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    Memory Modeling & Knowledge Representation

    Felix Putze 10.5.2012

    Lecture Cognitive Modeling SS 2012

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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 users 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 humans 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. Pawlows 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

    Millers 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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    Atkinsons & Siffrins 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 Siffrins and Atkinsons 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 information Duration of 15-30 seconds (unless rehearsed) Bottleneck between raw data from sensors and unlimited long term

    memory

    Long term memory: Information which is rehearsed often enough is stored here

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    Baddeleys Memory Model

    Model of short-term (or working) memory Three slave systems for different types of information Controlled by central executive

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    Baddeleys Memory Model The phonological loop consists of two main parts:

    Phonological store: contains ca. 2 seconds of audio information Phonological rehearsal: performs periodic rehearsal to keep

    information available ( inner voice) Evidence: Suppression of rehearsal impairs memory

    Visuo-Spatial sketchpad is divided in two components: Inner cache: forms, color Inner scribe: spatial information, movement (planning)

    Visually presented information can also be transferred to the phonological loop by verbalization

    Separation between phonologic and visual system explains differences in dual-tasking: Combining one acoustic and one visual task is easier than combining two tasks of the same kind

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    Baddeleys Memory Model Central Executive:

    attention retrieval strategies episode

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