Lexical decision task
The lexical decision task (LDT) is a procedure used in many psychology and psycholinguistics experiments. The basic procedure involves measuring how quickly people classify stimuli as words or nonwords.
Although versions of the task had been used by researchers for a number of years, the term lexical decision task was coined by David E. Meyer and Roger W. Schvaneveldt, who brought the task to prominence in a series of studies on the structure of semantic memory in the early 1970s. Since then, the task has been used in thousands of studies, investigating semantic memory and lexical access in general.
Subjects are presented, either visually or auditorily, with a mixture of words and logatomes or pseudowords (nonsense strings that respect the phonotactic rules of a language, like trud in English). Their task is to indicate, usually with a button-press, whether the presented stimulus is a word or not.
Lexical decision tasks can measure two things: time taken to decide that a string of letters is a word, or the time taken to decide that it belongs to a prespecified semantic category. When semantic categories are small and words are related (ex. house - buildings), reaction times appear to be significantly faster than the lexical decision.
The analysis is based on the reaction times (and, secondarily, the error rates) for the various conditions for which the words (or the pseudowords) differ. A very common effect is that of frequency: words that are more frequent are recognized faster. In a cleverly designed experiment, one can draw theoretical inferences from differences like this. For instance, one might conclude that common words have a stronger mental representation than uncommon words.
Lexical decision tasks are often combined with other experimental techniques, such as priming, in which the subject is 'primed' with a certain stimulus before the actual lexical decision task has to be performed. In this way, it has been shown[by whom?] that subjects are faster to respond to words when they are first shown a semantically related prime: participants are faster to confirm "nurse" as a word when it is preceded by "doctor" than when it is preceded by "butter".
- Meyer, David E.; Roger W. Schvaneveldt (1971). "Facilitation in Recognizing Pairs of Words: Evidence of a Dependence Between Retrieval Operations". Journal of Experimental Psychology 90 (2): 227–234. doi:10.1037/h0031564. Retrieved 7 March 2012.