Transcript Document

Implicit and Explicit Memory?
A Re-Investigation
Marshall, N. A., Tackitt, J. G., Lyles,
J. N., Bowersox, B.
Introduction
The question of whether separate systems for implicit and explicit,
or unconscious and conscious, forms of memory exist in the brain
has not been definitively answered due to the difficulty in ensuring
that ERP results indeed occur without conscious awareness (Rugg).
Our experiment attempts to overcome the difficulties of addressing
this question by selecting stimuli that we suspected would make
any differences between such memory systems more apparent. The
stimuli selected were words obtained from Dr. Tom Busey, which
were grouped in accordance to their level of imagery (either low or
high). We hypothesized that the difference in level of imagery
between the words would result in a notable difference in brain
activity, and that this difference would allow for a more decisive
conclusion to be drawn concerning the alleged separation of
implicit and explicit memory systems.
Methods
The experiment was composed of two segments: a study
period and a testing period. During the study period, the
subject was presented with 200 high imagery and 200 low
imagery words in a random order. During the testing period,
the subject was randomly presented the 400 words included in
the study period, in addition to 200 distracter words (random
words of both high and low imagery not present in the study
list). The test period involved recording the subject’s
responses to each word presented, as well as the
corresponding brain activity via ERP. The possible responses
were as follows. ‘Remember’ meant that the word was
specifically recalled from the list. ‘Know’ meant that the word
was not specifically recalled from the list, although a sense of
familiarity suggests to the subject that it may have been.
‘New’ meant that the word seemed to be not on the study list.
Methods (continued)
High imagery words tended to be words referring to more
tangible things than those of low imagery. For example, high
imagery words included such things as physical objects or titles
of people (i.e.. locker, miner, velvet), whereas low imagery
words included abstract concepts (i.e.. event, moment, proxy).
Results
Figure 1: Remember - New
Figure 2: Know - New
The above illustrations represent average overall brain activity
corresponding to responses of ‘new’ substracted from ‘remember’
or ‘know’. Numbers above each illustration indictates the time in
milliseconds at which the data was recorded.
Results: Discussion
Overall, the acivity is greater in Figure 2 than in Figure 1. The most
notable differences between the illustrations in the two figures
occur at 200, 300, 400, and 700 ms. At 200ms, Figure 2 indicates
more activity in the right hemisphere than in Figure 1. At 300ms,
Figure 2 has more overall activity than in Figure 1. At 400ms,
Figure 2 has much more intense activity in the left hemisphere then
in Figure 1, whereas Figure 1 indicates activity relatively isolated
to the frontal and parietal lobes. At 700ms, Figure 2 indicates less
activity than Figure 1 overall.
Conclusions
Spatial differences between both figures were minimal with the
exception of the readings at 200, 300, and 400ms. The apparent
differeneces suggests that two different memory systems may
exist. The similarites occuring overall suggest that the systems are
intimately related. However, a further and more detailed analysis
of the data (i.e. a greater number of spatial maps for the given ERP
data) may be beneficial in concluding the seperation of the two
memory systems.