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Lecture 9

Lecture 9

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Matthias Niemeier

PSYB51 November 12 , 2010 Lecture 9: Prediction of this theory: We seem to be unable to move our eyes without shifting our attention but we can shift our attention without moving our eyes - What explains this connection between shifting attention and eye movements? Pre-motor theory of attention was proposed by Rizzolatti; he stated that shifts of attention essentially are oculomotor programs. So you shift your attention at the point when your oculomotor program (that is meant to move your eyes to some point in space) is ready to be executed. So it takes some time to do some planning (OR process any kind of activity in the brain for that matter). So when the oculomotor program is ready to be executed = so that the eye can move to the target of interest  THAT IS THE POINT WHEN YOU SHIFT YOUR ATTENTION! - So attention actually precedes the eye movement! So the eye movement hasn’t happened but shift of attention already occurs! PSYB51 th November 12 , 2010 - But, the eye movement does not have to happen after a shift of attention. This is the difference between overt attention and covert attention. - Overt attention = actually make an eye movement [after shift of attention] (overt = obvious; reflecting shift of attention) - Covert attention = when you don’t move your eyes [the oculomotor program is ready to be processed but it never happens; it’s never executed! So it’s not passed onto neural structures that are directly involved in muscles of the eyes = so the activity might not enter the brain stem where these oculomotor neurons sit!] So, the pre-motor theory of attention predicts a close connection between shifts of attention and eye movements! - Medium = AIR; could be water - Longitudinal wave = are waves that have the same direction of vibration as their direction of travel. - When object vibrates it will hit the medium (water, air) it is embedded, and will compress the molecules around the medium on one side while making the density less on the other side - Creation of a sound wave – where molecules will oscillate in the direction at which the sound is travelling (increase or decrease in pressure) = longitudinal PSYB51 November 12 , 2010  As tuning fork hits air molecules it compresses/ decompresses air molecules and you get a sound wave that is longitudinal that has a phase, amplitude and frequency  Amplitude = sine wave is either small or pronounced o Larger amplitude = louder to your ears  Smaller tuning fork that vibrates at a higher rate = higher frequency ( doubled in this case due to octave) Intensity = amount of sound energy falling on a unit area falling on your ear! It’s a physical measure of how loud something else (expressed in decibels) How is amplitude associated with loudness? Loudness is the psychological aspect of sound related to perceived intensity or magnitude, while amplitude is the physical magnitude of displacement of a sound pressure wave. The more intense a sound wave, the louder it will sound. - Intensity is related but NOT EQUAL to LOUDNESS! Loudness is what we perceive. - Decibels: where p = is what you are looking at the moment, p0 = standard reference a minimum where human audition is possible - **decibel is twice as loud as the earlier one in energy - So as the intensity increases = you perceive things as becoming louder but regular steps in intensity doesn’t mean regular steps of perceived loudness (logarithmic relationship) - ** IN EXAM: do not define loudness or intensity like you talk about them in everyday language. Follow the definition as laid out here.** Huge range of intensities you can perceive. PSYB51 th November 12 , 2010 - frequency: measured in beats/s (Hz) - Frequency not the same as pitch; you perceive frequency as pitch - The relationship is again not direct - So as the frequency increases = the pitch increases  but regular steps in frequency doesn’t mean regular steps of perceived pitch (logarithmic relationship); skip phase - Limited range: this range also depends on age - High risk-threshold: listening to this sound isn’t good anymore [damage ears] - Pain threshold = sounds way above threshold  can actually kill ppl - Since waves: sounds somewhat like a flute; although flutes are somewhat more complex - Sine waves are building blocks of any kind of complex sound - Square-shaped wave (sound): set of sine waves of increasing frequencies and decreasing amplitudes = if you keep on adding up these sample sine waves, you eventually create something that is square-ish (an example of complex wave). What is a sine wave and why is it important in studying auditory perception? PSYB51 th November 12 , 2010 A sine wave is a waveform for which variation as a function of time is a sine function. It is important in studying auditory perception because all sounds are made of sine wave, usually a combination of various sine waves. Understanding them is important to understanding auditory perception. - What can be inferred by doing a Fourier analysis? A Fourier analysis is a mathematical theorem by which any sound can be divided into a set of sine waves. Combining these sine waves will reproduce the original sound. - Any kind of complex sounds can be made up of sine waves - Spectrum of frequencies (graph): Spectrum has bars, in a square wave function the spectrum bars occur at a regular rate with bars decreasing in length (means that power is decreasing) = representative of a harmonic spectrum - SO THE SQUARE WAVE FUNCTION IS COMPOSED OF VERY NARROW- RANGED SINE WAVES WITH A VERY SPECIFIC KIND OF FREQUENCY (on graph in slide) - So the frequency spectrum expresses the power of diff. frequencies - Through this spectrum, one can illustrate the reason as to why different instruments sound different or why do different vowels sound different - Regular steps mean that the frequencies increase as integer of multiples of fundamental frequencies (lowest frequency – first bar) - Say the lowest frequency an instrument can play is 1 X 200 Hz, the next one would be 2 X 200 Hz = 400 Hz, the next one would be 3 X 200 Hz and so on - For another instrument the lowest frequency [like 200 Hz in the last case] might be different but the number being multiplied before it will be the same [so 1xlowest frequency, 2xlowest frequency...etc] - How can we hear two instruments being played at the same pitch?  The reason is we perceive the pitch of a sound as being equal to the fundamental frequency  Frequencies of a sound usually are way more than what we consciously notice Timbre: The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics and other high frequencies. PSYB51 November 12 , 2010 OUTER EAR: pinna (ear lobe), and ear canal  Function: funnel, amplifies sound, protects the inner parts of the ear from any kind of damage  Outer ear ends with the tympanic membrane (ear drum) This membrane is hit by sound pressure waves If ruptured we can’t hear with the ear This membrane can self-heal, sometimes a scar may be left which means that you can’t perceive high frequencies What are the roles of the ear canal? The ear canal is responsible for: 1. conducting sound vibrations from the pinna to the tympanic membrane; and 2. preventing damage to the tympanic membrane. - MIDDLE EAR: ossicles (smallest bones in the human body) -Malleus -> incus-> stapes Chain of bones that pick up the vibrations of the tympanic membrane and transmit them to the oval window (part of the inner ear) Oval window is smaller than tympanic membrane; therefore when you have pressure coming from a larger membrane to a smaller membrane, it will amplify the pressure Ossicles are connected to muscles which are meant to do something about the amplification of loud sounds (done by tensing/contracting the muscles); so they reduce the loudness of the sound = ACOUSTIC REFLEX Quick and loud sounds (gun sounds) are most damaging to the ear (check below why = next page) Describe the three tiny bones in the middle ear. The three tiny bones in the middle ear are called ossicles; the malleus, the incus, and the stapes. They amplify the sound. The malleus receives vibration from the tympanic membrane and is attached to the incus. The incus connects between the malleus and the stapes. The stapes presses against the oval window of the cochlea on the other end. PSYB51 November 12 , 2010 - Acoustic reflex A reflex that protects the ear from intense sounds, via contraction of the stapedius and tensor tympani muscles. - Why can't the acoustic reflex help protect the ear from abrupt loud sounds, such as gun fire? The acoustic reflex is a reflex that protects the ear from intense sounds by the contraction of the stapedius and tensor tympani muscles. However, this reflex follows the onset of loud sounds by about one-fifth of a second, so it cannot protect against abrupt loud sounds. Remember: loudness is a function not only of intensity but also time (the time of some kind of a sound pressure wave to which your ear is exposed) INNER EAR: cochlea – snail kind of structure which includes the auditory organ (organ of corti).  Vestibular organ is responsible for our sense of balance  Oval window is the entry of sound pressure into the cochlea, running through the cochlea and then turns around and eventually comes out of the round window (if sound pressure wave has enough energy)  There are three canals (inside the cochlea): All filled with watery fluid Middle canal is wedged in between vestibular and tympanic canal Canals are separated by membranes; one of the membranes called basilar membranes has something on top of i this is the organ of corti = this organ enables us to hear - What is the function of the cochlea? * ORGAN OF CORTI The cochlea is a spiral structure of the inner ear containing the organ of Corti, which is responsible for transducing mechanical movement into neural activity. PSYB51 November 12 , 2010 - ORGAN OF CORTI: converts sound pressure waves into neural signals  Presence of auditory nerve fibres have soma in the brain stem, they reach out with the dendrites into the inner ear Organ of Corti: A structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers. (& scaffold of supporting cells) Auditory nerve fibers: A collection of neurons that convey information from hair cells in the cochlea to (afferent) and from (efferent) the brain stem. This collection also includes neurons for the vestibular system. Hair cells: Cells that support the stereocilia that transduce mechanical movement in the cochlea and vestibular labyrinth into neural activity sent to the brain stem; some hair cells also receive inputs from the brain. PSYB51 November 12 , 2010 - Inner hair cells are the sensory input (afferences) – this is what we hear with - Outer hair cells are not directly involved in hearing- they are involved in amplifying hearing  From the brain back to the ear: they stretch out and lift the scaffold (purple thing on the picture); membrane sitting on top – they do this in the way that amplifies the vibrations of the scaffold which then stimulates the inner hair cells  Scaffold = TECTORIAL MEMBRANE - Stereocilia are dendrites of nerves that are regularly arranged - They sense vibrations or movements of the tectorial membrane - As a traveling wave passes through the fluid within the vestibular canal and causes it to bulge out, the cochlear partition is displaced, causing the basilar membrane, along with the inner hair cells and outer hair cells, which sit atop the basilar membrane, to move down and then back up. - Hairlike bristles called stereocilia extend from the hair cells to the tectorial membrane. Because of the way it is attached to the cochlear partition, the tectorial membrane drags these stereocilia back and forth as the basilar membrane moves up and down. - The back-and-forth motion of the stereocilia on the inner hair cells starts a chemical chain reaction that (finally) results in a neural impulse being generated by the hair cell. These impulses are transmitted to the brain via auditory nerve fibers, which collect together and emerge from the cochlea in the cochlear nerve. Tectorial Membrane The tectorial membrane moves back and forth as the basilar membrane moves up and down, driving the stereocilia of the hair cells (which are embedded in, or at least touching the membrane) back and forth with it. Describe how the release of neurotransmitters results from the deflection of stereocilia. When vibration causes a displacement along the cochlear partition, the tectorial membrane and hair cells move in opposite directions (shearing motion) and the deflection of stereocilia in this action results in the release of neurotransmitters. Basically: when the stereocilia of inner hair cells are bent back and forth by the shearing motion of the tectorial membrane, the hair cells produce action potentials that are carried back to the brain via auditory nerve fibers. PSYB51 th November 12 , 2010 - We now want to be able to distinguish frequencies; this is done in two different ways 1 way: By Place Code = Depending on the frequency of the sound, different parts of the cochlea get stimulated - Red peak on the graphs – get most vibrations of the organ of corti  From 25 Hz to 1600 Hz the peak is shifting along High frequencies displace basilar membrane in base of cochlea Low frequencies displace basilar membrane in apex of cochlea (at the end of the coil) Note: The cochlea as a whole narrows from base to apex but the basilar membrane actually widens towards the apex. The basilar membrane is thick at the base and becomes thinner as it widens. - At different parts of the organ of corti, you have these auditory nerve fibers connecting to the hair cells they then indirectly connect to different parts of the brain that are specialized for different aspects of frequencies (Frequency selectivity) - Threshold tuning curves : not as regular as you seen in the v
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