The sentences we use as stimulus materials were obtained from Seana Coulson and Marta Kutas, distinguished researchers from University of California, San Diego. They used their sentences in an event related potential (ERP) study in which the event was the last word of the sentence. (They wanted to see if there was a systematic deflection in brain waves at a particular time following the last word. There was.) The 60 sentences, or "one liners," were each a sentence frame that when completed with last word created a joke or a control (not joke). The last word of each one-liner is called the disjunctor. Whether control or joke, the disjunctor is matched for length and frequency and cloze probability. The cloze probability is the probability of the word being generated by participants who were given the one-liner without the last word and asked to say the first word that came to mind. The disjunctor used in the ERP study all had a cloze probability of 3% to 5%. That is, only 3% to 5% of the respondents produced that word spontaneously.
The sentences are further subdivided into two constraint types within each category (joke, control), 30 of each constraint type. Coulson and Kutas (1998) noted when orignially collecting cloze probabilities that some sentences were spontaneously finished with a particular last word by many participants, whereas other sentences were completed with a much greater variety of last word. These were labeled high constraint and low constraint sentences, respectively. Note that the actual endings--disjunctors--generated for the high constraint sentences were not the last word used when the sentences were presented to subjects in the ERP study. For presentation, the dusjunctor used was a word that matched the cloze probability of words generated for the low constraint sentences. It was in this way that the disjunctors were matched for the cloze probability of 3% to 5% for each constraint type. Thus, the 60 one-liners were composed of 30 high constraint and 30 low constraint sentences, and half of each constraint type were a joke and half were control. For example, compare sentences (1) and (2):
(1) When I asked my bartender for something cold and full of rum, he recommended his daiquiri.
(2) When I asked my bartender for something cold and full of rum, he recommended his wife.
We have now presented the sentences to a bunch of students (50 to 60) and to 18 stroke survivors. Soon we will present them to age matched controls (for the stroke survivors) to be obtained from faculty and staff. I will tell you about some results and new developments with the project in the next post.
