  Nearly all discussions that focus on the type of consciousness that  is associated with a specific perceptual occasion (e.g., visual  consciousness with an instance of visual perception), seek to answer  the question of causal priority (which is prior, sensation or  cognitive apprehension?) by examining the nature of contact itself.  Thus, whereas in the Nikāyas contact (sparśa) is  the primary cause of the arising of cognitive awareness, in the  Abhidharma it becomes a derivative aspect of empirical consciousness  itself (or indeed a dharma in its own right) (see  Visuddhimagga XVII, 223–225; AKBh ad III,  30). However, the mere presence of objects in the range of perception does not by itself give rise to cognitive awareness. For the content  of experience to enter the domain of awareness, attention must be  directed to whatever is sensed. For this reason, attention  (āvartana), understood as the mind's turning toward a  certain object, is not a key term in the canonical literature, where  various cognitive functions are treated as distinct forms of  consciousness. The term becomes significant in the Abhidharma, where  the generality of consciousness is replaced with more concrete mental functions that perform specific tasks. However, Buddhaghosa in the  Atthasālinī maintains that while consciousness can arise without attention, it cannot arise in the absence of an  objective cognitive support (cf. Williams 1981, 230).