The word-length effect in reading: A review

Abstract

The finding that visual processing of a word correlates with the number of its letters has an extensive history. In healthy subjects, a variety of methods, including perceptual thresholds, naming and lexical decision times, and ocular motor parameters, show modest effects that interact with high-order effects like frequency. Whether this indicates serial processing of letters under some conditions or indexes low-level visual factors related to word length is unclear. Word-length effects are larger in pure alexia, where they probably reflect a serial letter-by-letter strategy, due to failure of lexical whole-word processing and variable dysfunction in letter encoding. In pure alexia, the word-length effect is systematically related to mean naming latency, with the word-length effect becoming proportionally greater as naming latency becomes more delayed in severe cases. Other conditions may also generate enhanced word-length effects. This occurs in right hemianopia: Computer simulations suggest a criterion of 160 ms/letter to distinguish hemianopic dyslexia from pure alexia. Normal reading development is accompanied by a decrease in word-length effects, whereas persistently elevated word-length effects are characteristic of developmental dyslexia. Little is known about word-length effects in other reading disorders. We conclude that the word-length effect captures the efficiency of the perceptual reading process in development, normal reading, and a number of reading disorders, even if its mechanistic implications are not always clear.

Keywords:

• Object recognition
• Visual word
• Alexia
• Hemianopia
• Confusability

We thank Rebecca Johnson for helpful comments on the manuscript.J.B. was supported by a Canada Research Chair and the Marianne Koerner Chair in Brain Diseases.

Notes

¹ Pseudowords could be considered an extreme example, as their frequency would be zero. Some pseudowords may have indirect frequency effects, though, if constructed by changing one letter of a real word that itself would have a certain frequency.

² Even studies of syllable number effects use “length” to refer to number of letters (see Yap & Balota, 2009).

³ The main sequence for the relation between saccadic peak velocity and amplitude is an analogous linear log–log relationship (Bahill, Clark, & Stark, 1975). The term was borrowed from the Hertzspring–Russell diagram in astronomy, of the relation between the luminosity and temperature of stars.