Intro to musical processing

Day 10

Music CognitionMUSC 495.02, NSCI 466, NSCI 710.03

Harry HowardBarbara Jazwinski

Tulane University

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Course administration

Spend provost's money

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Goals for today

Introduce a cognitive model of musical processing in general terms

Refer to a neurological model of musical processing

Incorporate one of Sacks’ musical disorders (cochlear amusia)

Do a better job of explaining how the cochlea works

Musical processing

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Reasons for recent advances in the understanding of musical disorders Background. 30 years ago …

the functional organization of the brain could only be studied by implanting electrodes in the common 'animal models': rats, cats, and monkeys, which are not known for their musical (or linguistic) abilities

detailed anatomical information about lesion patients was only available in the rare cases where there was accompanying pathological data.

The understanding of the normal functional organization of the brain has increased enormously from new, non-invasive imaging techniques:

haemodynamic (PET and functional MRI) and electrophysiological (EEG and MEG)

The understanding of the normal structural organization of the brain has increased enormously from the same techniques.

Lesions can now be defined precisely using structural MRI, allowing us to visualize which parts of the normal cortical network have been damaged.

Tools for evaluating different aspects of musical disorders have been refined, so that reports of musical disorders have progressed from historical anecdotes to systematic accounts.

These instruments are the musical equivalents of the better-known aphasia batteries.

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Models for new results

What would a cognitive model of musical processing look like?

What would a neural model of musical processing look like?

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Ingredients of music cognition mostly receptive, mostly from Levitin

pitchtimbre

rhythmloudnessharmony

Perception Anticipation Categorization(in memory)

Attention Emotion

Music Cognition

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Cognitive model of musical processing

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Brain substrates for musical listening disorders across (lesion) studies

Early music processingMusic, like any sound, is processed in the ascending auditory pathway to the

auditory cortex.

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The ascending auditory pathway, againThat processing includes active

analysis of the spectro-temporal structure of the

stimulus rather than the simple passive relay of information.

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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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Primary auditory cortex (PAC or A1)

tonotopic map

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Observation

Both the cochlea and the PAC are organized as a tonotopic map.

The layout of the ascending auditory pathway suggests that it is one-way (ascending).

What would happen if it were a two-way street?

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What is amusia?

Amusia refers to a number of disorders which are indicated by the inability to recognize musical tones or rhythms or to reproduce them.

It can be congenital (present at birth) or be acquired later in life (as from brain damage).

The term "amusia" is composed of "a-" + "-musia" which means the lack of music.

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Pitch imperfect: cochlear amusia Who is the protagonist?

Jacob L., a distinguished composer in his late 60s What were his symptoms?

“I hadn’t been playing or composing much for a month, and then I suddenly noticed the upper register of the piano I was playing [at a friend’s house] was grossly out of tune.”

These notes were sharpened by a quarter of a tone or so for the first octave and a semitone or so for the next octave up, more so in left ear than right.

He was already being treated for a hearing loss also in the upper ranges (2000 Hz ~ 3 octaves above middle C)

The E-natural 10 notes above middle C were flattened by almost a quarter tone.

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Accommodations

“Contextual correction” a single instrument sounded out of tune, but an

orchestral context ‘corrected’ itHe would work out a high passage on the

keyboard below the distorted range and then notate the music in the correct range

Conclusion he knew how music should sound; it was only his perception that was distorted.

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Analysis

How did the disorder progress? Eventually, Jacob got better.

Why? There are massive connections (the olivocochlear bundles)

from the PAC to the cochlea and outer hair cells. The outer hair cells tune tshe inner hair cells. Conclusion?

A two-way street, giving the PAC the ability to tune the cochlea, for instance, to attend to a tiny but significant sound in the environment.

PitchPitch is thought to be a fundamental component of music in every known

human culture.

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Primary auditory cortex (PAC or A1)

tonotopic map

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Regions and connections of primate and human prefrontal and auditory cortex

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Schematic diagram of the primate auditory cortex

The core is made up of the primary auditory cortex (AI), the rostral field (R), and the rostrotemporal (RT) area.

These three fields have a tonotopic organization as shown by the lower-case letters h (high frequency) and l (low frequency).

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Pitch

It is a percept, rather than a physical attribute of the sound stimulus. The exact relationship between the stimulus attributes and the

percept is still debated. Studies reveal activity in secondary cortex in lateral

Heschl’s gyrus rather than primary cortex > possible ‘pitch centre’ where there is encoding of the percept as opposed to the stimulus properties.

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Pitch in music

It is used to construct: melodies (patterns of pitch over time), chords (the simultaneous presentation of more than

one pitch) and harmonies (the simultaneous presentation of more

than one melody).

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Pitch experiments

In passive listening experiments, bilateral brain activation occurs in the anterior and posterior superior-temporal lobes with a degree of right lateralization (see Fig. 2), without any difference between random-pitch sequences and tonal melodies.

In experiments where subjects were required to follow a melody and compare the pitch at different points, additional activation was demonstrated in the right frontal operculum.

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Pitch processing in superior-temporal cortex (Fig. 2)

Next MondayExpand the model

Add more of Sacks’ disorders§1-2 of Levitin