Audition

perceptual: sound is the exp we have when we hear

physical: sound is pressure changes in the air or other medium caused by the vibration of an object

amplitude is the variation in the air pressure(diff between peak n trough), perception of loudness

frequency is number of cycles per sec(1 Hertz = 1 cycle/s),pitch

Ossicles in middle ear:malleus(hammer), incus(anvil) and stapes(stirrup)

amplify the vibrations of the tympanic membrane n transmit them to the inner ear at the oval window

pinnae( visible external parts of ear)

auditory canal (~3cm tube-like structure, protects middle ear)

tympanic membrane (eardrum)

-cone shaped membrane separating the outer n middle ear

-sound waves induce a diff in pressure either side of tympanic membrane, causing it to vibrate

-larger amplitude sounds result in larger

-higher frequency sounds result in faster vibrations

contains the cochlea, a snail-like liquid-filled organ

vibration of the oval window displaces fluid in the cochlea, resulting in a change in pressure which propagates up n down the spiral structure

vestibular

middle

tympanic

auditory transduction is triggered by motion of the basilar membrane,

organ of corti translates the motion of the basilar membrane into neural signals, a voltage is generated when specialized hair cells contained within the organ of corti r bent, producing impulses in auditory nerve cells sent to brain.

sound amplitude is coded in the firing rate of auditory nerve fibers

responses increase with increasing sound intensity

some fibers have spontaneous rates and saturate rapidly, others have low spontaneous rate n saturate slowly

for sound to be x2 loud the amplitude needs to be increase by approx 3.16(10dB)

sounds frequencies cause vibration in specific areas along the basilar membrane. high frequencies near base, low frequencies near apex

where the auditory system keep track of the number of times of occurrence of the ongoing amplitude fluctuations in sounds

auditory nerve responses are synchronised to changes in pressure(occur up to 4,000Hz)

pitch usually determined by fundamental frequency of the sound

perceived sound quality(ie.timbre) is related to the number, frequency ratios n relative amplitudes of the harmonics

there is the missing fundamental illusion

perceived pitch is consistent with the missing fundamental frequency, suggests that pitch isn't simply determined n cochlea-the brain infers the missing fundamental from the harmonics

relative location of objects is contained within the retinal image,

place activated by a sound on the cochlea does not indicate location

binaural cues: comparison of signals in the left n right ear

location of sound in azimuth(ITDs and ILDs)

monaural cues: works with one ear, localize the elevation(up-down plane) n distance of sound, filter properties of pinna, intensity n reverberation

the relative time at which a sound arrives at two ears depends on its location in azimuth, depends on speed of sound 330ms, bigger head give bigger ITDs (max ~0.06ms)

interaural level differences, relative sound pressure reaching the 2 ears depends on the location of the source in azimuth. reduction in sound lvl occurs for the far ear, due to acoustic shadow. reduction occurs for high frequency not low frequnecy

binaural localisation cues processed by diff types of neurons, located in diff parts of superior olivary complex(superior olive)

-lateral superior olive(LSO) contains neurons sensitive to ILDs

-medial superior olive(MSO) contains neurons sensitive to ITDs

ITDs n ILDs provide complementary information about azimuth location, ITDs work well for low frequency sounds, ILDs provide information about high frequency sounds

ambigious info about elevation n distance

set of points from which a sound source will produce identical ITDs and ILDs

sounds hits the pinnae the relative intensity of diff frequencies sound waves changes, changes with sound source elevation

relative intnesity(sound intensity decrease with distance)

reverberation (the way sound reflects off objects provides cue to distance), multiple reflections combine to produce a persistence of sound called reverberation.

due to reverberation there is multiple sounds reaching the listener from multiple directions we can tell the location

because similar sounds are arriving in quick successions from diff location according to direction of first sound

provided delay is short (<10-20ms) single sound perceived

frequency components of a sound are more likely to be grouped into a single sound likely to be caused by same sound producing event.

common frequency change(analogous to principle of common fate), frequency that change together tend to group together

auditory stream segregation, organising sounds over time into separate perceptual events

similarity of pitch

temporal proximity(sounds occurring in rapid progression tend to be produced by same source)

similarity of timre

continuity(sounds stay constant n perceived continuous when interrupted by noise)

effect of sequential grouping for continuity is not restricted to tones but also occurs with speech

participants are presented with a given number of stimuli, and ltr they are asked to rmbr the stimuli

or asked to rmbr smtg they alrdy have in their memory(open essay questions)