Task 4-BCI, connectionism, activation functions, graceful degradation, delta rule

Question 1

BCI

Answer 1

• CONNECTS THE BRAIN WITH A COMPUTER / PROTHESIS ETC BY SIGNAL ACQUISITION (OF THE BRAIN) & SIGNAL PROCESSING
• CAN BE INVASIVE AND NON-INVASIVE
• ASSISTIVE BCI: AIMS TO REPLACE LOST FUNCTIONS (E.G.
  COCHLEAR IMPLANT, ARM PROTHESIS)
• REHABILITATIVE BCI: AIM TO FACILITATE RESTORATION OF BRAIN FUNCTION

feature extractor= transforms raw signals(EEG) into readable signal
control interface: gtarmsforms the signals into semantic commands
device controller: executes these demand s

Question 2

Connectionism

Answer 2

• EMPHASIZES IMPORTANCE OF CONNECTIONS AMONG
  NEURONLIKE STRUCTURES IN A MODEL (INTERCONNECTED
  NETWORKS OF SIMPLE UNITS) WHICH WORK PARALLEL TO EACH
  OTHER
• CONSISTS OF DIFFERENT LAYERS: INPUT, HIDDEN AND OUTPUT
  UNITS
• LOCAL REPRESENTATION: EACH UNIT IS INDEPENDENTLY
  ASSOCIATED WITH ONLY ONE REPRESENTED THING (SIMPLE,
  “GRANDMOTHER-CELL) -> SYMBOLIC, units, links
  DISTRIBUTED REPRESENTATION: SPECIFIC KNOWLEDGE IS REPRESENTED BY ACTIVITY OF DIFFERENT UNITS (MORE COMPLEX) LIMITATIONS: ADDITION OF NEW INFO CAN CAUSE
  LOSS OF OLD INFO; LEARNING CANNOT BE IMMEDIATE -> SUB SYMBOLIC, feedforward, recurrent network

Practical applicability: backprpagation techniques have been used by engineers for prediction of stressors on materials

Connectionist models are always models of learning
Decision making : you can store decisions by learning 2 different outcomes and recalling them

Question 3

ACTIVATION FUNCTIONS

Answer 3

THRESHOLD) LINEAR (/), SIGMOID (S) AND BINARY THRESHOLD (I)

Question 4

Delta rule

Answer 4

METHOD USED TO CALCULATE THE DIFFERENCE BETWEEN ACTUAL AND DESIRED OUTPUT (ERROR) AND CHANGE THE

A rule for changing the weight of the connection, which will in turn change the activity level of i (Δwij = [ai (desired) – ai (obtained)] aj), where Δwij is the change in weight of the connection from unit j to unit i to be made after learning.

Question 5

graceful degradation

Answer 5

ABILITY TO PRODUCE REASONABLE APPROXIMATIONS TO THE
CORRECT OUTPUT FOLLOWING A DAMAGE TO SINGLE UNITS

loss of a few units ist detremental

Question 6

Generalisation

Answer 6

if recall cue is similar to the pattern, the output will produce similar response

Question 7

Fault tolerance:

Answer 7

Even if pattern is incomplete or damaged, output will recognize it

network is robust against errors in representation

Question 8

prototype extraction

Answer 8

: if more than 1 pattern is possible, output will produce pattern with the most activation

Question 9

Autoassociator

Answer 9

Replaces at output the same pattern that was presented at input

Learning occurs when the weights change, so that the internal input to each unit matches the external input

Resistant to incomplete and noisy pattern (and cleans them up)
Uses the delta rule

Question 10

Difference autoassociator to pattern associator:

Answer 10

Recurrent connections that give feedback
Same input pattern at output
Doesnt need external teacher

Question 11

traditional hebbian learning

Answer 11

Traditional: doesnt specify how much a connection should increase and the exact conditions that need to be met for increase

Question 12

Neo Hebbian learning

Answer 12

\: solves this traditional problem
Mathematical equations (dynamical differential)weights change in their strength
Nodes = instar/outstar

Question 13

Differential Hebbian learning:

Answer 13

solves the problem that connection only increase in strength
Connections change according to the difference between the nodes activation and the incoming stimulus signal: change can be positive/ negative/ null

Question 14

Drive reinforcement theory

Answer 14

solves the problem that the change is only linear = sigmoid curve
considers recent history of stimuli, e.g. recent trials of learning (=temporal memory)

Question 15

Hippocampus

Answer 15

During behavior, memories are stored in Hippo
During sleep these memories are consolidated into neocortex by synchronous bursts (Hebbian Learning) Autoassociative memory: recall a memory with just a cue (subcomponent of the memory unit)

DG=>Competitive learning (sparse memories)
CA3=> recurrent connections, autoassociation
CA1=> Competition

Question 16

distributed representation

Answer 16

attributes of concepts distributed through network => good representational and neurobiological power

Networks that learn how to represent concepts or propositions in more
complex ways and distribute over complex neuronlike structures

Question 17

bachpropagation

Answer 17

calculates error between desired and actual level of activation, therefore changes weights

Question 18

local representation

Answer 18

Neuronlike structures are given an identifiable interpretation in terms of
specifiable concepts + propositions

a kind of NN neutrons are specific concept like “apple” limiting representational power

Question 19

pattern associator

Answer 19

often works with Hebb rule, learns to associate one pattern with another

Question 20

sub symbolic

Answer 20

knowledge spread over units , learning as change of connection between chunks and production rules

Question 21

symbolic learning

Answer 21

learning of new chunks and production rules by e.g. compilation

Question 22

Both representations can be used to perform PARALLEL CONSTRAINT SATISFACTION

Answer 22

distributed and local representation

Question 23

parallel constraint satisfact8on

Answer 23

processing simultaneously satisfies numerous constraints

each input is setting constraints on the final state, a design is reached when there is reasonable fit between the input and teh output

used with problem solving

Example: When putting together a school schedule one needs to take into account various constraints imposed by classroom availability and the preferences of professors and students

Question 24

relaxation

Answer 24

aim of the network is compelded after repeatedly activating until u til it reaches stable level=> learning has eben a achieved

constraints can be satisfied in parallel by repeatedly passing activation among all the units, until after some number of cycles of activity all units have reached stable activation levels

process is called RELAXATION

Question 25

problem solving

Answer 25

Problem Solving Example: Is Alice outgoing or shy? Concepts are represent by units The problem has both positive constraints, such as between “likes parties” and “outgoing”, and negative constraints, such as between “outgoing” and “shy” Positive constraints are represented by excitatory connections Negative constraints are represented by inhibitory connections An external constraint can be captured by linking units representing elements that satisfy the external constraint and is linked to it either positively or negatively For example, the external constraint could be that we know that Alice likes programming and likes parties A problem solution consists of when a group of units is activated by the set containing outgoing, while correctively deactivating the set containing shy Consequently, outgoing will win over shy because outgoing is more directly connected to the external information that Alice likes parties Constraints can be satisfied in parallel by repeatedly passing activation among all the units, until after some number of cycles of activity all units have reached stable activation levels process is called RELAXATION SETTLING – achieving stability

Question 26

planning

Answer 26

Constructing plans is usually a more sequential process understand in terms of rules or analogies rather than parallel processing uses rule based systems

Question 27

decision

Answer 27

We can understand decision making in terms of parallel constraint satisfaction The elements of a decision are Actions and Goals Actions that facilitate a goal have positive constraints and negative restraints come from incompatible relations positive internal constraints come from facilitation relations: if an action facilitates a goal, then the action and goal tend to go together The external constraint on decision making comes from goal priority, in which some goals are inherently, desirable, providing a positive constraint Once the elements and constraints have been specified for a particular decision problem, a constraint network can be formed Units represent the various options and goals, and pluses and minuses indicate the excitatory and inhibitory links that embody the fundamental constraints Analogy can also be useful in decision making, since a past case where something like A helped to bring about something like B may help one to see that A facilitates B But reasoning with analogies may itself depend on parallel constraint satisfaction

Question 28

explanation

Answer 28

Explanations should be understood as activation of Prototypes encoded in networks Example: Understanding why a particular bird has a long neck can come via activation of a set of nodes representing swan, which includes the prototypical expectation that swans have long necks Units representing pieces of evidence are linked to a special evidence unit that activates them, and activation spreads out to other units

Question 29

learning

Answer 29

Learning There are two basic ways in which learning can take place in a connectionist model: Adding new units or changing the weights on the links between them Work to date concentrates on weight learning, as is demonstrated in the Hebbian Learning, in which a link between A and B gets stronger with subsequent activation A technique called Backpropagation adjusts the weights that connect the different units by assigning weight randomly, determining errors and propagating backwards Assign weights randomly to the links between units Activate input units based on features of what you want the network to learn about Spread activation forward through the network to the hidden units and then to the output units Determine errors by calculating the difference between the computed activation of the output units and the desired activation of the output units. For example, if activation of quiet and studies hard activated jock, this result would be an error Propagate errors backward down the links, changing the weights in such a way that the errors will be reduced Eventually, after many examples have been presented to the network, it will correctly classify different kinds of students Disadvantages: Requires supervision Tends to be slow, requiring many hundreds or thousands of examples

Question 30

language

Answer 30

Word recognition can be understood as a parallel constraint satisfaction problem by representing hypotheses about what letters and words are present example with cat Relaxing the network can pick the best overall interpretation of a word

Question 31

cm psychological p

Answer 31

Connectionist models have furnished explanations of many psychological phenomena, but also suggested new ones Backpropagation techniques have simulated many psychological processes

Question 32

cm neuro p

Answer 32

the artificial networks are similar to brain structure in that they have simple elements that excite and inhibit each other. Real neural networks are much more complicated and complex than the units in artificial networks, which merely pass activation to each other Furthermore, in local representations each unit has a specifiable conceptual or propositional interpretation, but neurons do not have such local interpretation Artificial units leave out the chemical parts, like neurotransmitter We can think of each artificial unit as representing neuronal group, a complex of neurons that work together to play a processing role Many local networks use symmetric links between units, whereas synapses connecting neurons are one- way While Hebbian learning does occur in the brain, backpropagation

Question 33

cm practical application

Answer 33

Connectionist models of leaning and performance have had some interesting educational applications, for example knowledge required for reading Reading is a kind of parallel constraint satisfaction where the constraints simultaneously involve spelling, meaning and context Backpropagation techniques have been used to assist engineers in predicting the stresses and strains of materials needed for buildings Connectionist models are widely used in intelligent systems For example, in training networks to recognize bombs, underwater objects, and handwriting interpret the results of medical tests and predict the occurrence of disease

Question 34

ASSISTIVE BCI SYSTEMS

Answer 34

substitute lost functions, enable control of robotic devices or provide functional electrical stimulation

Question 35

REHABILITATIVE BCI SYSTEMS

Answer 35

restore brain function and/or behaviour by manipulation of self-regulation of neurophysiological activity

Question 36

Cortical Resource Allocation

Answer 36

Variable-resolution representations in the sensory cortex: spatial resolution is highest at the center of gaze Plasticity

Question 37

NEURAL INTERFACE SYSTEM (NIC)

Answer 37

translates neuronal activity into control signals for assistive devices

Question 38

grandmother cell

Answer 38

example of local representation in perception Neurons selectively respond to more and more complex attributes, so there might be ‘grandmother cell’ which are so specific as they fire in recognition of your own grandmother Hypothesis is fundamentally unsound rejected

Question 39

NEURAL NETWORKS

Answer 39

Not all is lost if there is any deterioration in stimulus signal or loss of individual units • REDUNDANCY – although some info might be lost, enough is still available to get the message across Gradual deterioration in performance of a distributed system

Question 40

weight

Answer 40

Weight = strength of connection

Question 41

what can connectionist models do for us

Answer 41

An auto associator network can be trained to respond to collections of patterns with varying degree of correlation between them When the input patterns being learned are highly correlated, the network can generate the central tendency or prototype that lies behind them, another form of spontaneous generalization A single auto associator network can learn more than one prototype simultaneously, even when the concepts being learned are related to each other. Cueing with the prototype name will give recall of the correct prototype (which was never presented to the network complete) An auto associator network can extract prototype info while also learning specific info about individual exemplars of the prototype Thus, the network’s capability to retrieve specific info from cues (content addressability) means that, given a specific enough cue, it can retrieve the specific info of the individual exemplars from which the prototype generalization is constructed Such behaviour is an example of a unitary memory system that can support both ‘episodic’ and ‘semantic’ memory within the same structure

Question 42

connectionist modelling

Answer 42

Connectionist Modelling is inspired by information processing in the brain and a typical model consists of several layers of processing units Unit can be thought of as similar to a neuron, with each layer summing info from units in the previous layer This info processing is derived from observations of the organization of the brain: The basic computational operation in the brain involves one Neuron passing info • Related to the sum of the signals reaching it to other neurons Learning changes the strength of the connections between neurons and thus the • Influence that one has on the other Cognitive Processes involve the basic computation being performed in parallel by a • Larger number of neurons Info, whether about an incoming signal or representing the network’s memory of • Past events, is distributed across many neurons on many connections In contrast to models in Artificial Intelligence (AI) which contain a set of rules, connectionist models are said to be neurally inspired by our brain

Question 43

connectionism and the Brain

Answer 43

Neurons integrate Information Neurons pass Information about the Level of their Input Brain Structure is Layered Learning is achieved by changing StrengthStrength between Neurons

Question 44

threshold linear

Answer 44

Real neurons have thresholds firing occurs only if net input is above threshold

Question 45

sigmoid

Answer 45

Range of possible activity has been set from 0 to 1. When the net input is large and negative, the unit has an activity level close to 0. As the input becomes less negative the activity increases, gradually at first and then more quickly. As the net input becomes positive the rate of increase in activity slows down again, asymptoting at the maximum value which the unit can achieve. They prevent saturation and are good in noise suppression.

Question 46

binary threshold

Answer 46

Models neurons as two state devices as either being on or off. This ensures that if the net input is below threshold, there is no activity. Once the net input exceeds the threshold, the neuron becomes activated.

Question 47

DISTRIBUTED PROCESSING

Answer 47

In connectionist models info storage is not local, but distributed across many different connections in different parts of the system

Question 48

LOCAL PROCESSING

Answer 48

Traditional models of cognitive processing usually assume a local representation of knowledge stored in different, independent locations

Question 49

GRACEFUL DEGRADATION

Answer 49

ability to continue to produce a reasonable approximation to the correct answer following damage, rather than undergoing failure Any info processing system which works in the brain must be fault tolerant, because the signals it has to work with are seldom perfect An attractive aspect of content-addressable memory is that it is indeed Fault Tolerant (because no input unit uniquely determines the outcome)

Question 50

Properties of Pattern Associators

Answer 50

gneralizatioh During recall, pattern associator generalize If a recall cue is similar to a pattern that has been learnt already, a pattern associator will produce a similar response to the new pattern as it would to the old fault tolerance Properties of Pattern Associators

Question 51

competitive learning can be divided into three phases:

Answer 51

EXCITATION: Excitation of the output units proceeds in the usual fashion by summing the products of the activity of each input unit and the weights of its connection COMPETITION: The units compete with each other and the identification of the winner may be achieved by selecting the unit with the highest activity value WEIGHT ADJUSTMENT: Weight adjustment is only made to connections feeding into the winning output unit in order to make it more similar to the input vector for which it was the winner

Question 52

goal of bcc

Answer 52

provide new channel or output for the brain that requires voluntary adaptive control by user Helping handicapped people BCI system: allow user to interact with device Interaction is enables through intermediary functional components, control signals and feedback loops Intermediary functional components: perform specific functions in converting intent into action Feedback loops inform each component in the system of the state of one or more components

Question 53

problem machine learning

Answer 53

Concerns about the biological plausibility of current machine learning approaches: if our brains’ abilities are emulated by algorithms that could not possibly exist in the human brain then these artificial networks cannot inform us about the brain’s behavio z.b.humans learn with supervisor most successful deep networks have relied on feed-forward architectures whereas the brain includes massive feedback connections no equivalent to backprpagation humans influenced by chemicals

Question 54

competitive networks

Answer 54

connection. between winning in and output will be strengthened loosing will be weekend 3 phases excitement competition weight adjustment