Transcript Introduction to perception Day 6 Music Cognition MUSC 495.02, NSCI 466, NSCI 710.03 Harry Howard Barbara Jazwinski Tulane University.

Introduction to
perception
Day 6
Music Cognition
MUSC 495.02, NSCI 466, NSCI 710.03
Harry Howard
Barbara Jazwinski
Tulane University
Course administration
Spend provost's money
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
2
Introduction to
perception
Early perception and efficient
encoding
A question about perception
 What does perception do?
 Or, following up on our previous discussion, what
question should a theory of perception answer?
 Take a few minutes to discuss it with someone.
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
4
Your answer here!
The class says that perception is:
1. Attributing meaning to outside stimuli;
2. Both conscious and subconscious;
3. The way the brain reacts to and organizes sensory
information;
4. Linking the electrical signals caused by external
stimuli to memories and emotions that are used to
interpret these stimuli;
5. Differentiation of stimulus type.
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
5
Your answer here!
I think there might be at least the following
two schools of thought
perception creates a faithful or truthful copy of
reality (veridicality)
perception creates a useful copy of reality
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
6
What does 'perception' mean?
In psychology and the cognitive sciences,
perception is the process of attaining
awareness or knowledge of sensory
information.
The word 'perception' comes from the Latin
word percepio, meaning "receiving, collecting,
action of taking possession, apprehension with
the mind or senses".
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
7
My favorite example
What do you see?
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
8
The evolution of color vision
 It has been suggested that trichromacy in primates
and the reflectance functions of certain tropical fruits
are aspects of a coevolved seed-dispersal system:
primate color vision has been shaped by the need to find
colored fruits amongst foliage,
and the fruits themselves have evolved to be salient to
primates and so secure dissemination of their seeds.
 We show that the spectral positioning of the cone
pigments found in trichromatic South American
primates is well matched to the task of detecting fruits
against a background of leaves.
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
9
Normalized absorption spectra of
human cone (S,M,L) and rod (R) cells
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
10
Increasing chromacy
top left: Monochromatic view
(no blues, greens, or reds)
top right: Dichromatic view
(only blues and greens)
bottom left: Trichromatic view
(blues, greens, and reds)
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
11
Revision
Shall we revise our theory of perception in
light of the example of the evolution of
trichromacy?
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
12
Taking natural selection into account
 In the theory of natural selection,
 favorable heritable traits become more common in successive generations
of a population of reproducing organisms,
 and unfavorable heritable traits become less common.
 Over time, this process may result in adaptations that specialize organisms
for particular ecological niches, i.e. evolution.
 With respect to perception, the process of natural selection guarantees a
strong connection between the design of an organism’s perceptual systems
and the properties of the physical environment in which the organism lives.
 In humans, this connection is implemented through a mixture of
 fixed (hardwired) adaptations that are present at birth and
 facultative (plastic) adaptations that alter or adjust the perceptual systems
during the lifespan.
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
13
Segue to environmental statistics
There is an enormous amount of information
in the environment that a perceptual system
could become attuned to
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
14
A natural image
Let us say that the image is a veridical representation of the world
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
15
Is veridicality maintained at
higher levels of processing?
That is, does visual processing propagate
something like a photograph all the way up?
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
16
Let’s take a closer look
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
17
Zoom in 300%
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
18
Zoom in 300% again
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
19
Some redundancies
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
20
Correlation
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
21
The efficient coding hypothesis
 Motivated by developments in information theory,
Attneave (1954) suggested that the goal of visual
perception is to produce an efficient representation of
the incoming signal.
 In a neurobiological context, Barlow (1961)
hypothesized that the role of early sensory neurons is
to remove statistical redundancy in the sensory input.
 Thus at least the early levels of a sensory system
should be sensitive to the statistical properties of the
environment.
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
22
The environmental statistics
of sound
I’ll talk about it next time
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
23
Is that all?
After all redundancies are removed, is there
anything left?
Hopefully, the objects that the organism is
‘interested’ in (i.e. drive natural selection)
For example, the purpose of trichromacy is not for
monkeys to see red, but rather for monkeys to see
ripe fruit
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
24
Introduction to
perception
Late perception and object
recognition
What is an object?
 According to the Oxford English Dictionary, object means
 something placed before the eyes, or presented to the sight or other sense;
an individual thing seen or perceived, or that may be seen or perceived; a
material thing
 Its etymology explains its visuocentric connotation:
 object derives from the Latin ob-, 'before' or 'toward', and iacere, 'to throw'
and used to mean:
 something 'thrown' or put in the way, so as to interrupt or obstruct the course of
a person or thing; an obstacle, a hindrance
 Indeed, most visible things are obstacles or a hindrance to sight; they
prevent you from seeing something that lies behind them because they are
opaque
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
26
A cross-modal theory of
objecthood
Perceptual objects have the following
properties
they can be figures for figure-ground segregation
they have edges (or contours or boundaries)
they can be grouped
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
27
What do you see?
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
28
Most people see
a white vase against a black background,
two black heads facing each other in profile
against a white background,
and the image can switch rapidly back and
forth between the two interpretations.
It is known as the Rubin vase/profile illusion
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
29
Figure and ground
 Notice that I couldn't describe the illusion without
postulating an object against a background
 It is famous for showing the difference between
figure and ground
the figure is that which draws our attention,
and stands out against an undifferentiated (back)ground
 The process of parcelling sensory input into figure
and ground is called figure-ground segregation
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
30
Auditory figure-ground
segregation
The same thing happens in audition, though it
is difficult for me to put an example on a slide
Can you think of one?
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
31
What do you see?
 This left image has been processed by a computer program that attempts to
retain the edges in the right image and throw away everything else
 The fact that the left is still informative shows the importance of edges to
visual object recognition
 Edge: an abrupt change in contrast (light ~ dark)
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
32
Edges in audition: [ba] vs. [pa]
Edge: an abrupt change in frequency
b
a
11/7/2015
p
Music Cognition - Jazwinski & Howard - Tulane University
a
33
What do you see?
 Most people see the
image divided into
rows, not columns
 This is grouping by
similarity
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
34
What do you hear?
All around the mulberry bush, The
monkey chased the weasel. The monkey
thought 'twas all in fun. Pop! goes the
weasel.
A penny for a spool of thread, A penny
for a needle. That's the way the money
goes. Pop! goes the weasel.
Up and down the City Road, In and out of
the Eagle, That's the way the money goes.
Pop! goes the weasel.
Half a pound of tuppenney rice, Half a
pound of treacle, Mix it up and make it
nice, Pop! goes the weasel.
11/7/2015
 The first 3 verses of
each stanza have
alternating weak/strong
syllables
 This is a kind of
grouping by similarity,
which presumably
accounts for the
'musicality' of poetry
Music Cognition - Jazwinski & Howard - Tulane University
35
Vision vs. audition
Source of
information
Primary
Secondary
11/7/2015
Vision
Audition
Surfaces
Sources
Location and
color of sources
Surfaces
Music Cognition - Jazwinski & Howard - Tulane University
36
Summary & outstanding
questions
 What objects are in the (current) visual scene that
enhance my survival?
 What objects are in the (current) auditory scene that
enhance my survival?
 What will the next visual scene probably be?
 What will the next auditory scene probably be?
 What is the current note?
 What will the next note probably be?
 What did music evolve for, anyway?
11/7/2015
Music Cognition - Jazwinski & Howard - Tulane University
37
Back to our regularly
scheduled program
Ingredients of music
cognition mostly receptive, mostly from
Levitin
Music Cognition
Perception
pitch
timbre
11/7/2015
Anticipation
Categorization
(in memory)
Attention
Emotion
rhythm
loudness
harmony
Music Cognition - Jazwinski & Howard - Tulane University
39
Next Monday
Ok I will really talk about sound &
music perception
§1-2 of Levitin