Experiment HP-19: Lexical Decision Task

The lexical decision task (LDT) is a procedure used in many and experiments. The basic procedure involves measuring how quickly people classify stimuli as words or non-words; the participant needs to decide about whether combinations of letters are words or non- words. As an example, "GIRL" is a real word, the response should be “yes, this is a real word", but the letters "XLFFE" would have the correct response of "No, this is not a real word". The Lexical Decision Task (LDT), The task was introduced by Meyer and Schvaneveldt in the 1970s. Their study was to understand how long-term is organized and how we retrieve information from it. In the original study, Meyer and Schvaneveldt found that people respond more quickly to words that are related in their meaning than to words that are entirely unrelated. This demonstrates that reading a word "activates" related information that facilitates the recognition of other related words. Since then, the task has been used in thousands of studies, investigating , word recognition and lexical access in general. 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 a 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. Lexical decision tasks are often combined with other experimental techniques, such as , in which the subject is 'primed' with a certain stimulus before the actual lexical decision task is be performed. Other experiments have shown 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". This is one example of the phenomenon of priming; and a whole set of other experiments have been derived from here. 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.

Equipment Required PC or Mac Computer IXTA, USB cable, iWorxpower supply Sample Lab 2 – EM -220 Event Markers OR 1 – RPD-400 4-Button Response Pad (optional)

Human Psychophysiology – Lexical Decision – Background HP-19-1 Start the Software 1. Click on LabScribe 2. Click Settings → Human Psychophysiology → LexicalDecisionTask 3. Once the settings file has been loaded, click the Experiment button on the toolbar to open any of the following documents: • Appendix • Background • Labs • Setup (opens automatically)

Sensor Setup 1. Locate the EM-220 Event Markers and plug them into the Channel EM1 and EM2 inputs on the back of the IXTA ( Figure HP-19-S1) . 2. Or locate the RPD-400 4-Button Response Pad ( Figure HP-19-S2 ) in the iWorx kit. Plug the connector in the RPD and into the Digital Input on the back of the IX-TA.

Figure HP-19-S1: EM-220 Event Marker.

Figure HP-19-S2 RPD-400 4-Button Response Pad.

iWorx Sample Lab

Human Psychophysiology – Lexical Decision – Background HP-19-2 Figure HP-19-S3: The IXTA shown with one EM-220 Event Marker, the 2 nd will will plug into the EM2 port on the TA as shown.

General Directions: All Tests will follow the same directions. • Subjects will be shown a series of 25 two letter sequences, one above the other ◦ For each trial, a fixation box will be shown for 1 second ◦ The stimulus pair will be shown for 2 seconds ◦ The screen will go blank for 1 second • Subjects must press the appropriate response key within that time period. ◦ After the stimulus is shown: ▪ the subject will press the event marker in their right hand, or the letter “D” on the response pad, for “YES” if one or both of the letter pairs is a word ▪ TheiWorx subject will press the event Sample marker in their left hand, or the Lab letter “A” on the response pad, for “NO” if the letter pairs are not words

Human Psychophysiology – Lexical Decision – Background HP-19-3 Exercise 1: Test 1 – Word-Pseudoword (Non-word) Pairs

Procedure Warning: In this exercise, it is important to remember to press the event marker in the correct hand for answering YES or NO. Right hand = YES; left hand = NO. If using the response pad, D = YES: A = NO.

1. Click on the Record button. 2. Click the Test1 sequence on the toolbar and run the sequence to begin the sequence of stimulus pairs. 3. Follow the general directions as outlined above. 4. After the twenty-five stimuli have been shown, click Stop to halt recording. 5. Click on the Save button to save the data file. 6. Let your subject rest for a minute or so before moving on to Test2 .

Figure HP-19-L1: Sample of what the data may look like. This sample only shows one graph of data. For this experiment, there will be two graphs of data, one representing the YES answer and one for the NO answers. iWorx Sample Lab

Human Psychophysiology – Lexical Decision – Background HP-19-4 Data Analysis

Figure HP-19-L2: LabScribe toolbar.

WORDS: 1. Click the Double Display time button until approximately 10 responses show on the screen. 2. Move one red cursor line to the mark made when the STIMULUS was shown and the 2 nd to the start of the click of the event marker or response pad. ◦ The stimuli will be labeled: ▪ NN – non-word pairs ▪ NW – non-word above ▪ WN – word above ▪ WR – words related ▪ WU – words not related 3. Look at T2-T1 (upper right corner) and record that number. 4. Repeat for the next 9 word pair stimuli. 5. Repeat the procedure for the next 15 word pairs. 6. Enter the data into the table on the next page.

Questions: 1. What was the mean reaction time of the subject for this set of stimuli? 2. What was the mean reaction time for the Non-Word above stimuli? The Word above stimuli? 3. What was the total percentage correct for all the stimuli? Percent error? Exercises 2 (Related/Non-RelatediWorx Words) Sampleand 3 (Mixed stimuli): Lab Procedure Repeat the same directions from Exercise 1.

Human Psychophysiology – Lexical Decision – Background HP-19-5 Data Analysis Repeat the same directions from Exercise 1.

Questions: 1. What was the overall mean reaction time of the subject when the stimuli were both words? 2. What was the mean reaction time of the subject for all related words stimuli? 3. What was the mean reaction time of the subject for all non-related words stimuli? 4. What was the mean reaction time for the 3 categories when mixed stimuli were shown in Exercise 3? 5. What could cause a difference in reaction times for each of the 3 categories when they were mixed (Exercise 3) vs the mean reaction times in Exercises 1 and 2. 6. What was the percent error for each of the above?

Table HP-19-L1 – Reaction Times for Exercises 1, 2 and 3

Stimulus Reaction Time (sec) Reaction Time (sec) Reaction Time (sec) TEST 1 TEST 2 TEST 3 Non-word Word Related Non-Related Non- Mixed Words above above Words Words Words 1 2 3 4 5 6 7 8 9 10 11 12 13 14 iWorx Sample Lab 15 16

Human Psychophysiology – Lexical Decision – Background HP-19-6 17 18 19 20 21 22 23 24 25 Mean Overall Mean

iWorx Sample Lab

Human Psychophysiology – Lexical Decision – Background HP-19-7