Foundations of perception
George Mather
Summary
Chapters 1, 3-10, 12
1
,Table of content
INTRODUCTION.................................................................................................................. 3
CLASSIFICATION OF SENSES.................................................................................................3
STUDY OF PERCEPTION.......................................................................................................3
GENERAL PRINCIPLES OF SENSATION AND PERCEPTION..........................................................4
TUTORIALS NOT INCLUDED!........................................................................................6
INTRODUCTION.................................................................................................................. 7
THE SOMATOSENSORY SYSTEM............................................................................................7
THE VESTIBULAR SYSTEM....................................................................................................9
TUTORIALS .................................................................................................................. 10
SOUND AS A PHYSICAL STIMULUS......................................................................................11
THE PHYSIOLOGY OF THE AUDITORY SYSTEM......................................................................14
TUTORIALS NOT INCLUDED!......................................................................................19
Perception of sound 20
LOUDNESS PERCEPTION....................................................................................................20
PITCH PERCEPTION...........................................................................................................20
AUDITORY LOCALIZATION.................................................................................................22
SPEECH PERCEPTION.........................................................................................................23
AUDITORY SCENE ANALYSIS ..............................................................................................23
HEARING DYSFUNCTION...................................................................................................24
TUTORIALS NOT INCLUDED!......................................................................................24
WHAT IS LIGHT?.............................................................................................................. 25
SOME IMPORTANT PROPERTIES OF LIGHT...........................................................................26
EYE ................................................................................................................................ 27
EYE MOVEMENT............................................................................................................... 28
TUTORIALS NOT INCLUDED!......................................................................................28
BINOCULAR CUES..............................................................................................................31
Our capability 32
32
Index 33
2
, Foundations of perception – George Mather
Chapter 1
General principles
page 3-37
Introduction
Complexity of brain processes:
1. large proportion of the brain’s most highly developed structure
(cerebral cortex) is devoted entirely to perception
2. computers haven’t been able to mimic brains processes
3. brain damage does weird things that we took for granted (eg
prosopagnosia: where you don’t recognize familiar faces)
In sport, participants often make opposite decisions in “close” calls.
However psychophysical research has taught us that in marginal
conditions when stimuli are very close together or indistinct,
perceptual responses are probabilistic.
Classification of senses
- By transduction: where sensory receptor cells convert environmental
energy into electrical neural signals
- By where in the cerebral cortex (what area). The relative area of
cortex devoted to different senses is indicative of their relative
importance to the survival of each animal.
Study of perception
- Lesion Experiment: surgically remove or destroy a specific area of
an animal’s brain, and then observe the consequences for behavior.
- Clinical studies: studies of the consequences of brain damage (are
less tidy then lesion’s)
- Single unit recordings:
microelectrode recording: a technique in which electrical activity is
recorded from single cells in life animals using fine insulated wires.
Feature detectors: individual neurons in the brain act as detectors for
individual stimulus features.
- Brain imaging:
CT (computerized tomography): 3D X-ray
3
, MRI (magnetic resonance imaging): 3D detect magnetic properties of
brain molecules. Detect changes in harmoglobin (transports
oxygen). fMRI for brain function.
- Psychophysics: studies relationship between physical stimuli and
perceptual phenomena. (eg ability to discriminate small differences
in stimulus)
- Artificial intelligence (AI): airms to produce a device capable of
behavious normally associated with human cognition, such as
language, understanding, reasoning and perception.
Timeline
- 1800: cortex not sub-divided, but perception represented diffusely
throughout cortex
- Lesion: maybe localization of function (different functions at different
spots in the brain)
- 1988: cortex mapped topographically: a spatial arrangement of
neurons in a neural structure (eg cortex) in which nearby cells respond
to nearby locations in the visual field of view.
- Intelligence comparable with computers (if technique developed
further)
General principles of sensation and perception
Psychological principles
- Neural impulses and transduction
Neural impulses travel from a cell’s
dendrites and body to its terminal
buttons, typically via an axon (see
image). Terminal buttons connect
to dendrites of another cell at
synapses. The impulse causes the
release of neurotransmitter.
Excitatory neurotransmitter (e.g.
ACh) increases probability that the
receiving neuron will generate an
impulse. Inhibitory (e.g. GABA) decreases that.
Eyes have photoreceptors, movement has mechanoreceptors.
- Hierarchical processing (fig 1.10)
Signals from each sense organ pass through a series of synapses at
successive higher level of neural processing.
4
,In all the senses except olfaction, one of the synapses on the route
from sense organ to brain is located in the thalamus.
A signal arrive at receiving areas in the cortex, then passed on to
association areas.
- Selectivity
Auditory system humans: 20Hz to 16 000Hz
Sensory space: range of effective stimuli for a particular system (what
stimuli we can observe)
Receptive field: The area of a stimulus field in which presentation of a
stimulus causes a change in the firing rate of a given sensory neuron.
- Organization
Staining: using chemical stains that are selectively taken up by certain
kinds of tissue (eg. cell bodies) to identify substances in and around
cells.
Cortical magnification: the small region of the image near to fixation
occupies a relatively large proportion of the cortical surface.
- Law of specific nerve energy (1838): differences between the senses
are not reflected in the nature of the sensory signals themselves, but
in their destination in the brain.
- Adaptability: the ability of a sensory system to vary it’s response
characteristics to match prevailing stimulations (you get used to the
dark, get used to an itchy sweater)
Typical rate of impulses for a very active cell is 100 to 200 impulses/s
Noise has two sources:
1. fluctuation in electrical excitability of neurons, mainly caused by
random opening and closing of ion channels (= a specialized protein
molecule that allows certain ions to enter or leave a cell, so altering
it’s electrical state)
2. in synaptic transmission caused by, among other factors, the
random nature of diffusion and chemical reaction across synapses.
Perceptual principles
Qualia: primitive mental states, such as sensory impression induced by
stimulation of a sense organ. = sensations
Psychometric function: a graph relating stimulus value (e.g. intensity) to
the response rate of an experimental subject (e.g. proportion of “yes”
responses). Note: detection is probabilistic.
5
,Magnitude estimation: relationship between physical stimulus
magnitude and sensory magnitude. Graphs of magnitude estimations
are not linear.
Steven’s power law: a non-linear relationship between stimulus intensity
and perceived magnitude, in which equal ratios of intensity produce
equal ratios of magnitude. (so logarithmic)
Continuous exposure to a relatively intense stimulus has
consequences:
1. sensitivity changes, need a more intense stimulus
2. apparent intensity of the stimulus diminishes
3. the rate at which sensory magnitude increases with stimulus
level steepens.
Theoretical principles
- Representation
Internal brain states represent the stat of the outside world.
Brain analogical or symbolic: like a matrix or like combinations of
symbols?
-computation
Algorithm: a specific computational procedure used to transform one
representation into another. Brain is a computing device, it
manipulates quantities and symbols according to sets of rules
(algorithms)
Linking proposition: a proposition positing a specific causal link between
neural activity in the brain and perceptual experience. (e.g. euditory
system transforms loudness of sound into rate of firing, then later it
gets turned into a perceptual experience)
TUTORIALS NOT INCLUDED!
6
, Foundations of perception – George Mather
Chapter 3
The body senses
page 54-79
Introduction
Two sensory systems
1. The somatosensory system: deals with touch, proprioception and
kinesthesis
Proprioception: about the position of body parts
Kinesthesis: about the movement of body part
2. Vestibular system: deals with balance
The somatosensory system
Physiology of somatosensation
Somatosensory receptors
Touch receptors:
• Free nerve endings: all skin, superficial pain,
temperature, tickle
• Meissner’s corpuscles: glabrous skin, superficial dynamic
touch
Intermediate temporal response (30-50Hz)
• Markel’s disks: all skin, superficial static
pressure
Best-suited to relatively stable signals, unchanging mechanical
stimulations
• Pacinian corpuscles: all skin, deep pressure,
vibration
respond to high frequency vibrations like moving over texture (250-
350Hz)
• Rufini’s corpuscles: all skin, deep stretching of skin
Not all receptors play an equal role, it depends on the income stimuli
Proprioception
Prioprioceptors: For perception of body position and movement.
• Muscle spindles muscles muscle length
• Golgi tendon organs tendons (NL: pees) muscle tension
• Joint receptors joints (NL: gewrichten) joint position
7
, Muscles used for very fine and accurate movements (eg hand/eyes)
have more muscle spindles. (spindles are 4 to 8 muscle fibres in
connective tissue)
Somatosensory pathway (fig 3.3)
- Dorsal root ganglia: rounded swellings lying in the vertebrae just
outside the spinal cord, each containing thousands of afferent cell
bodies whose axons enter the spinal cord.
- Action potential will be transmitted along:
1. spinothalamic pathway: for pain and temperature signals from free
never endings.
Lightly or unmyelinated axons and therefore low speed of 2 m/s
2. lemniscal pathway: for somatosensory signals from
mechanoreceptors.
Myelinated axons so that they have a higher speed (20 m/s)
- both branches also contain branching projections in the spinal cord
that are responsible for reflexes, such as withdrawal from painful
stimuli, and the knee-jerk reflex (=myontatic reflex)
Cortical representation of somatosensation
Primary somatosensory cortex: a long thin strip of cortical surface
running from ear to ear across the head
Mountcastle (1957) found that each cell in primary somatosensory
cortex receives input from only one type of receptor
Centre-surround receptive fields: A receptive field containing
concentrically organized regions of excitation and inhibition, as a result
of lateral inhibition. (same concept as with eyes)
Cortex:
- Vertical organization (perpendicular to surface).
Cells in a cortical column (running down vertically from the surface)
are connected to the same type of sensory receptor.
Receptive fields on the finger tips are small (3-4mm diameter) and
trunk over 100 larger.
- Horizontal organization (parallel to the surface of the cortex):
depending on what part of the body.
Cortical magnification: more important (sensitive) body parts have
bigger areas in the brain.
Not much is understood about the projection of pain.
Two point acuity: how close together you can distinguish two separate
points from one; best on the tongue and hands, worst on the back and
legs. Very small receptive fields also better because the calipers can
stimulate different neurons (centre-surround cells)
8
George Mather
Summary
Chapters 1, 3-10, 12
1
,Table of content
INTRODUCTION.................................................................................................................. 3
CLASSIFICATION OF SENSES.................................................................................................3
STUDY OF PERCEPTION.......................................................................................................3
GENERAL PRINCIPLES OF SENSATION AND PERCEPTION..........................................................4
TUTORIALS NOT INCLUDED!........................................................................................6
INTRODUCTION.................................................................................................................. 7
THE SOMATOSENSORY SYSTEM............................................................................................7
THE VESTIBULAR SYSTEM....................................................................................................9
TUTORIALS .................................................................................................................. 10
SOUND AS A PHYSICAL STIMULUS......................................................................................11
THE PHYSIOLOGY OF THE AUDITORY SYSTEM......................................................................14
TUTORIALS NOT INCLUDED!......................................................................................19
Perception of sound 20
LOUDNESS PERCEPTION....................................................................................................20
PITCH PERCEPTION...........................................................................................................20
AUDITORY LOCALIZATION.................................................................................................22
SPEECH PERCEPTION.........................................................................................................23
AUDITORY SCENE ANALYSIS ..............................................................................................23
HEARING DYSFUNCTION...................................................................................................24
TUTORIALS NOT INCLUDED!......................................................................................24
WHAT IS LIGHT?.............................................................................................................. 25
SOME IMPORTANT PROPERTIES OF LIGHT...........................................................................26
EYE ................................................................................................................................ 27
EYE MOVEMENT............................................................................................................... 28
TUTORIALS NOT INCLUDED!......................................................................................28
BINOCULAR CUES..............................................................................................................31
Our capability 32
32
Index 33
2
, Foundations of perception – George Mather
Chapter 1
General principles
page 3-37
Introduction
Complexity of brain processes:
1. large proportion of the brain’s most highly developed structure
(cerebral cortex) is devoted entirely to perception
2. computers haven’t been able to mimic brains processes
3. brain damage does weird things that we took for granted (eg
prosopagnosia: where you don’t recognize familiar faces)
In sport, participants often make opposite decisions in “close” calls.
However psychophysical research has taught us that in marginal
conditions when stimuli are very close together or indistinct,
perceptual responses are probabilistic.
Classification of senses
- By transduction: where sensory receptor cells convert environmental
energy into electrical neural signals
- By where in the cerebral cortex (what area). The relative area of
cortex devoted to different senses is indicative of their relative
importance to the survival of each animal.
Study of perception
- Lesion Experiment: surgically remove or destroy a specific area of
an animal’s brain, and then observe the consequences for behavior.
- Clinical studies: studies of the consequences of brain damage (are
less tidy then lesion’s)
- Single unit recordings:
microelectrode recording: a technique in which electrical activity is
recorded from single cells in life animals using fine insulated wires.
Feature detectors: individual neurons in the brain act as detectors for
individual stimulus features.
- Brain imaging:
CT (computerized tomography): 3D X-ray
3
, MRI (magnetic resonance imaging): 3D detect magnetic properties of
brain molecules. Detect changes in harmoglobin (transports
oxygen). fMRI for brain function.
- Psychophysics: studies relationship between physical stimuli and
perceptual phenomena. (eg ability to discriminate small differences
in stimulus)
- Artificial intelligence (AI): airms to produce a device capable of
behavious normally associated with human cognition, such as
language, understanding, reasoning and perception.
Timeline
- 1800: cortex not sub-divided, but perception represented diffusely
throughout cortex
- Lesion: maybe localization of function (different functions at different
spots in the brain)
- 1988: cortex mapped topographically: a spatial arrangement of
neurons in a neural structure (eg cortex) in which nearby cells respond
to nearby locations in the visual field of view.
- Intelligence comparable with computers (if technique developed
further)
General principles of sensation and perception
Psychological principles
- Neural impulses and transduction
Neural impulses travel from a cell’s
dendrites and body to its terminal
buttons, typically via an axon (see
image). Terminal buttons connect
to dendrites of another cell at
synapses. The impulse causes the
release of neurotransmitter.
Excitatory neurotransmitter (e.g.
ACh) increases probability that the
receiving neuron will generate an
impulse. Inhibitory (e.g. GABA) decreases that.
Eyes have photoreceptors, movement has mechanoreceptors.
- Hierarchical processing (fig 1.10)
Signals from each sense organ pass through a series of synapses at
successive higher level of neural processing.
4
,In all the senses except olfaction, one of the synapses on the route
from sense organ to brain is located in the thalamus.
A signal arrive at receiving areas in the cortex, then passed on to
association areas.
- Selectivity
Auditory system humans: 20Hz to 16 000Hz
Sensory space: range of effective stimuli for a particular system (what
stimuli we can observe)
Receptive field: The area of a stimulus field in which presentation of a
stimulus causes a change in the firing rate of a given sensory neuron.
- Organization
Staining: using chemical stains that are selectively taken up by certain
kinds of tissue (eg. cell bodies) to identify substances in and around
cells.
Cortical magnification: the small region of the image near to fixation
occupies a relatively large proportion of the cortical surface.
- Law of specific nerve energy (1838): differences between the senses
are not reflected in the nature of the sensory signals themselves, but
in their destination in the brain.
- Adaptability: the ability of a sensory system to vary it’s response
characteristics to match prevailing stimulations (you get used to the
dark, get used to an itchy sweater)
Typical rate of impulses for a very active cell is 100 to 200 impulses/s
Noise has two sources:
1. fluctuation in electrical excitability of neurons, mainly caused by
random opening and closing of ion channels (= a specialized protein
molecule that allows certain ions to enter or leave a cell, so altering
it’s electrical state)
2. in synaptic transmission caused by, among other factors, the
random nature of diffusion and chemical reaction across synapses.
Perceptual principles
Qualia: primitive mental states, such as sensory impression induced by
stimulation of a sense organ. = sensations
Psychometric function: a graph relating stimulus value (e.g. intensity) to
the response rate of an experimental subject (e.g. proportion of “yes”
responses). Note: detection is probabilistic.
5
,Magnitude estimation: relationship between physical stimulus
magnitude and sensory magnitude. Graphs of magnitude estimations
are not linear.
Steven’s power law: a non-linear relationship between stimulus intensity
and perceived magnitude, in which equal ratios of intensity produce
equal ratios of magnitude. (so logarithmic)
Continuous exposure to a relatively intense stimulus has
consequences:
1. sensitivity changes, need a more intense stimulus
2. apparent intensity of the stimulus diminishes
3. the rate at which sensory magnitude increases with stimulus
level steepens.
Theoretical principles
- Representation
Internal brain states represent the stat of the outside world.
Brain analogical or symbolic: like a matrix or like combinations of
symbols?
-computation
Algorithm: a specific computational procedure used to transform one
representation into another. Brain is a computing device, it
manipulates quantities and symbols according to sets of rules
(algorithms)
Linking proposition: a proposition positing a specific causal link between
neural activity in the brain and perceptual experience. (e.g. euditory
system transforms loudness of sound into rate of firing, then later it
gets turned into a perceptual experience)
TUTORIALS NOT INCLUDED!
6
, Foundations of perception – George Mather
Chapter 3
The body senses
page 54-79
Introduction
Two sensory systems
1. The somatosensory system: deals with touch, proprioception and
kinesthesis
Proprioception: about the position of body parts
Kinesthesis: about the movement of body part
2. Vestibular system: deals with balance
The somatosensory system
Physiology of somatosensation
Somatosensory receptors
Touch receptors:
• Free nerve endings: all skin, superficial pain,
temperature, tickle
• Meissner’s corpuscles: glabrous skin, superficial dynamic
touch
Intermediate temporal response (30-50Hz)
• Markel’s disks: all skin, superficial static
pressure
Best-suited to relatively stable signals, unchanging mechanical
stimulations
• Pacinian corpuscles: all skin, deep pressure,
vibration
respond to high frequency vibrations like moving over texture (250-
350Hz)
• Rufini’s corpuscles: all skin, deep stretching of skin
Not all receptors play an equal role, it depends on the income stimuli
Proprioception
Prioprioceptors: For perception of body position and movement.
• Muscle spindles muscles muscle length
• Golgi tendon organs tendons (NL: pees) muscle tension
• Joint receptors joints (NL: gewrichten) joint position
7
, Muscles used for very fine and accurate movements (eg hand/eyes)
have more muscle spindles. (spindles are 4 to 8 muscle fibres in
connective tissue)
Somatosensory pathway (fig 3.3)
- Dorsal root ganglia: rounded swellings lying in the vertebrae just
outside the spinal cord, each containing thousands of afferent cell
bodies whose axons enter the spinal cord.
- Action potential will be transmitted along:
1. spinothalamic pathway: for pain and temperature signals from free
never endings.
Lightly or unmyelinated axons and therefore low speed of 2 m/s
2. lemniscal pathway: for somatosensory signals from
mechanoreceptors.
Myelinated axons so that they have a higher speed (20 m/s)
- both branches also contain branching projections in the spinal cord
that are responsible for reflexes, such as withdrawal from painful
stimuli, and the knee-jerk reflex (=myontatic reflex)
Cortical representation of somatosensation
Primary somatosensory cortex: a long thin strip of cortical surface
running from ear to ear across the head
Mountcastle (1957) found that each cell in primary somatosensory
cortex receives input from only one type of receptor
Centre-surround receptive fields: A receptive field containing
concentrically organized regions of excitation and inhibition, as a result
of lateral inhibition. (same concept as with eyes)
Cortex:
- Vertical organization (perpendicular to surface).
Cells in a cortical column (running down vertically from the surface)
are connected to the same type of sensory receptor.
Receptive fields on the finger tips are small (3-4mm diameter) and
trunk over 100 larger.
- Horizontal organization (parallel to the surface of the cortex):
depending on what part of the body.
Cortical magnification: more important (sensitive) body parts have
bigger areas in the brain.
Not much is understood about the projection of pain.
Two point acuity: how close together you can distinguish two separate
points from one; best on the tongue and hands, worst on the back and
legs. Very small receptive fields also better because the calipers can
stimulate different neurons (centre-surround cells)
8
