Functional imaging of visual perception and attention

People usually perceive what is in front of their eyes without any difficulty,
and are able to act in response to that visual information without effort. This
apparent ease belies the fact that visual information processing the brain is
an extremely complex and incompletely understood process, with over half of the
cerebral cortex dedicated to the purpose. Some situations bring the internal
mechanisms of visual information processing to light. One example is the case
of so-called 'ambiguous images', a kind of puzzle-figure that has not one but
two possible perceptual interpretations. A well-known example is the
'duck-rabbit illusion': when looking at this image, which itself does not
change, the observer perceives a duck at some moments and a rabbit at others,
thus revealing the active and interpretative nature of visual processing in the
brain. A different example is formed by the eye movements we make when entering
a room or driving a car. In those situations there is an abundance of visual
information to choose from, and our system selects just a specific part of this
information using either eye position or attention, while we ignore the
remaining information.

The main objective of this study is to understand how the brain selects
information using attention: what determines which information is selected and
how does this selection occur? An important component of this project will be
aimed at researching how this directing of attention relates to the other
example mentioned above: the changing perception of 'ambiguous images'.
Existing studies indicate that these perceptual alternations between distinct
interpretations arise from processes that have much in common with the
processes behind switches in attention between parts of the visual input. This
potential connection offers a fruitful new angle for studying visual perception
and its dependence on attention.

Observers will be scanned in an MRI scanner while they view images projected
onto a screen. These images can be ambiguous figures, such as the
above-mentioned 'duck-rabbit' illusion and other images that can be perceived
in two different ways. Observers will be able to indicate their perception at
any given moment using response buttons. The projected displays can also
consist of multiple objects, usually geometric shapes like squares and circles,
in which case observers will be asked to move their attention between objects
in the display. Our analysis of measured brain activity will primarily focus on
the activity that occurs around the time of perceptual switches in the face of
ambiguous visual information, and around the time of attention shifts in the
case of multi-element displays.

relatedness (if applicable):
One scan session will last for about 60 minutes. Functional MRI is a
non-invasive technique with no known rists. The data will primarily be used for
research purposes. However, if we encounter important brain defects we will
contact a radiologist for advise. If the radiologist deems it important to
follow up on the observation, then the participant will be notified. There are
no immediate benefits for the participants, apart from the monetary
compensation. Participants will be made familiar with the visual displays and
their task beforehand, outside the scanner.