  In his principal work, the Collection on Valid Cognition (PS I, k5a-6cd; Hattori 1968, 27) Dignāga discusses what appear to  be three distinct types of cognition under the rubric of perception:  sense perception, mental perception, and perception of the yogi.  Dignāga also admits self-awareness (svasaṃvedana) as a distinct type of cognition, although there is some debate about  whether this is to be interpreted as a type of perception (see   §7.2  for a discussion of svasaṃvedana). The disagreement  centers on whether self-awareness should be understood as a dual  aspect cognition (Nagatomi 1979) or as a new type of perception.  Wayman (1991), following Hattori (1968), argues that it should,  whereas Franco (1986, 1993) argues to the contrary. Franco bases  his argument on a piece of textual evidence that appears to endorse  the view that Dignāga takes the self-apprehension of internal  states such as desire to be a case of mental perception. Drawing from the commentarial literature on Dignāga preserved in Chinese, Yao (2004) offers some compelling arguments as to why scholars, from  traditional commentators such as Prajñākaragupta (ca. 800)  to Franco appear to have consistently misunderstood the relationship  between self-awareness and mental perception. Yao maintains that the  resolution to the question of whether Dignāga does or does not  accept four types of perception depends on correctly understanding  the function of mental perception, which he takes to apply only to  the direct apprehension of mental objects (2004, 63). Thus, for Yao  mental perception (manasa-pratyakṣa) and the mental  faculty of cognitive awareness (mano-vijñāna) are  to be clearly differentiated, the first being just an aspect of the  latter. Likewise, self-awareness and yogic perception too are taken  to be just different states of this mental cognitive awareness (see  Tillemans 1989; Steinkellner 1978, 1982, 1999; and Dunne 2006 for  discussions of this issue).