Exam 3 (Final) Flashcards
Absolute threshold
A listener’s ability to detect the presence of a tone (sinusoid) at various frequencies
Difference threshold
A listener’s ability to detect a change in either frequency or level of a tone (sinusoid)
Audibility threshold graph
a plot of just barely audible tones of varying frequencies
Measurements vary depending on which speaker or headphones are used
Weber’s law for differential selectivity
the weber fraction is often the same (constant) for all values of a physical parameter to be discriminated
the just-noticeable difference (JND, Dw) that could be detected was proportional to the smaller weight value (w)
Frequency weber fraction
Frequency JND is the smallest change in frequency (Δf) that can be perceived
X-axis: frequency (Hz)
Y-axis: difference threshold (Δf) in dB
Intensity weber fraction
Intensity JND is the smallest change in intensity (ΔI) that can be perceived
Best JNDs for sound level are ~1dB for sound levels above 20 dB SPL
Small improvement in discrimination as SPL increases is referred to as the “near miss to Weber’s law”
Masking relationship to signal
farther from masker, less masking occurs
closer a masker is in frequency to the signal, more masking occurs
psychophysical tuning curve
a frequency map of the masker sound levels needed to mask a fixed signal
masking pattern
a frequency map of the signal sound levels that are just detectable in the presence of a fixed masker
- Fix the intensity at a specific frequency
- Other frequencies will change
Asymmetry of masking or upward spread
Masking is much stronger for signals at frequencies above the masker than below
Broadband noise
fills up the internal auditory filter (AF) so its the filter BW matters
Narrower noise
has all power within the auditory filter, so the noise BW matters
Less maskining (easier to detect) as noise bandwidth gets smaller
Critical ratio (CR) filter
in the case of tone detection in broadband noise
Detection occurs at a fixed signal to noise ratio
Critical band (CB) filter
in the case of tone detection in narrowband noise
When the noise BW is smaller than the auditory bandwidth masking will increasing as BW noise gets bigger until BW noise= BW AF
Notched Noise, equivalent rectangular bandwidth (ERB) filter
generally accepted as the most reliable filter
Varying the notch width of band-reject noise varies the amount of noise within the auditory filter and controls the amount of masking (wider notch width, less noise, less masking)
- Detection thresholds measured as a function of notch width
Consistent findings from ERB
Filter BW increases as center frequency increases
- Consistent with neural tuning BWs
Filter BW increases as sound level increases
- Reduction in OHC amplification as SPL increases (protecting the ear)
Filter BWs are broader in listeners with sensorineural hearing loss
binaural hearing
The fact that we can listen with 2 ears provides two main functional benefits
Three primary acoustic cues for horizontal sound localization
ILD
ITD
Spectral cues
ILD (Interval level difference)
Prominent at high frequencies
The difference in level (intensity) between a sound arriving at one ear versus the other
Frequencies > 1000Hz
Head blocks some of the energy reaching the opposite ear
ILD is largest at 90 and-90 degrees
Nonexistent for 0 and 180 degrees
ITD (Interval time difference)
Prominent at low frequencies
ITD for sound sources varying in azimuth (horizontal)
Peak of graph, directly opposite the RE
ITD time differences for different positions around the head
90 degrees= 640us
180 degrees= 0us
Can vary depending on the size of the head
Spectral cues from pinna
Most prominent as direction-dependent spectral notches at high frequencies
Seen in HRTFs
Duplex theory of localization
ITD used at low frequencies
ILD used at high frequencies
Head related transfer functions (HRTFs)
A measure that describes how the pinna, ear canal, head and torso change the intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation)
Each person has their own HRTF (based on their body) and uses it to help sound localization
binaural masking level differences (BMLDs)
Comparisons of tone-detection-in-noise performance across different combinations of signals and masker being the same or different at the two ears
Monotic
Signal and masker same
Poor signal detection
Diotic
Signal and masker are the same at both ears
Poor signal detection
Dichotic
Signal different (only one ear)
Masker same at both ears
Good signal detection
Subjective measures of sound
loudness and pitch
Objective measures of sound
threshold for intensity and frequency
Loudness
attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud
Pitch
the auditory attribute of sound according to which sounds can be ordered on a scale from low to high
Phon
level in dB SPL of an equally loud 1-kHz tone (the reference is the loudness of a fixed level 1 kHz tone)
Sone
1 sone is defined as the loudness of a 1000 Hz tone presented at 40 dB SPL (=40 phons)
1 sone is equal to 40 phons
also called loudness scaling
Loudness recruitment
steeper growth in loudness with elevated thresholds
People with cochlear hearing loss also show this more rapid increase in loudness
Important in fitting hearing aids
Need gain at low sound levels to provide audibility
Fundamental frequency (F0)
lowest frequency of harmonic spectrum
Auditory system is acutely sensitive to natural relationships between harmonics
Missing fundamental effect (missing F0)
The pitch a listener hears corresponds to F0 even if it is missing
Periodicity information is still available so it can still be heard
General theories for pitch perception
Temporal theory
Spectral theory (template matching)
Temporal theory
Pitch can be estimated from the temporal periodicity of complex sounds
Temporal periodicity is unaffected by missing fundamental
Spectral theory (template matching)
Pitch can be estimated from the frequency spacing of harmonics
Even if the fundamental (or other harmonics) are missing, this can still work by finding the best F0 to match the harmonic spacing
Any random set of harmonics can produce pitch
Resolved harmonics
Because apical (low-frequency) filters have small bandwidths, they only pass individual harmonics (pure tones)
This allows spectral theories to work well for low harmonic numbers
Unresolved harmonics
Because basal (medium-high) frequency filters have larger bandwidths, they pass several harmonics (which interact to create modulations, periodicity at F0)
Allows for temporal theories to work well for medium-high harmonic numbers
- But a less salient pitch
Timbre
subjective attribute of sound
psychological sensation by which listeners can judge that two sounds with the same fundamental loudness and pitch are dissimilar
Conveyed by spectral shape of harmonics and other frequencies
Motor theory of speech perception
Motor processes used to produce speech sounds are used in reverse to understand the acoustic speech signal
Supported by McGurk Effect
- McGurk and MacDonald showed that what someone sees can affect what they hear
Statistical learning
certain sounds (making words) are more likely to occur together and babies are sensitive to those probabilities
2 types of assessment techniques
Behavioral and Electrophysiologic
behavioral assessment
Patient has to respond
- Raise hand when you hear beep
- Repeat the word/sentence
Involves the entire auditory system and brain
electrophysiologic assessment
No response required from patient
- sit/lie quietly
- Relax or sleep in armchair
Measures specific aspects of auditory function
- TM, middle ear
- OHC
- Brainstem, cortex
Goals of audiologic assessment
Degree of hearing loss
Type of hearing loss
- Site of lesion and/or cause of the problem
Configuration of hearing loss
- Flat, sloping, etc
Impact of hearing loss on the individual
Patient’s needs
Air conduction (AC) testing
Tests entire auditory system
- Outer, middle and inner ear
Uses earphones
- Threshold: level where tone is just detectable 50% of the time
Bone conduction (BC) testing
Tests the inner ear (cochlea) and beyond directly by vibrating skull bones and contents
Uses a bone oscillator (vibrator)
- Another threshold test
With AC testing, determines the location of the problem
- Outer or middle ear vs inner ear
Degrees of Hearing Loss
Normal (10-25 dB)
Mild (36-40 dB)
Moderate (41-55 dB)
Conductive hearing loss (CHL)
Disorder in outer or middle ear
- Will have a normal inner ear
Can be treated medically
Impaired AC thresholds and normal BC thresholds result in air-bone gap
Difference in threshold between air and bone
Conductive mechanism
outer and middle ear “conduct” sounds to the inner ear
CHL communication difficulties
Problems with conductive mechanism leads to loss of amplification
Usually need additional volume
Speech understanding is relatively unaffected
Causes of CHL
Cerumen occlusion
External otitis
TM perfoations
Ossicular damage
Otitis media
- Ear infection, fluid in ear
Middle ear tumors
Sensorineural hearing loss (SHL)
Disorder in inner ear (sensory loss)
- Will have normal and middle ear
AC and BC thresholds measure the same inner ear disorder
No air-bone gap
Sensorineural hearing loss (SNHL) is usually permanent and can’t be treated medically
Senorineural mechanism
inner ear (sensory) and nerve (neutral)
SHL communication difficulties
Problems with delicate cochlear mechanism
Frequency coding
Intensity coding
Leads to loss of volume
Leads to decreased speech understanding (distortion)
Increased difficulty in noise
Tinnitus
SHL causes
Age (presbycusis)
Noise exposure
Trauma
Genetics
Maternal infections
Structural malformations
Illness/infections
Ototoxic drugs
Tumors of the VIII nerve (vestibulocochlear nerve)
Mixed Hearing Loss
Disorder in outer or middle ear and inner ear
Impaired AC thresholds
- Measure effects of both problems
Impaired BC thresholds
- Measure effects of inner ear disorder only
Results in air bone gap, but BC thresholds are not normal
causes of mixed hearing loss
Any combo of outer or middle ear and inner ear disorder
- Excess cerument and noise induced HL
- Ear infection and age related HL
(Central) Auditory Processing Disorder
Normal peripheral hearing sensitivity
- Normal outer, middle and inner ear
Normal AC and BC thresholds
Difficulty in challenging listening environments
Comprehension goes down with background noise
Poor perfomance on degraded speech tests
Auditory Neuropathy
Disorder in the neural mechanism
- Inner hair cell to VIII nerve transmission or VIII nerve itself
Audiometrically presents at SNHL
AC and BC thresholds measure the same neural disorder
No air bone gap
Communication difficulties and causes of auditory neuropathy
Communication difficulties
- Extreme difficulty in understanding speech
- Poorer than expected based on audiogram
Causes
- Unknown
- Risk factor: stay in the neonatal intensive care unit (NICU) at birth
