced audibility and to restore the distorted
  sensory signal
• Different noise backgrounds put different demands
  on cognitive skills in the individual.

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Aging

• Extra problems with speech understanding in the
  elderly (CHABA, 1988)
• Models of explanation (Humes, 1996)
• 1. Peripheral auditory
• 2. Central auditory
• 3. Cognitive

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Cognitive factors in aging

• Knowledge is preserved
• Context is helpful
• but
• Slowing
• Working memory deficits
• Attention (ignore distracters)
• Less automatic processing
• Trouble coordinating sources of information

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Effects of noise on speech processingS/N 10 dB

• Task To decide if an auditory presented word is
  a real word or not.
• Cognitive and speech processing task.
• without noise with noise (10 dB S/N)
• correct answers 82.4 74.6
• response time 1540ms 1630ms
• perceived effort moderate (3.0) high (5.0)

? Even at this relatively easy listening
situation, noise affects speech processing
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Speech comprehension in noise

• Masking effects
• Distracting effects

Unmodulated noise
Speech
Reversed speech
sec
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Methods -Tests

• Speech recognition in noise test
• Hagermans test
• Cognitive test
• Lexical decision test
• Number of correct answers and reaction time are
  recorded

• The test was performed in background conditions
  of
• Unmodulated noise
• Speech
• Reversed speech

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Hagermans test

• The sentences
• The noise
• Hagermans unmodulated noise
• Sentences in noise

Adaptive interleaved method
Word recognition ()
increasing noise level
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Lexical decision test

• One hundred test-items
• 50 words
• and
• 50 non-words
• are used.
• Percent correct answers and reaction-times are
  measured.
• The test taps activity of verbal-information
  processing speed of word related information

• Is the word below a real word?

PNI
SUN
No
Yes
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Test Subjects

• Hearing
• Hearing impaired
• Symmetric sensorineural hearing impairments
• Age
• 56 - 83 years
• Younger mean 60.3 years (56-63)
• Elderly mean 72.0 years (64-83)

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Results
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Age X Noise
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Effects of noise on speech processing- different
kind of noises

• Different noises have different effects on speech
  recognition at different S/N ratios
• Meaningful content is distracting

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Effects of noise on speech processing- cognitive
ability
Task 1 Speech recognition - repeat auditory
presented short sentences (Hagerman's test) Task
2 Cognitive ability - decide if a word presented
as text is a real word or not (lexical access)
Correlations (correlation coefficients)
Cognitive ability S/N required for
50 0.28 S/N required for 80 0.45
(N42)
Remains after correction for peripheral hearing
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Effects of noise on speech processing- cognitive
ability
High cognitive ability (N14)
Cognitive abilities important possible to
compensate for reduced acoustic information
Word recognition ()
Low cognitive ability (N14)
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To conclude

• Noise affects speech processing negatively
• more pronounced for the elderly
• -
• Different background noises have different
  masking and distraction effects
• -
• Speech comprehension in noise requires both
  hearing and cognition
• -
• The degree of cognitive load in the SRT measure
  depends on e.g. S/N, degree and type of hearing
  impairment, age and
• type of noise background

Thanks are due to the EU-project HEARCOM and to
The Swedish Council for Working Life and Social
Research (FAS)
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THANKS!
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