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    Memory Modeling & Knowledge Representation

    Felix Putze

    16.5.2013

    Lecture „Cognitive Modeling“

    SS 2013

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    Structure of Lecture

    • Introduction and Motivation

    • Memory Modeling

    • Knowledge Representation

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    Why do memory modeling?

    • Any process that spans a period of time requires the handling of limited human memory capacity • Memory capacity is a robust indicator of general intelligence

    • Memory access is not of guaranteed success and with instantaneous reaction time • Modeling of memory performance relevant to predict errors

    • For Human-Machine-Interaction: User has limited capability of remembering and recalling • Not all presented information is stored or available at all times

    • Interaction systems should know what is on the user‘s mind and what is not • Which information can the system implicitly refer to?

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    Requests to a Memory Model

    • There is a number of questions a memory model should be able to answer: • How is memory organized?

    • What items are currently active on the human‘s mind?

    • How is new information integrated?

    • Is a certain bit of information retrievable?

    • What is associated with a certain input?

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    Types of Memory • Squire (1992) distinguishes several distinct types of memory

    and associates them with different parts of the brain:

    • Declarative Memory: Explicit and conscious recollection of… • facts (semantic memory, e.g. “France is a country in Europe.”)

    • events (episodic memory, e.g. “Last summer, I spend my holidays in France.”)

    • Procedural Memory: Implicitly learned skills (e.g. riding bicycle)

    • Priming: Automated associations caused by frequent repetition

    • Conditioning: Automatic stimulus-reflex pairs (e.g. Pawlow‘s dogs)

    • In this lecture, we will focus on semantic memory

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    Short-term and long-term Memory

    • Short-term memory: Storage for a limited number of items • Small capacity

    • Limited duration for storage (seconds), decay

    • Longer storage duration requires rehearsal, i.e. periodic repetition

    • Acoustically and visually coded (e.g. multiple phonetically similar items are hard to keep in memory)

    • Long-term memory: • Nearly unlimited capacity

    • Items can last for years without rehearsal

    • Items are mostly retrieved and coded semantically, however there is a phonetic component (tip-of-tongue effect)

    • Other types of memory: sensory memory, working memory

    • The existence of distinct memory systems in the brain is controversial; experiments support both theories

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    The magic number 7 (+/- 2)

    • Miller (1956): Determined the capacity of short-term memory to be about 7 items • Estimated by having people recall sequences of digits or words

    • Performance is very good for around five to six items

    • Performance degrades rapidly for more items

    •  Miller’s conclusion: Memory span is not a function of encoding length in bit, but a function of the number of elements

    • Later, Miller acknowledged that the “magic number” was a coincidence and heavily context-dependent

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    Chunking and Mnemonics

    • How can people remember longer phone number if their short- time memory is limited to 7 (or fewer) elements? • Most people do not remember the number 0123456789 as 0-1-2-3-4-5-

    6-7-8-9 but as 01-23-45-67-89 (or similar)

    • This division of information into smaller pieces is called chunking

    • This is also a question of skill: A trained person can chunk a stream of binary digits into larger blocks, convert them to decimal numbers and remember those

    • There are many other mnemonic techniques: • Make use of linguistic or phonetic similarities

    • Construct images or stories to connect multiple items into one (e.g. „man“, „horse“, „fish“  A man riding on a horse hunting a fish)

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    Controversy regarding memory limitations

    • There are a lot of conflicting viewpoints on memory limitation:

    • A general limit exists but is lower than seven (≈ 4 without possibility for chunking or mnemonic techniques)

    • The acoustic encoding of items in short-term memory influences this capacity: • Of long words (which take longer to speak), only shorter sequences can

    be remembered

    • Memory span decreases when remembering phonetically similar words

    • There are specialized parts of short term memory with separate capacity limits

    • There is no limitation of short term memory at all (observed limitations are an effect of general scheduling conflicts)

    • There is no special faculty for short term memory at all, only an attention limitation on generic memory

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    Influence of Emotion on Memory

    • Emotion-congruent information is encoded better • In a happy mode, we encode more „happy“ facts than „sad“ ones

    • With high arousal, central information is encoded better • …while peripheral information is encoded worse

    • Yerkes-Dodson law: Relation between arousal and performance is described as an „inverted u-curve“

    • Consequence: Do not study memory as an isolated concept!

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    Structure of Lecture

    • Introduction and Motivation

    • Memory Modeling

    • Knowledge Representation

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    Atkinson‘s & Siffrin‘s Memory Model

    • Incoming information is extracted from parts of sensory input, initially stored in STM and later transferred to LTM or displaced  linear process

    • Monolithic modeling (one model for each type of information)

    http://upload.wikimedia.org/wikipedia/en/4/41/Multi-store-diagram(psychology).png

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    Components of Siffrin’s and Atkinson’s Model

    • Sensory Memory: • Specialized for different sensory inputs (e.g. visual, auditive, …)

    • Lasts for a very short time (milliseconds for visual, few seconds for aural information)

    • Contains raw data, used to select relevant information (partial report)

    • Decoupled from other components (localized, unconscious)

    • Short term memory: • Keeps currently relevant informati