AuditionDay 8

Music CognitionMUSC 495.02, NSCI 466, NSCI 710.03

Harry HowardBarbara Jazwinski

Tulane University

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Course administration

Spend provost's money

Macrostructure of the brain

The parts of the brain that you can see with the naked eye

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Questions

What are the axes of the brain? What are the lobes of the brain and what do

they do? What are the main connections between parts

of the brain? What are the three ways of referring to areas

of the brain?

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Macrostructure overview

Three axes of the brain Vertical Horizontal

Longitudinal Lateral

Connections Naming conventions

Gyrii ~ sulcii Brodmann’s areas Stereotaxic (“Talairach”) coordinates

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Vertical axis: ventral/dorsal

Orientation of picture Which way is forward?

to the left: cerebellum at back

Which hemisphere do we see? medial side of right; left is cut away >

sagittal view

Vertical axis Dorsal is up, like dorsal fin (dorsal

comes from Latin word for back) Ventral is down (ventral comes from

Latin word for belly) Cortical vs. subcortical division Cerebrum vs. cerebellum Cerebral cortex (neocortex) vs. cerebellar

cortex

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Longitudinal axis: anterior/posterior

Lobes Sylvian fissure Perisylvian area

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Longitudinal axis, functions

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Lateral axis: left/right

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Lateral axis

General Which way is anterior? Motor and sensory organs are

crossed Ipsilateral, contralateral

LH Language Math Logic

RH Spatial abilities Face recognition Visual imagery Music

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Connections

Corpus callosum Arcuate fasciculus

Naming conventions

How to refer to specific areas of the brain

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Gyrii AnG - angular gyrus FP - frontal pole IFG - inferior frontal gyrus IOG - inferior occipital gyrus ITG - inferior temporal gyrus LOG - lateral occipital gyrus MFG - middle frontal gyrus MTG - middle temporal gyrus OG - orbital gyrus oper - pars opercularis (IFG) orb - pars orbitalis (IFG) tri - pars triangularis (IFG) poCG - postcentral gyrus preCG - precentral gyrus SFG - superior frontal gyrus SOG - superior occipital gyrus SPL - superior parietal lobe STG - superior temporal gyrus SmG - supramarginal gyrus TP - temporal pole

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Sulcii cs - central sulcus (Rolandic) hr - horizontal ramus ifs - inferior frontal sulcus ios - inferior occipital sulcus ips - intraparietal sulcus syl - lateral fissure (Sylvian) los - lateral occipital sulcus ls - lunate sulcus pof - parieto-occipital fissure pocs - postcentral sulcus precs - precentral sulcus sfs - superior frontal sulcus tos - transoccipital sulcus vr - vertical ramus

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Brodmann’s areas

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Brodmann’s areas, functions

Frequency

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Sound creation

Sound creation is created in most instruments, including the voice, by turbulent oscillation between phases in which air is compressed and phases in which it is rarefied.

The following figure depicts such a transition, in which increasing darkness symbolizes increasing compression of the airflow.

The heavy line represents the pressure of airflow as a single quantity between a minimum and a maximum. as air is compressed, its pressure rises; as air is rarefied, its pressure falls.

A single cycle of compression and rarefication is defined by the distance between two peaks, marked by dotted white lines.

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Graph of turbulent oscillation (of vocal air)

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Frequency

This cycling of airflow has a certain frequency the frequency of a phenomenon refers to the number

of units that occur during some fixed extent of measurement.

The basic unit of frequency, the hertz (Hz), is defined as one cycle per second.

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Two sine functions with different frequenciesA simple illustration can be found in the next

diagram. It consists of the graphs of two sine functions. The one marked with o’s, like beads on a necklace,

completes an entire cycle in 0.628 s, which gives it a frequency of 1.59 Hz.

The other wave, marked with x’s so that it looks like barbed wire, completes two cycles in this period. Thus, its frequency is twice as much, 3.18 Hz.

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Graph of two sine functions with different frequencies

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Fundamental frequency

The pitch of an instrument corresponds to the lowest frequency of oscillation, called fundamental frequency or F0.

Fundamental frequency & gender the fundamental frequency of a man’s voice averages 125 Hz, the fundamental frequency of a woman’s voice averages 200

Hz This 60% increase in the pitch of a woman’s voice can be

accounted for entirely by the fact that a man’s vocal folds are on average 60% longer than a woman’s.

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The fundamental & higher frequencies This brief introduction to

frequency leads one to believe that an instrument vibrates at a single frequency, that of its fundamental frequency, much as the schematic string on the left side of the next diagram is shown vibrating at its fundamental frequency.

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Higher frequencies

However, this is but a idealization for the sake of simplification of a rather complex subject.

In reality, instruments vibrate at a variety of frequencies that are multiples of the fundamental.

The diagram depicts how this is possible – a string can vibrate at a frequency higher than its fundamental because smaller lengths of the string complete a cycle in a shorter period of time.

In the particular case of the central diagram, each half of the string completes a cycle in half the time.

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Superposition of frequencies This figure displays the outcome of

superimposing both frequencies on the string and the waveform.

The result is that a pulse of vibration created by the vocal folds projects an abundance of different frequencies in whole-number multiples of the fundamental.

If we could hear just this pulse, it would sound, as Loritz (1999:93) says, “more like a quick, dull thud than a ringing bell”.

Audition

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Overview of the auditory pathway

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Auditory transduction: the cochlea

The cochlea is filled with a watery liquid, which moves in response to vibrations coming from the middle ear via the oval window.

As the fluid moves, thousands of "hair cells" are set in motion, and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells.

These primary auditory neurons transform the signals into electrical impulses known as action potentials, which travel along the auditory nerve to structures in the brainstem for further processing.

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Cross section of the cochlea The basilar membrane within the cochlea

is a stiff structural element that separates two liquid-filled tubes that run along the coil of the cochlea.

The tubes transduce the movement of air that causes the tympanic membrane and the ossicles to vibrate into movement of liquid and the basilar membrane.

This movement is conveyed to the organ of Corti, composed of hair cells attached to the basilar membrane and their stereocilia embedded in the tectorial membrane.

The movement of the basilar membrane compared to the tectorial membrane causes the sterocilia to bend.

They then depolarise and send impulses to the brain via the cochlear nerve.

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Frequency dispersion

The basilar membrane is a pseudo-resonant structure that, like the strings on an instrument, varies in width and stiffness, which causes sound input of a certain frequency to vibrate some locations of the membrane more than others and thus ‘maps’ the frequency domain that humans can hear.

High frequencies lead to maximum vibrations at the basal end of the cochlear coil (narrow, stiff membrane)

Low frequencies lead to maximum vibrations at the apical end of the cochlear coil (wide, more compliant membrane).

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The cochlea & basilar membrane

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More recent auditory pathway- note complexity

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Schematic auditory pathway

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Auditory regions of the brain

A lateral view of the cerebral cortex that highlights the prominent neural regions for auditory perception. The temporal lobe is shaded and the numbers refer to the Brodmann areas of primary auditory cortex (area 41) and secondary auditory cortex (areas 22 and 42). The right hemisphere contains homologous regions.

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Auditory cortex

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Primary auditory cortex (A1)

tonotopic map

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Absolute vs. relative pitch

Thus A1 represents absolute pitchWe do not know how relative pitch is

represented

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Timbre

Different parts of a musical instrument vibrate with different onsets (attack)

See Levitin’s discussion of Schaeffer’s perceptual experiments on onset (attack), pp. 53-4.

at different frequencies (steady state) for different durations (flux or decay)

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The timbre of the human voice

Respiratory

Laryngeal

Supralaryngeal

Back to our regularly scheduled program

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Ingredients of music cognition mostly receptive, mostly from Levitin

pitchtimbre

rhythmloudnessharmony

Perception Anticipation Categorization(in memory)

Attention Emotion

Music Cognition

Next Monday

Go over other musical perceptual attributes

§1-2 of Levitin