Extra Reading Hearing Flashcards
describe Studdert kennedy 1970
sound categorisation in humans
4 criteria for categorisation for human speech
- distinct categories w sharp boundaries
- no discrimination btw stimuli in same category
- peak discrimination at category boundaries
- agreement btw actual discrimination and predicted
Wyttenbach et al 1996 - animal sound categorisation
used common patterns in human psychophysics to test categorical perception in crickets.
Crickets categorise sounds between attractive (>16 kHz) and repulsive (<16kHz). choice basedon freq but temporalpattern also cue.
sounds of speech are perceived categorically - discriminated btw voice onset time. categories Ba or Pa - negligable intermediates.
Hudspeth 1997
2 ways hearing deteriorates.
- hearing loss is permenant, human hair cells not replaced by mitotic turnover alhtough can be restored by cochlear prostheses. Birds - cochlea damage envokes proliferation of new hair cells. Fish and inverts - hair cells added all throughout life. why not humans?
- failure of cochlea amplifier - even is haircells still present causes hearing deterioration.
hair bundle is organelle of mechanoelectrical transduction. Stereocillia (cylindrical actin filled rods in hexagonal array) slide along with sound, mvt sensed by tip links causes cascade of second messengers. causes amplification of mechanical input.
chemical damage to cochlea reduces sensitivity, by reducing ability of outer hair cells to sensitise inner HC.
overstimulation also transiently damages outer HC non mammals lack outer hair cell
Hudspeth - freq tuning
in fish, amphibians, birds and reptiles
electrical resonance - freq selectivity. ion channels form mini electrical circuit at specific freq, in basolateral membrane of hair cells.
Mammal: hair cells mapped smoothly along sensory epithelium in cochlea, at cochlear base haircells have highest freq, apex has lowest.
Lardner and bin Lakim 2002
Metaphrynella sundara
exploit acoustic properties of tree holes and used as egg deposition sites.
tested: opaque plastic tubes used as treeholes and partially filled with water frog sounds recorded overnight as water level reduced.
frog call pitch analysed in relation to air column depth in dynamic resonance units.
longer call pulses peaked when resonating.
first example of animals sampling resonance qualities and adjusting call pitch and strategy.
Hudspeth 1997
how do hair cells get energy, why is amplification needed?
Hair cells work by positive feedback, use repetitive sinosoidial nature of sound waves and resonance to accumulate energy from sound waves, and increase motion of hairbundle - receptive organelle.
viscous damping occurs as hair bundles immersed in engolymph. active process to overcome viscous damping by amplifying low intensity sounds.
must be active system because passive system does not have as great degree of discrimination.
Hudspeth Otoacoustic emission
otoacoustic emission originate from inside the ear, possibly cochlea amiplifier is source of OAE.
OAE suppressed when stimulus tone presented at a nearby freq.
Robert 2001
Ormia small IID ITD
Ormia ochracea have small ITD of only 2 microseconds (humans is 5-700). also IID problem - WL of cricket song likely to just bend around fly’s body.
independent pressure receivers 0.5mm apart, whereas fly tympana undergo large difference of 4.5kHz.
shows mechanical response has large directionality, IID and ITD are larger than those in acoustic field. intertympanal bridge is thicker and stiffer than membranes. microscanning laser doppler vibrometry shows different patterns of deflection produced by intertympanal coupling.
Robert and Gopfert 2002
Hyperacuity neural coding at submillisecond scale documented for electric fish and barn owls - convergence for many sensory afferents onto interneuron acts as a coincidence detector.
Male cricket song so loud could be self damaging. Inhibitory corollary discharge reserves neural sensitivity during song. inhibits neurones pre and post synaptically.
