M.Sc Thesis

M.Sc StudentTzaran Andrey
SubjectInattentional Blindness: fMRI Research
DepartmentDepartment of Biomedical Engineering
Supervisor ASSOCIATE PROF. Moshe Gur
Full Thesis textFull thesis text - English Version


The effects of attention on visual perception have long been investigated using psychophysical tools. Recently, there is increasing interest in looking at brain mechanisms that are activated by attention using a host of neurophysiologic techniques. Functional MRI (fMRI) has been used successfully to show, in humans, various cortical areas that are activated during attention guided perception. In this study we used fMRI, to look, for the first time, at the phenomenon of inattentional blindness (IB).

IB occurs when objects presented in one part of the visual field are not perceived when attention is directed to another side of the field. We flashed stimuli briefly at attended and non-attended parts of the visual field so that the subjects did not move their eyes during presentation. Event-related fMRI methodology was used to define activity in various cortical areas, visual and non-visual (Brodman areas, 37, 39 and 7) while attending a visual field with and without visual stimuli and during IB. Changes in blood oxygenation (BOLD fMRI signal) were used as an indicator of brain activity.

We found that attention caused significant changes in BOLD activity in areas 9 and 7 even in the absence of any stimuli. Attending to the part of the visual field where stimuli were presented caused, as expected, an increase in brain activity at cortical areas receiving input from that part of the field, but, surprisingly, also in the opposite (ipsi-lateral) hemisphere. This is taken as an indication of strong top-down bilateral attention influence. Finally, we showed, for the first time, that activity generated in the ipsi-lateral hemisphere by attentional mechanisms, is strongly suppressed by IB. This result is intriguing in showing a complex interaction between top-down attentional mechanisms and bottom-up input that is different in the two hemispheres.