Reading MIXed caSE ITEms is harder than reading UPPERCASE or lowercase items, but whether the type of case transition in mixed-case items affects performance is unknown. We investigated whether the type of case transition (e.g. PLAnt vs. plaNT) impacts lexical decision performance—deciding whether a letter string is a word. Abstract letter identification models propose that due to perceptual learning, we should process uppercase-to-lowercase items better than lowercase-to-uppercase ones. Eleven students participated in a lexical decision experiment consisting of twelve 32-trial blocks. In six blocks, the type of case change was constant (all uppercase-to-lowercase or all lowercase-to-uppercase); in the other six blocks, type of case change varied over trials. Within each block, item length was constant, and word frequency varied. On each trial, a letter string was presented on a computer screen, and the participant was to respond whether the string was a word or a nonword by pressing buttons as quickly as possible. In overall analyses (of correct responses to words and nonwords), there were significant effects of lexicality and item length, but no significant effect of format. In correct responses to words, there was a significant effect of word frequency, but no significant effect of format
