CHAPTER TWO
Memory
2.1 Memory as a Psychological Construct
2.1.1 Introduction
Memory is perceived as the outcome of several cognitive
functions, and refers to the ability to encode, retain, and
retrieve information at different points in time (Vanderploeg,
2000). Moreover, memory is not a unitary system but is fractioned
into different components (Stracciari, Ghidoni, Guarino, Poletti
& Pazzaglia, 1994). Memory is broadly differentiated into shortterm store and long-term store (Neath & Suprenant, 2003). Within
these major divisions, memory is differentiated into types and
aspects. Recall and recognition are types of memory, and are used
to assess the manner in which information is encoded and
retrieved. Furthermore, verbal memory and visual memory describe
the memory stores for auditory-verbal, and visual-spatial and
visual-verbal information.
2.1.2 Short-term Memory
Short-term store is the temporary store for newly registered
information, has a limited capacity system, and lasts for less
than one minute, unless it is lengthened by rehearsal (Lezak,
2004). Information passes through short-term store to enter longterm store, from where long-term memories are retrieved
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(Vanderploeg, 2000). Immediate, working, primary, and secondary
memory are aspects of short-term store, and relate to encoding
processes (Matlin, 2001).
Primary memory refers to the aspect of the short-term store
that retains information that utilizes current attention and
current thoughts. The information in this store does not have to
be consciously recalled in order to be utilized. While short-term
memory highlights the role of time in remembering, primary memory
underscores the role of attention, conscious processing and
memory capacity (Neath & Suprenant, 2003). By contrast, secondary
memory is an aspect of the short-term store that retains
information that is currently being processed with the knowledge
that this information has been previously experienced or thought
of. Working memory is an aspect of short-term memory that
describes a workspace or memory buffer, which retains information
that is currently being processed (Baddeley, 1992).
Working memory is used interchangeably with immediate memory.
This aspect of memory refers to the sensory processing of
information in working memory (Matlin, 2001).
2.1.3 Short-term Memory Span
2.1.3.1 Auditory-verbal short-term memory span
Span refers to the measurement capacity of memory, and is tested
with digit span or word span tasks. The capacity of short-term
memory is not determined by the physical properties of a
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stimulus. Instead, it depends on one’s ability to chunk or recode
a stimulus into higher-order units (Matlin, 2001). The digit span
of short-term memory is limited to seven (plus or minus two)
random digits whereas the word span retains four to five random
words. This phenomenon is referred to as the span of apprehension
(Baddeley & Hitch, 1992).
Letters load the short-term capacity to the same extent as
digits. In addition, random words load the short-term capacity to
a greater extent than a meaningful sentence (Parkin, 1993). While
the increased length of sentence tasks improves performance, the
increased length of a list span tasks reduces performance
(Matlin, 2001). This occurs because list span depends on the
auditory familiarity of the stimulus while sentence span relies
on intact comprehension (Matlin, 2001).
Although, the short-term store is limited regarding the
amount and duration of information it can store, rehearsal boosts
the short-term span (Matlin, 2001). Span impairment is
characterized by the difficulty in retaining information (Matlin,
2001).
2.1.3.2 Visual short-term memory
Visual span for symbolic or meaningful stimuli can be tested by
briefly exposing the stimulus. This prevents recoding stimuli
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into a spoken form. Under these conditions, four to five items
can be retrieved in normal individuals (Matlin, 2001).
The retention of single stimulus items is intact in
individuals who exhibit impaired visual retrieval (Kinsbourne &
Warrington, 1962) [cited in Matlin, 2001]. Moreover, when items
are presented in pairs, retrieval is possible for only one of the
items. Errors of omission and substitution are made, and recall
of the second item is not possible. The impairment does not
result from perceptual or attention deficits, but is specific to
symbolic stimuli that cannot be verbally encoded (Kinsbourne &
Warrington, 1962) [cited in Matlin, 2001]. Furthermore, auditoryverbal short-term span can be normal in the presence of an
impaired visual-verbal span (Parkin, 1993).
Visual-verbal span tasks tend to dissociate from tasks that
require the retention of the spatial organization of a stimulus.
Corsi & Milner (1971) [cited in Neath & Suprenant, 2003]
developed a test whereby nine identical blocks are distributed
such that no definable pattern in the arrangement emerges. In the
presentation of the block, the examiner taps a sequence of blocks
at a rate of one block per second. The subject is required to
reproduce the sequence immediately afterward. Selective
impairment on this task reflects a span of three items rather
than the normal five to six item span. If the identical
arrangement is presented with numbers visible on the stimuli,
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performance is within normal levels (De Renzi, Luchelli, Muggia,
& Spinnler, 1995).
2.1.4 Serial position curve
The serial position curve reflects the free recall of the serial
presentation of items as a function of each item’s position in an
item list (Parkin, 1993). The curve can be divided into three
portions, namely, recency, which refers to the enhanced recall of
the last few items on the list; primacy, which refers to the
enhanced recall of the first few items on the list; and finally,
the asymptote which describes the low performance in the middle
of the curve (Parkin, 1993). A popular notion is that recency
reflects the effortless output of the short-term store whereas
primacy occurs via the long-term store (Matlin, 2002).
The transfer of information from the short-store to the
long-term store critically depends on consciously recycling
information (Matlin, 2001). Rundus (1971) [cited in Parkin, 1993]
asserted that the different parts of the curve have different
properties that reflect the operation of different stores. The
serial position curve is the joint product of the short-term and
long-term stores. In addition, words in the primacy and asymptote
portions of the serial position curve reflect a positive
relationship between rehearsal frequency and improved recall.
Moreover, variations in word frequency, presentation rate, interitem relatedness, list length, and mental status significantly
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affect the primacy and asymptote portions but not the recency
segment. Lezak (2004) asserts that amnesic patients exhibit
normal recency, and impaired primacy.
Recent items are easily recalled since they are strongly
represented, while the primacy effect results from items early in
the list receiving more rehearsal (Parkin, 1993). However, there
is no correlation between rehearsal frequency and the recency
effect. Recent items do not have sufficient time to be
incorporated into the rehearsal process, thus recall depends
entirely on the short-term store. Furthermore, the size of the
recency effect cannot be measured in word units, and depends on
the nature of the target information and the duration of a
distraction task (Glanzer & Razell, 1974) [cited in Parkin,
1993].
The negative recency effect (Craik, 1970) [cited in Parkin,
1993] formed another arm of the short-term/long-term dichotomy.
Craik (1970) administered a series of free recall word trials;
each of which generated a typical serial position curve. On
completion of the experiment, a surprise recall test of all
possible words was administered. Words that reflected recency
effects in the immediate recall trials, later had a significantly
lower level of recall, even when compared to words formerly in
the asymptote. Craik attributed this effect to the failure of
rehearsing the recent items since the second test was unexpected.
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These items had a lower chance of being transferred to the longterm store and were, therefore, difficult to recall at a later
time. The constant ratio rule states that the possibility that a
single theory may account for both types of recency effects.
2.1.5 Level of Processing Model
The level of processing model (Craik & Lockhart, 1972) [cited in
Matlin, 2001] conceptualizes memory in terms of the encoding
processes undertaken during learning, and the pattern of
subsequent retention (Matlin, 2001). (Craik & Lockhart, 1972)
[cited in Parkin, 1993] proposed that the retention of a stimulus
is a positive function of the depth to which the stimulus is
processed during learning, hence, the depth effect. The depth
effect is corroborated by established research on incidental
learning (Neath & Suprenant, 2003). This concept refers to the
relative ease of retention that occurs when one is not asked to
retain information during a task.
Information is encoded along a continuum of encoding
dimensions, while processing occurs at three different levels
(Craik & Lockhart, 1972). Orthographical processing produces the
poorest level of memory, followed by phonological processing. By
contrast, semantic processing produces the highest level of
retention, and performance is as good as that found in
intentional learning. These results are attributed to processing
that occurs via a central processor (Craik and Lockhart, 1972).
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Possessing a limited but flexible capacity, the central processor
processes new information. In addition, retention depends on the
way in which the central processor is deployed during learning,
with deeper levels of processing yielding better retention. A
stimulus first undergoes a minimal core encoding, which includes
a degree of semantic analysis (Parkin, 1993). This is followed by
conscious and directed processing appropriate to the task
demands. The notion of a continuum between the shallow and deeper
levels of processing was abandoned, and replaced by separable
domains of processing (Sutherland, 1972) [cited in Matlin, 2001].
The revised theory reflects the original idea that it is not
possible to gradually pass from one level to the next because
each level contains qualitatively different dimensions of
information processing, which cannot merge in any way (Matlin,
2001).
Stimuli that evoke a “yes” response rather than a “no”
response, are retained better (Parkin, 1993). This phenomenon is
termed the congruency effect. The effect is pronounced in the
semantic domain, and ensues since “yes” responses are more likely
to allow coherent associations between the stimulus and the
retrieval cues (Parkin, 1993; Matlin, 2001). In addition, longer
processing time does not reflect deeper processing or greater
retention (Craik & Lockhart, 1972). Thus, memory can be affected
by qualitative differences in the way information is encoded
(Matlin, 2001).
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The Level of Processing model was criticized for proposing that
semantic processing typically produces better retention than nonsemantic processing, since the former involves deeper processing
than the latter (Matlin, 2001). However, the enhanced retention
following semantic processing depends on the type of retention
test used (Craik and Lockhart, 1972). Thus, semantic processing
does not have an absolute advantage over non-semantic processing.
This phenomenon is referred to as transfer-appropriate
processing, which holds that the most appropriate learning
strategy is the one that most closely addresses the information
required at testing.
2.1.6 Working Memory
The commonly received notion was that a single, indivisible
structure, primary memory or the short-term store underlies the
memory capacity essential for normal conscious mental activity.
Memory is organized and assumes an orderly transition from shortterm to long-term storage (Matlin, 2001). Memory span is accepted
as the definitive measure of short-term storage, therefore
performance on the digit span is related to long-term storage.
Refuting this unitary view of short-term store, Baddeley
and Hitch (1977; 1992) [cited in Matlin, 2001] suggest that
short-term storage does not rely on a single structure or
process. In fact, they assert that short-term storage is an
integrated, multifaceted system, comprising various components
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that execute varying tasks. It can then be assumed that different
deficits within the short-term store emerge as a consequence of a
deficit within a specific subcomponent of the short-term store
(Matlin, 2001).
The working memory model (Baddeley & Hitch, 1977; 1992)
emphasizes the ways in which the memory system is adapted to meet
the needs of real-life conscious mental activity. The basic
premise of the model is that the short-term store comprises
various sub-systems. In addition, the digit span does not reflect
the short-term store capacity nor indicate that this store is a
single structure (Baddeley & Hitch, 1977; 1992).
Using these two assumptions as a point of departure, it was
hypothesized that it would be difficult to retain a digit
sequence while simultaneously performing a word-learning task
that required the same short-term store capacity. Since the digit
span reflects the maximum short-term storage capacity, a marked
impairment of retention was expected since short-term storage
capacity would be fully utilized. However, this did not occur.
Thus the system responsible for memory span differs from the
system supporting other conscious mental activity (Parkin, 1993).
The task of retaining short digit sequences might be executed by
a system dissimilar from the systems involved in reasoning and in
learning word lists (Baddeley & Hitch, 1977; 1992).
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The memory span for short words is higher than that for long
words, hence the word length effect (Baddeley & Hitch, 1977;
1992). The word length effect led to the conclusion that the
system underlying memory span is speech-based, and supported the
notion of the articulatory loop (Parkin, 2001). In addition, the
articulatory loop accounts for digit retention ability (Baddeley
& Hitch, 1977; 1992). The concept draws on the idea that memory
span is adversely affected if similar-sounding items are
recalled, since the mechanism underlying memory span utilizes a
sound-based code (Matlin, 2001). Articulatory suppression causes
the word length effect to disappear, whereby short and long words
are recalled to the same degree (Parkin, 1993). When this occurs,
the memory for short and long words depends on the same
processes, and is, therefore, recalled to the same degree
(Parkin, 1993).
2.1.7 The Working Memory Model
Baddeley (1977; 1992) identified three components of the working
memory model viz. the phonological loop, visuo-spatial scratch
pad, and central executive. The phonological loop and visuospatial scratch pad hold auditory, verbal, and visuo-spatial
information within a limited attentional capacity. Specifically,
the visuo-spatial scratch pad provides a workspace within which a
visual image can be stored and manipulated in order to execute a
task concerning a visual stimulus. The central executive
organizes and decides what to do with this information.
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Daneman and Carpenter (1980) [cited in Parkin, 1993] termed the
fixed capacity of the central executive, working memory span. The
function of the central executive is explained through the
dysexecutive syndrome (Baddeley, 1990) [cited in Matlin, 2001].
This is an umbrella term of deficits resulting from frontal lobe
damage that reflect impairment in the executive control of
memory.
The frontal lobes are critical for planning and executing
response strategies, and Norman & Shallice (1991) [cited in
Parkin, 1993] assert that schemata control most of these actions.
This term refers to the established responses required for
particular situations; once triggered, they allow a sequence of
actions to be executed automatically. When additional conscious
control is required, the supervisory attentional system is
activated. This system is operative where planning, problem
solving, and decision-making are required (Matlin, 2001).
Recall is a reconstructive process, whereby a hypothesis is
devised in order to initiate a memory search (Matlin, 2001).
Recall can be likened to a form of problem solving which depends
on the intact functioning of the supervisory attentional system.
Recognition, however, sidesteps the problem-solving aspect
described above. As a result, impairment of the supervisory
attention system may be disrupted to a lesser extent in
recognition (Matlin, 2001).
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The dysexecutive syndrome may be characterized by a form of
memory deficit resulting from damage to the supervisory
attentional system (Neath & Suprenant, 2003). Thus, on an aspect
of memory requiring a form of executive strategy, a deficit
appears; when a memory task is not strategy-dependent, deficits
are not evident. The pattern of memory loss may be attributed to
the inability to plan or to execute retrieval processes (Matlin,
2001). Consequently, performance on recall tests is poorer since
these tasks require the strongest executive demand.
The articulatory loop comprises two systems, namely a
phonological store, responsible for holding speech-based
information, and an articulatory control process that recycles
limited amounts of this information (Baddeley & Hitch, 1977;
1992) [cited in Matlin, 2001]. The distinction between the two
processes is necessary since it accounts for the fact that, under
articulatory suppression, individuals can still make judgements
concerning the phonology of an item (Matlin, 2001). Under
articulatory suppression, a distinction can be made between words
and non-words that sound like words (Besner, 1981) [cited in
Parkin, 1993]. Thus articulatory suppression prevents the
transfer of information from the phonological store to the
articulatory control process (Baddeley, 1992).
Initially, Baddeley coined the term inner voice to describe
the direct relationship between the articulatory control process
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and the mechanism governing overt speech (Matlin, 2001). The
articulatory control process is not linked to the mechanisms of
overt speech but rather reflects a central form of motor
programming that precedes speech production. When reading
silently, Baddeley’s inner voice is operative. Huey (1908)
commented that: “The carrying range of inner speech is
considerably larger than vision…. The initial sub-vocalization
seems to help hold the word in consciousness until enough others
are given to combine with it in touching off the unitary
utterance of a sentence which they form….”(cited in Parkin, 1993,
p. 128). When vocalization is suppressed, recall is better for
easy rather than for difficult stimuli (Hardyk & Petrinovich,
1970) [cited in Parkin, 1993]. This indicates that the
articulatory loop executes a more critical function for complex
reading stimuli.
The articulatory loop provides a useful memory system for
encoding sequences of phonemes in the correct order, and
establishes a means of holding the intonation contour (Parkin,
1993). The intonation contour occurs when different aspects of
phonology enable different meanings of the same sentence to be
understood. Under articulatory suppression, visual memory
declines when sentences are simultaneously presented. Levy (1977)
[cited in Parkin, 1993] confirmed that articulatory coding is
specifically involved.
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2.1.8 The Multi-store Model of Memory
William James (1890) termed the memory system supporting
consciousness, primary memory and that which supports the
permanent record of the past as secondary memory. This view was
later refined as the multi-store model of memory (Atkinson &
Shiffrin, 1968) [cited in Parkin, 1993]. Accordingly, memory is
perceived as the flow of information between three inter-related
stores (or repositories), namely the sensory store, the shortterm store and the long-term store.
The sensory store receives new information, is transient,
and contains information relating to the pattern of sensory
stimulation. The sensory storage of visual information is known
as iconic memory (Sperling, 1960) [cited in Parkin, 1993] and is
implicated in the early stages of visual analysis. Owing to the
assortment of sounds that are recognized, the aspect of memory
that retains auditory stimuli over a short period of time was
later identified (Matlin, 2001). Thus, the auditory equivalent to
iconic memory is echoic memory (Parkin, 1993).
Information in the sensory store is transferred into the
short-term store (Matlin, 2001). Immediate memory is the
intermediate memory store between sensory store and short-term
store (Parkin, 1993). Short-term store activities are represented
as various control processes, which respond to specific
information requirements (Matlin, 2001). Furthermore, these
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processes also determine the contents of the short-term store, in
that the information being processed at a given time can be
displaced by new information (relevant to the task being
undertaken at that time). In addition, rehearsal describes the
tendency to repeat information when trying to remember it, and is
important for transferring information from the short-term store
to the long-term store (Atkinson & Shiffrin, 1968).
Words have three distinct encoding dimensions, namely
orthographic, which refers to the pattern of letters comprising
the word; phonological, referring to the sound of the word; and
semantic, which refers to the meaning of the word (Baddeley &
Hitch, 1949) [cited in Neath & Suprenant, 2003]. The phonological
confusability effect describes the difficulty in recalling
stimuli that are phonologically confusing (Conrad, 1964) [cited
in Parkin, 1993]. This effect also occurs during the immediate
recall of similar-sounding words compared to that of unrelated
words (Baddeley, 1949) [cited in Parkin, 1993]. This effect,
however, is not evident when semantically related words are used
(Baddeley, 1949). In delayed recall, the phonological
confusability is ineffectual, but semantically confusable words
are recalled more poorly than unrelated words (Baddeley, 1949).
These findings spearheaded the notion that the short-and-longterm stores could be distinguished in terms of encoding
differences. The short-term store utilizes phonological encoding
as well as semantic encoding.
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2.1.9 Long-term Store
2.1.9.1 Permanent store model
Tulving (1972) [cited in Parkin, 1993] refuted the shortterm/long-term dichotomy. Instead, he proposed a tripartite
system, in which a distinction is drawn between memories
associated with personal recollection from those that are not.
Tulving (1972) noted that the long-term store consists of three
functionally distinct yet interactive components, namely
episodic, semantic, and procedural memory.
Episodic memory is the memory that enables one to be aware
of having experienced an event before. It refers to an
individual’s autobiographical record of past experiences, and
represents temporally dated episodes that can later be retrieved.
Semantic memory refers to knowledge concerning facts, concepts,
and vocabulary; the context for which is explicitly known, and
available for retrieval. By contrast, procedural memory refers to
the memory that is reserved for skills. Moreover, the terms
episodic and semantic can be replaced by a single term namely,
declarative memory (Tulving et al., 1973) [cited in Parkin,
1993]. This aspect of memory refers to any memory that is
consciously accessed.
Tulving later supplemented his definition of semantic
memory to include the memory “that allows the individual to
construct mental models of the world . . . . It makes possible
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the cognitive representation of objects, situations, facts, and
events” (Tulving, 1985) [cited in Parkin, 1993, p. 41]. The
revision accounts for how one can possess a memory of an event
without having specific information about why one knows that the
event occurred in the past. Tulving (1985) termed this form of
semantic memory experience noetic (knowing), in contrast with
that of an episodic memory experience, termed autonoetic (selfknowing). Memories that are retrieved without conscious
recollection are termed anoetic.
A memory is derived from an experience or a learning event
(Neath & Suprenant, 2002). Retaining an episodic memory does not
require the learning event to be retained. In semantic memory,
learning may only occur within the context of an episodic memory
that confirms why the semantic stimulus means what it does
(Tulving, 1985). Over time, the semantic stimulus becomes
assimilated into semantic memory, and is represented
independently of the events that gave rise to it (Parkin, 1993).
Since the memory representation and learning event do have to be
linked, a great saving in storage can be achieved (Parkin, 1993).
The multi-store model is founded on the idea that the
record of an experience resides separately from the knowledge
gained from the experience. Santee (1981) [cited in Parkin, 1993]
asserted that experimental evidence supporting this distinction
is problematic, given the interdependence that exists between the
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episodic and semantic memory systems. Accordingly, evidence from
amnesic patients constitutes the primary support for the two
separate systems. An amnesic patient is likely to exhibit intact
semantic and procedural memory, impaired episodic memory, and
normal conversational skills (Neath & Suprenant, 2002). In
addition to the inability to learn new information, most amnesic
patients suffer a parallel loss of memories acquired before the
injury or illness (Lezak , 2004). This form of deficit, termed
retrograde amnesia, is more pronounced for memories acquired
close to the onset of amnesia.
2.1.9.2 Explicit and implicit memory
Advancing an alternate theory, Schacter (1987) [cited in Parkin,
1993] proposed that the long-term store could be understood by
explicating the ways in which it responds to explicit and
implicit memory tests. Explicit memory refers to the memory for a
learning event that requires conscious processing, and explicit
reference to the event. A test of explicit memory directly
assesses the recollection of a previous learning event (Lezak,
2004). Explicit memory can be tested using three different
procedures (Parkin, 1993). A free recall test requires an item to
be recalled without cuing. Cued recall tests require recalling
the target information in the presence of a specific cue. In a
recognition test, a stimulus is presented and a decision is made
whether it is the target item or not. Recognition can be tested
by eliciting either a “yes” or “no” response whereby each item is
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judged individually, or by a forced choice procedure whereby one
item from an array must be selected as the target. Thus, the cued
recall test is a form of a recognition testing.
Implicit memory refers to the memory for a learning event
without making specific reference to that event. The memory
tested under implicit conditions forms automatically. The idea
that a memory from an experience can be expressed indirectly is
not a new concept. Descartes (1649) noted that frightening
childhood experiences could remain imprinted on a child’s memory
“without any memory remaining afterward” (cited in Parkin, 1993,
p. 49). Leibniz (1916) stressed the role of unconscious memories
in everyday life, and argued that one could have “remaining
effects of former expressions without remembering them” (cited in
Parkin, 1993, p. 49). Implicit memory tasks thus test memory
indirectly.
2.1.9.3 Priming in long-term memory
Priming refers to the learning that facilitates performance
through prior exposure to words and other material (Parkin,
1993). Cues that elicit priming do not necessarily have to share
any physical properties with the target item. Priming effects are
conceptually, perceptually, and semantically driven (Squire,
1987) [cited in Neath & Suprenant, 2002].
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Procedural memory is spared in amnesia since the acquired
information is embedded in procedures (Lezak, 2004). An alternate
account is that priming reflects impairment in the way that preexisting cognitive operations are executed (Crowder, 1985) [cited
in Neath & Suprenant, 2002]. Skills and priming are expressed
through a memory system that prevents explicit access to the
contents of the knowledge base (Parkin, 1993). Memory, is thus
expressed only in performance, and prevents an individual’s
accumulative experience from being reflected in verbal or nonverbal tests that require judgment or familiarity (Lezak, 2004).
In amnesia, declarative memory describes the learning and memory
that is impaired in amnesia as this information is explicit
(Lezak, 2004). Thus, the recall and recognition impairment, and
the preservation of skill learning and priming in amnesiacs,
support the hypothesis of two distinct memory systems (Parkin,
1993).
2.1.10 Forgetting
Storage failure refers to the inability of the memory system to
produce a permanent memory trace of a given event. Storage
failure may occur either because the transfer from the short-term
store to the long-term store was not initiated or because the
permanent memory trace was lost. By contrast, retrieval failure
arises from the inability of the memory system to locate an
existing memory trace.
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2.1.10.1 Memory strength theory
According to the model, a memory representation is a record of a
stored word in memory. A memory representation incorporates
information about the context within which the word was learnt,
other test items, and the target item itself. Retrieval, thus,
depends on context cues, association cues, and item cues.
Moreover, retrieval improves with increased presentation time,
since the strength of the association and item cues are
increased. An increase in the retention interval decreases
retrieval because the context cues have changed greatly during
the interval.
Each learning event possesses a signal strength. A range of
factors determines strength values, and includes: rehearsal
frequency, processing depth, target familiarity, and the
similarity between the context cues during encoding and
retrieval. The model proposes that frequently rehearsed items
possess greater item strength than items rehearsed less often and
are, therefore, more likely to be retrieved. Within working
memory, information is activated by the interaction of a cue in
working memory with the associated information in long-term
memory.
Recognition and recall differ in the manner in which the
target item in long-term memory is identified. During
recognition, the target item and the context form a compound that
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elicits a representation in memory. The familiarity of the
representation is computed to critical value. If familiarity with
the item is higher than the critical value, the item is
recognized as old, otherwise, it is recognized as new. During
recall, the context initiates the retrieval process by triggering
search cycles until a word is recalled. A starter word is
selected, followed by a selection of additional words, and a
decision is made whether the selected word fits the correct
context. The most active word in the retrieval structure is
recalled first, which tends to be the most recent item (Mixted,
Ghadisha & Vora, 1997) [cited in Neath & Suprenant, 2002].
However, if activation is relatively low, retrieval cannot occur
and the search stops after several failed attempts.
2.1.10.2 The feature model
The feature model conceptualizes immediate memory in terms of
performance on immediate serial recall tasks. The order of
information is encoded multi-dimensionally and stored with cues
in primary memory (Neath, 1999) [cited in Neath & Suprenant,
2002]. Each item is encoded in a manner that allows the items to
possess a constant position along its relevant cue dimension and
cannot occupy a new position upon encoding a new item (Estes,
1972; 1997) [cited in Neath & Suprenant, 2002].
Recall begins by determining which cue most likely occupies
the first position along the relevant cue dimension; this is
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necessary for sampling cues from secondary memory. A sampled item
must be recovered prior to output, and recall begins with the cue
in primary memory that has the highest probability of being the
cue for the second item. In addition, the similarity between
primary memory and secondary memory cues increase the probability
of sampling. Incorrect recall results from errors in the sampling
procedure where the correct cue for the target item is chosen but
subsequent sampling does not occur in chronological order.
2.1.10.3 Theory of distributed associative memory
Murdock’s theory of distributed associative memory (1982; 1995)
[cited in Neath & Suprenant, 2002] explains the memory for serial
list recall and recognition. The model proposes that individual
memories are distributed within one memory system. Furthermore,
the memory system stores two kinds of information, namely item
information that enables recall, and associative information
between the items that allow them to be recalled in the correct
order.
Serial recall is driven by cues, the first of which is the
context cue. The instruction to recall the target item is the cue
that initiates retrieval. Accordingly, recall occurs through the
process of correlation termed chaining, and continues until an
item cannot be recalled. When a link in the chain is missing,
recall stops. By contrast, recognition occurs through
familiarity. If the item is recognized, it is perceived as old;
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if it is not recognized it is perceived as new. Furthermore, a
memory comparison stage occurs whereby the presented item enters
a decision cycle, and a decision is made whether the item is old
or new.
The strength of the model is that it includes both item and
associative information. When an item cannot be recalled, the
associative information cues for the next item, explaining how
recall still proceeds in spite of failing to recall other items
on the list. One shortcoming however, is that recognition is also
explained through the concept of a competitor set. This concept
includes a set of items that an individual thinks is likely to
have occurred on the trial. The target item is compared to the
item in the competitor set, and whichever item is most similar is
perceived as the target item. If recognition is successful (that
is if the match is correct), that item in the competitor set is
removed. This occurs since individuals rarely repeat an item. The
retrieved item is then convolved back into the memory system,
explaining how an individual remembers which item has been
recalled. The problem is that by the time the last item is ready
to be recalled, it is the only item in the competitor set and,
therefore, will always be matched with the last item since there
is no other possibility.
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2.1.10.4 Generation-recognition models
Generation-recognition models of memory (Watkins & Gardiner,
1979) [cited in Neath & Suprenant, 2002] conceptualize retrieval
as a reconstructive, search-guided process. At the outset of
retrieval, the memory system generates possible candidates as the
target stimulus. These candidates are then subjected to a
recognition process, which if successful, results in that
candidate being retrieved as a memory.
Each known word is represented by a node. When a word is
presented, a tag or occurrence marker is established, indicating
that the word is part of the target list. At recall, various
candidates are generated, and the corresponding nodes are
examined for tags, which if detected, result in recognition and,
hence, retrieval. During recognition, access to the node occurs
automatically, and recognition is dependent on the detection of a
marker.
High-frequency words are better recalled than low-frequency
words since they are more likely to be generated as candidates
for recognition. The poor recognition of high-frequency words
arises because these words are associated with several markers,
making it more difficult to determine whether the target word was
presented in a specific list.
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2.1.10.5 Encoding specificity principle
According to the generation-recognition models, recall involves
successful generation and recognition, whereas recognition
involves successful recognition only. Given this, an item that is
recalled must be capable of being recognized since recognition is
involved in recall. However, the failure to recognize recallable
words does occur; this is termed recognition failure (Tulving et
al., 1972) [cited in Neath & Suprenant, 2002].
The encoding specificity principle (Tulving & Thompson,
1973) [cited in Neath & Suprenant, 2002] explains how this
phenomenon occurs. Retrieval critically depends on the degree of
overlap between the features encoded in the memory trace and
those in the retrieval environment. Recall and recognition are
different manifestations of a single retrieval system, and are
independent of one another since they possess different featureoverlap with the encoded target. A strong associative cue
possesses a high degree of featural overlap. Recognition provides
the most featural overlap with a target trace, resulting in
recognition superiority over recall. However, the memory system
can be manipulated such that cued recall for an item can be
better than recognition for the same item.
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