Missing letter effect

In cognitive psychology, the missing letter effect refers to the finding that, when people are asked to consciously detect target letters while reading text, they miss more letters in frequent, function words (e.g. the letter "h" in "the") than in less frequent, content words. The missing letter effect has also been referred to as the reverse word superiority effect, since it describes a phenomenon where letters in more frequent words fail to be identified, instead of letter identification benefitting from increased word frequency.

The effect is usually measured using a paper-and-pencil procedure, where readers are asked to circle a target letter every time they come across it while reading a short passage. The missing letter effect is more likely to appear when reading words that are part of a normal sequence, than when words are embedded in a mixed-up sequence (e.g. readers asked to read backwards).

Two primary hypotheses tried to explain the missing letter effect: Healy (1994) emphasized identification processes playing a crucial role, almost entirely focusing on word frequency. However, Koriat & Greenberg (1994) viewed the structural role of the word within a sentence (i.e. function words vs. content words) to be crucial. Both accounts were thoroughly investigated, but neither could completely explain the effect.

A new model called the guidance-organization model was recently proposed to potentially explain the missing letter effect. It is a combination of the two models proposed by Healy and Koriat & Greenberg. As Greenberg et al. explain: "The time spent processing high-frequency function words at the whole-word level is relatively short, thereby enabling the fast and early use of these words to build a tentative structural frame."

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