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3.8 - Music Perception.pdf

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McMaster University
Joe Kim

Arnav Agarwal 2011 Music Perception Module 1: Introduction Introduction - Can be found in all cultures and has taken many forms over tens of thousands of years - Can stir up emotion, trigger memories, etc. McMaster Institute for Music and the Mind - Group includes music theorists, musicians, psychologists, neuroscientists, mathematicians, kinesiologists, health scientists, and engineers - Work together to study physical structure, evolution, neural processing, performance and perception of music Music is more than a collection of individual notes - Music perceived as organized whole, not individual notes strung together in certain order - Organized whole can form acoustic pattern so salient that one can even hum the tune after hearing it only once Acoustic Patterns Are Very Easily Remembered - Acoustic pattern is easily recognizable, even if played in different key or with different instruments - Relation between notes is important to perception of the pattern, not individual notes themselves What is Music? - Why is the relation between some sequences of notes perceived as music and others as less musical? Module 2: Auditory Scene Analysis Gestalt Principles and Auditory Analysis - Despite being surrounded by a mixture of sounds from the environment, we are able to tell which sounds belong together, and where any given sound began and ended; we are able to make sense of the sounds around us and organize our auditory world - Gestalt principles that apply to organization of visual scene apply to organizing an auditory scene as well o Eg: incoming stream of sounds are separated into figure and ground Arnav Agarwal 2011 Figure Is Sound, Ground Is The Noise - Example used: subway environment - Ground/background: whatever sounds are not focused on (eg: random sound of subway station) - Figure: sound being focused on (eg: sound of particular arriving train) Figure Ground Principle and Audition - Sounds that make up the figure and ground are not permanent; will change as one focuses attention o Eg: attention moving from friend talking to PA system announcement -> figure and ground switch  Figure 1: friend  Ground 1: subway station noise (including other announcements)  Figure 2: subway station announcement  Ground 2: friend talking and other subway station noise Proximity - Organizes sounds that occur close together in time or space - If series of high and low tones both spaced apart in time were played: one would perceive two separate tones - If the tones were played together: single tone would be heard Similarity - Allows one to group auditory input that is similar (sounds of similar frequency, timbre, etc.) - Eg: can group series of sounds belonging to one voice out of a bunch of voices Continuity - Following along with one sound, even if simultaneous alternative sounds were played with the same instruments - Eg: following along with one song, even if simultaneously hearing another song played by same instruments Closure - Can understand conversation, even if occasional sound is muffled or missing Concept Check 1) We tend to group sequences of notes that rise and fall together. This best illustrates which gestalt principle? a. Proximity Arnav Agarwal 2011 b. Similarity c. Figure-Ground d. Continuity e. None of the above Module 3: Pitch Perception Introduction - How the frequency of a sound affects our perception - Frequency measured in hertz - Human frequency perception: 20 to 20,000 Hz - Sound wave -> ear canal -> ossicles amplify waves -> eardrum vibrates -> wave in cochlea fluid -> fluid movement -> basilar membrane -> hair cells move -> signal sent down auditory nerve -> key regions in the brain Frequency Theory: Vibration of Entire Basilar - Two theories required to explain pitch perception along entire frequency range we can hear o Frequency theory: entire basilar membrane vibrates at frequency of incoming sound wave  Causes impulses of corresponding frequency to travel up auditory nerve Arnav Agarwal 2011  Allows brain to decipher frequency by counting the number of neural impulses  Pros:  Physiological evidence indicates hair cells on basilar membrane do vibrate together -> predicted and proven  Problems:  Axons are incapable of firing more than 1000 impulses per second o Works fine if all important sounds for reproduction and survival were less than 1000 Hz o Doesn’t explain sounds humans can hear between 1000 and 20,000 Hz Arnav Agarwal 2011 Volley Principle and Frequency Theory - Single axon -> max. 1000 impulses per second sent to brain - Volley principle: group of auditory nerve fibres -> series of impulses as a team -> signal to brain of frequency of sound waves up to 5000 Hz o Still not enough to cover entire frequency range up to 20,000 Hz o Unexplained frequency range: 5,000 to 20,000 Hz - Relation between notes is important to perception of the pattern, not individual notes themselves Place Theory and Basilar Membrane Arnav Agarwal 2011 - Although hair cells along basilar membrane move together (as frequency theory predicts), they move as a traveling wave -> forms a peak at a particular place along the basilar membrane - Place theory of pitch perception: brain can decipher frequency of sound wave by being tuned to specific place of the peak of its traveling wave along the basilar membrane - Recall: each inner hair cell has roughly 20 direct links with brain o Allows region of each inner hair cell on basilar membrane to be represented very specifically in the auditory cortex - When sound causes a wave in the basilar membrane: o high frequency sounds maximally displace hair cells closest to oval window (initial cochlea entrance) o low frequency sound’s waves peak at opposite end of the cochlea (round window) Arnav Agarwal 2011 Tonotopic Representation of Pitch in A1 - Tonotopic representation of pitch maintained all the way till primary auditory cortex - Neighboring regions of cortex respond maximally to neighboring frequencies - Neurons are arranged in such a way that high frequency sounds activate neurons at one end of cortical and low frequency sounds activate neurons at other end and each neuron is maximally sensitive to sounds at a certain frequency Hair Cells Respond Maximally To One Frequency - Although each cell is maximally responsive to a certain frequency, will still respond to a range o Similar to visual receptors: will respond maximally to light of specific wavelength, but will also respond to a range of wavelengths of light Stebbins et al’s Animal Studies with Antibiotics - Animal studies using drugs that damage hair cell provided direct evidence for tonotopic coding of pitch - One experiment: Arnav Agarwal 2011 o Drug administered and monkey’s ability to perceive different frequencies of sound tested; coachae later observed o Result:  brief exposure damaged hair cells near the oval window entrance to the cochlea  longer exposure caused the damage to hair cells to extend towards the other end of the basilar membrane Damage to hair cells near the oval window - Monkeys with damage to hair cells near the oval window were unable to perceive high frequency sounds - More damage along basilar membrane -> growing inability to hear progressively lower frequency sounds - Conclusion: different frequencies represented at specific places along basilar membrane o High frequencies: entrance of cochlea o Lower frequencies: opposite end of cochlea Problems with Place Theory - As frequency of the sound gets lower, location of wave peak along basilar membrane gets increasingly variable - For very low frequencies (eg: under 50 Hz), peak disappears completely Arnav Agarwal 2011 Solution? Use Both! - Neither theory can account for full audible range of hearing - Both theories needed to explain full range - Frequency theory: hearing low frequencies below 1000 Hz - Place theory: hearing high frequencies above 5000 Hz - Both mechanisms: Frequencies between 1000 to 5000 Hz o We can coincidentally discriminate these frequencies the most effectively Concept Check 1) Which of the following is a serious problem with frequency theory? Arnav Agarwal 2011 a. Neurons don’t connect to hair cells b. Neurons can’t fire more than 1000 times per second c. The volley principle d. All of the above e. None of the above 2) The primary auditory cortex contains a map of different locations on the basilar membrane. This type of map is called: a. Tonotopic map 3) Match the range of frequencies with the theory that best explains how each range is processed: a. <5000 to 1000 Frequency theory b. 1000 to 5000 Both c. >5000 Place theory Module 4: Bird Song Introduction to Bird Song - Birds can sing very complex songs, but not every vocalization made by a bird is a song and not every bird is capable or producing song Bird Song - Bird song: music-like vocalizations made primarily by male birds of a species attract females or defend territory from other males Two Song Areas in Brain: HVC and RA - Two key brain regions have evolved to deal with song production complexities: o High vocal center (HVC) o Robust nucleus of the archistratum (RA) - Males are the primary producers of sound -> both these brain regions are larger in males than females o Sex difference controlled partly by hormones  Female given testosterone will show brain region size increase and will begin singing like a male o Further modified by experience  Males are particularly skilled at song have enlarged HVC and RA regions Arnav Agarwal 2011 Bird Song Requires Gene-Environment Interaction - Bird song: collaboration between inherited and learned components during development o Result: species-typical behavior - Birds may inherit a genetic predisposition to sing, but must learn and practice to produce correct songs Evidence for Learning - Marler and Tamura: Studied white crowned sp
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