Focus on Physiology
Lexical Decision Task
The Lexical Decision Task (LDT)
In one LDT study, subjects are presented, visually, with a mixture of words and logatomes (nonsense syllables), also called pseudowords. These pseudowords respect the phonotactic rules of a language, like trud in English. The subject's task is to indicate, with a button-press, whether the presented stimulus is a word or not.
Data analysis is usually based on the reaction times and error rates for the various conditions for which the words or pseudowords differ. A very common effect is that of frequency: words that are more frequent are recognized faster. Another is based on the position of a pair of stimuli; if the pseudoword is on top of the word, the error rate is lower than if the word is positioned above the non-word. From these experiments, theoretical inferences can be drawn from differences like this. For example, one might conclude that common words have a stronger mental representation than uncommon words.
Subjects will use the iWorx data recording software and event markers to respond "Yes" or "No" when presented a series of stimuli representing words and non-words. Both timing and error rate will be determined to see how the subjects respond best to these stimuli.
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4-Button Response Marker
The RPD-400 is a four channel hand-held, push button switch. It connects to the digital input connector of the IX-TA-220 or the IX-RA-834. When any of the four buttons are pressed, the RPD-400 delivers a TTL pulse on the corresponding digital Input. Using this response marker, an experimental subject is able to indicate a response chosen from up to four alternatives.
Visit our Web Resources page to find more information about Posner's paradigm.
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