Craik and Lockhart (1972) argued that the concept of rehearsal alone is not sufficient to account for long-term memory. Rehearsal is a kind of processing but it is not very deep. Craik and lockhart believed that it is the"depth"of processing which determines whether information is stored over a long rather than a short period. Craik and lockhart defined "depth" in terms of a continuum: an example of shallow processing would be to say whether …showed first 75 words of 665 total…

…showed last 75 words of 665 total…in 1978. Badderley criticised the levels of processing model, on the grounds that the concept of levels was circular, and did not really lead anywhere. The theory states that material which has been strongly processed will be remembered better, but it also works, backwards, if we find that material is well remembered, then we argue that it has been processed deeply! This makes the theory very difficult to test and badderley challenged it on those grounds.