The Levels of Processing model, created by Fergus I. M. Craik and Robert S. Lockhart in 1972, describes memory recall of stimuli as a function of the depth of mental processing. Deeper levels of analysis produce more elaborate, longer-lasting, and stronger memory traces than shallow levels of analysis. Depth of processing falls on a shallow to deep continuum. Shallow processing (e.g., processing based on phonemic and orthographic components) leads to a fragile memory trace that is susceptible to rapid decay. Conversely, deep processing (e.g., semantic processing) results in a more durable memory trace. There are three levels of processing in this model. Structural processing, or visual, is when we remember only the physical quality of the word E.g how the word is spelled and how letters look. Phonemic processing includes remembering the word by the way it sounds. E.G the word tall rhymes with fall. Lastly, we have semantic processing in which we encode the meaning of the word with another word that is is similar of has similar meaning. Once the word is perceived, the brain allows for a deeper processing. This theory contradicts the multi-store Atkinson-Shiffrin memory model which represents memory strength as being continuously variable, the assumption being that rehearsal always improves long-term memory. They argued that rehearsal that consists simply of repeating previous analyses (maintenance rehearsal) doesn't enhance long-term memory. In a study from 1975 (Craik and Tulving) participants were given a list of 60 words. Each word was presented along with three questions. The participant had to answer one of them. Those three questions were in one of three categories. One category of questions was about how the word was presented visually ("Is the word shown in italics?"). The second category of questions was about the phonemic qualities of the word ("Does the word begin with the sound 'bee'?"). The third category of questions was presented so that the reader was forced to think about the word within a certain context. ("Can you meet one in the street [a friend]"?) The result of this study showed that the words which contained deep processing (the latter) were remembered better. Modifiers Familiarity, transfer-appropriate processing, the self-reference effect, and the explicit nature of a stimulus modify the levels-of-processing effect by manipulating mental processing depth factors. Familiarity A stimulus will have a higher recall value if it is highly compatible with preexisting semantic structures (Craik, 1972). According to semantic