The role of phonetic processes in letter detection: A reevaluation

In seven experiments we investigated the finding that subjects often fail to detect the letter f in the word of. This effect was depressed in Experiment 1 when asterisks were inserted between all letters in a passage, suggesting that unitization processes contributed to the effect. Experiment 2 compared detection of the letters o and f and found a significant but much smaller effect for o, indicating that unitization can only provide a partial explanation for the effect with f. In Experiment 3 the effect was maintained for the letter f but not the letter o when subjects searched an auditory version of the passage, which implies that phonetic processes are involved in the effect for f. Experiments 4, 5, and 6 demonstrated that the effect is still observed when subjects are told to search for v as well as f, even with an auditory presentation of the passage and even when instructed to detect the phonemes rather than the letters. These findings are inconsistent with the proposal by Read (1983, Memory and Cognition, 11, 390–399) that subjects miss the f in of because they are searching only for the phoneme /f/. Experiment 7 showed that the effect can be reduced if subjects are led to interpret the letter sequence of as a misspelled version of the word off and can be eliminated entirely if subjects are also required to write down every letter of the passage. The findings of Experiment 7 provide further evidence that unitization and phonetic processes together contribute to the effect. The results as a whole are taken to imply that both letter and phoneme levels need to be included in models of word identification as well as a cross-checking or communication between the two levels.