Definitions of attentions:
Munu:
“Attention, from whatever angle we consider, it is in the last analysis a motivational process.”
Stout:
“Attention in simply connection so far as it requires for its satisfaction further cognizance of its subjects.”
Mc Dougal:
“Attention is merely conation or striking considered from the points of its effect on cognitive process.”
Shiffrin:
'Attention has been used to refer to all those aspects of human cognition that the subject can control......and to all aspects of human cognition having to do with limited resources or capacity, and methods of dealing with such constraints '

Process of Attention