**SAMPLE SIZE & SAMPLE DEMOGRAPHICS**
I expect to collect data from 80 participants. The sample will consist mostly of students of Charles University in Prague (including students of psychology) who will participate on the experiment for course credit. 10 randomly chosen participants will be rewarded by 150 CZK (approximately 5.5 €).
**MATERIALS - OVERVIEW**
Materials will be presented and answers will be collected using Google form. More detailed information about the materials used within the study can be found in the Materials node.
**DESIGN**
Participants will be presented with five kind of tasks:
1) In the first set of tasks it will be tested how well participants know Greek numerals. Participants solving correctly less than 12 tasks (from 15) will be excluded from the analysis.
2) In the second set of tasks participants will solve 9 matchstick algebra tasks with the time limit of 2 minutes for solving each of them. Participants will be randomly assigned to two conditions which differ in the probability of cognitive impasse induction and lack of control. This effect is achieved by using more/less difficult matchstick algebra tasks. The more difficult tasks are those which require insight for its solution (Knoblich et al., 1999; Öllinger et al., 2008) or which are unsolvable.
3) In the third set of tasks participants will solve 8 tasks from the first experiment of Griffiths and Tenenbaum's study (2007) with psychokinesis cover story (data from experiments testing 8 people who claim to possess psychic powers) and with both posterior (How likely it is that the person has psychic powers, taking into account the results of the experiment?) and coincidence instructions (Are results just a coincidence, or compelling evidence?). In the case of the posterior instruction participants will use a scale from 1 to 10, where 1 indicates NOT AT ALL LIKELY and 10 indicates EXTREMELY LIKELY. In the case of the coincidence instruction the decision participants will make is binary.
4) In the fourth set of tasks participants will solve 12 tasks from the second experiment of Griffiths and Tenenbaum's study (2007). Participants' task will be to rate how big a coincidence the distribution of bombs fallen on London during WW II seems to them using a scale from 1 to 10, where 1 means VERY SMALL (OR NO) COINCIDENCE, and 10 means VERY BIG COINCIDENCE.
5) In the fifth one participants will fulfill 12 item Personal Need for Structure inventory (Thompson, Naccarato, & Parker, 1992; Neuberg & Newsom, 1993).
The order of administration of individual sets of tasks is fixed with exception of two Griffiths and Tenenbaum's experimental task sets which randomly change their respective position (from the 3rd to the 4th place and vice versa) in the between-subject manner.
*References*
Griffiths, T. L., & Tenenbaum, J. B. (2007). From mere coincidences to meaningful discoveries. *Cognition*, 103, 180-226.
Knoblich, G., Ohlsson, S., Haider, H.,& Rhenius, D. (1999). Constraint relaxation and chunk decomposition in insight problem solving. *Journal of Experimental Psychology: Learning, Memory and Cognition*, 25, 1534–1555.
Neuberg, S. L., & Newsom, J. T. (1993). Personal Need for Structure: Individual Differences in the Desire for Simple Structure. *Journal of Personality and Social Psychology*, 65 (1), 113-131.
Öllinger, M., Jones, G., & Knoblich, G. (2008). Investigating the effect of mental set on insight problem solving. *Experimental Psychology*, 55, 269–282.
Thompson, M. M., Naccarato, M. E., & Parker, K. E. (1992). Measuring cognitive needs: The development and validation of the Personal Need for Structure (PNS) and Personal Fear of Invalidity (PFI) measures. Manuscript submitted for publication.
