The Error-related negativity and selective attention

When people are working on a cognitively demanding task for a prolonged period
of time, they start experiencing mental or cognitive fatigue. When people
become fatigued, they typically report having a lack of attention and being
easily distracted. However not much of the underlying neuronal processes is
known. What is known is that a certain electrophysiological effect called the
ERN decreases over time. The ERN has been linked to response competition, and
may signal the need for strategic adaptations in attentional processing.

The present study will investigate the link between the ERN, and selective
attention. There have been studies performed into the relation between mental
fatigue, which is linked to a decrease in ERN activity, and selective
attention, but effects that were found could not be clearly attributed to
attention. Therefore, in the present study, a suited experimental task and
analysis technique will be used. The stimuli will be presented in a quadrant of
the visual field, instead of centrally, which will make it possible to record
electrophysiological signals from the primary and secondary visual processing
areas in the cortex. By applying independent component analyses, activation
levels in these brain areas can be tracked temporally, in order to see how they
are influenced by attention.

Attention can be looked at as a top down neuronal gain control mechanism, that
acts on sensory processing areas in the brain. The role of this mechanism is to
enhance task relevant signals, and to attenuate irrelevant signals. By
manipulating the size of relevant and irrelevant stimuli, attentional effects
on the specific processing of relevant and irrelevant information can be made
measurable.

The main research question is whether a larger ERN is followed by an increase
in the intensity of the processing of relevant signals and a decrease in the
intensity of the processing of irrelevant signals, as reflected in ICA
component amplitudes.
The secondary objective of this study is whether time on task influences the
processing of relevant signals, compared to irrelevant signals.

During this experiment, EEGs will be measured, while subjects are performing on
an adapted version of the flanker task (Eriksen & Eriksen, 1974). In order to
measure specific effects of attention on relevant and distracting information,
a size manipulation will be applied. Our interest will specifically go out to
electrophysiological effects that have sources in early visual processing
areas. Here interaction efects between flanker size and other independent
variables can be interpreted as the influence of these variables on the gain
modulation of distracting sensory signals and interaction effects between
target size and other independent variables can be interpreted as the influence
of these variables of the gain modulation of relevant sensory signals.

In order to be able to record the attentional effects in early visual
processing areas, stimuli will have to be presented in a quadrant of the visual
field of the subjects. In this experiment, the targets and the flankers will be
placed in a quarter circular arrangement, equidistant from a fixation cross, on
which the subjects will have to keep their eyes focussed during the experiment.
Measured from this fixation cross, the target will be placed at an angle of
45º, and the flankers at angles of 15º, 30º, 60º and 75º. The targets and
flankers in this task consist of the letter characters O and H, where in each
trial the four flankers will be identical. Stimuli can be congruent (e.g.
HHHHH) or incongruent (e.g. HHOHH). In each trial, either the size of the
target or that of the flankers is manipulated.

Subjects have to report the identity of the central target stimulus, by
pressing a button (left button for H and right button for O). In total, they
will have to perform this task for two hours.

The subjects may experience the experimental task as fatiguing, because of it's
duration. For what is known, E.E.G. measurements pose no risks.