This paper is the first of a series aimed at developing a theory of early visual processing in reading. We suggest that there has been a close parallel in the development of theories of reading and theories of vision in Artificial Intelligence. We propose to exploit and extend recent results in Computer Vision to develop an improved model of early processing in reading. This first paper considers the problem of isolating words in text based on the information which Marr and Hildreth's (1980) theory asserts is available in the parafovea. We show in particular that the findings of Fisher (1975) on reading transformed texts can be accounted for without postulating the need for complex interactions between early processing and downloading information as he suggests. The paper concludes with a brief discussion of the problem of integrating information over successive saccades and relates the earlier analysis fo the empirical findings of Rayner.