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Part 1. Review of the CNS
The Central Nervous System is made
up of 100 Billion NEURONS
Neurons are Cells
Anatomy of a Neuron
Myelin is supplied by support
cells known as Glia (Glue)
White Matter and Gray Matter
• White Matter
– Axons (highways)
• Gray Matter
– Cell bodies (cities)
Nervous System Cells
• Neurons and communication
– Neurons are “charged” like batteries and
have the ability to send electrical messages
over long distances to other cells.
• Sensory neurons carry information from
sense organs to the central nervous system.
• Motor neurons carry information from the
CNS to muscles
Charging the Neuron
Action Potential
A fast burst of electrical energy
sent down the axon to the synapse,
a gap between two neurons.
Integrate and Fire!!
• Neurons add up information from excitatory and
inhibitory sources
• If the net activity raises the level of excitation
above a certain threshold, the neuron will fire an
action potential down its axon
• A neuron is either sending a message or it isn’t.
– It’s a binary system (more on this later!)
Nervous System Cells
• Neurons and communication
– Sending a message results in the depletion
of the battery’s power, so the neurons need
to be constantly recharged.
Nervous System Cells
• Nerve Impulses
– Each neuron can either increase or decrease
the likelihood that the next cell will continue
to transmit.
• Excitatory messages increase the probability that
the next cell will “fire” - continue the
transmission.
• Inhibitory messages decrease the likelihood that
transmission will continue to travel.
Synaptic
Transmission
• Electrical message
is converted to a
chemical message
– Activates another
neuron
– Moves a muscle
– Triggers hormonal
release from a gland
Neural Networks
• Each neuron receives
information from many others
and sends information to many
others.
– The significance (or weight) of a
synaptic connection depends on
the number and size of synapses
shared by two neurons
Synaptic Weight
• Although both neurons A and B have excitatory
synapses with C, Activity in cell A will have a
bigger effect on C than the same amount of
activity in cell B.
A
C
• Neurotransmitters can be either excitatory or inhibitory
• Lock and Key System
Neurotransmitters & Behavior
• Our understanding of neurotransmitters is the key
to treating many brain-related disorders
• Parkinson’s Disease
– Parkinson’s Disease is a condition in which the
individual has trouble executing voluntary
movements, and has tremors, rigidity and a
depressed mood.
– This condition has been linked to a gradual decay
in a system of axons that release the
neurotransmitter dopamine.
Summary
• The Brain is an Electrical System
– Neurons fire in an all-or-none fashion
– Neurons may either increase or decrease
another neuron’s chances of firing
• Some Terms
– Axon, threshold, dendrite, integrate and
fire, neurotransmitter, excitation,
inhibition, synapse, weight
History of Connectionism (Ch. 7)
• Logical operations are not new (ancient Greece)
• Connectionists seek to develop models based on what
we know about the human brain.
• A computer is not a very good connectionist model
– A computer is a serial processor
– Brain is a parallel processor
• Connectionists believe that the phenomenon known as
“mind” can be explained by interconnected neural units
that follow the rules of neurons.
The McCullough and Pitts Neuron
• They proposed that simple electrical circuits
that behaved like neurons could perform some
basic logical functions.
– Neurons were either ON or OFF (binary)
– Neurons had thresholds
• A certain amount of activation was required in
order to get them to fire
– Connections (synapses) had weights that
could vary in intensity and polarity (+ or -)
McCullough and Pitts (1943)
Neuron is either ON or OFF: Activity is either
1 or 0
Θ = Threshold
W = Weight or connection Strength
W=2
Θ=2
McCullough and Pitts (1943)
• Logical “OR” operation
Θ=2
McCullough and Pitts (1943)
• Logical “AND” operation
Θ=2
McCullough and Pitts (1943)
• Logical “NOT” operation
Θ=2
McCullough and Pitts (1943)
• They were not the first to notice the electrical
properties of neurons.
• They were the first to construct electrical
circuits that mimicked the basic function of
neurons.
Part 2. The Modular Brain
• Module - A self-contained part of a larger system. It
takes a specific bit of input and generates a specific
bit of output.
• Damage to a module will result in the loss of a
specific function (a dissociation)
• If the mind uses RULES, they are probably processed
by modules that can be identified and studied
• A damaged module will result in the loss of a rule
Back to the Future
• Phrenology
Mapping from the Outside
• Franz Josef Gall (1758-1828)
– Used the clinical method to map
the brain and confirm:
• Existence of white and gray matter
• Fibers from each brain side to the
opposite spinal column side
• Fibers connecting the two brain
hemispheres
– “How do the size and shape of
the brain reveal information
about brain facilities?”
– Can it be mapped from the
outside?
– Theory flopped - was it
abandoned too quickly?
Cerebral Hemispheres
Paul Broca (1824-1880)
– The Clinical Method (1861)
– Broca’s area: the speech center in the 3rd
frontal convolution of the left hemisphere
of the cerebral cortex
Anti-Module Data
Ivan Pavlov (1849-1936)
• Shifted from physiology to psychology
with research into psychical reflex
(classical conditioning).
• Variations of classical conditioning:
- US, UR, CS, CR
• Many researchers began to see the brain
as a device that simply linked input and
output (predecessor of Behaviorism)
Physiology of the Nervous System
• Camillo Golgi (1844-1926)
– Italian neurologist
• S. Ramón y Cajal (1852-1934)
– Spanish neuroanatomist
– Nobel Prize 1906
Pavlov and S-R Psychology
• Pavlov’s Findings combined with the study of
neuroanatomy led many to believe the brain was a
large homogeneous network. Hence, Behaviorism.
Not So fast
• It LOOKS modular!
• Brain damage in certain areas leads to
predictable deficits.
Memory and Modules
• Long-Term memory
– What is your name?
– Duration: Decades
• Working memory (Short-term memory)
– What did I just say?
– Duration: If not actively manipulated (rehearsed)
most info is gone in 10 seconds
• Examples of people losing one without losing
the other. Dissociation suggests modules.
Modules within WM
Can we Compromise?
Nyet!
Non!
Part 3. Rules
• Basic IF (antecedent) - THEN (consequent)
statements
• More flexible than standard logic
– Allows alternatives and “best fit” solutions (e.g. penicillin)
– Serves as a general procedure that can accept many types of
input and process them similarly
– Rather than
• Skipped class + Yesterday = Skipped class
– Use
• Any action on object + before today = -ed added to
the end of verb plus object
Rules and Problem Solving
• Each Rule can narrow your choices and make
the next decision easier or alters the outcome
• Heuristics: Rules of thumb that spare us from
the need to search all possibilities
Problem Solving
• Rules can help us reason forward and backward
– Planning: How can I prevent heart disease?
– Explanation: How did I get heart disease?
• Both can be limited and biased by what you
already know.
– A string of rules can be described as a PLAN
– Choosing among competing plans can be
difficult, but exhaustively searching every
possibility would take an eternity
Psychological Plausibility
• Rule-Based computational systems show promise
– SOAR (Newell, 1990) Good at Cryptarithmetic
problems without doing an exhaustive search
• DONALD + GERALD = ROBERT
– Makes “human-like” errors in reasoning
• Rate of learning (improvement) slows down as
more is learned
Psychological Plausibility
• Perhaps working memory stores goals
and compares plans?
• Perhaps synapses are modified as we
acquire and update rules?
ACT-R Model and Addition
• A cognitive skill is composed of
production rules
• Multi-Column addition
– The ACT-R approach (Cycle-by-cycle)
has proven effective in tutoring
• Tic-Tac-Toe
TIC TAC TOE
•
Priority of rules
1.
2.
3.
4.
5.
6.
7.
IF row of X or row of O THEN - Game over
IF there is a row, column or diagonal with two of my pieces
and a blank space THEN play the blank space - Game over
IF there is a row, column, or diagonal with two of
opponent’s pieces and a blank space, THEN play the blank
space to block - Opponent Play
IF the center is blank THEN play center - Opponent Play
IF there is an empty corner THEN play corner according to
clock rule - Opponent Play
IF empty space THEN play according to clock rule Opponent Play
Game Over
Rules of Language
• Steven Pinker
– Harvard U.
– Language Acquisition and
the evolution of language
• Syntax - Rules of language
– Are they learned? He thinks
not!...mostly.
Rules of Language
• Inflections
– Adding -ed to past tense verbs
– Adding -s to plural nouns
– (Sometimes) adding -ess/er to female/male
nouns
• Are we wired to inflect?
Rules of Language
•
Two schools of thought
1. Associationism
•
•
Similar to behaviorist approach
Present and past tense forms are both
stored and somehow linked
2. Rule-and-representation
•
•
We have the verb plus a rule that generates
the past tenses on the fly.
There is no need to store past tense forms
Try These
•
•
•
•
•
•
Today I will crittle the house.
Yesterday I _______ the house.
Today I will strow the car.
Yesterday I ______ the car.
Today I will bling my outfit.
Yesterday I _____ my outfit.
Try These
• Regular familiar
– Today I will crittle the house.
– Yesterday I _______ the house.
• Irregular unfamiliar
– Today I will strow the car.
– Yesterday I ______ the car.
• Irregular “familiar”
– Today I will bling my outfit.
– Yesterday I _____ my outfit.
Regular and Irregular Verbs
• Regular verbs (lift, walk): add -ed for past tense
– Today I walk
– Yesterday I _______
• Irregular verbs (go, drink, throw)
– Some are truly unique (be-was, go-went), but others
can be grouped
• sing, ring, spring, fling
• grow, blow, throw
– Unfamiliar verbs that fit a subgroup often get
channeled into the regular verb processing system
Regular and Irregular Verbs
• When a verb is intuitively perceived as being
derived from a noun or adjective are processed as
regular
– Fly-out
– Grandstand
• Once the -ed rule has been established, irregular
verbs must be practiced and associations must be
formed to pull them away from the rule (children
and overgeneralization).
Regular and Irregular Verbs
• When people are provided with present tense
verb forms…
• Past tense forms of irregular verbs have been
learned (hard wired) and are generated faster
than the past tense forms of regular verbs which
are processed from scratch each time.
Rule-Associative Memory Hybrid Theory
Link to past tense form activated
Irregular
Verb+ Yesterday
Past Tense Form
Generated
Regular
Regular verb processor
“-ed” added
Evidence - Children
Link to past tense form activated
Irregular
Yesterday +
Sing
Regular
Bang!
I Sing’d-ed
Regular verb
processor
“-ed” added
Evidence - Aphasics
Link to past tense form activated
Irregular
Smile + yesterday
Regular
Regular verb processor
“-ed” added
I “smile”
Evidence - SLI
Link to past tense form activated
Irregular
Smile + yesterday
Regular
Rule system might not
exist!
I “smile”
Williams Syndrome
• Broken arm of chromosome 7
• Remarkable language Skills
despite cognitive difficulties in
many other areas
• Evidence that language is
autonomous of many other aspects
of cognition.
Summary
• Rules offer a means of explaining many
types of cognitive processes
– ACT-R’s approach to addition might be
comparable to human thought process. It has
proven effective in education
• Linguists see syntax as a collection of
rules and there is evidence that, in some
cases, the brain does too.
Key points in Medin
• The classical view of concepts based on defining
features is unacceptable because of failure to
specify defining features, goodness of example
effects, and unclear cases.
• Prototype theories have also had empirical
problems, with respect to context dependency,
artificial categories, and ease of learning.
• Concepts are organized by theories, not just by
similarity.
• Similarity involves interdependent features and
higher-order relations.