Effects of letter case on processing sequences of written words

In four experiments, we investigated the impact of letter case (lower case vs. UPPER CASE) on the processing of sequences of written words. Experiment 1 used the rapid parallel visual presentation (RPVP) paradigm with postcued identification of one word in a five-word sequence. The sequence could be grammatically correct (e.g., "the boy likes his bike") or be an ungrammatical reordering of the same words (e.g., "his boy the bike likes the"). We replicated the standard sentence superiority effect (more accurate identification of target words when embedded in a grammatically correct sequence compared with ungrammatical sequences), and also found that lowercase presentation led to higher word identification accuracy, but equally so for the grammatical and ungrammatical sequences. This pattern suggests that the lowercase advantage was mostly operating at the level of individual word identification. The following three experiments used the grammatical decision task to provide an examination of letter case effects on more global sentence processing measures. All these experiments revealed a significant lowercase advantage in grammatical decisions, independently of the nature of the ungrammatical sequence (Experiments 2 and 3) and independently of whether or not the letter case manipulation was blocked (Experiment 4). The size of the effects observed in grammatical decisions again points to individual word identification as the primary locus of the lowercase advantage. We conclude that letter case mainly affects early visuo-orthographic processing and access to case-independent letter and word identities. (PsycInfo Database Record (c) 2023 APA, all rights reserved).