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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.