James (1890, pp. 403-404):
”Everyone knows what attention is. It is the taking possession of the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others …”
A little bit more recently Shiffrin 1988, p. 739):
“Attention has been used to refer to all those aspects of human cognition that the subject can control … and to all aspects of cognition having to do with limited resources or capacity, and methods of dealing with such constraints”
And even more recently Cowan (1995) writes about selective attention’ in a sense that is close to James’ definition of attention. The selective attention is not necessarily voluntary. Also selective attention is a limited capacity process.