טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYael Zahar
SubjectBrain Activation during Recognition of Sparse, Camouflaged
Figures - an fMRI Study
DepartmentDepartment of Biomedical Engineering
Supervisor Professor Gur Moshe


Abstract

Camouflaged images are hard to interpret at first sight. However, after watching them for a while, the observer uses his own mental configurations to develop a hypothesis about what the whole pattern might be. Once the viewer is able to see the hidden figure, the picture becomes dramatically reorganized into figure and ground. If the same image is presented again, the viewer will see the figure instantly, since the whole pattern has been consolidated in memory.


We used fMRI to study the brain areas involved in the process of perceiving the figure from camouflaged input.

                                                                                                                   

Two research paradigms were used:


The first paradigm explored the process of recognizing the figure within a camouflage. Subjects viewed the camouflages inside the magnet for the first time, and were asked to indicate if and when they recognized the figure. fMRI data were taken throughout  the viewing period. Our results show that Retinotopic areas are involved in pre-recognition processing stages that are common to both recognized and unrecognized camouflages, while higher visual areas are involved in processes related to the recognition of the figure in camouflages.


In the second experiment we've used fMRI-Adaptation paradigm to test whether common or distinct neural populations respond to camouflages in comparison with grayscale photographs of the same figures. The results show that perception of camouflages, when their solutions are well-established in memory, recruits many of the same brain areas as grayscale photos. In particular, their perception is accomplished at extra-retinotopic areas which show decreased activations for repeated objects across changes in their format.