When you repeat a stimulus (such as showing the same image of the same face twice in row), neural responses in the brain decrease (see image below for an example). This decrease occurs across sensory modalities in both humans and non-human primates and is considered one of the simplest forms of learning.
Example mean (averaged across 9 participants) fMRI signals to nonrepeated stimuli (black) and repeated stimuli (blue) plotted as a function of time (the length of 1 block was 12 s) for six stimulus categories from a face-selective region. Note that signals reflecting responses to stimuli that are not repeated (black) are higher than signals reflecting responses to stimuli that are repeated (blue) across the six categories. This decrease is known as adaptation, habituation, or repetition suppression. Data from Weiner et al., 2010
The CNL is interested in understanding the nature of this signal and how it matriculates at the single voxel level, as well as in patterns across cortical structures (see image below). The CNL is also interested in understanding the relationship between this decrease as measured with fMRI (in which each fMRI voxel contains tens of thousands of neurons depending on the size of the voxel) relative to other methods. Presently, we are examining the relationship between fMRI adaptation and adaptation observed in electrocorticography (ECoG) in order to better understand the spatiotemporal dynamics of adaptation in human ventral temporal cortex. Finally, in future studies, we are interested in understanding the relationship between signal decrement vs. signal enhancement and how the combination of the two affects subsequent learning and behavior.
Left: Each panel shows the right hemisphere ventral inflated surface of a representative participant zoomed into ventral temporal cortex. The pattern of distributed responses to three object categories for nonrepeated (top) and repeated (bottom) conditions is depicted for a block design experiment which we refer to as short-lagged because only a maximum of 3 seconds separated image repeats. A long-lagged experiment was also conducted in which a maximum of 174 seconds separated image repeats. Right: Quantifying the effect of stimulus repetition on the VTC pattern for the different experiments using a classification analysis shows that classification performance decreases for short-lagged repetitions, but increases for long-lagged repetitions. This effects is not driven by the voxels illustrating the highest category selectivity (right bars in each subplot). Dotted line indicates chance level performance. Error bars: between subjects standard error of the mean. Images adapted from Weiner et al., 2010
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