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EEG effects of repetition interval
lengths during natural scene
perception
Hielke Prins
Iris Groen
Steven Scholte
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When participants perceive natural images, their EEG
response correlate with Weibull distribution parameters
Weibull distributions have two free parameters (beta andgamma) and describe distributions of low-level features
in the stimuli (here: contrast values)
For contrast features, distributions vary from power lawlike to Gaussian depending on the amount of clutter in
the stimuli
Background: image statistics
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Background: image statistics
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A model (Scholte et al. 2009) describes processing of
the stimuli by the brain
This model effectively calculates the two parameters of
the Weibull distribution
Explained variance between the model and the EEG
response increases with the number of presentations
(Ghebreab et al., in submission)
Background: stimuli repetition
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Background: stimuli repetition
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Question
How long does the effect of repetition lasts?
Goals1. Confirm the effect of a previous encounter of the
stimulus on the EEG response of participants perceiving
the stimuli
2. Determine whether the length of the interval between
successive repetitions of the stimuli affects the response
Experimental question / goal
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16 participants
1 hour of EEG acquisition per session
4 conditions reflecting different repetition intervals
Short Intermediate
Long
Over-night
2 sessions on the same time on 2 subsequent days
400 stimuli per condition
All 4 stimulus sets have equal spread in beta-gamma
values
Experimental design: numbers
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Experimental design: intervals
Set Repetition Interval Number of Stimuli
I 4-8 minutes 2 * 200
II 12-20 minutes 2 * 200
III > 30 minutes 2 * 200
IV 23-24 hours 400
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Participants have to categorize the stimuli in man-made
and natural environments according to their first
impression
A small questionnaire serves as a pilot to determine
whether an influence of long-term previous visual
experience can be determined
Experimental design: task
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Computing the explained variance between model
Weibull parameters and early deflections in the ERP
Comparison of the explained variance between the firstand second presentation of the stimuli for each repetition
interval
Data analysis
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Analysis of differences in the effect of repetition between
the repetition intervals provides information about the
duration of the effect
Long lasting effects require different mechanisms of
plasticity then fading shorter ones
An answer on the research question might thus provideclues on how to improve the model to account for the
observed effect of repetition on the explained variance
Conclusions under various outcomes
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40 blocks of 40 stimuli
Short, intermediate and long blocks repeated once
Over-night blocks repeated in second session
Discussion
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Discussion
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How to counter-balance stimuli in order to minimize theeffects of processing history or fatigue?
Is it possible to quantify the best solution?
Discussion
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