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Introduction to perception Day 6


Introduction to perception Day 6 Music Cognition MUSC 495.02, NSCI 466, NSCI 710.03 Harry Howard Barbara Jazwinski Tulane University – PowerPoint PPT presentation

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Title: Introduction to perception Day 6

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

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.

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.

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

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".

My favorite example What do you see?
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.

Normalized absorption spectra of human cone
(S,M,L) and rod (R) cells
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)
  • Shall we revise our theory of perception in light
    of the example of the evolution of trichromacy?

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
  • 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 organisms 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.

Segue to environmental statistics
  • There is an enormous amount of information in the
    environment that a perceptual system could become
    attuned to

A natural image Let us say that the image is a
veridical representation of the world
Is veridicality maintained at higher levels of
  • That is, does visual processing propagate
    something like a photograph all the way up?

Lets take a closer look
Zoom in 300
Zoom in 300 again
Some redundancies
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.

The environmental statistics of sound
  • Ill talk about it next time

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

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
  • object derives from the Latin ob-, 'before' or
    'toward', and iacere, 'to throw' and used to
  • 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

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

What do you see?
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

Figure and ground
  • Notice that I couldn't describe the illusion
    without postulating an object against a
  • 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
  • The process of parcelling sensory input into
    figure and ground is called figure-ground

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?

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
  • Edge an abrupt change in contrast (light dark)

Edges in audition ba vs. pa
Edge an abrupt change in frequency
b a
p a
What do you see?
  • Most people see the image divided into rows, not
  • This is grouping by similarity

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.
  • 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

Vision vs. audition
Source of information Vision Audition
Primary Surfaces Sources
Secondary Location and color of sources Surfaces
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?

Back to our regularly scheduled program
Ingredients of music cognition mostly receptive,
mostly from Levitin
Next Monday
  • Ok I will really talk about sound music
  • 1-2 of Levitin