|M.Sc Student||Adler Gilad|
|Subject||Attention Modulates Repetition Suppression in Object-|
Selective Regions - an fMRI Study
|Department||Department of Biomedical Engineering||Supervisor||ASSOCIATE PROF. Moshe Gur|
|Full Thesis text|
Neuroscience research has managed to map the functionality and organization of many cortical regions involved in visual processing.
Using fMRI to explore high level regions, such as object selective regions, reveals a phenomenon of decreased BOLD signal to a repeated stimulus.
This phenomenon, "repetition suppression", is commonly considered to be local in nature, reflecting adaptation of underlying neural mechanisms. However, perceptual effects which are easily measured with long term adaptation are mostly absent in this case.
The necessity of attention for fMRI repetition suppression has been discussed. The current study approaches attention as a continuous modulating factor, where different aspects and levels of attention have different effects.
The current study uses similar paradigms for inducing repetition suppression and for studying psychophysical effects. We tested object-selective regions - LO and pF (lateral occipital and posterior fusiform) with faces stimuli to ensure strong responses.
We show that although robust, repeatable suppression is generated, it is not accompanied by any significant effect on psychophysical performance.
In an fMRI experiment comparing two types of top-down attention repetition suppression was 31% with task-driven attention and only 18% with spatial only attention. In a psychophysical experiment mimicking the fMRI one, these large values of repetition suppression had insignificant effect on psychophysical performance.
Other fMRI experiments in this study compare repetition suppression with bottom-up attention induced by stimulus saliency with spatial top-down attention (31% vs. 18% respectively) and semantic tasks with top-down attention tasks.
The current study demonstrates that repetition suppression is modulated by top-level attention, and that even large scale suppression is not connected with a significant perceptual effect. These results also show that when addressing attention as a modulating factor of repetition suppression, a distinction between top-down and bottom-up, spatial and semantic tasks should be made, as their effects are considerably different.