The Mind And Brain Of Short Term Memory

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  • 1. The Mind and Brain of Short-Term Memory John Jonides, Richard L. Lewis, Derek Evan Nee, Cindy A. Lustig, Marc G. Berman, and Katherine Sledge Moore Annual Review of Psychology
  • 2. Outline
    • What is the structure of short-term memory?
    • What processes operate on the stored information?
    • Why do we forget?
  • 3. What is the structure of short-term memory?
    • Multi-store Models
    • The evidence of Unitary-Store Models
    • Focus capacity of attention
    Outline
  • 4. Multi-Store Model
    • Model of STM developed by Baddeley
    • STM are separate from LTM
      • Phonological Loop
      • Visuospatial sketchpad
      • Recently proposed Episodic buffer
      • Central executive
  • 5. Evidence for Multi-Store Model
    • Studies of brain-injured patients in STM but not LTM or vice versa
      • Parietal and temporal lob damage-> impaired STM
      • Medial temporal lob(MTL)damage-> impaired LTM
  • 6. Mixed Result of Neuroimaging Data
    • Healthy subject
    • Metaanalysis comparing regions activated during verbal STM and LTM tasks -> great deal of overlap in neural activation in the frontal and parietal lobes
    • Three studies that directly compared STM and LTM DID reveal some regions selectively for each memory system
    • Yet, only one found MTL was uniquely activated for LTM
  • 7. Evidence for separate buffers in STM
    • A series of studies of selective interference
      • Verbal tasks interfered verbal STM but not visual STM or vice versal
    • The result of neuroimaging
      • Verbal STM shows a marked left hemisphere preference
      • Spatial and object STM can be distinguished mainly by a dorsal versus ventral separation in posterior cortices
  • 8. Evidence for separate storage and executive processes
    • Support by both lesion and neuroimaging data - Patients with frontal damage have intact STM under conditions of low distraction; when distraction is inserted, they show significant memory deficits
    • A metaanalysis of 60 functional neuroimaging study
      • Increased demand for executive processing recruit dorsolateral frontal cortex and posterior parietal cortex
      • Storage processes recruit predominately posterior areas in primary and secondary association cortex
  • 9. Evidence for Unitary-Store Model
    • The role of MTL
      • Ranganth & Blumenfeld(2005) have summarized evidence showing MTL is engaged in STM tasks
      • Growing evidence show a critical function of the MTL is to establish representations involving novel relations
  • 10.
    • Examine the past behavioral data about the distinction between STM and LTM
      • Patients with LTM deficits but intact STM also show deficits in situations requiring STM for novel relations
      • The case of patient s with perisylvian cortical lesions who are often claimed to have selective deficits in STM; This deficits may be substantially perceptual
  • 11. History of unitary-store models
    • Perhaps, the first formal proposal that STM consists of activated long-term representations was by Atkinson & Shiffrin(1971, but also Hebb 1949)
    • First detailed computational treatment by Anderson(1983)
    • Revived and greatly developed by Cowan(1988,1995,2000), McElree(2001) , Oberauer(2002), Vehaeghen et al.(2004), Anderson et al.(2004), and others
  • 12. Architecture of unitory-store models
    • The shared assumption of these models is that STM consists of temporary activation of LTM representations or of representations of items that were recently perceived
    • These models differ from each other in specifics, but Cowan’s model is representive
      • According to this model, There is only one set of representations of familiar material─the representation in LTM
      • These representations can vary in strength of activation
  • 13. Different interpretation of frontal cortical involvement in STM
    • Early work showed a importance of frontal cortex for STM, which was first seen as support for multi-store model
      • EX. Single-unit activity in dorsolateral prefrontal cortex regions(princiiple sulcus, inferior convexity) that was selectively responsive to memoranda was interpreted as evidence that these regions were the storage sites for STM
  • 14. Another interpretation to the experiment
    • The result does not necessarily mean that region is a site of STM storage
    • Many other regions of neocortex also show activation during the physical presence of a stimulus and provides possible neural basis for STM representations
    • There are increasing evidences suggesting that frontal activations reflect the operation of executive processes [including keep the representations in focus of attention]
  • 15.
    • And, modeling work and lesion data provide further support for the idea
      • The representations used in both STM and LTM are stored in those regions of cortex that are involved in initial perception and encoding
      • The frontal activations reflect processes involved in selecting this information for the focus of attention and keeping it there
  • 16. About information-specific buffers
    • This concept is used in Multi-store model, but unitary-store model also allow this
      • Separate resources(Cowan 2000)
      • Feature components(Lange & Oberauer 2005, Oberauer & Kliegl 2006)
    • Posterior regions are clearly differentiated by information type (e.g., auditory visual spatial)
    • And for unitary-store model, these information-specific properties occur at lower levels of perception and representations
  • 17. Controversies over capacity
    • STM capacity is a prominent issue for both multi-store model and unitary-store model
    • To unitary-store models, capacity is the limit that how many number of items can be activated in LTM, which can also thought of as the bandwidth of attention
    • Many unitary-store models differ in this bandwidth
  • 18. The classic seven plus or minus two
    • Is an overestimate
      • Because it is based on studies that allowed participants to engage in processes of rehearsl and chunking
      • Reflected contributions of both the focus and LTM
  • 19. Magic number 4
    • Cowan(2000) suggested a limit of approximately 4 items based on performance discontinuities
    • Early behavioral evidence came from studies showing sharp drop-offs in performance at 3 or 4items on short-term retrieval
      • is criticized that the limit might reflect output interference occurring during retrieval
  • 20.
    • Additional evidence came from change-detection and other tasks without serial recalls ----- Ex. Luck & Vogal(1997)
    • Electrophysiological and neuroimaging studies supporting this idea of 4-item capacity limit.
      • Vogal & Machizawa(2004)
        • ERPs
        • Signal plateaued when when array size reached between 3 and 4 items
      • Todd & Marios(2004,2005)
        • fMRI
        • Similar load- and accuracy-dependent activations in intraparietal and intraoccipital sulci
          • This regions have been implicated by others(e.g., Yantis & Serences 2003) in the control of attentional allocation
  • 21. Evidence for more severe limits
    • Another set of researchers thought the focus capacity should be 1
      • Study by Garavan(1998) show that only one internal counter can be held(focused) in STM at a time
      • Study by McElree(1998) using a speed-accuracy tradeoff procedure
  • 22. Compromise solution to the 1 vs 4 debate
    • Proposed by Oberauer(2002)
      • Up to 4 items can be directly accessible, but only 1 of these items can be in the focus of attention
      • Similar to the model of Cowan(2000),but add an assumption that an important method if accessing STM is to focus attention on one item, depending on task demands(The mechanism to attend to several items is to Change focus of attention among temporarily activated representations in LTM serially )
  • 23. Alternatives to limits based on number of items
    • Object complexity and similarity play an important role in determining capacity
    • The reason why some other researchers disagree with fixed item-based limits is that They have demonstrated the limits is mutable
  • 24. Summary
    • STM an LTM are identical
      • The same neural representations initially activated during the encoding of imformation
    • Memory in STM consists of items in the Focus of attention in LTM
    • These items in the focus of attention number no more than 4, and may be limited to just a single representation