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Psyb51 Lec 9.docx

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University of Toronto Scarborough
Matthias Niemeier

Psyb51 Lec 9 SAQ: Explain the premotor theory of attention - When making eye movements, they predict where your attention will go - Theory about the fact that eye movements and attention shifts in space are closely related - Attention and eye movements are connected - The program for making eye movement gets completed o Premotor theory of attention states this - Oculomotor system completes movement of saccade – shifts attention - Can shift attention without moving eyes by – execution of eye movement is inhibited o Connections to downstream areas is inhibited somehow - Might be something like this on exam Sounds are created when objects vibrate - Medium – often air, could be water or anything else - Vibrations occur in the air - Longitudinal direction  goes back and forth o Like hollow spheres expanding o Regions where there are increases in air pressure Different frequencies rd - Frequency sine wave has same amplitude as the first but is closer spaced together (3 picture) o One cycle fits in a smaller piece of space Basic qualities of sound waves - Amplitude: how much molecules swing back and forth – directly related to intensity - Intensity: amount of sound energy falling on a unit area – how it hits tympanic membrane of the ear o Measured in decibels spl o Have some reference to which some sound energy is reflected o Difference between 6 and 12 decibels – second sound is twice as loud and carries twice as much energy as the first sound  Goes in steps of 6 - Loudness: the psychological aspect of sound is related to the intensity of the sound but only as it is perceived o Not the same as the real thing o Our perception - Can have negative decibels – very good hearing - 120 decibels – something a million times louder - Frequency: for sound, the number of times per second that a pattern of pressure changes repeats o Number of sine waves per one time o Associated with its psychological aspect  PITCH  Pitch is psychological - Phase (skip this) Interactions between amplitude and frequency - Sensitivity for light contrast increases as a function of spatial frequency - Threshold: the lower you are, the better you are - Lower area of dark blue area = absolute threshold of audition - Absolute threshold arbitrarily divided by the zero - For some frequencies, can go below 0 dBs – sound energy can be less - Horizontal lines mean it is the same level of energy. In terms of frequency, loudness is different - High risk threshold – that frequency of sound can damage ears ; extremely damaging o Consistent in all frequencies - Pain threshold – can kill people - Range of frequencies is very large One of the simplest kinds of sounds: - Sine wave: waveform for which variation as a function of time is a sine function - Complex sounds can be pieced together by sine waves - If you take a set of sine waves and add all together, get a square shaped wave o If enough sine waves get added together o Adding infinite sine waves gives a perfect square - Spectrum: representation of the relative energy present at each frequency o Bar represents frequency of sine wave o One fo the vertical bars is shorter  means it is less intense Harmonic spectrum: follow specific mathematical pattern - Harmonic sounds are typically caused by simple optics or sources that are vibrating o Ex. guitar strings  We like simple sounds - Have frequencies with components that increase in regular integer multiples of the lowest frequency o Fundamental frequency: lowest frequency of a sound st  1 harmonic o When you plot, get stripes that are in regular steps - Timbre: profile of energy of diff frequencies that you filled out o Hear the timbre of the profile o Way we can tell diff between tenor sax and piano or A and E Anatomy and physiology of the auditory system Outer ear - Pinna: where sound is first collected - Have ear canal which is part of the outer ear o Main function is to protect middle and inner ear o Outer ear ends at tympanic membrane Middle ear - Most importantly 3 bones: (KNOW!!!) called OSSICLES o Malleus, incus, stapes  Smallest bones in body  Malleus connects to tympanic membrane  Stapes connects to oval window leading to inner ear  Connect 2 membranes  Enhance sound – amplifies Inner ear - Consists of 2 things: vestibular organ - Cochlea like a hose/tube that is wrapped around Cochlea - Spiral structure of the inner ear with the organ of Corti - Filled with watery fluids in 3 parallel canals o Middle canal o Vestibular canal o Tympanic canal Vibrations transmitted through tympanic membranes and middle-ear bones - Go through fluid in canals - Vibrations in fluid travel to the vestibular canal. If it is really intense going through the helicotrema Organ of corti - Movements affect a certain part of cochlea – how frequencies are coded - Translates sound energy into neural signals - Specialized neurons called hair cells Tectorial membrane: extends atop organ of Corti; gel structure - Hair cells on top - 3 rows of outer hair cells and 1 row of inner hair cells - Inner hair cells have to do with hearing directly - Afferent – from sensory mechanisms toward the brain – inner hair cells - Efferent – info coming from the brain and going somewhere o Goes to outer hair cells - Outer hair cells are neurons and have muscle features – expand and contract o Lift up membrane on top of these hair cells o Influences how tectorial membrane is able to stimulate inner hair cells - Purpose of outer hair cells is to amplify sounds – have lower thresholds - Because there are so many outer hair cells moving membrane, ears hear this - When putting a seashell on your ear, the “wave” noises we hear are the blood flowing in our ear -> usually just ignore this noise Tectorial membrane and basilar membrane are moving up and down due to vibrations running through these fluids - When these two membranes move up and down, they shift relative to each other - Causes a shearing force  shearing causes complicated processes that are then converted into action potentials Coding of amplitude and frequency in the cochlea - If the cochlea was rolled out, basilar membrane would seem flat - Basilar membrane is differently thick and wobbly in different places o Like scuba diving shoes o Top is rigid and the end is floppy - Closer to the base, responds to higher frequency and things at the very end respond to lower frequencies - Have a higher wave moving up - Different neurons sit at different places in the organ of Corti which runs across basilar membrane but they are diff cells - Diff neurons respond to diff frequencies - Place code: frequencies coded in terms of space in the basilar membrane and the cochlea – different areas are tuned by different frequencies o Ex. open a piano and sing into it, voice will set into motion only some strings of the piano – those that are of the same sound as your voice The auditory nerve (AN) - Fibers are sensitive to certain frequencies depending on their place on the cochlear partition - Threshold tuning curve: like maps that plot thresholds of the neuron in response to sine waves with varying frequencies at lowest intensity that will give rise to a response - Tuned to FREQUENCIES - Not a nice bell shaped function - High and lower frequencies need more energy to stimulate cell - Wide range to which it responds - If the focus of the vibration is far from auditory nerve fiber, will not respond if the vibrations are very little - Big vibrations will stimulate all auditory nerve fibers across a wide range – basilar membrane moves a lot Two toned suppression - Sine wave sound playing through the ear, get simple curves with optimal needing little energy - Playing another tone at the same time; second tone can affect the first tone - Area will have a reduction due to the second tone - Pink areas show where it would have an impact - Decrease in firing rate of one auditory nerve fiber doe to one tone, when a second tone is presented at the same time Rate saturation: point at which a nerve fiber will not be able to fire more strongly
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