Summary Sensation and Perception chapter 11 - 13 PDF

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PSYC 2020 1 Perception chapter 11 notes: Hearing Perceptual Process (1) Identify the environmental stimulus, which manifests itself as longitudinal sound waves. Physical Aspects of Sound Sound as both a physical stimulus and a perceptual response (think tree falling in a wood answers) o Physical Sou...

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PSYC 2020

1 Perception chapter 11 notes: Hearing

Perceptual Process (1)  Identify the environmental stimulus, which manifests itself as longitudinal (condensation/rarefaction) sound waves. Physical Aspects of Sound  Sound as both a physical stimulus and a perceptual response (think tree falling in a wood answers) o Physical = Sound is pressure changes in the air/medium o Perceptual = Sound is the experience of hearing o Specify a difference between (1) Sound stimulus and (2) sound perception in essays  Sound as pressure changes o Condensations (pushing together) and rarefactions (pulling apart) of air molecules creates low and high pressure regions of air – travelling at 340m/s through air (and 1500m/s through water) o Important to remember air molecules themselves stay relatively stationary  Pure Tones o Produced by a sine-wave pattern of condensation/rarefaction, having a recurrent frequency (1Hz=1cycle/s) and amplitude (dB). o The Decibel scale is used to transform large pressure ranges into small values  dB= 20 x log(p/po)  p=pressure po=reference pressure (usually 20micropascals)  SPL=sound pressure level  Complex tones o As pure tones are naturally very rare we must understand complex tones o Many complex tones are also periodic tones – meaning they repeat with a frequency called the fundamental frequency  These can be split into a number of pure tone ‘components’, with each component being called a harmonic. The first harmonic (or fundamental of the tone) holds the same fundamental frequency as the tone.  Higher harmonics are pure tones with a while number multiple of the fundamental frequency. o Frequency Spectra are a way of visually representing the harmonics - graphing them on frequency (not time).

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o Removing harmonics will not change the frequency.

Perceptual aspects of sound  Thresholds and Loudness o Loudness relates to the level or amplitude of the stimulus, expressed in dBs o However loudness also depends on the frequency.  Thresholds across the frequency range: The Audibility Curve o We can hear between 20Hz-20,000Hz but are most sensitive between 2,000-4,000Hz (Speech range)

Blue line=feeling (painful sound) A= a tone an elephant could hear, but we cannot. Each red line represents a constant level of perceived sound.

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Pitch o Definition = the property of auditory sensation in terms of which sounds may be ordered on a musical scale o But remember – pitch is a psychological property of sound. o Tone height is the perceptual experience of increasing pitch which accompanies an increase in fundamental frequency. o Going along a musical scale every repeating letter after an octave holds the same tone chroma – meaning they are whole multiples of the fundamental frequency o The effect of the missing fundamental refers to removed harmonics. When this pitch is perceived it is a periodicity pitch indicating the pitch is determined by the period (of repetition) therefore the tone is not necessarily determined by the presence of the fundamental frequency but by information – such as the spacing and repetition rates related to the fundamental frequency Timbre o This refers to the quality of the sound – allowing distinction between two sources producing the same pitch and loudness. o This is caused by a difference in harmonics which are present, constructing the tone. o Attack (build up of sound at start) and decay (decrease at end) also change the timbre.

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From pressure changes to Electricity  Three basic tasks o (1) delivers sound stimulus to receptors o (2) transduces stimulus from pressure to electrical signals o (3) Processes to indicate qualities of sound (pitch, loudness, timbre, location)

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Outer ear o Pinnae are the structures sticking out from the head, help with location. o Sound first travels through the auditory canal (3cm) stores wax to protect the tympanic membrane (eardrum) o This also helps with resonance which acts to increase the intensities of some sounds – the range between 1,000-5,000Hz Middle ear o A small cavity about 2cm^2 containing the Ossicles (three small bones) 1. Malleus/hammer is vibrated directly by the tympanic membrane, which it is attached to this then vibrates the: 2. Incus/anvil which transfers the vibrations to the: 3. Stapes/Stirrup which transfers these to the inner ear through the oval window o This is necessary as the outer/middle ear is filled with air but the inner ear contains a much denser fluid – only 1% of vibrations would be transferred without the Ossicles. o Throughout the middle ear the vibrations are amplified by the small stapes causing a pressure increase of 20x while the lever action of the eardrum also helps this.  Fish don’t need an outer/middle ear as the liquid they live in is similar to that in their inner ear.

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o Middle ear also contains the middle ear muscles – smallest skeletal muscles in the body – which help to dampen the ossicles’ vibrations at very high sound levels. Inner Ear o Contains the liquid filled cochlea, a coiled structure who’s liquid vibrates due to the stapes pressing on the oval window  This is separated by the cochlear partition creating the Scala Vestibuli and Scala Tympani almost all the way from the base to the apex  The partition is where vibrations are transferred into electricity. Through the organ of Corti which runs the length of the partition.  The organ of Corti contains hair cells and two membranes: the basilar and tectorial. o Hair cells and membranes  Cilia protrude from the surface of the Basilar membrane, which contains inner and outer hair cells in a ratio of 1:3  Vibrations cause the hair cells to bend, as the basilar membrane begins to move resulting in (1) the organ of corti moves with it and (2) the tectorial membrane moves back and forth causing the cilia to bend  Bending causes electrical signals: This transduction involves an ion flow which is triggered by the bending of hair cells which result in tip links opening. When these open positive potassium ions flow into the cell. When the cilia bend in the opposite direction the ion channels close.  Therefore back and forth motion creates alternating bursts of electrical signals, resulting in neurotransmitter release, which diffuse across the synapse separating the inner ear from the auditory nerve fibres, causing them to fire  A sound’s frequency determines the timing of the electrical signal – Phase locking is the multiple firing at the peak of sound stimuli, however the refractory (rest) period must be taken into account.  Temporal coding shows the connection between the frequency of the tone and timing of the nerve fibre Vibration of the Basilar Membrane  Békésy discovered that the movement along the Basilar membrane is similar to a traveling/transverse wave o The intensity of this vibration, and its location of greatest intensity, depends on the frequency (higher frequency = closer to base) 

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o This introduced the place theory of hearing which states that the frequency of a sound is indicated by the place along the cochlea which nerve firing is the highest.

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Evidence for place theory o Measuring of electrical response to different frequencies along the length of the cochlea to form a tonotopic map by Culler et al (1943)  Each hair cell and nerve fibre responds to a narrow range of frequencies determined by the frequency tuning curve. We can see that the fibres near the base have high characteristic frequencies while the fibres near the apex have low. Practical application o The understanding of the cochlea resulted in development of a cochlear implant, which helps to restore hearing to those with damaged hair cells. The implant consists of 1. An exterior microphone 2. A sound processor, to divide the sound into a number of frequencies 3. A transmitter sending the signals to the: 4. Array of 22 electrodes implanted along the cochlea. Updating Békésy: The Cochlear Amplifier

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o More recent measures have found a much greater amount of localisation in vibrations, due to testing in live subjects. This action of outer hair cells, contracting and relaxing, is called the cochlear amplifier  The cell expands and contracts respectively to each direction of movement, increasing the motion and therefore sharpening the response. Complex Tones and vibration of the Basilar membrane o The cochlear appears to respond to a complex tone’s harmonics, meaning multiple cites of vibration. o These are separated along it’s length, and is termed an acoustic prism

The Physiology of Pitch Perception  Pitch perception occurs in the brain not the ear  Pitch and the ear o Pitch is related to frequency and repetition rate o Two types of physiological information from the stimulus frequency  (1) Timing information, the firing rate of the nerve fibres (higher Hz=more firing)  (2) Place information, the place on the cochlea where maximum firing occurs. o However, unlike Békésy’s place theory, evidence suggests that pitch perception cannot be explained by place alone – phase locking occurs only below 5,000Hz, suggesting our sense of pitch is limited in that range.  Above 5,000Hz our discrimination may be based on place cues – but this provides a non-musical pitch. o In complex tones, when removing the fundamental frequency the pitch remains the same – again disagreeing with place theory  Pitch and the Brain o Auditory cortex is located in the temporal lobe, with the primary auditory receiving area – A1 o The A1 is arranged into areas, similar to that of the Cochlea, of frequency sensitivity (lower frequencies further towards the front) o Daniel Bendor and Xiaoquin Wang (2005) measured neurons responses, just outside the auditory cortex, to complex tones with different harmonic structures yet all sounded the same to humans. Using marmosets they found that the stimuli all caused an increase in firing, but only when the

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fundamental frequency was present. They termed these neurons pitch neurons. We can conclude that frequency is coded in the cochlea and auditory nerve.

How to damage your hair cells  Outer hair cell damage is the most common cause of hearing loss, resulting in the inability to hear quiet sounds.  Presbycusis o Can be caused by living in an industrialised environment, through long term exposure to noise. It effects high frequencies and is more severe in males  Noise-induced hearing loss o This occurs when loud noises cause degeneration of the hair cells, damage to the organ of Corti is often observed. o Although this is often workplace noise – resulting in the OSHA (US Occupational safety and health agency) restricting sound levels to 85dB for 8-hour work shifts – leisure noise is also a huge cause. Developmental – Infant hearing  New-borns do have some hearing capabilities  Thresholds and the Audibility curve o Lynne Werner Olsho et al (1988) used a method whereby an observer would watch a baby with headphones on and determine whether they had heard a tone or not (through reaction)  Responses were more often (or just more obvious) at higher frequencies, creating an audibility curve from 2,000Hz at 25dBs.  By 6 months the audibility curve reflected that of an adult much stronger, and was out by only 10-15dB

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Recognising their mother’s voice. o Anthony DeCasper and William Fifer (1980) showed that 2day-old infants will modify their sucking on a nipple in order to hear their mother’s voice. If the baby suckled for a longer time they would hear the mother, and a shorter time a stranger – these conditions were reversed in the second condition. They found that the babies would regulate their suckling periods in both conditions to hear the mother’s voice.  This is an amazing feat for a 2-day-old, and the researchers put it down to hearing the mother during development in the womb. o DeCasper and Spence (1986) did a study whereby the child (while in the womb) was read The Cat in the Hat numerous times during, while a second group read it replacing Cat and hat with dog and fog. When the children were born they regulated their suckling to hear the version they heard in the womb. o Similarly Moon et al (1993) shower 2-day-old infants regulated their suckling to hear their native language. o Kisilevsky et al (2003) measured the foetus’s response, of fullterm pregnant women, when listening to a 2 minute reading by either their mother or a stranger (played through a loudspeaker at 95dB, 10cm from abdomen). During the mother’s reading the foetus’s movement and heart rate increased – concluding the recognition of the voice.

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Chapter 12

Perception Chapter 12 Notes: Auditory Localisation and Organisation Three key problems: (1) Auditory localisation (2) Problem of reflected sound (3) Auditory scene analysis Auditory Localisation  Varying locations of sound creates an auditory space, locating them is auditory localisation  As the Cochlea’s location of firing is dependent on the frequency (not location) it cannot be here. It is therefore due to location cues – to do with the interaction with the persons head and ears. o There are two types of cues monaural cues and binaural cues. These have been studied in 3 dimensions the Azimuth (left-right), Elevation (up-down) and the distance from the listener. Binaural Cues for Sound Localisation  Interaural time difference (ITD) o This is the time difference between each ears reception of the sound. Noted as more effective for low-frequency sounds  Interaural level difference (ILD) o This happens as the head is a barrier which creates an acoustic shadow, reducing intensities for one ear. This reduction occurs in higher frequencies.  This happens as the low-f sound waves are larger than the object (head) blocking their way, therefore are not disrupted. Therefore can help to locate high-frequencies  Cone of confusion o The ITL and ILD complement each other, providing low and high frequency assistance. However when we raise a source on the elevation axis, while being equidistant from our ears we won’t have any change in these cues. o Similarly, there is the ‘cone of confusion’ where multiple areas can correspond to the same levels of ILD and ITD

Monaural Cue for Localisation

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 Spectral cues are the most common. They occur due to reflections off the pinnae folds – which reflect different frequencies differently.  This has been tested through placing microphones in the ear, and firing frequencies at 15 degrees above or below the head. These would produce different reflections in the pinnae. o Similarly, smoothing out the folds makes it harder to locate elevated sound sources.  Hofman et al (or King et al. similar, RIGHT) inserted a mould to smooth the contours. For one participant the response to elevated stimuli increased over the 19 day trial. They would still respond well to the azimuth coordinate (binaural cues). However when the moulds were removed localisation performance returned to the pre-tested levels – suggesting the new associations were coupled with the old ones.  The Physiology of Auditory Localisation  Auditory Pathway and Cortex o Signals from the cochlea are sent along the auditory nerve to the auditory cortex (A1) through a number of subcortical structures below the cerebral cortex  From the Cochlear nucleus it goes to the superior olivary nucleus in the brain stem, then the inferior colliculus in the mid-brain and the medical geniculate nucleus in the thalamus. From here they go to A1 in the temporal lobe of the cortex. REMEMBER SONIC MG – a sports car (Superior Olivary Nucleus, Inferior Colliculus, Medical Geniculate nucleus) o Processing in the SON (superior olivary nucleus) is important for binaural localisation, because this is where the signals from both ears meet o At A1 (reciving area) the signal travels to other cortical auditory areas (1) the core area, which includes the primary auditory cortex (A1) and nearby areas (2) the belt area surrounding the core and (3) the parabelt area Jeffress Neural Coincidence Model (1948 – see diagram, next pg) o This proposes that neurons are wired so they each receive signals from the two ears, as the signal passes down it’s axon, all neurons are stimulated in turn, but not activated. If they both reach neuron 5 (of 10), the middle, at the same time that neuron fires, and this signals the sound is dead ahead. This activation of only one neuron, dependent on ITD is called the place code.

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Chapter 12 o ITD tuning curves support this model, as they react as the model would predict, as each neuron is seen to react best to a specific ITD.  Broad ITD tuning curves in mammals o Comparing the tuning curve of a Gerbil and a Barn Owl the gerbil’s ranges from -400 to +400(microseconds) while the owl ranges from -40 to +40. The gerbil’s in fact extends far past the range of ITDs, this is also found in monkeys

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o A new idea of broadly tuned neurons emerged, the location is indicated by the ratio of response of two types of broadly tuned neurons (right hemisphere for left stimuli, and visa versa) o This process is similar to the tricolour system of cone pigments.  We can conclude that neural binaural localisation is based on sharply tuned neurons for birds and broadly tuned neurons for mammals. The Birds have a place code while mammals have a distributed code Localisation in area A1 and the auditory belt area o Nodal et al (2010) used a brain ablation technique in ferrets and found that destroying A1 decreased their localising ability but did not eliminate it o Malhora and Lomber (2007) found a similar reaction by deactivating cats’ A1.  However both studies also found that destroying areas outside A1 affected localisation. o Gregg Recanzone (2000) recorded spatial tuning of neurons in the A1 to those in the posterior belt by moving the auditory source. He found A1 responded when moving the sound within a specific area but not outside this area. The cells in the posterior belt responded to a smaller space, concluding this area is more accurate Moving beyond the temporal lobe: Auditory Where and What pathways o Two pathways extend from the auditory areas (in the temporal lobe) to the frontal lobe. o The what pathway starts in the front (anterior) part of the core/belt and extends to the prefrontal cortex – this identifies sounds

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Chapter 12

o The where pathway starts at the rear (posterior) of the core and belt and extends to the prefrontal cortex – and locates sounds  The core of monkey’s A1 responds more to simple sounds  The anterior area of the belt responds to more complex sounds (what pathway) o Malhora and Lomber (2008) deactivated a cat’s anterior auditory area, finding this disrupts the ability to differentiate tones, but not localise them. And the reverse was also tested, with the correct results.  This has also been seen in humans – J.G. had temporal lobe damage and E.S. had parietal and frontal lobe damage. This found J.G. could localise sounds, but not recognise, and E.S. could recognise but not locate. Hearing Inside Rooms  Direct sound = the sound reaching the ears direct from the source  Indirect sound = the sound reaching the ears once reflected off surfaces. 

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Perceiving two sounds hat reach the ears at different time o Precedence effect allows the perception of only a single sound, and occurs when the second sound appears 5-10ms after the original.  This is seen by presenting two speakers and playing sounds after each other – only in that range would ...