et al. (2002) demonstrated that changing the font in which repeated presentations of nonwords were presented reduced the short-term perceptual priming of those stimuli, especially for massed items. Upon a recognition memory test, there was no spacing effect found for the nonwords presented in different fonts during study. These results support the hypothesis that short-term perceptual priming is the mechanism that supports the spacing effects in cued-memory tasks when unfamiliar stimuli are used as targets. Furthermore, when the font was changed between repeated presentations of words in the study phase, there was no reduction of the spacing effect. This resistance to the font manipulation is expected with this two-factor account, as semantic processing of words at study determines performance on a later memory test, and the font manipulation is irrelevant to this form of processing. Mammarella, Russo, & Avons (2002) also demonstrated that changing the orientation of faces between repeated presentations served to eliminate the spacing effect. Unfamiliar faces do not have stored representations in memory, thus the spacing effect for these stimuli would be a result of perceptual priming. Changing orientation served to alter the physical appearance of the stimuli, thus reducing the perceptual priming at the second occurrence of the face when presented in a massed fashion. This led to equal memory for faces presented in massed and spaced fashions, hence eliminating the spacing effect. Encoding variability The encoding variability theory holds that performance on a memory test is determined by the overlap between the available contextual information during the test and the contextual information available during the encoding. According to this view, spaced repetition typically entails some variability in presentation contexts, resulting in a greater number of retrieval cues. Contrastingly, massed repetitions have limited presentations and therefore fewer retrieval cues. The notion of the efficacy of the increased variability of encoding is supported by the position that the more independent encodings are, the more different types of cues are associated with an item. There are two types of encoding variability theory that address the spacing effect. The first assumes maintains that the spacing effect refers to the changes in the semantic interpretations of items which cause the effect while the second holds that variability surrounding context is responsible for the spacing effect, not only semantic variability. To test the encoding variability theory, Bird, Nicholson, and Ringer (1978) presented subjects with word lists that either had massed or