Presentation topic

Learning & Memory

Connectionist Model

Presented by : Mangal Kardile

Connectionist Model

A neural network modelof Cognitive psychology

Memory &Learning

Language(written & spoken)

Cognitivedevelopment

Cognitive control

Attention

Action

The dawn of the model concept

• Cognition 1960- Human information- processing system was compared with device like von Neumann computer

• Memory consisted of a set of separate stores(; Waugh & Norman, 1965; Atkinson & Shiffrin,1968)

• Processing viewed as sequence of discrete operations (Sternberg,1969)

How the concept evolved?

• Humans – like computers, process information serially

• Human cognition explained in terms of serial processing

• Psychological findings and cognitive research- aspects of human cognition are “Parallel processing”

• Term-“Connectionist model” by Feldman & Ballard, 1982

Parallel Distributed Processing

PDP models are instances of connectionist models that stress the notion that processing activity results from the processing interactions occurring among rather large number of processing units

PDP – Connectionist model

• “Connectionist model”, can handle very large numbers of cognitive operations at once through a network distributed across incalculable numbers of locations in the brain – ( James McClelland & PDP Research group, 1986)

Connectionist network

• Very large numbers of cognitive operations are handled at once, through a network distributed across incalculable numbers of locations in the brain.

• (McClelland & Seidenberg model(1989)

Brain areas involved in Learning & Memory

Neural & Computer processing

• An individual neuron take up 3 millisecond to fire in response to a stimulus, whereas a computer can begin responding to an input in nanoseconds

• James McClelland & David Rumelhart introduced PDP models in the mainstream of Psychology to understand number of different domains in cognitive functioning

Concept: Connectionist network

• All forms of knowledge- represented within the network structure

• Fundamental element – the “NODE”• Each node connected to many • Patterns of nodes enable to organize

knowledge within connections• In PDP- Connections represent a concept

Connection patternsNeural network pattern

Patterns of connections in PDP

(PDP)-Brain-inspired model differs from Computer model

• Computer model – a set of instruction• Brain model- Different patterns of activation, handled

by different cognitive processes• In brain at any one time a given neuron may be: • Inactive neuron- not stimulated beyond excitation

threshold

• Excitatory neuron- release neurotransmitters that stimulate receptive neurons at synapse

• Inhibitory neuron- release neurotransmitters that inhibit receptive neurons

Similarity- PDP & Brain model

• Action potential of a Neuron- all or none• Neurotransmitters, Neuromodulators releasing

amount & frequency of firing may vary

• Affects degree of excitation or inhibition

• PDP individual units- activity varies• May send excitatory or inhibitory signals• PDP indicates specific neural pathways for

knowledge representation

---Can PDP, map specific neural information?????

What PDP possess?

Rather uses physiological process of the brain as metaphor for understanding cognition

PDP and Brain

• According to PDP-

• Human mind is flexible

• Accommodates incomplete information

• Do not require precise match to activate a pattern

• Degraded information does not prohibit new information or recreation of pattern

Architecture-PDP

• Explains various general characteristics of human cognition

• Rapid, dynamic and flexible response with partial or degraded information

• Explaining cognitive processes- perception, reasoning, reading, language & memory

• Other PDP models- Constraint satisfaction network, Control of Automatic Processes, Extended Parallel process , Analysis process model, Structural equation model, etc.

Flaws - PDP

• May not remember a single day event?• No satisfactory explanation of quickly

unlearning established patterns-specifically in contradictory information

PDP leads to empirical research….

• May be two learning systems in Human brain• One system responds to connectionist model• Complementary system handles newly

acquired information• Holds information for short time, integrates

newer info with existing info in PDP model And evidences from neuropsychology and connectionist network modeling seem to corroborate this account

“Connectionist model” continues to explore….

Thank you