Lecture 20 - Cortical Processing and Scene Analysis

Question 1

basic unit

Answer 1

frequencies of sound

Question 2

auditory cortex is hierarchically organized

Answer 2

Neural signals travel through the
core (including A1), then belt,
followed by the parabelt area.
– Simple sounds (pure tones) cause activation in the core area.
– Belt and parabelt areas are
preferentially activated in response to more complex stimuli (tones, voices) made up of many
frequencies.

Question 3

Simple sounds

Answer 3

retain tonotopy in the cochlea

cause activation in the core area.

Question 4

belt and parabelt areas

Answer 4

are preferentially activated in response to more complex stimuli (tones, voices) made up of many
frequencies.

Question 5

Bendor & Wang (2005)

experiment about tonotopy beyond A1

Answer 5

presented complex harmonic tones with the same fundamental frequency (182 Hz). [Work done in monkeys.]
• Single-cell recordings were done outside A1 (belt and parabelt area)

• Six different sounds were played, each made up of diff harmonics

Question 6

Bendor & Wang (2005) recorded from a cell just outside A1 (belt and parabelt) and
found that it responded to…

Answer 6

.....complex tones with the same 
fundamental frequency (fundamental frequency perceived as the same basic tone). Such cells were called pitch neurons 

(basically same cell responded to all those complex tones because it like the fundamental frequency even though the frequencies themselves different)

• Demonstration of hierarchical organization in auditory cortex.
• Also links perception to physical quality of sound.

Question 7

pitch neurons

Answer 7

cells just outside of A1 that respond to complex tones with the same fundamental frequency

right outside of A1

seem to like particular perceived pitches: always looking for that repeating pattern established by the spacing of the two frequencies

organized by HOW WE PERCEIVE the stimulus, not their physical components

Question 8

Are the representations modular?

Effect of training (experience-dependent plasticity) on tonotopic maps:

Answer 8

– Owl monkeys were trained to discriminate between two frequencies near 2,500 Hz.

– Trained monkeys showed tonotopic maps (in A1) with enlarged areas with neurons that responded to 2,500 Hz compared to untrained monkeys.
Importantly, the monkey’s were better at the task after training.

• the cells spread out: it wasn’t just one small region that responded to the particular frequencey (had more cortex working on the discrimination problem: IT CHANGED!!)
• there is certainly hierachical organization, but not necessary modular

Question 9

Single cell fires to the fundamental frequency….

Answer 9

….regardless of which harmonics

are played.

Question 10

we do have a well ordered tonotopic map, BUT it is….

Answer 10

malleable, not purely innante, not static, changes over time!!!

change the environment or stimuli = change the neural representation

Question 11

Experience-dependent plasticity

Experiment by Fritz et al. (single-cell recordings)

Answer 11

– Ferrets were trained to stop licking a water spout in response to a pure tone embedded within a stream of complex tones.

– Single neuron recorded before and after training. Originally responds best to ~9 kHz tone.

– The neuron became quickly tuned to the target frequency (6 kHz, blue arrow) and maintained the effect for hours after the testing session.

this task was starting to take over some of the functionality of other neurons:

!!! there’s a lot of plasticity, and plasticity is enforced by behaviors and environment !!!

Question 12

What, or ventral stream

Answer 12

starts in the anterior portion of the core and belt and extends to the prefrontal cortex.

– Responsible for identifying
sounds: being able to tell what pitch a tone is, being able to tell tones or pitches apart

Question 13

Where, or dorsal stream

Answer 13

starts in the posterior core and belt and extends to the parietal and prefrontal cortices.

– Responsible for locating sounds (auditory localization task).

Question 14

fMRI evidence for

what/where streams

Answer 14

– Pitch recognition (what)
tasks activate more ventral regions.

– Location detection (where)
tasks associated with greater
activation in dorsal areas.

Question 15

Brain damage evidence

Answer 15

Patient with temporal lobe damage (‘what’ pathway) has trouble recognizing sounds, but can localize.

• Patient with parietal lobe damage (‘where’ pathway) can recognize sounds, but is very poor with localization.
• Nice double-dissociation!!

Question 16

Patient with temporal lobe damage

Answer 16

has trouble recognizing sounds, but can localize.

can’t say that that’s a bird or a car horn

can’t tell if the pitch went up or down

Question 17

Patient with parietal lobe damage

Answer 17

can recognize sounds, but is very poor with localization.

trouble with spatial processing for auditory tones

Question 18

Double-dissociation of

‘what’ and ‘where’ functions

Answer 18

– Temporarily deactivating the anterior auditory area (‘what’ pathway), impaired a cat’s
ability to distinguish tone
patterns (but spared localization).

– Deactivating the posterior
auditory cortex, (‘where’ 
pathway), eliminated the 
ability to localize sounds (but 
spared identification).

Question 19

anterior auditory area

Answer 19

‘what’ pathway

Question 20

posterior

auditory cortex

Answer 20

‘where’ pathway

Question 21

Transduction takes place at the

Answer 21

Organ of Corti

Question 22

fundamental problem with audition

Answer 22

anytime there is sound coming in you have sound pressure waves coming in from different locations and lots different sounds coming in, and all of that is immediately getting mixed in the cochlea

how do we mix these things apart?

Question 23

Auditory Scene:

Answer 23

The array of
all sound sources in the
environment.

Question 24

How do we make sense of all the sounds coming to us?

Auditory Scene Analysis:

Answer 24

Process by which sound sources in the auditory scene are separated into individual perceptions.

– This does not happen at
the cochlea since simultaneous sounds are together in the pattern of vibrations on the basilar
membrane.

Question 25

The auditory scene: perceptual heuristics

A number of auditory grouping principles help us organize
elements of the auditory scene

( we don’t really know wtf is happening)

Answer 25

1) location
2) onset time
3) Similarity of timbre and pitch:
4) Proximity in time -
5) Auditory Continuity
6) Effect of past experience [familiarity]

Question 26

location

Answer 26

A single sound source tends to be at one location and to move
continuously. [Common fate?]

if a particular set of sounds is coming from a particular location we group those sounds to that location: those sounds belong to that space

if that sound source starts to move then the sounds start to move with it

Question 27

Onset time

Answer 27

Sounds that start at different times are likely to come from
different sources, if sounds start together they probably came from the same source

Question 28

Similarity of timbre and pitch:

Answer 28

Similar sounds are grouped together (e.g. flute trills belong to the flute, while trumpet blares belong to the trumpet.) [Similarity? we group things of like colors or shapes, etc…]

– Strong CUE: Such grouping allows us to perform auditory stream segregation based on attributions of different timbres or pitch to multiple sources.

similarity of PERCEPTUAL properties

Question 29

auditory stream segregation

Answer 29

identify extremes of notes that are changing together, but they have the same pitch and timbre

segregate complex streams and keep these streams distinct

Question 30

proximity in time

Answer 30

• sounds that occur in rapid succession usually come
  from the same source. [Proximity?]

greater the time lag (based on experience) the more willing you are to break up those sounds

Question 31

The auditory scene: perceptual heuristics

Compound melodic line in music is an example of

Answer 31

auditory stream segregation

Question 32

Experiment by Bregman and Campbell (1971) demonstrated how compound melodic line in music is an example of auditory stream segregation.

Answer 32

– Stimuli were alternating high and low tones

– When stimuli played slowly, the perception is one of hearing high
and low tones alternating (not broken into diff melodic lines - don’t hear separately).

– When the stimuli are played quickly, the listener hears two streams; one high and one low (hear them at the same time).

– Pulled together by the similarity of pitch and timbre groups the notes, but only at high
speeds (only if the proximity allows it).

Question 33

Grouping by similarity experiment by Bregman & Rudnicky (1975)

Answer 33

– Listener hears two standard tones (X & Y) and can easily perceive the order.

– Two distractor (D) tones are placed around X & Y and the listener now has difficulty perceiving the order.

– Adding a series of captor tones (C) forms a stream with the D tones, and the listener can once again easily hear the order of X & Y.

Question 34

Outer hair cells act as a ____ and heighten sensitivity of inner hair cells to a _______ .

Answer 34

cochlear amplifier

characteristic frequency.

Question 35

Place Coding

Answer 35

suggests that the specific locations on the basilar membrane are stimulated by certain frequencies.

This results in a tonotopic map

Question 36

tonotopic map

Answer 36

high frequencies activating hair cells near the base and low frequencies active at the apex.

Question 37

Signals are sent from the cochlea via a sub-cortical route

[CoNuc SON-IC MG] to the

Answer 37

primary auditory receiving area

in temporal cortex [A1].

Question 38

In A1 we have tonotopic organization that becomes
increasing….

Signals then go to ____and ____
streams for further processing.

Answer 38

…..hierarchical in core, belt and parabelt regions.

dorsal (Where?) , ventral (What?)

Question 39

Grouping by pitch similarity

Answer 39

A repeating tone (pitch) is able
to capture an ascending and
descending scale as they cross.

Question 40

once pitches become close enough

Answer 40

it’s hard to distinguish them

sounds become tangled and are sort of “galloping”

Question 41

auditory continuity

Answer 41

Sounds that stay constant or change smoothly are usually from the same source. [Good continuation?]

we’re explicitly tuned to hearing gaps

Question 42

Auditory continuity experiment by Richard Warren et al. (1972)

Answer 42

Tones were presented and interrupted by gaps of silence or noise.

– In the silence condition, listeners perceived that the sound stopped during the gaps.

– In the noise condition, the perception was that the sound continued behind the noise.

things that are continuous (smooth background) will fade and the thing that grabs our attention will come to the foreground

Question 43

Effect of past experience [familiarity]

Experiment by Dowling & Harwood (1986)

Answer 43

• Melody “Three Blind Mice” is played with notes alternating
between octaves

• Listeners find it difficult to identify the song

• But after they hear the normal melody, they can then ‘hear’
(recognize) it in the modified version using melody schema.