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Chapter 5: Short-Term & Working Memory
THE IMPORTANCE OF MEMORY
• 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. This “mental time travel” can
allow re-experience of events that occurred long ago, but also to guide our future behaviour and to use
skills in new circumstances.
• Memory needed for labeling familiar objects (known from past interactions with them), having
conversations (to keep track of its flow), knowing what to do in a restaurant (a schema for a situation),
• Clive Wearing: Viral encephalitis destroyed the hippocampi and parts of temporal lobe, so he now only
lives within the most recent 1-2 minutes of his life due to an inability to form new memories: no past to
anchor and no future to conceive of with moment-to-moment consciousness
• Modal Model of Memory (Atkinson & Shiffrin): Stages are called structural features.
o 1) Sensory Memory is an initial stage that holds all incoming information for seconds
o 2) Short-Term Memory (STM) holds 5-7 items for 15-30 seconds
o 3) Long-Term Memory (LTM) holds a large amount of information for years or decades
• Control processes are active processes controlled by the person to shape memory. For example,
rehearsal with repeating a stimulus over and over helps hold information in the short-term memory.
Other examples include strategies to make a stimulus more memorable, such as mnemonics, or
strategies that help you focus on information
that is particularly important or interesting.
• Encoding involves storing information
from short-term into long-term memory;
alcohol interferes with this process
(Korsakoff’s in chronic alcoholism due to
• Retrieval is the process of remembering
information in LTM, which involves bringing
that to consciousness in STM.
• Sensory Memory: The retention, for brief periods of time, of the effects of sensory stimulation (large
The Sparkler’s Trail & the Projector’s Shutter
• Persistence of Vision: The trail of the sparkler is not created by light “left” by the sparkler in the air, but
is a creation in one’s mind which retains a perception of the sparkler’s light for a fraction of a second.
• Similar with films which flash an image 24 times per second, but the brief period of darkness between
images is not perceived.
Sperling’s Experiment: Measuring Capacity & Duration of the Sensory Store
• Sperling: How much information can people take in from briefly presented stimuli?
• Flash array of letters on the screen for 50 milliseconds, then whole report method where subjects are
asked to report as many letters as possible from the whole matrix; average 4.5 out of 12 letters (37%). Page 116-142, 26 pgs Page 2 of 9
Was this because participants only saw 4.5/12, or was it because the perceptual memory faded rapidly
as they were reporting?
• Partial Report Method: Flashes matrix for 50ms as before, but immediately after a tonal cue is
sounded to indicate which row of letters the participants were to report – high-pitched for top row,
medium for middle, low-pitched for bottom row. Since the tones are presented after the letters are turned
off, attention is directed to the memory of the letters. Average report of 3.3/4 letters regardless of row
• Based on this, conclude that subjects see around 82% of letters in
whole display, but fail to report all of them because the sensory
memory fades during reporting.
• Delayed Partial Report Method: Presentation of tonal cues
delayed for a fraction of a second after the letters were extinguished
to determine time course of fading.
• With delay of 1 second, only report 1/row (or 4 for the whole
matrix). Plot of percentage of letters available from the whole display
as function of time following presentation of display.
• Short-lived sensory memory registers all or most of the information
that hits the visual receptors, but this iconic memory/visual icon
decays within less than a second.
• Echoic memory of the persistence of sound sensory memory lasts
for a few seconds after stimulus presentation
• Sensory memory is important for collecting large amoutns of
information to be processed, holding information briefly during initial
processing, and filling in the blanks when stimulation is
Special Memory Abilities
• Eidetic Memory (Photographic): Anecdotal evidence
by Charles Stromeyer, claimed to have found a subject
Elizabeth with photographic memory. Show right eye a
noise image, then show left eye another noise image the
next day; claimed she could fuse the two in mind’s eye for
• Savantism: Individuals with special abilities, e.g. Daniel
Tammet can recite pi to over 22,000 digits.
• Synesthesia: Stimulation of one sensation or cognitive pathway automatically stimulates another
unrelated pathway, perhaps due to lack of complete pruning of sensory cross-wiring remaining from
development. E.g. Tammet has number-shape synesthesia.
• Short-Term Memory (STM) is involved in storing small amounts of information for a brief period of
time; attention decides what from sensory memory is transferred to STM. Most of this is eventually lost,
with only some reaching the more permanent long-term memory.
• STM is our window on the present, everything we think about or know at a particular moment
• Recall Test: Subjects are presented with stimuli and then, after a delay, are asked to remember as
many of the stimuli as possible. Memory performance is measured as percentage of the stimuli
remembered, e.g. 3 of 10 items is 30% recall. These responses are analyzed to determine if there is a
pattern to the way items are recalled, such as whether items are grouped. Page 116-142, 26 pgs Page 3 of 9
• This is in contrast to measuring recognition, where people are asked to pick an item they have
previously seen or heard from items that are new to them. These are mostly used to test LTM.
What is the Duration of Short-Term Memory?
• Brown & Peterson: Subjects are told a series of trigrams and a number. They must repeat the number
and begin counting backwards by 3s from that number, e.g. “ABC 309” must count 309, 306, 303, etc.
Until the experimenter says “Recall”, the subject must immediately stop counting and say the three
• Counting out loud prevents the subject from rehearsing the letters.
• Subjects are able to remember 80% of the letters after counting for 3 seconds, but only 12% after 18
seconds. Memory trace decays due to passage of time after hearing the letters?
• However, if consider performance on just the first trial, little decay between 3s and 18s delay Why
would memory become worse after a few trials?
• Proactive Interference (PI): Interference when information previously learned disrupts the learning of
new information, especially if the new info is similar to the old one – recalling early letters in the list
creates interference for later letters.
• Due to this constant interference, effective duration of STM without rehearsal is 15-20 seconds
What is the Capacity of Short-Term Memory?
• Digit Span: The number of digits a person can remember, tested by the longest string of numbers one
is able to reproduce without error. Typical digit span is between 5 and 9 digits (Miller suggested this as 7
• Luck & Vogel (1997): Measure capacity of STM by
flashing two arrays of coloured squares separated by a
brief delay. The subject must indicate whether the second
array was the same as or different from the first (where
colour of one square is changed).
• Performance perfect with 1-3 squares in the array, but
decreased with 4 or more squares. Perhaps STM capacity
is only 4 items.
• Chunking: Small units are combined into larger
meaningful units, such as words into phrases, or even
sentences and stories. A chunk is a collection of elements
strongly associated with one another, but weakly
associated with elements in other chunks. For example,
ringtail is associated with monkey, but not child or city.
• Chunking increases our ability to hold information in STM, increasing memory span to 20 words or
more. E.g. Two lists with the same letters, but in the second arranged to names of familiar organizations
like CIA or NBC
• Ericsson (1980): Subject S.F. with typical memory span of 7 digits can, after extensive 230 hours of
training, repeat sequences of up to 79 digits without error. This was achieved by using chunking to
recode the digits into meaningful sequences, e.g. 2801201416001730 into 28/01/2014/16:00-17:30
• Chase & Simon (1973): Show chess players arrangements of chess pieces from actual games, for 5
seconds, and then asked to reproduce the positions. A chess expert places 16/24 pieces correctly,
compared to 4/24 for a novice on first trial, and only requires 4 trials to reproduce all positions correctly
instead of >7 trials. Page 116-142, 26 pgs Page 4 of9
• However, the chess experts do not have more highly developed STM for randomly arranged chess
pieces – perform just as poorly. The advantage was due to ability to group chess pieces into meaningful
chunks, having top-down knowledge and experience from patterns played in real chess games.
How is Information Coded in Short-Term Memory?
• Coding: How information is presented. Physiological approach to coding determines how a stimulus
is represented by the firing of neurons (more reductionist). Mental approach to coding determines how
a stimulus is represented in the mind, including auditory, visual, or semantic.
• Auditory Coding involves representing items in STM based on their sound.
• Conrad (1964): Subjects see a number of target letters flashed briefly on a screen, and must write them
down in the order presented. Errors were most likely due to misidentification of the target letter with
another that sounded like the target, e.g. “F” misidentified as “S” or “X” instead of “E” that looks similar.
• Conrad concluded that the code for STM is auditory rather than visual, perhaps due to auditory
• Visual Coding involves representing items visually, such as the details of a floor plan or streets on a
• Sala (1999): To test recall of visual patterns, subjects look at a figure for 3 seconds, then indicate which
of the squares in another figure must be filled in to duplicate the previous
figure. This depends on visual memory as patterns are difficult to code
verbally. Subjects can complete patterns of an average of 9 shaded squares
before making mistakes.
• Why is this number so much higher than the 4 from previous studies? Ability
to combine individual squares into subpatterns as an example of chunking.
• Semantic Coding: Representing items in terms of their meaning.
• Wickens (1976): Subjects are presented with words related to either fruits or professions. They listen to
the three words (e.g. banana, apple, peach), count backwards for 15 seconds, and then attempt to recall
the 3 words. They do this for 4 trials with different words on each.
• Attempt to create proactive interference by presenting words in a series of trials from the same
category (trial 1 above, trial 2 with plum, apricot, lime). Indeed, performance drops from 86% on trial 1 to
trials 2, 3, and 4 as more fruit names are presented.
• As with fruits, performance is high on trial 1 for professions group, and then drops due to interference.
But if fruits are presented on trial 4, proactive interference is reduce (release from proactive
interference) so performance improves. This release occurs depending on the word categories, and
therefore meanings – semantic coding
• STM is mainly described as a short-term storage mechanism, but STM information needs to be
transferred into LTM and then back again to be used.
o A better model of STM needs to consider dynamic processes that unfold over time for info
o It is also possible to hold one piece of information in one’s mind while carrying out another task.
STM must consist of a number of components that can function separately.
o STM is to random access memory (RAM) in a computer as working memory is to the central
processing unit (CPU) responsible for computation and manipulation of information. Page 116-142, 26 pgs Page 5 of9
• Working memory problems associated with: Alzheimer’s disease, Parkinson’s disease, schizophrenia,
depression, ADHD, etc. with cognitive impairments
Baddeley’s Working Memory Model
• Baddeley: Working Memory is a limited-capacity system for temporary storage and manipulation of
information for complex tasks such as comprehension,
learning, and reasoning.
o STM is concerned mainly with storing
information for a brief period of time, while working
memory is concerned with the manipulation of
information that occurs during complex
o STM consists of a single component, while working memory consists of a number of
• Phonological Loop: Consists of the phonological store which has a limited capacity and holds
information for a few seconds, and the articulatory rehearsal process responsible for rehearsal that
keeps items in the store from decaying. This holds both verbal and auditory information, e.g.
remembering a phone number.
• Visuospatial Sketch Pad: Holds visual and spatial information, such as forming a picture in one’s mind
or finding your way around campus.
• Central Executive: Pulls information from long-term memory and coordinates the activities of the
phonological loop and v