Neighborhood Density Effect

The neighborhood density effect is a finding in visual word recognition research concerning a word's orthographic neighborhood, the set of other real words that can be formed by changing just one letter of the original word while keeping its length the same, such as the neighbors cat, hat, and bad for the word bat. Words with many such neighbors, described as having a dense neighborhood, are processed measurably differently in laboratory word-recognition tasks than words with few neighbors, though the direction of the effect depends on the specific task used: in a lexical decision task, where a participant judges whether a letter string is a real word, a dense neighborhood tends to slow responses, since the many activated neighboring words compete with the target word for selection, while in some other tasks, such as reading a word aloud, a dense neighborhood can instead speed responses by contributing extra overall activation supporting that a real word is present. The psychologist Max Coltheart and colleagues formalized a standard numerical measure of orthographic neighborhood size in the late 1970s, a measure still commonly called Coltheart's N, which remains a standard variable that reading and word-recognition researchers control for or manipulate directly when designing word-list stimuli for an experiment.