Shortterm and Working Memory 1 Definition of memory

Short-term and Working Memory 1

Definition of memory • The processes involved in retaining, retrieving, and using information about stimuli, images, events, ideas and skills after the original information is no longer present. • Important implications of this definition: – Memory includes learning – Memory involves a variety of processes that can function with autonomy 2

Importance of memory • Obviously being able to remember past experiences and learned skills is important for ability to make decisions, etc. in the present • Memory also important in predicting the future. Much of what we know about the future results from our knowledge of the past 3

Stage theory of memory • External sensory short-term long-term stimuli memory • Attention and sensory memory covered in the previous section • Now we turn to the study of short-term memory (STM) and then later to the more encompassing working memory 4

Limited capacity of. STM • Miller (1956) proposed the magic number 7 + 2 • We can only receive, process, and retrieve approximately 7 pieces of information at a time • His study asked people to recall in order lists of numbers of varying length 5

Overcoming this limitation • Chunking – organizing or grouping individual pieces of information into a single “chunk” • 18005551212 • 1 -800 -555 -1212 • Today referred to as recoding 1, 8, 0, 0 is recoded as 1 -800. 4 pieces of information is recoded into 2 pieces 6

Recoding • Recoding can occur in STM if there is the time and mental resources available to reorganize the information • Using long-term memory to recode information – mnemonic devices – Using a well learned strategy to recode information – An example is verbally recoding information because language usage is over learned 7

How accurate is this magic number 7+ • It is accurate for relatively simple information groups digits, words, etc. • Not as accurate for more complex information – Example: with 3 or 4 word phrases the magic number becomes 3 to 5 8

Decay from STM • Brown-Peterson task: – Subjects shown three letters and then a 3 digit number – Subjects told to count backwards from the number given by 3’s until asked to recall the letters – Counting backwards prevented the rehearsal of the letters – Results: • 3 second delay – little over 50% retained • 9 second delay – little over 20% retained • 18 second delay – less than 10% retained 9

Interpretation of Brown. Peterson • Memory loss in STM is the result of decay; “the memory trace decays” without rehearsal • STM different than long-term because it was believed that forgetting in long-term memory results from interference 10

Can intereference occur in STM? • Could the counting backwards have actually interfered with memory – not just preventing rehearsal • Reexamination of Brown and Peterson data (Keppel and Underwood (1962)) • Waugh and Normal (1965) – Was the memory loss the result of the passage of time- more loss as more time passed Or was increasing the amount of counting backwards interfering with retention? 11

Keppel and Underwood (1962) • They saw that on the first trial, memory performance was nearly perfect • As subjects participated in more trials their performance declined • Their conclusion: previous trials interfered with later trials – proactive interference 12

Release from proactive interference • Changing the nature of the items to be remembered reverses the decline in performance due to proactive interference • Wickens et al, 1963 – Two groups of subjects given 3 trials following the Brown. Peterson task (letters) - Memory performance declined with each trial – Control group given a 4 th trial using letters – Experimental group switched to remembering digits – Experimental group, but not control group, performed perfectly; they were released from proactive interference 13

Waugh and Norman (1965) • Subjects verbally presented with lists of 16 digits – some lists were presented at a rate of 1 digit per second others at 4 digits per second • The last digit was the repeat of an earlier digit. Subjects asked to write down the digit that followed the earlier digit. 4, 2, 6, 8, 9, 2 correct answer is 6 14

Waugh and Norman (1965) • One group of lists took 16 seconds to present the other group took 4 seconds • If decay causes loss of information from short-term memory, the 16 second group should remember less because more time would have passed before they responded • Problem for decay theory was there was no difference between groups. With no interference performance was the same 15

New decay theory • Interference theory appears to fit the data better than decay theory • Active decay in a special situation – subjects switch from one task to another and must “forget” the previous instructions 16

Altmann and Gray (2002) • Subjects shown one number at a time 1, 2, 3, 4 or 6, 7, 8, 9. • 1 group of trials asked is the number odd or even? • 2 nd group of trials asked is the number from the group of large numbers or small numbers? • One group of subjects were switched very frequently, the other infrequently • Frequently switched group had faster reaction times and were more accurate • Conclusion: forgetting previous decision rule was faster in this group because they needed to remember the new rule – old info actively decayed 17

Recall and the serial position effect • Present subjects with a list of 20, 30 or 40 items 1 every second, and ask them to recall them in order. • Primacy effect – more of the 1 st items presented are remembered • Recency effect – more of the final items are remembered • 1 st items rehearsed long enough to get in long -term memory; last items still in STM 18

Recall and the serial position effect II • Glanzer and Cunitz (1966) • Same study except subjects told to count backwards after list given – Recency effect disappeared, not primacy • Glanzer (1972) • Again same study except subjects given 3, 6, or 9 seconds between each item – longer to rehearse – Increase in primacy effect, no increase in recency 19

Purpose of STM • Rehearsal important part of STM – Rehearsal maintains a memory trace for a short period of time – Rehearsal helps transfer information from STM to LTM 20

Retrieving information from STM • Donder’s reaction time studies – 1880’s • Subtractive tasks – A - a simple reflex – see light-push button – B – decision + reflex – see blue light- push button – see red light don’t push button – C – decision + choice + reflex – see blue light push button 1 – see red light - push button 2 – How long does it take to make a decision? • Subtract time to perform A from time to perform B 21

Sternberg Task • Problem with Donder Subtractive tasks – there could be an interaction between A and B such that the reflex might not be the same with the decision as when it is alone • Sternberg invented an additive task 22

Sternberg Task (cont. ) • Subjects shown a list of letters ranging from 1 letter to 6 letters, then shown a single letter as a memory probe. • They were to respond as quickly as possible indicating if the letter was in the list or not • Reaction time was recorded • Two important variables were involved – The number of letters in each list – The location of the letter in the memory probe – in the beginning, middle, or end 23

Sternberg Task (cont. ) • Three possible results: – STM is searched in a parallel fashion – if true then length of list or location should have no effect – STM searched in a serial fashion, we search until we find the letter – both length and position important – All of STM is searched and then we make a decision, a serial exhaustive search – length would have an effect location in the list would have no effect 24

Results of Sternberg Task • Results: – 1 letter list - 37. 9 ms – 2 letter list – 75. 8 ms – Each additional letter increased reaction time by 37. 9 ms – Location of the letter in the list or if the letter not in the list had no effect • Conclusions: we scan all of STM before making a decision • Many limitations found to this research, but it led to major advances in cognitive sciences 25

Coding information in STM • Baddeley (1966) – information coded acoustically or verbally – Subjects asked to remember either a 5 word list or a 10 word list – Remembering 5 word list STM; 10 word list exceeds STM and is LTM – In all lists, the words either sounded alike (cat, hat, cat) had similar meanings (tiny, small, little) or were unrelated 26

Baddeley (1966) • Results: – 5 word list errors – most errors were made when words sounded alike – house instead of mouse. Fewer errors on lists with similar meaning or unrelated – 10 word list most errors with semantically similar words – labor instead of work • Conclusion: Similar sounding words confused in STM because memory code was acoustic. Semantically similar words confused in LTM because memory code was using meaning 27

Wickens (1972) – Release from proactive interference • Proactive interference occurring as a result of semantic coding in STM • 5 groups of subjects given 3 trials of lists of 3 words each all from the same category – – – Group 1 – names of fruit Group 2 – vegetable names Group 3 – flower names Group 4 - names of meats Group 5 – names of different professions • Then all groups given a 4 trial where all list contained names of fruit 28

Wickens (1972) – Release from proactive interference • Results: – – 1 st trial all groups about 90% correct 2 nd trial all groups about 50% 3 rd trial all groups 35 – 45 % 4 th trial professions 80%, meat 50%, flowers 47%, vegetables 40% and fruit 32% • Conclusion: Information was coded using semantic information causing groups to confuse current list with previous lists 29

Visual coding in STM • Mental rotation task of Shepard and colleagues • Subjects shown 2 objects and asked if they were the same or different in different orientations • Interpretation people held the 1 st figure in STM and mentally rotated the 2 nd to make a comparison – Objects were either different or the same but rotated to a different orientation – Subjects took longer to answer when the object had been rotated further 600, 900, 1200 30

Working memory • Developed as a result of STM memory not being useful in explaining how short term memory processes were used in problem solving • Also finding that some people with brain damage can have impaired STM – a digit span of only 2 items, but no deficits in learning, comprehension, or memory 31

Components of working memory • Executive control system – planning, initiating, and integrating information – high cognitive abilities • Two subordinate systems: – Articulatory or phonological loop – rehearses verbal information – auditory and semantic coding – Visual-spatial sketchpad – maintains images and spatial representations – visual coding 32

The working memory process • Central executive gives subordinate systems information to hold until it needs it again • Example in textbook: – (4 + 5)2 3+ (12/4) Central executive does (4+5) 2 = 18 sends answer to articulatory loop to remember while it calculates 3+(12/4) = 6 It then retrieves 18 to calculate 18/6 = 3 33

Limited capacity of working memory • The subordinate systems have few attentional resources; when they are involved in a demanding task they must get resources from central executive • These resources are limited • Creates the concept of dual tasks – two tasks being performed at the same time • The validity of working memory can be tested using dual task methods 34

Dual task studies • Subjects given reasoning tasks of varying complexity – performed by the central executive • Then asked to perform different secondary tasks that were similar in articulatory demands but whose memory requirements differed • It was found that the most complex reasoning tasks were most effected by secondary tasks that required the most memory resources • As the articulatory loop took more resources from the central executive, it found solving the complex reasoning tasks more difficult 35

Other supporting data for working memory • 8 -arm maze • Neuropsychological evidence – Damage to areas of the left frontal lobe creates deficits in verbal working memory – Damage to areas of the left frontal lobe creates deficits in spatial and visual working memory – PET scans have shown that the Dorsolateral prefrontal cortex is most active when working memory task are performed, same left and right distinction 36