Missing-letter effect
The tendency to detect a target letter less often in common function words than in less frequent content words, despite equal or greater exposure.
Function word: A frequent grammatical word, such as an article, preposition, or conjunction, that expresses relationships between other words. Target letters in these words are often missed more than letters in content words.
Missing-letter task: A reading experiment in which participants mark every occurrence of a designated letter in a text. This task makes the detection difference across word types observable.
Rayner and Sticht 1979: A study by Keith Rayner and Thomas G. Sticht examining letter detection during reading. It is an early experimental investigation associated with the missing-letter effect.
Perceptual span: The region of text from which a reader can obtain useful visual information during a fixation. The effect raises questions about which letters within this region receive effective processing.
Content word: A word that carries substantial lexical meaning, such as a noun, verb, adjective, or adverb. Readers tend to notice target letters in these words more reliably than in function words.
The: The definite article in English, used to identify a particular person, thing, or group. It is a frequent function word in which target letters are often overlooked.
Keith Rayner: An American psychologist known for research on eye movements during reading. His work connected letter detection failures with the processes guiding eye movements in reading.
Parafoveal processing: The processing of visual information outside the point of direct gaze but near the fovea. Letters can be encountered away from fixation without becoming available for accurate report.
Word superiority effect: The finding that letters are identified more accurately within real words than within isolated letters or meaningless strings. Both effects show that letter detection depends on how text is processed as words.
Tachistoscope: An instrument that presents visual stimuli for precisely controlled, brief durations. Brief presentation can test whether missed letters reflect limited visual exposure.