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Vision Lab
Slides
from IGERT project 2004
My research experience began as a research assistant in the Vision Lab
at Brandeis University in the fall of 2003. I began my tenure there by
assisting graduate researchers in project analysis, working through transcripts
of testing sessions and cataloguing data for further analysis by lead
researchers. By the spring semester, I was working under the guidance
of the PI conducting a follow-up experiment to a project conducted by
a former graduate of the lab. The PI wanted to investigate whether there
was occurrence of hysteresis in repeated trials with varied auditory
and visual stimuli. During that semester I worked with lab members to
develop a sufficient test for hysteresis, updated old code from the original
experiment to implement our new experiment design, ran subjects through
trials and did a limited amount of data analysis. We did not find significant
evidence of hysteresis in the effects of repeated exposure to stimuli,
but I had the opportunity to learn about experiment design and human
subject testing.
The following summer, I received a position in the IGERT Summer Research Program
to continue research in the same lab. My project, “Configural Information
in Episodic Visual Recognition,” aimed to discover whether an inter-stimulus
relation within a series of abstract stimuli enabled subjects to recall them
more easily. I worked cooperatively with other lab members to develop the
experiment design, particularly with one collaborating research partner,
but was the lead researcher on the project. Our test stimuli were compound
gratings with varying frequencies. Before the experiment, each subject was
given a threshold test to determine the least noticeable difference in frequencies
for each subject. The experiment trials were then scaled to fit a particular
subject’s threshold. This was necessary to ensure that each subject
was experiencing as close to the same trials as possible, despite differing
abilities in distinguishing spatial frequency. In each trial a subject was
presented with a series of three gratings, and then asked whether a fourth
grating had been present in that series. Target trials did include the test
stimulus in the series, while lure trials did not. Trials were arranged into
two blocks. A type blocks consisted of mathematically related stimuli (where
the change in frequency followed a linear progression through the trial),
while B-type blocks consisted of the same stimuli as the A block, but 80
percent of trials had been re-ordered so as not to be sequential. Monetary
compensation was given for time spent in testing sessions, and a bonus was
given for high percentages of correct answers as an incentive for accuracy.
We did not find any significant difference between the overall performance
between Block A and B trials. We did find that in block B trials that were
not arranged linearly subjects were able to more accurately recognize the
second stimulus presented in a trial, while subjects performed better in
recognizing the first or third stimulus in the trials that did contain linear
progression. However, we also noted that the overall accuracy was relatively
low and that subjects had low sensitivity to signal in both the linear and
non-linear trials. We attributed this to not having enough difference between
the lures and targets in trials due to the limited frequency range available
to us. At the end of the summer, I gave a 30-minute presentation on my findings.
The most useful skills I developed were using unexpected results to learn
about the phenomenon we were studying and diagnosing problems in an experiment
based on the results.
In a related study, I designed, programmed and executed an experiment to determine
whether a subject’s perception of similar space is isomorphic with
physical space. On each trial, subjects were presented with three complex
gratings arranged equidistance from one another. Subjects were asked to select
the most similar and most different pairs of gratings from the set. The three
pairs of stimuli were then given similarity rankings based on the subject's
judgment: the highest ranking was given to the most similar pair, lowest
rank to the least similar, and by default the median ranking was given to
the pair not deemed to be either the most similar or most different. The
subject-defined similarities were then compared to the physical similarities
of the stimuli. Early results showed that subjects put a greater emphasis
on the similarity between gratings of higher frequencies than the lower frequency
stimuli, which does not correspond to the consistent physical similarity
between all of the gratings in this experiment.
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