1. Early theories for short-term memory (STM)
    1. Waugh and Norman's (1965) two-store model
    2. Atkinson and Shiffrin's (1968) model
    3. Critics of the two-store model: STM was considered as a unitary system
  2. Tracking mental work on-line
    1. single cell activity: Fuster and Jervey (1981), see Fig. 3-1, 3-2
      1. delayed matching-to-sample paradigm
      2. recorded from inferior temporal cortex of monkeys
      3. found increased electrical activity in specific neurons implicated in visual processing
      4. interpreted the increased activity as a reflection of mental work necessary to retain the information of the sample stimulus
  3. Multiple-component model of working memory: Baddeley's working memory model
    1. Definition: the term working memory refers to a system that has evolved for the short term maintenance and manipulation of information necessary for the performance of such complex tasks as learning, comprehension and reasoning.
    2. three components, each fulfilling specific functions, see Fig. 3-3
      1. phonological loop
        1. concerned with auditory and speech-based information
      2. visuospatial sketchpad
        1. maintains and manipulates visual and spatial information
      3. central executives
  4. Evidence comes from different lines of research
    1. case studies
    2. dissociations observed in dual-task studies
    3. neuroimaging research
  5. Case KF
    1. Described by Warrington and Shallice (1969)
    2. A victim of a motorcycle accident
    3. injury to the left parieto-occipital region
    4. Severe limitations of verbal STM
    5. No recency effect in free recall learning
    6. Could not remember > 2 digits
    7. HOWEVER, able to acquire new information for the long term
  6. Experimental dissociation: Lee R. Brooks (1968), see Fig 3-4, 3-5
    1. Rationale of the duel task technique
      1. two tasks to be executed concurrently
      2. if performance suffers, then the two tasks engage the same working memory component
      3. if performance remain intact, then the two tasks depend on different working memory components
    2. 2 x 2 factorial design: covaried the task (visual vs. verbal) and mode of response (visual vs. verbal)
    3. Visual task: visual imagery, Ss were asked to visualize a block letter, trace the letter mentally and indicate whether the letter has an outside or inside corner.
    4. Verbal task:
      1. memorizing sentences such as "A bird in the hand is worth two in the bush"
      2. think of the sentence word by word and indicate for each whether it was a noun.
    5. Found dissociation between the two tasks, suggesting two separate components of working memory
      1. the visual response was faster in the verbal task
      2. the verbal response was faster in the visual task
    6. Support the distinction between the phonological component and the visuospatial sketchpad.
  7. Neuroimaging studies for working memory
    1. Delayed response paradigm combined with neuroimaging or single-cell recordings.
    2. Friedman and Goldman-Rakic (1994), spatial task
      1. Recorded blood-flow activity from monkeys trained to remember the location of stimuli on the screen for a brief interval.
      2. During the interval, PET activity increased in the prefrontal cortex and inferior parietal cortex.
      3. The greater the accuracy of the monkeys in remembering the stimuli, the greater was the brain activity
    3. Cohen et al (1994), nonspatial task
      1. Human learners monitored letter sequences on a screen
      2. Press a key when a target letter was repeated, e.g., as in MXM as compared to MXB
      3. Prefrontal cortex became active as the Ss worked on the task
      4. The more the number of intervening letters, the larger area of the cortex was activated
  8. Jonides (1995)'s PET study on phonological buffer and visuospatial sketchpad, see Fig 3-6
    1. Two-back task (a phonological task)
      1. Ss see a sequence of individual letters (e.g. M P F P...) presented at a rate of one letter every 3 sec
      2. Ss make a yes response whenever a letter is shown that had occurred two positions back
      3. otherwise, no is the correct response.
    2. Dot-location task (a visual spatial task)
      1. presentation of three dots in different locations on screen for 200 msec
      2. followed by a blank screen for 3 sec
      3. test: an outline circle is presented on a location of the screen
      4. Ss must indicate whether the location was occupied by one of the dots of the previous screen.
    3. Neuroimaging revealed that
      1. the verbal task activated in several regions in the left hemisphere, in the frontal lobe, Broca's area, the parietal lobe
      2. the spatial task activated in several regions in the right hemisphere, in the frontal lobe, the parietal lobe and the occipital lobe.
      3. the PET data for the two tasks present a "clear dissociation between working memory for phonological and spatial information.
  9. Spatial vs. visual processes in visual spatial sketchpad, see Fig 3-7
    1. Smith and Jonides (1997): separate spatial and visual subsystems in working memory
      1. The target stimuli were two irregular objects located in random locations of the screen
      2. The probe stimulus consisted of a single object
      3. In spatial memory task, the Ss were asked whether the probe was in the same location as one of the target stimuli
      4. In visual memory task, the Ss were asked whether the probe had the same form as one of the target stimuli
    2. Although the stimuli and trial sequence were identical in the two tasks, neuroimaging results revealed a clear dissociation
      1. Given the spatial memory instructions, it was the right hemisphere that became active, esp. the prefrontal cortex, the premotor cortex, the occipital cortex, and the parietal cortex.
      2. Given the visual memory instructions, two regions in the left hemisphere were activated: the parietal cortex and the inferotemporal cortex
  10. The Central Executive
    1. Frontal lobe patients suffer from dysexecutive syndrome, this condition involves reduced control of behaviour and difficulty in coordinating action to meet a specific goal
    2. Wisconsin card sorting task, the patients are said to be susceptible to proactive interference, the inhibiting effects of prior learning on new learning
    3. angulate cingulate gyrus and stroop effect