This paper reviews the most important studies which have delt with the
early and late effects on attention of acute and chronic benzodiazepi
nes use. Different methodological aspects are approached and also the
results obtained. The paper also describes a poligraphical trial that
have proved it's sensibility to detect the action of hipnotic medicine
s in humans. The first part of the article consists of general reflect
ions about this field of research. After that the effects of benzodiaz
epines on performance of vigilance task are pointed out. At last the r
esidual effects on EEG activity and psychophysiological variable are s
hown.