reverse names 2 Flashcards
-Which fibers are responding
-Specific groups of hair cells on basilar membrane activate a specific set of nerve fibers
-Suggests that different frequencies will disturb different regions of the basilar membrane (i.e. different cells)
-Helmholtz first proposed a “resonance” theory
basilar membrane wider at apex
suggested that fibers in basilar membrane resonated at different frequencies at different locations along its length (long fibers at apex, short at base)
-Problems for resonance theory
no fibers
not under tension:
The Neural Encoding of Pitch: Place Theory
Bekesy observed the movement of the basilar membrane directly – drilled hole in cochlea of cadaver and viewed movement
sound produced ? along the basilar membrane
waves affected all of the membrane, but the location of maximum displacement varied with frequency
Peak of envelope moves towards basal end of basilar membrane with increasing frequency
low freq/long at apex, high freq/short at base
TRAVELLING WAVES
Rate or pattern of firing of nerve impulses
-Proposes the basilar membrane vibrates in synchrony with the pressure changes (at the same frequency as the sound)
-Frequency representation based on a match between the frequencies in incoming sound waves and the firing rates of auditory nerve fibers.
-similar to a diaphragm in a speaker
vibrates as a unit
results in impulses in the auditory nerve at same frequency as sound itself
-Two problems:
basilar membrane not like a diaphragm
Nerve fibres can’t fire above about 1000 Hz
The Neural Encoding of Pitch: Frequency Theory or Temporal Code
frequency could be coded by pattern of activity in a number of cells
Volley Theory & Phase Locking
~mechanical impediment to sound transmission~ Common causes -blockage in external ear -Otitis media (infection) -Otosclerosis Diagnosis -Relatively “flat” loss or low -frequencies more affected -Difference between bone and air thresholds -maximum loss no more than about 6o dB Treatment -Medical/surgical -Hearing aid
Conductive loss:
Persistent noise in the absence of any auditory stimulation
Chronic
Debilitating
May be related to “Phantom Limbs”
Tinnitus
The range of amplitudes that can be heard and discriminated; when applied to an individual auditory nerve fiber, the range of amplitudes over which the firing rate of the fiber changes.
dynamic range
~damage to neural transduction (i.e. hair cells)~
Common causes
-Age: gradual deterioration (presbycusis)
-Noise: progressive cumulative effects
-Ototoxic drugs: nicotine, aspirin, streptmycin
-Infections: mumps, maternal rubella, syphilis
Diagnosis
-Similar bone and air thresholds
-Typical high frequency loss (“ski-slope”)
-Loss may be profound
Treatment
-Hearing aids very limited
-In severe cases, cochlear implants
Sensori-neural loss:
Hearing loss with age
Progressive sensori-neural loss
More severe in males than females
Presbycusis:
preferred frequency
characteristic frequency
location cues based on the comparison of the signals received by the left and right ears
Binaural cues
- difference in sound pressure level reaching the two ears
- Reduction in intensity occurs for high frequency sounds for the far ear
- The head casts an acoustic shadow
- This effect is minimal for low frequency sounds
Interaural intensity (or level) difference
-Heuristics that help to perceptually organize stimuli
>Location - a single sound source tends to come from one location and to move continuously
>Similarity of timbre and pitch - similar sounds are grouped together
>Auditory stream segregation - separation of stimuli into different perceptual streams
Auditory Grouping
- the array of all sound sources in the environment
- process by which sound sources in the eviornment are separated into individual perceptions
Auditory Scene
Auditory Scene Analysis
Distributed coding – trichromatic theory of colour vision
Population code
Pattern Theory
