Effects of Caffeine and Mental Fatigue on Selective Attention

When people are working on a cognitively demanding task for a prolonged period
of time, they start experiencing mental or cognitive fatigue, reflected in
deteriorated task performance. An important observation is that mentally
fatigued people often report having a hard time keeping their attention focused
and that they are easily distracted. In a previous study that we performed, we
found neurophysiological evidence that selective attention is indeed negatively
affected by mental fatigue. Mentally fatigued people find it mainly harder to
block out irrelevant information.
Caffeine is a stimulating substance, that is used to counter fatigue. Little is
known about the effects of caffeine on mental fatigue, as induced by time on
task, and the sustainability of the it's effects. Nevertheless it is not
unlikely that caffeine does have a attenuating effect on mental fatigue as
well, because of similarities between the two. Under normal circumstances,
mental fatigue causes gradual changes in both overt behaviour and
neurophysiological markers of attentional processing, however, how caffeine
influences this remains unknown. Therefore, the main question that we seek to
answer is how caffeine alters the development of the effects of mental fatigue
over time.
Besides investigating performance degradation, this study will specifically
investigate how caffeine changes the relation between processing of relevant
and irrelevant sensory information during different stages of mental fatigue.
The method that we used in our previous study has shown that it can be used to
specifically discriminate between these two effects of selective attention.

The main research questions are whether caffeine influences the development of
mental fatigue during task performance as reflected in task performance and how
caffeine influences the strength of visual selective attention, reflected in
electrophysiological differences in the processing of relevant and irrelevant
visual information.

The experiment is divided into two sessions for the two conditions, the
caffeine and control/placebo condition. The order of these conditions will be
assigned randomly. In both conditions the participant will have to drink a cup
of decaffeinated coffee. In the caffeine condition 3mg of caffeine per kg of
body weight will be added. In the control condition a similar amount of a
physiologically inert substance will be added. The order of assignment to the
experimental or control condition will be determined double blind.
During the experimental session, EEGs will be recorded, 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 go out to
electrophysiological effects that have sources in visual processing areas. Here
interaction effects 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.
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. In order to acquire subjective
measures of fatigue, participants will be asked to fill out a short form,
consisting op 20 questions with 4 response options (AD-ADL; Thayer, 1989),
before and after each experimental session.

Pseudo random and counter balanced administration of caffeine.

The subjects may experience the experimental task as fatiguing, because of it's
duration. The recording of EEG poses no risks.