Transcript Is There Evidence That Memory Is Separated Into Implicit

Is There Evidence That Memory
Is Separated Into Implicit and
Explicit Systems?
John Chuckalovcak, Megan Rathburn
Q301 Brain and Cognition, Indiana University
Memory is a mystery. What process or processes lay
down events and facts in our minds to be recalled at
a later date? Why do we sometimes fail to recall?
Science still has not found the answer. Recently
there has been a growing convergence between
cognitive psychology and neuropsychology with
focus on memory ret4ention and the study of
learning impaired subjects (Tolving). This is the
place we pick up the problem. A major theme in
current studies is that memory is not a single
process but rater it is composed of multiple separate
processes (Weiskrantz 1990; Squire, 1992; Schake
and Tulving, 1994; Squire and Knowlton, 1994).
The separation is between explicit and implicit
memory. Explicit memory is declarative and
conscious while implicit is non-declarative and
thought to be unconscious (Rugg, 1995). Each
system is thought to be accessed independent of one
another so that they can be retrieved I parallel
(Tulving 1994).
If in fact two separate systems do exist then it seems
logical that two separate brain areas would be
working during the activation of the systems. In
order to test this theory we devised a direct memory
task and used EEG recording techniques. A subject
will be given a set of words which are either concrete
or abstract to study then at test they will be shown
those words again plus some new words of that type.
They subject must then make a subjective response
about there memory by replying remember, know, or
new to the test words. The remember response taps
the explicit (conscious) system while the know
response keys into the implicit (unconscious) system.
We hypothesize the existence of the explicit and
implicit systems and that they will be evidenced by
spatial distributions of voltage specifically we
believe that the remember and know conditions will
produce different patterns of electrical response
(have different ERPs). We have chosen to use words
with high ratings values for concreteness and
abstractness. We believe that each will tap into the
proposed memory systems in different manors so that
if separate systems are not found in one condition
they may be in another.
In order to test for a clear and concise physiological
difference between the implicit and explicit memory
systems, a method needed to be devised that would
spark both systems to perform with enough
amplitude that decipherable ERP data could be
compiled. This system takes the form of a directmemory test with aspects of subject priming, and
essentially uses various types of words as stimuli.
The words used for the testing were gathered from a
list composed by Dr. Thomas Busey (accessed via
Microsoft Excel file at
http://cognitrn.psych.indiana.edu/busey/Q301/Q301
Words.xls).
The list made approximately 5,000 words available
and each word was given a numerical rating based
upon certain factors, such as: concreteness,
abstractness, and imagability. In order to try to
differentially affect either the implicit or explicit
memory systems, two separate types of words were
chosen, based upon the ratings they were assigned
from the available word pool. Condition One
consisted of a total of 300 abstract words, i.e. words
that possess an abstract connotation (love, victory,
etc.).
Of these 300 words, 200 were decided to be target
words (given to the subject to study), and the
remaining 100 would act as distracter words (not
given to the subject during the study session).
Condition Two consisted of a total of 300 concrete
words, i.e. words that possess a concrete connotation.
As in Condition One, 300 of the concrete words were
chosen from the available word pool, 200 of which
being target words and the remaining 100 serving as
distracter words. The word stimuli were collected
from the previously mentioned word pool, based
upon the effectiveness rating for the appropriate
condition. The top-rated 300 words for both
Condition One and Condition Two were chosen for
stimuli. Of the 300 words in each condition, the 200
with the highest appropriate rating were chosen to act
as target words, whereas the remaining 100 would
act as distracter stimuli.
Condition 1:Response=Remember:
In the color representations of the brain,
initial readings at the 200 m.s. time
frame show high levels of electrical
activity occurring primarily in the
dorsal medial portion of the parietal
lobe, as well as the rostral portion of the
occipital lobe. Subsequent readings
occurring at the 300-700 ms time frame
show a localization of processing in the
left hemispheric medial and lateral
sections of the parietal and frontal
lobes. Throughout the readings, high
levels of activity continue to occur in
the dorsal medial section of the parietal
lobe.
Condition 2: Response: Remember:
Readings taken at 200 m.s. show high
amounts of activity occurring in the
medial parietal lobe of both
hemispheres, as well as moderate
amounts of activity occurring in the
medial and lateral frontal lobe of the
right hemisphere. Readings taken at
300-500 m.s. illustrate that the highest
levels of electrical activity take place in
the medial parietal lobe of both
hemispheres. Measurements taken at
600-700 m.s. show a large increase of
activity mostly in the left hemisphere of
the occipital, parietal, and frontal lobes.
Condition 1:Response=Know: The color
representations show an extremely high
concentration of electrical activity occurring
in the medial parietal and medial occipital
lobe of both hemispheres at the 200 m.s. time
frame. In addition, high levels of activity
take place in the right hemisphere section of
the parietal and frontal lobe, as well as in
both hemispheres of the pre-frontal cortex.
Readings at the 300 m.s. time show a large
drop of activity in the lateral frontal and
lateral parietal lobe of the right hemisphere,
whereas high amounts of activity continue to
occur in the prefrontal cortex as well as in the
dorsal parietal and rostral occipital lobe.
Readings taken at 400 m.s. portray a large
increase in activity throughout the majority of
portions of the brain, with the exception of a
small portion in the frontal lobe of the right
hemisphere. Readings taken at 500 m.s.
show a centralization of processing in the left
hemisphere as well as an almost non-existent
level of activity in the lateral portion of right
frontal lobe. Activity in the lateral portion of
the frontal lobe picks up at 600-700 m.s. time
frame; large increases of activity also occur in
the pre-frontal cortex (primarily at 700 m.s.)
and the parietal lobe.
Condition 2: Response: Know: Readings
at 200 m.s. show a great amount of
activity at the caudal parietal lobe as
well as the rostral occipital lobe. Lower
levels of activity can be seen in both the
medial and lateral sections of the
frontal lobe. Measurements taken at
300-600 m.s. show a decrease of
activity in the medial and lateral
sections of the frontal lobe, as well a
centralization of the processing to the
caudal parietal lobe and the rostral
occipital lobe. Readings at 700 m.s.
show a fairly large decrease in activity
at the caudal parietal lobe and rostral
occipital lobe.
Overall: Response=Remember:
Readings from 200-500 m.s. show the
majority of processing occurring in the
caudal parietal lobe as well as in the
entire section of the occipital lobe. At
600 m.s., an increase in activity can be
seen in lateral and medial sections of
the parietal lobe in the left hemisphere.
At 700 m.s., this trend continues with a
greater amplitude
Overall: Response=Know: At 200 m.s.
a great deal of activity is occurring in
both hemispheres of the caudal parietal
lobe, as well as in many sections of the
occipital lobe. From 300-700 m.s.,
processing occurs mainly in caudal
parietal and rostral occipital lobes.
Moderate amounts of activity can also
be seen in all sections of the left
hemisphere, as well as in the caudal
quarter of the right hemisphere.
Based upon the ERP data collected from the memory testing, it can be said that no conclusive physiological
difference between explicit and implicit memory systems can be surmised from the available results. The
data collected simply did not offer enough spatial or amplitudal differences between the ‘Remember’ and
‘Know’ responses to conclude that there is, in fact a different system for processing implicit memories as
opposed to that which processes explicit memories. The major differences between amplitudal and spatial
relations of the neural processing seem to occur only when the two conditions are compared. In both the
‘Remember’ and ‘Know’ responses for Condition One, the brain relatively more active than that of the
‘Remember’ and ‘Know’ responses for Condition Two. These differences are possibly due to the fact that a
greater amount of processing is required to recall abstract words as opposed to concrete words which showed
a more concise ‘streamlined’ effect. This could be due to the fact that no specific memory will personify an
abstract word or concept completely, therefore the brain might have to “search” through different areas to
assign a meaning to the word.