Download Lecture 8 : Memory

Chapter 8
Memory
Memory is the process of maintain information over time. It is the most basic concept of human
cognition. We use memory in our everyday life as remembering an incident from childhood or some
event from the recent past. Memory helps us learn from our experiences. It is only when we remember
what has happened in the past we do not repeat the behavior again, or indulge in it more if it was
gratifying.
Memory is internal record of some prior event or experience; a set of mental processes that receives,
encodes stores, organizes, alters, and retrieves information over time. The basic processes of memory
are encoding, storage and retrieval. Encoding is the process of translating information into neural codes
that will be retained in memory. Information which is presented in the form of language is encoded in
the form of mental representations. Storage is the process of retaining neural coded information over
time. If any piece of information is stored properly it can be retrieved later. Retrieval is the process of
recovering information from memory storage. Retrieval failure is possible if the information is not stored
properly or is not accessed. Such retrieval failure is called forgetting.
MULTI STORE MODEL OF MEMORY:
Atkinson and Shiffrin proposed the modal model of memory. According to this model there are three
different kinds of memory namely, sensory memory, short term memory and long term memory. This
model assumes that each type of memory receives processes and stores information differently. The
sensory memory receives information from the sensory registers namely eyes, ears, nose, skin. Vast
amount of information is received from the sensory registers as it includes every object seen, heard or
felt in the environment. The information which is paid attention to in this stage enters the short term
memory. In short term memory or short term storage the information is stored for 20 to 30 seconds.
Short term memory has limited capacity and can store 5 to 9 bits of information at a time. If the
information is rehearsed and paid even more attention to enter the unlimited store of information called
the Long term memory also known as Long term storage. Information which is required to be known for
a longer period of time is stored in the long term storage. For example, spellings of words are stored in
Long term memory which can be retrieved with ease at any point of time.
SENSORY MEMORY:
Sensory memory is the memory for events from the sensory inputs which we encounter every now and
then in our surrounding. It is the raw material which forms the basis of any sort of memory stored by
the human mind. The two main types of sensory memory studied widely are, Iconic memory i.e.
memory for events or aspects which are visually encountered and Echoic Memory i.e. memory for
auditory information.
Iconic memory:
Sperling suggested that when stimuli consisting of a number of
items are shown briefly to an observer, only a limited number of the
items can be correctly reported. The fact that observers assert they
can see more than they can report suggests the memory sets a limit
on a processes that is otherwise rich in information. He conducted
the first experiment to understand the properties of iconic memory.
He presented the participants with display of letters or numbers
(figure 1). Letters were presented for a brief period of time, for 50
milliseconds. Sperling found that participants could recall 4 or 5
letters of the 12 letters presented.
Figure 1: Display used
by Sperling
He further extended the display time to 500 milliseconds but it did not improve the performance. He
then invented the partial report technique. After presenting the display the participants were presented
with a low, medium, or a high pitched tone. Low pitched tone indicated recalling the letter in the bottom
row, medium tone - middle row and high tone - upper row. Participants could recall 3 out of 4 items
from any row when presented with the tone. Sperling explained that in the initial display of recalling all
letters together, which he called the whole report technique, participants forgot the letter which came
letter in the attempt to name the initial letters. Even when they were recalling the display, the
information was fading from wherever it was being stored. This explains that information lasts only
briefly in this memory system.
Neisser gave the term ‘icon’ for the visual sensory memory. It holds the visual information for up to 1
second. Sperling presented participants with consonants and vowels and different tones for the recall for
either vowels or consonants. However the participant’s performance was no different than the whole
report technique. Sperling thus inferred that icon holds information that has not yet been categorized.
Echoic memory:
Neisser called the auditory sensory memory ‘echo’. Moray, Bates, and Barnett (1965) studied the echoic
memory in a clever demonstration. Participants were made to listen to multiple messages
simultaneously. In the whole report technique participants were made to recall all the letters they heard.
In partial report technique participant was visually cued to report letters spoken on the specific speakers
by presenting lights corresponding the speakers. Results of this study showed that a greater number of
letters could be recalled through the partial report procedure than whole report technique. Thus, they
concluded that one second after the auditory display, there is more information available than can be
reported by the whole report procedure. Information was lost after about 4 seconds.
Crowder (1982) studied the duration of the echo. He presented the participants with two vowels, one
after the other. Sometimes the vowels were identical and other times they were different but similar.
He used a Varied inter stimulus interval from 1/2 sec to 5 sec. The participants had to report whether
the letters were the same or different than what was earlier presented. The results of the study showed
that performance was most accurate where less than a second occurred between presentations reaching
asymptote at about 3 sec. He thus concluded that the duration of the echo is 3 seconds. Cowan (1984)
posited a short auditory store that decays in less than 1 sec and is pre categorical in nature.
Echoic memory is similar to Iconic memory in that there is more information accessible than can be
recalled. Echoic memory is different in that the trace lasts longer than a second
SHORT TERM MEMORY:
Short term memory Atkinson and Shiffrin proposed that information that had been attended to in the
sensory stores went into a short-term store (also called short-term memory). There are three key
aspects of short term memory:
It has limited capacity .i.e., only about 5 to 9 items can be stored at a time
It has limited duration i.e., storage is very fragile and information can be lost with distraction
or passage of time
Encoding in short term memory is primarily acoustic. It also translates visual information into
sounds.
Chunking is a phenomenon where participants group the information they are trying to remember.
Participants demonstrate "chunking" in serialand free recall tasks. Test items may be formed of words,
lists of letters ornumbers. Chunking is a process wherein responses based on the
items' semantic relatedness or perceptual features are made. The chunks are often meaningful to the
participant.
Capacity:
Miller’s (1956) Magic number 7 (plus or minus two) offersproof for the capacity of short term memory.
Most adults can store between 5 and 9 items in their short-term memory. He thought that short term
memory could hold 7 (plus or minus 2 items) because it only had a certain number of “slots” in which
items could be stored. However, Miller didn’t specify the amount of information that can be held in each
slot. Indeed, if we can “chunk” information together we can store a lot more information in our short
term memory.
Miller’s theory is provided evidence to by means of various studies, such as Jacobs (1887). He made use
of the digit span test with every letter in the alphabet and numbers. However he did not use the
alphabet “w” and the digit “7” because they had two syllables. The results of his study suggested that
people can recall numbers better than letters.
According to Atkinson and Shiffrin (1971), the duration of short term memory seems to be between 15
and 30 seconds. Items can be kept in short term memory by repeating them verbally (acoustic
encoding), and by means of rehearsal.
Peterson and Peterson (1959) showed that the longer the delay, the less information is recalled. They
used a technique called the Brown-Peterson technique which prevents the possibility of retrieval by
having participants count backwards from a digit for up to 3s. There was a rapid loss of information
from memory when rehearsal was prevented which is as an indication of short term memory having a
limited duration.
WORKING MEMORY:
Baddeley and Hitch (1974) developed an alternative model of short-term memory which they
called working memory. They argue that the picture of short-term memory (STM) provided by the
Multi-Store Model is far too simple. According to the Multi-Store Model, STM holds limited amounts of
information for short periods of time with relatively little processing. It is a unitary system. This means
it is a single system (or store) without any subsystems. Working Memory is not a unitary store.
Working memory is STM. Instead of all information going into one single store, there are different
systems for different types of information. In the diagram above, Short term memory is replaced with
working memory as proposed by Baddeley and Hitch.
Components of working memory:
1. Central Executive: The central executive, an important component of working memory model, is
hypothesized to be responsible for the selection, initiation, and termination of processing routines
(e.g., encoding, storing, and retrieving). Baddeley (1986, 1990) equates the central executive
with the supervisory attention system (SAS) described by Norman and Shallice (1980) and by
Shallice (1982). According to Shallice, the supervisory attention system is a limited capacity
system and is used for a variety of purposes, including:
tasks involving planning or decision making
trouble shooting in situations in which the automatic processes appear to be running into difficulty
novel situations
dangerous or technically difficult situations
situations where strong habitual responses or temptations are involved
Evidence of Central Executive:
Baddeley (1996) made participants randomly generate digits by pressing a keypad. The task was done
on its own or in combination with reciting the alphabet, counting from 1, or alternating numbers and
letters (A 1 B 2 C 3…). The randomness of the digits produced reduced for the alternating condition. The
interpretation was that the central executive is needed to constantly switch retrieval plans and so
disrupts performance
2. Phonological Loop: The area of the working memory that holds and processes auditory and
verbal information. The phonological loop has two components, the phonological store and
articulatory rehearsal system. The phonological store is short-term and holds information for
about 2 seconds before it begins to decay. The articulatory rehearsal component revives the
memory traces that have begun to decay.
Evidence of Phonological loop:
The word length effect. People can recall more items in free recall tasks that use short words
than in tasks that use long words. Baddeley et al (1975) showed that people can store as many
words as can be uttered in about 2 seconds. Performance is related to duration of utterance, not
number of syllables.
The unattended speech effect. Irrelevant concurrent speech inhibits recall. For example, Colle
and Welsh (1976): serial recall of visually presented numbers, accompanied by auditory
presentation of German language speech. This is explained by assuming that all auditory material
enters the phonological store and therefore the spoken German interferes with the recall task
The phonological similarity effect. Immediate recall of phonologically similar items is harder
than with dissimilar items. Explained by less distinction between similar phonemes in the
phonological store. Larsen et al. (2000) found that word lists like “FEE, HE, KNEE, LEE, ME, SHE”
were remembered 25% less than “BAY, HOE, IT, ODD, SHY, UP”
3. Visuo spatial Sketchpad: The visuospatial sketchpad or scratchpad (VSSP) is one of two
passive slave systems in Baddeley's (1986) model of working memory. The VSSP is responsible
for the manipulation and temporary storage of visual and spatial information.
Evidence of Visuo Spatial Sketchpad:
Baddeley et al. (1975) presented participants with details of the location of digits within a matrix.
Tracking a moving light disrupted theparticipants performance on visualised message but it was not
found to be the case the other way round.
4. Episodic Buffer: Episodic buffer was added to the theory of working memory much later
(Baddeley, 2000). It takes the modality specific information from the phonological loop and the
visuo-spatial sketchpad and combines them into a unitary multi-dimensional representation. The
main motivation for introducing this component was the observation that some (in particular,
highly intelligent) patients with amnesia, who presumably have no ability to encode new
information in long-term memory, nevertheless have good short-term recall of stories, recalling
much more information than could be held in the phonological loop.
Evidence of episodic buffer:
Papadopoulou & Wresinksi (1999) studied memory span for Arabic numerals and digit words (1, one).
They found that participants used both verbal and visual coding while performing the task. Information
from both the Phonological loop and Visuo-Spatial sketchpad were being stored together in working
memory.
LONG TERM MEMORY:
Long term memory is fundamental to nearly every mental process, to almost every act of cognition.
Long term memory is an enormous area of research with a long history. Squire (1986,1993) suggested
a taxonomy of long term memory. An overall distinction can be made between declarative or explicit
memory and nondeclarative or implicit memory. Declarative memory is a long term memory knowledge
that can be retrieved and reflected on consciously. The two kinds of declarative memory are episodic
and semantic memory. Episodic memory is the memory of personally experienced and remembered
events. Semantic memory is the general world knowledge. Nondelcarative memory also known as
procedural memory is knowledge that can influence thought and behavior without any necessary
involvement of conscious awareness. It consists of skills and habits which cannot be explicitly explained
priming, simple classical conditioning and non-associative learning.
These various parts of long-term memory do not operate in isolation from one another. While it is not
clear how they work together, it is clear that they are related and overlap. For example, a teacher who
is asked to write a letter of recommendation for a former student might wish to retrieve information
about the ability of that student compared to other students. To do this, she might first use episodic
memory to form an image of that student as a real person performing real activities in her class several
years ago, and this image might help her recall specific details of class performance and term papers
written by that student. Likewise, a college student writing a paper in a history course on mercantilism
might first listen to or read a semantic presentation on the topic, perform an episodic memory search to
recall instances in his own life when he himself experienced what the teacher was talking about, recall
the semantic definitions of related terms from another course, and continue this process until he felt he
could understand and integrate the new information.
There are two major problems related to the use of long-term memory: (1) to transfer the information
accurately to long-term memory and (2) to retrieve the information accurately. The primary strategy for
transferring information from working memory into long-term memory is referred to
as encoding or elaboration. These terms refer to the process of relating information to other information
that is already stored in long-term memory.
The key ingredient that facilitates long-term storage is meaningfulness. This term refers not to the
inherent interest or worthiness of information, but rather to the degree to which it can be related to
information already stored in our long-term memory. One concept or piece of information is more
meaningful than another if the learner can make a larger number of connections between that piece of
information and other information already in long-term memory.
Since meaningfulness is a critical factor in storing information, one of the most important strategies for
promoting long-term storage and retrieval of information is to have the student learn it in a meaningful
context. Since meaningfulness refers to the number of connections between new and old information,
one of the best ways to promote meaningfulness is for the learner to have an abundance of information
related to a topic already well organized in long-term memory
Serial position effect:
Experiments show that when participants are presented with a list of words, they tend to remember the
first few and last few words and are more likely to forget those in the middle of the list.
This is known as the serial position effect (see fig. above). The tendency to recall earlier words is
called the primary effect; the tendency to recall the later words is called the recency effect.
Murdock (1962) asked participants to learn a list of words that varied in length from 10 to 30 words
and free recall them. Each word was presented for one to two seconds. He found that words presented
either early in the list or at the end were more often recalled, but the ones in the middle were more
often forgotten.
Murdock suggested that words early in the list were put into long term memory (primacy effect)
because the person has time to rehearse the word, and words from the end went into short term
memory (recency effect). Words in the middle of the list had been there too long to be held in short
term memory (STM) (due to displacement) and not long enough to be put into long term memory (LTM).
In a nutshell, when participants remember primary and recent information, it is thought that they are
recalling information from two separate stores (STM and LTM).
Levels of processing:
The levels of processing model of memory (Craik and Lockhart, 1972) was put forward partly as a result
of the criticism leveled at the multi-store model. Instead of concentrating on the stores/structures
involved (i.e. short term memory & long term memory), this theory concentrates on the processes
involved in memory. Unlike the multi-store model it is a non-structured approach. The basic idea is that
memory is really just what happens as a result of processing information. Psychologists Craik and
Lockhart propose that memory is just a by-product of the depth of processing of information and there
is no clear distinction between short term memory and long term memory.
Craik defined depth as "the meaningfulness extracted from the stimulus rather than in terms of the
number of analyses performed upon it.”
We can process information in 3 ways:
Shallow Processing: This takes two forms
1. Structural processing (appearance) which is when we encode only the physical
qualities of something. E.g., the typeface of a word or how the letters look.
2. Phonemic processing – which is when we encode its sound.
Shallow processing only involves maintenance rehearsal (repetition to help ushold something in the
STM) and leads to fairly short-term retention of information. This is the only type of rehearsal to
take place within the multi-store model.
Deep Processing: This involves
3. Semantic processing, which happens when we encode the meaning of a word and
relate it to similar words with similar meaning.
Deep processing involves elaboration rehearsal which involves a more meaningful analysis (e.g.,
images, thinking, associations etc.) of information and leads to better recall. For example, giving words
a meaning or linking them with previous knowledge.
Levels of processing: The idea that the way information is encoded affects how well it is
remembered. The deeper the level of processing, the easier the information is to recall.
Strengths of the levels of processing approach:
Gives importance to the circumstances at time of learning (e.g. environment, attention, previous
experience)
Explains fMRI data showing increased activity for semantic treatment of stimuli (Gabriele et al. 1996)
Weaknessesof the levels of processing approach:
It is hard to decide the level of processing being used by someone in a given real world situation
It does not offer any explanation for implicit learning