Inf1: Intro to Cogni ve Science
Types of memory and models of memory
Alyssa Alcorn, Helen Pain and Henry Thompson
March 21, 2012 Intro to Cognitive Science 1 1. In the lecture today
A review of short-term memory, and how much stuff fits in there anyway 1. Whether or not the number 7 is magic 2. Working memory 3. The Baddeley-Hitch model of memory h p://www.cartoonstock.com/directory/s/ short_term_memory.asp
March 21, 2012 Intro to Cognitive Science 2 2. Review of Short-Term Memory (STM) Short-term memory (STM) is responsible for storing small amounts of material over short periods of me A short me really means a SHORT me-- up to several seconds. Anything remembered for longer than this me is classified as long-term memory and involves different systems and processes. !!! Note that this is different that what we mean mean by short- term memory in everyday speech. If someone cannot remember what you told them five minutes ago, this is actually a problem with long-term memory. While much STM research discusses verbal or visuo-spa al informa on, the dis nc on of short vs. long-term applies to other types of s muli as well.
3/21/12 Intro to Cognitive Science 3 3. Memory span and magic numbers Amount of informa on varies with individual’s memory span = longest number of items (e.g. digits) that can be immediately repeated back in correct order. Classic research by George Miller (1956) described the apparent limits of short-term memory span in one of the most-cited papers in all of psychology. He opens (drama cally!) “My problem is that I have been persecuted by an integer. For seven years this number has followed me around, has intruded in my most private data, and has assaulted me from the pages of our most public journals. This number assumes a variety of disguises, being some mes a li le larger and some mes a li le smaller than usual, but never changing so much as to be unrecognizable.”
3/21/12 Intro to Cognitive Science 4 Memory span and magic numbers, con nued The persecutory number in ques on is the now-famous “magical number 7 plus or minus two” For STM, this means that the general span is 5-9 remembered items with an average of 7 “Magical number 7” was derived from research with absolute judgement tasks • People were asked to discriminate between s muli varying on only ONE dimension • For example, judging tones that vary only in their pitch He notes performance on s muli varying on mul ple dimensions may be quite different, giving examples illustra ng that most of the s muli we encounter in everyday life are of this type. ....but is 7 the number to quote when we talk about remembering more complex s muli like le ers, words, or digits? 3/21/12 Intro to Cognitive Science 5 4. Maybe not a magic number? Memory span results were widely confirmed and replicated for many years, but (rela vely) recent research suggests the es mate of a magical 7 is too high • Some researchers suggest it should be closer to 3 or 4 • In any case, definitely less than 10! Alternately, the problem may be that Miller’s original discussion and much subsequent literature are not making the straigh orward limit they THINK they are measuring. - For example, Miller’s original retrieval task and similar ones tap into both short AND long-term retrieval - There also appears to be varia on in the reten on proper es for different types of informa on See Shiffrin & Nosofsky 1994 for a review and further references. 3/21/12 Intro to Cognitive Science 6 5. Stretching our short-term memory span (aside from whether the “magic number” is really 7 or not....) Short-term memory span can be “stretched” by meaningfully grouping or chunking informa on - easier to remember one year, 1918, than four numbers 1, 9, 1, 8 - naturally “recode” informa on into chunks as aid to memory! - remember postcodes, phone numbers and words as units rather than lists of individual pieces Memory span for words in a sentence is significantly longer than for unrelated, context-less words • About 15 words (per Brener, 1940), compared to a magical single- digit number • Constraints imposed by the rules of grammar, context, are not sufficient to explain this! (what is longest number/ text you can recall?) 3/21/12 Intro to Cognitive Science 7 6. Are “Short-term memory” and “working memory” synonymous?
In a psychology class, textbook, or elsewhere, you may have also heard about working memory. Short-term memory and working memory may sound ini ally similar, but their rela onship is more complex. These are NOT interchangeable terms. • Working memory (abbreviated to WM) is the part of memory conceived as a “mental workspace” where informa on is temporarily maintained and manipulated. • Short-term memory as discussed earlier in this lecture is more specifically concerned with storage, maintaining small amounts of informa on (e.g. “keeping them in mind” but not manipula ng them or processing them more deeply)
3/21/12 Intro to Cognitive Science 8 STM v. WM contd. As you will see in this lecture, the dis nc on between STM and WM has evolved over me. Short term memory is currently conceived as one component of the larger working memory system.
3/21/12 Intro to Cognitive Science 9 7. Working memory and models of memory We will consider two models of memory: • Modal model of memory (Atkinson & Shiffrin, 1968) • Baddeley-Hitch model of memory (Baddeley & Hitch 1974; and many more) Remember modelling memory to generate predic ons and test theories • How much of the current data from humans can the model explain? • How well does a model explain current human behavioural data? • What hypotheses does the model suggest? Are these confirmed/ disconfirmed by new behavioural data? Plus addi onal benefits in that modelling a memory phenomenon or component means specifying and explaining underlying assump ons and resolving ambigui es. 3/21/12 Intro to Cognitive Science 10 8. The Modal Model of memory Early memory model (Atkinson & Shiffrin, 1968) proposes the following general sequence of processing steps:
1. Informa on enters from the environment
2. Brief processing in sensory systems
3. Informa on goes to a short-term store (STS)
– Passes informa on in and out of LTM – Workspace to perform opera ons, select/ rehearse informa on
– Items would be learned if held in this store
4. Informa on is output OR goes into long-term store (LTS)
3/21/12 Intro to Cognitive Science 11 8. The Modal Model of memory
From Baddeley textbook
3/21/12 Intro to Cognitive Science 12 9. Difficul es with the Modal Model While a simula on of the modal model performed well on rote-learning tasks, it ran into trouble when compared to some aspects of human performance. Based on the model’s connec on of STS and LTS, we would predict.... • A STS deficit will lead to impairment in the LTS, because the STS is key for transferring informa on into and out of the LTS (encoding and retrieval) • If STS is a “workspace” for manipula ng informa on, a STS deficit would impair a person’s ability to do complex cogni ve tasks (e.g. reasoning)
3/21/12 Intro to Cognitive Science 13 9. Difficul es with the Modal Model, contd. However, empirical evidence contradicted both predic ons (these are just two examples) • A case in Shallice & Warrington 1970 reported a pa ent with severe deficits characteris cs of the STS, but who also had an unimpaired LTS. • Other pa ents had impaired STSs, but managed various complex tasks like taxi-driving or running a business (Vallar & Shallice, 1970). Clearly, the Modal Model was too simplis c and the proposed components needed to be altered in some way.
3/21/12 Intro to Cognitive Science 14 10. The Baddeley-Hitch model: Pu ng the “work” in working memory..... The Baddeley-Hitch (abbreviated B-H) model of memory is in part a “response” to the shortcomings of the earlier Modal Model. Baddeley and Hitch conducted further work to try to find out more about the underlying nature and func ons of STM (see the Memory textbook chapter 3 for the details) The new and more complex model was of working memory, and assumes that intermediate maintenance and manipula on of informa on is necessary for many complex tasks, such as adding digits in one’s head.
3/21/12 Intro to Cognitive Science 15 10. The Baddeley-Hitch model: Pu ng the “work” in working memory..... In Alan Baddeley’s own words, “The emphasis on ‘working’ aimed to dissociate it from earlier models of STM, which were primarily concerned with storage, and to emphasize its func onal role as a system that underpins complex cogni ve ac vi es, a system that supports our capacity for mental work and coherent thought” (Memory, Ch 3, p43). This more complex and ac ve view of memory as enabling mental work is one contradicts the way that we o en treat memory in everyday speech-- as a sta c photo album or filing system. 3/21/12 Intro to Cognitive Science 16 11. The Baddeley-Hitch model of memory The B-H model (Baddeley, 2003): - modified and updated several mes, remains a widespread and useful explanatory tool. - different components for different types of informa on, unlike earlier Modal model. More typically called the mul component theory The components connect to one another as shown. - Arrows indicate in which direc ons informa on can move. 3/21/12 Intro to Cognitive Science 17 12. The B-H model components The components are : 1. A phonological loop for processing and encoding verbal and auditory informa on 2. The visuo-spa al sketchpad for processing/encoding visual and spa al informa on 3. A central execu ve as an “a en onal controller” to direct the “work” performed by working memory. As we discussed in the a en on unit more generally, this controller selects, manipulates, and switches between pieces of informa on. 4. A mul -dimensional episodic buffer which enables the WM subcomponents to communicate with LTM 5. LTM as a “crystallised” system of long-term knowledge. We will not discuss this part of the model further.
3/21/12 Intro to Cognitive Science 18 13. The phonological loop Component of the B-H model which temporarily stores speech or verbally encodable informa on The phonological loop is composed to two subcomponents: - A short-term store of limited capacity - An ar culatory rehearsal process which repeats (rehearses) informa on to maintain it in memory Informa on goes into this store if… • It is from speech that we physically hear • It is “read out” from a short-term memory trace - For instance, sub-vocally rehearsing an item. This is essen ally re- entering it in the loop again! • You see visual informa on but remember by “saying it to yourself” (digits, le ers, nameable objects)
3/21/12 Intro to Cognitive Science 19 14. For which phenomena can the phonological loop account? 1. The phonological similarity effect • People show poorer recall for a list of similar sounding items • Has been suggested that these individual items may have few dis nguishing features and are easier to confuse
3/21/12 Intro to Cognitive Science 20 2. The word length effect
- Verbal memory span decreases as participants are asked to recall longer words (shorter words are easier) - Suggested that this is because each word takes more time to rehearse in the phonological loop and to recall - A robust and well- replicated finding!
3/21/12 Intro to Cognitive Science 21 15. The visuo-spa al sketchpad This store is responsible for image-based informa on, and is also subject to memory span limits. Appears to consist of two subsystems which work closely together to hold and manipulate informa on • Memory for objects and their features (what) • Memory for spa al loca ons (where) Note the similarity of this dis nc on to the organisa on of the visual system! Special tasks have been devised to selec vely study one aspect or the other, see textbook
3/21/12 Intro to Cognitive Science 22 15. The visuo-spa al sketchpad - task One illustra on of a span limit on the sketchpad is visual pa ern span (Della Sala et al. 1999) - Par cipants are shown matrices with some cells shaded in, required to recall them - Matrices start small (2x2) and are increased in size un l par cipant’s recall span is reached
3/21/12 Intro to Cognitive Science 23 16. A new addi on: the episodic buffer The original B-H model struggled to explain interac ons between working and long-term memory. The episodic buffer suggested as addi onal component to link memory subsystems with percep on and LTM input/output • A mul -dimensional (mul -modal) space • Streams of informa on from various modali es such as sound, imagery are bound into objects, scenes, and other meaningful units Binding is the process of linking individual features into objects • Also can apply to crea ng a meaningful sentence out of words • This module could explain the memory span finding that we can remember twice as many words in a sentence as we can individual, unrelated words. 3/21/12 Intro to Cognitive Science 24 17. The central execu ve: `Control Tower’ for memory Central Execu ve is an a en onal controller: a en on crucial for deeper processing of informa on, and for binding different types of informa on together. • The execu ve selects which possible pieces of informa on to manipulate (the “work” in working memory!) • Switches between tasks (not necessarily a func on specific to the memory system) • Is finite - its func ons and the informa on it manipulates are limited by a en on. Resources are finite, and processing has an associated cost. Many of these func ons discussed more generally in the a en on unit and reappear in other cogni ve topics. The central execu ve as a director of mental work is an important concept with far-reaching implica ons outside of memory.
3/21/12 Intro to Cognitive Science 25 18. Back to the big picture of the Baddeley- Hitch model 1. Phonological loop for speech or any informa on that can be verbally encoded and rehearsed 2. Visuo-spa al sketchpad for image informa on, objects and features, spa al loca ons/rela onships 3. Central execu ve for selec ng and controlling informa on flow 4. Episodic buffer for addi onal mul - dimensional storage and binding informa on 5. Long-term memory for prolonged storage of declara ve and non- declara ve informa on
3/21/12 Intro to Cognitive Science 26 References Course materials Memory (Baddeley, Eysenck, & Anderson, 2009) Other references The magical number seven, plus or minus two (Miller, 1956) Working memory: looking backward and forward (Baddeley, 2003) An experimental inves ga on of memory span (Brener, 1940) Seven plus of minus two: A commentary on capacity limita ons (Shiffrin & Nosofsky, 1994) Human memory: A proposed system and its control processes (Atkinson & Shiffrin, 1968) Working memory (Baddeley & Hitch, 1974)
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