In my current
research, I am investigating the underlying mechanisms of
subsequent memory effects using behavioral and ERP methods. I
wish to develop a more complete understanding of the neural
basis for these effects using fMRI. The proposed experiment is
based on a study by Turk-Browne, Yi, & Chun (2006) that found
correlations between attenuation of the BOLD signal at study and
subsequent memory at test. I wish to build on this study by
obtaining separate measures of conceptual and perceptual priming
and also by asking subjects to make “remember / know” judgments
at test. Predictions are made for which brain regions will show
subsequent memory effects.
Also I am working on
a study looking at the role of perceptual information in the
formation of false memories. People in my experiment
judge thematically-related words in various unusual-looking
fonts and are later given a recognition test for which half the
foils use the same font as the study items from the same theme.
I plan to use ERP and later fMRI to look at how perceptual
encoding mediates subsequent false memory.
I
am completing an ERP
(event related potential) project involving
problem-solving with Dr. Kenneth Kotovsky.*
When subjects are given a task called the balls-and-boxes
puzzle, they typically make a large number of correct moves in
succession near the end but are then unable to explain how they
solved the puzzle, indicating some sort of non-conscious insight
mechanism. We are giving subjects this task while measuring
response-locked ERPs to learn about the neural correlates of
this non-conscious problem- solving mechanism.
My first project at
Carnegie-Mellon built on my experience of using EEG methodology
by finding the ERP correlates of
initial feeling-of-knowing. This project sought in part to
replicate a behavioral study conducted in our lab[1]
which found that subjects were very good at quickly assessing
whether they would be able to retrieve the answer to a problem.
This assessment was made in a brief time window (under 850ms)
that was much shorter than the time required to actually
retrieve the answer itself. This rapid, metacognitive judgment
was shown to use a heuristic based on the familiarity of terms
in the question, not the availability of the answer per se. We
believe that this heuristic enables efficient and flexible
strategy selection during cognitive tasks. The study we just
completed built on this work by adding an EEG component. In it,
subjects were presented with a series of previously unfamiliar
math problems, some of which repeated over the course of the
experiment. Upon first seeing the problem, subjects rapidly
decided within 850 milliseconds whether to solve it by
retrieving the answer from memory or calculating it on scrap
paper. Subjects had 25 seconds to type the answer if they
choose “calculate,” but only 2 seconds if they choose
“retrieve.” A large bonus was given for successful retrieves so
subjects had an incentive to learn the answers. For the EEG
analysis, we were particularly interested in differences in
brain wave patterns in the initial strategy selection phase.
Patterns unique to retrieve trials during the first 850
milliseconds reflected those processes relevant to initial
feeling-of-knowing. More specifically, we looked at
differential patterns of theta wave activity, an important
marker of hippocampal activation, as well as the P300 component,
a brainwave pattern indicating recognition of a stimulus as
task-relevant. Previously unfamiliar math problems were
repeatedly tested over the course of the experiment and the
feeling of knowing or not-knowing judgment had to be completed
in 850 milliseconds (much less time than needed to retrieve the
answer itself). ERP analyses uncovered waveform differences
between accurate retrieve vs. calculate trials as early as 200
ms following onset of the problem. Accurate retrieve
trials showed activation primarily in the right hemisphere
following problem onset, while calculate trials and inaccurate
retrieve trials showed activation primarily in the left
hemisphere. I submitted the results of our study for
publication to
Neuropsychologia.
I also presented a poster of our results at the Psychonomic Society's Annual Meeting in Long Beach, CA in
November 2007.
