Manasikāra: 'attention', 'mental directing', 'reflection'.
1. As a psychological term, attention belongs to the construction-group sankhāra-khandha Tab. II. and is one of the 7 mental properties cetasika that are inseparably associated with all states of consciousness see: cetanā In M. 9, it is given as one of the factors representative of mind nāma It is the mind's first 'confrontation with an object' and 'binds the associated mental properties to the object.' It is, therefore, the prominent factor in two specific classes of consciousness: i.e. 'directing āvajjana at the five sense-doors' Tab. I, 70 and at the mind-door Tab. I, 71. These two states of consciousness, breaking through the subconscious life-continuum bhavanga form the first stage in the perceptual process citta-vīthi see. viññāna-kicca See Vis.M XIV, 152.
2. In a more general sense, the term appears frequently in the Suttas as yoniso-manasikāra 'wise or reasoned, methodical attention' or 'wise reflection'. It is said, in M. 2, to counteract the fermentations āsava, it is a condition for the arising of right view see: M. 43, of Stream-entry see: sotāpattiyanga and of the factors of enlightenment see: S. XLVI, 2.49,51. - 'Unwise attention' ayoniso-manasikāra leads to the arising of the fermentations see: M. 2 and of the five hindrances see: S. XLVI, 2.51.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.