8. Memory: varieties and mechanisms
Chapter introduction
● Memory allows us to learn from the past, understand the present and plan the future.
● All cognitive abilities depend on memory to one degree or another:
- Perception: the result of an interaction between sensory stimuli and stored
knowledge about the world
- Attention: past experiences guide the processes of searching for selecting
relevant information
- Emotional responses: identical stimuli can elicit very different emotional
responses in different people, depending on their life experiences.
- Language: depends on concepts and grammatical rules stored in memory
- Decision-making: often requires information that must be retrieved from
memory
- Sense of self and the capacity to project ourselves into the future: depend on
our personal memories.
● Memory is not an unitary phenomenon → it is distinguished in separate
systems
Introductory box: the case of H.M
● Suffered from severe epilepsy
● Bilateral damage in temporal lobe → surgically removed for seizure relief
● Surgery left H.M with anterograde amnesia: an inability to form new memories of
events (=episodic memory) and facts (=semantic memory) that happened after the
damage (=declarative memory/explicit memory)
● Memories expressed through performance (e.g, motor or cognitive skills) were not
impaired (=non-declarative memory/implicit memory).
● The ability to retain information for brief periods of time was not impaired (=working
memory).
● Memory deficits were generalized to all kinds of information and to all sensory
modalities.
Conclusion: bilateral temporal lobe damage in H.M led to impaired declarative/explicit
memory, but not in working memory or nondeclarative/implicit memory.
8.1 Memory Phases, Processes, Systems and Tasks
● Memory: series of processes whereby the nervous system acquires information
from new experiences, retains this information over time and eventually uses it to
guide behavior and plan future actions.
Phases shared by all forms of memory:
1. Encoding: processes whereby experiences can alter the nervous system. These
alterations (=memory traces) primarily involve changes in the strength and/or
number of synaptic connections between neurons.
2. Storage: the retention of memory traces over time. Long-term retention requires
cell-and system-level stabilization processes (=consolidation).
3. Retrieval: the accessing of stored memory traces, which may lead to a change in
behavior. It is sometimes associated with the conscious experience of remembering.
● Learning: a synonym of encoding or the combined effect of encoding, storage and
retrieval leading to gradual enhancement in the performance of a particular task.
, ● Memory systems: groups of memory processes and associated brain regions that
interact to mediate performance over a class of similar memory tasks.
- Some tasks depend primarily on one memory system. Most tasks however,
are sensitive to the contributions of more than one memory system
- This is why drawing inferences requires converging evidence from several
different tasks.
● Memory processes
1. Working memory: mediates the maintenance and manipulations of
information online for a few seconds or minutes.
2. Long-term memory: mediates the retention of information for longer periods
(days, months, decades). It is typically divided into:
- Declarative memory (or explicit memory): the conscious memory for
events (=episodic memory) and facts (=semantic memory).
- Non-declarative memory (or implicit memory/procedural memory):
memories that are expressed through performance independent of
consciousness.
8.2 Disassociating Memory Systems
● Types of amnesia:
- Childhood amnesia: normal lack of memory for events that took place during
the first few years of our life.
- Psychogenic amnesia: memory loss due to psychological trauma
- In the case of brain damage there is:
1. anterograde amnesia: memory loss affecting information acquired
after the damage
2. retrograde amnesia: information acquired before the lesion
3. Both retrograde and retrograde amnesia.
● Most telling evidence supporting the idea of memory systems is provided by cases of
amnesia:
❖ Bilateral damage to the medial temporal lobe (MTL) results in severe
anterograde and retrograde amnesia. Declarative memory is impaired, but
working memory is not.
- Patients cannot form new memories for events or facts.
- They can maintain a normal conversation which implies that working
memory is spared, since conversing requires remembering what was
said during the last few seconds or minutes.
- Best example: patient H.M.
❖ Unilateral damage to the MTL produces relatively mild memory deficits
because the spared medial temporal lobe regions can still support some
aspects of memory.
❖ Lesions to the (left) temporoparietal cortex results in severely impaired
working memory, but not in impaired declarative memory
- Best example: patient K.F who performed significantly worse than
average on repeating a memorized list of numbers. His declarative
, memory performance was slightly better than normal → to learn
longer lists with fewer repetitions than control participants and
remembered the lists for long periods of time.
Conclusion: there are different memory systems in the brain. Declarative memory is
associated with the MTL and working memory with the temporoparietal cortex. This
distinction is supported by the type of amnesia occuring after damage.
8.2.1 Declarative versus non declarative memory
● MTL lobe amnesia impairs declarative memory tasks but not nondeclarative memory
tasks (e.g, skill learning and priming).
- Impaired performance in explicit (declarative) recognition tests.
- In an implicit (nondeclarative) test they demonstrate priming.
- They perform well in a cued recall test
● (Right) Occipital lobe damage may impair nondeclarative/implicit memory, but not
declarative memory.
- Example: Patiënt M.S:
- In an implicit (nondeclarative test) M.S did not demonstrate priming
- Explicit (declarative test) recognition test M.S performance was normal.
Conclusion:
● MTL damage tends to impair declarative, but not working memory or nondeclarative
memory functions.
● (Left) temporoparietal damage can disrupt working memory while sparing declarative
memory.
● (Right) Occipital lobe damage impairs non-declarative memory, but spares
declarative memory.
8.3 Nondeclarative Memory
● All forms of nondeclarative memory are expressed through performance and are
independent of conscious awareness.
● Non declarative memory is evidenced by a change in behavior, even if the person is
unaware that memories from specific past experiences are being assessed.
3 major forms of nondeclarative memory
● They share properties but are very all different from each other
1. Priming: a change in the processing of a stimulus due to a previous
encounter with the same or a related stimulus (e.g, completing a word
fragment with a previously read word)
2. Skill learning: a gradual improvement in performance due to repeated
practice.
3. Conditioning: simple responses to associations between stimuli.
● Priming can result from a single encounter with a stimulus,
● Skill-learning requires repeated learning trials.
● Conditioning also involves multiple learning trials, but typically consists of simpler
responses and associations than skill learning.
, 8.4 Priming
● A change in the efficacy of stimulus processing arising from a previous encounter
with the same or related stimulus in the absence of conscious awareness of that first
encounter.
● Repetition suppression: previously encountered (primed) stimuli result in weaker
hemodynamic activity/neurons firing.
● Sharpening theory: explains priming effects as neurons that carry critical
information about a stimulus continuing to fire vigorously when a stimulus
is repeated, whereas neurons that are not essential for processing the
stimulus respond less and less (leading to reduced hemodynamic
response in fMRI) → cortical representation that has fewer and more selective
(only critical) neurons.
A typical priming paradigm:
● First session in which participants read words and a second session in which they
solve word puzzles (e.g, completing word fragments with the first word that comes to
mind) seemingly unrelated to the words previously read.
● Priming is measured as an increase in the probability of completing word fragments
with words presented during the first phase (it can also be measured a processing
speed or changes in eye movement patterns).
● Facilitation effect found even if participants are unaware that they solved the
fragments using words previously read in the experiment.
● A critical requirement is that participants are unaware that they’re using information
from the first session.
● ‘Contaminated by explicit memory strategies’: when participants realize that some
fragments can be completed with words previously seen and then try to retrieve
these words to complete the fragments. The results are not a valid measure of
implicit memory. It then measures recall from study.
Direct and indirect priming
● There is semantic priming, conceptual priming and perceptual priming.
● Depending on the relationship between the stimulus that generates the priming effect
(=the prime) and the stimulus eliciting that effect (=the target), priming can be
classified as:
1. Indirect priming: the prime and target stimuli are different.
- Semantic priming: the prime and target are semantically related (e.g,
letter and envelope).
➔ automatically facilitates cognitive tasks in everyday life such as
problem solving and reading comprehension, but are not
consciously considered.
➔ Faster reaction-time (in decision-making) for semantically
related words following each other up.
➔ Presumed mechanism is based on the assumption that
semantic memory is organized as a network in which each
node corresponds to a concept and each link corresponds to
an association between two concepts. When a node is
accessed it becomes activated and the activation spreads
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