What are some auditory processing difficulties?
- Some children with language-based learning difficulties may have deficits in auditory processing
- Older adults have difficulty processing the temporal aspects of speech
- Excessive noise or trauma may lead to auditory processing deficits in the presence of normal audiometric thresholds
What is the FFR?
ABRs to complex sounds
- FFR uses acoustically complex sounds such as speech and music
FFR has fidelity (response is similar to stimulus)
- Can be seen in time domain (response is same length of stimulus)
Frequency domain:
- Fundamental frequency is observed
- Higher frequency energy/harmonics can be observed
Why record ABRs to speech?
To generate an ABR, a quick, transient stimulus is needed
W/ speech stimulus, onsets and offsets can be measured
- Periodic peaks are the frequency following response
Why record from the brainstem?
Reliable across time
- Important factor in clinical assessments
Responses should be replicable
Why don’t we obtain thresholds using speech stimuli?
Looking fro threshold responses
- Need a very brief stimulus to generate the synchronous neural firing necessary to generate an ABR at threshold
A clear FFR is only generated when stimuli that are presented at levels of at least moderate intensity
Not a threshold response, but objective measure of suprathreshold processing
How is the FFR analyzed?
Time domain
- Response measures the stimulus
- Any given peak can be measured and its timing and amplitude can be obsessed
Traditional analysis: measure time/amplitude of each given peak
Measure RMS amplitude over a given range
- Doesn’t require peaks to be picked manually (more objective)
Also in time domain:
- Stimulus can be directly compared via Pearson’s correlation
- Response in 2 conditions (noise and quiet) can be compared
What is phase locking?
- Robustness of signal encoding
- Not as much phase locking for the high frequency components
- Enables subtle features of the response to be assessed across time
What does the FFR response look like in quiet vs. noise in subjects with dyslexia?
Noise
- Increases peak latencies
- Decreases peak amplitudes
- Responses are delayed
What does the FFR response look like in subjects with reading disorders?
Poor readers do not have a robust representation of a speech stimulus
Children that have reading disorders may not have good mapping because sounds are not being recorded correctly
Can we use the FFR to predict later language/reading skills in children?
Early identification, treatment of hearing loss –> better language outcomes
In toddlers aged 3-4 years, FFR measures of speech encoding in noise relate to measurements of phonological processing at time of test
- Higher consonant in noise scores were related to higher scores in phonological processing
Can FFR measures predict later reading skills?
Discrimination function analysis correctly classified 69% of children based on a language disorder diagnosis
Can be obtain reliable responses to speech in infants?
It is possible to evaluate responses to the envelope (fundamental frequency) and temporal fine structure (formants) in infants
- Temporal fine structure looks at higher frequency components (first formants)
What are some deficits in children with autism spectrum disorders?
- Production and perception of prosody
- Neural encoding of speech
- Neural encoding of pitch changes over time
What does pitch tracking look like in children with autism spectrum disorders?
Children have disrupted pitch tracking
- Falling contour with pitch analysis
- Can indicate command or similar things
- Way we communicate intent in English
- Pitching tracking over time in children with ASD looks like noise
What are some animal models of aging?
- Every time there is a synapse, there should be an afferent terminal connecting to the synapse
- With noise damage, synapse to afferent terminal connection is disrupted
- IC has neurons that are sensitive to duration (structure is able to code gaps very well)
Do the ABR/FFR reflect biological aging?
ABR
- Wave I is smaller in older adults compared to younger adults
- Prolongation of Wave V in older adults
- Increased neural conduction time
- Processing is slowing down around the auditory nerve/brainstem
FFR
- Weaker synchrony
- Smaller amplitudes
- Phase locking is higher in younger than in older groups
- Neural encoding of speech in noise
- Noise effects on response amplitude are greater in younger than in older adults
