Correlating neural activity with changes in visual experience

In the proposed research project, we intend to find evidence to assess to what
extent neural competition occurs in absence of perceptual rivalry. To answer
this question, we intend to use a frequency-tagging approach to binocular
rivalry, and supplement this approach with an n-back task to capture the
subject*s attention in a part of the experiment. Measuring EEG with 64
electrodes will result in a spatial resolution that makes it possible to
investigate the amplitudes in the SSVEP as well as its spatial extend.
Furthermore, the spatial resolution will be reasonable for the analysis of
changes in neuronal synchrony. If successful, the proposed research will fill a
void in our knowledge of the neural basis of binocular rivalry, which is a
model phenomenon in the study of conscious perception.

How do a spatial shift of attention and an increased working memory load
influence the dynamics of neural competition?

The stimuli for rivalry are presented each on one side of a computer display;
an opaque screen bisecting the display makes sure that each eye only receives
stimuli from one side of the display. Both the stimuli will be tagged with a
unique frequency which will permit to study the neurodynamics of the
alternating percepts. Participants are instructed to fuse the images so that
binocular rivalry is the result. Above the stimuli for rivalry, identical
letters for the n-back task are shown so that fusion of the images results in a
perception of a single letter. Between the letters and the images, dots are
presented, and the subjects are asked to direct their focus to these dots.
In one part of the experiment, subjects are asked to ignore the letters, and
report their perceptual experience, using one key to report experience of the
left image and another for the right image. In the other part of the
experiment, the subjects are asked to do the n-back task. This way, attention
has to be directed at a different spatial location and the subjects*
working-memory load can be manipulated.
The relation between perception and dynamic changes in brain activity will be
investigated neurophysiologically, by correlating perceptual reports with
patterns of alternation in stimulus-evoked amplitude and synchronization of EEG
activity in the brain. Behavioral measures of response accuracy for the n-back
task will be analyzed to make sure that subjects are performing the task
sufficiently well.

The application of the electrocap on participants head takes about 45 minutes
in total. The experimental task during which the EEG is measured takes about
one hour, depending on the duration of the breaks participants decide to have
between the conditions. The task is presented in 4 blocks of about 15 minutes,
including small breaks between conditions. When the experimental session is
concluded the electrodecap will be removed and participant*s hair washed. There
are no risks in participating in the experiment.