[Posner's theory of attention: right hemisphere processing advantage in extended attention]

Posner proposed a theory of attention based on target detection, visual orienting, and alertness. The latter is supposed to use brain structures mainly located in the right hemisphere. Whitehead found a right hemisphere processing superiority during sustained attention. An additional auditory stimulus is thought to produce a change of alertness and should interfere with this asymmetry, which Whitehead was able to show, too. It remains unclear how the left hemisphere is activated by right hemisphere pathways. Therefore we tried to replicate Whitehead's findings. In our first experiment the expected interaction between visual field, foreperiod duration, and tone was obtained. Probably the tone used in our experiment was not intense enough to produce a sufficient change in alertness. We used a more intense tone in a second experiment. This time a three-way interaction was present but could not be interpreted in terms of Whitehead's assumptions. Instead, the additional alerting stimulus seems to influence the state of alertness in a much more general and long-lasting way.