It is difficult to maintain the semantic level of arousal for more than 15 minutes.
On the other hand, we are told by those who teach Public Speaking classes, that we really canāt attend to speeches for more than 15 minutes without loosing our level of concentration. Hence, we should expect a certain amount of fluctuation.
But how can we influence these fluctuations to maximize the amount of time that we focus our energies at the Semantic Level.
There are a number of environmental factors, which can impact upon the level of energy we have for the perceptual processes.
These include among others: motivation, nutrition, sleep and fatigue, and stimulation through other modalities.
There is another, which is outside the scope of this discussion, and that is body rhythm.