Human Factors

Human Factors

Efficient mind reading with the Stroop semantic priming test-Schmettow


Mind reading refers to getting a grasp on what someone is currently thinking off, without the person noticing.

Opposed to some common belief, psychologists are well able to read people’s minds. The key to mind reading is to use so-called implicit techniques (Robinson & Neighbors, 2005), in contrast to the prevalent self-reports. The variety of implicit methods falls into two classes. In free association tasks (e.g., Schmettow & Keil, 2013), the response is free form (such as telling a brief story after viewing a picture), which is then interpreted by the researcher using some detailed scoring rules. In experimental tasks, differences in response times or other behavioral measures are used to infer the direction of thought.

This assignment is about using the well-known Stroop task. Participants first view a picture, followed by a word that is written in color. The participant is asked to respond to the color as quick as possible. When the participant has a strong association between picture and word, this leads to a distraction from the color naming task and can be measured as a delay in response time. By using words out of several categories, one can determine the broad direction of thought, the participant experienced.

To give an example: Supposed, you want to find out whether someone knows the fairytale of “Red Riding Hood”. You would prepare a set of pictures that cover the themes of the fairytale, for example showing and old lady, a wolf or a basket with food. Another set of pictures is neutral and serves as a control condition. In the same way you would create a two sets of target words. During the experiment you would present picture-word pairs. When the \response time for pairs that are both associated to the fairytale (e.g., picture of a wolf, followed by the word grandma) are delayed, you would conclude that the person knows the fairytale. For real applications see Schmettow, Noordzij, & Mundt (2013) and Sparrow, Liu, & Wegner (2011).

Importantly, the effect that causes the delay is different from the Stroop effect, as there is no specific interference due to conflict between target word and ink color. Rather is it a general distraction from the task (Mitterer, La Heij, & Van der Heijden, 2003).

Possible research question

Validating the Stroop semantic priming task

The SSPT has been used in a small number of studies so far and seems to produce usable results. However, no rigorous validation has been undertaken, yet. An experiment for validation could be done as follows: participants are tested on picture-word pairs, where pairs have an association, given the participant has a certain knowledge or background. For example, the participants knows or doesn’t know a certain fairytale, has seen a movie, read a novel, has a certain cultural background.

After the SSPT, an interview (or questionnaire) assesses whether the participant has the background that induces the association.

Replicating (Sparrow et al., 2011)

(Sparrow et al., 2011) used the SSPT to examine whether the WWW has changed the way we think about “knowledge problem”. They found that participants, when confronted with a trivia question (e.g., name a national flag that has three colors) show delayed response times on words that are related to computers and the WWW. This sounds intriguing, but in times of replicability crisis (Open Science Collaboration, 2015), skepticism is in order. In an experiment you will replicate the study, perhaps with some improvements on the experimental design.

Finding the most effective procedure

The Stroop task is a well-established experimental paradigm in cognitive psychology and so are the rules for creating experiments that validly replicate the Stroop effect. For the purpose of mind reading, however, it is most relevant to create an experimental procedure that capitalizes most efficiently on the distraction effect. The goal is to create strongest contrasts between associated and non-associated pairs. To give two examples: first, the Stroop effect is known to be quite robust to training (Macleod, 1991), which may not be the case for the distraction effect. In consequence, one would choose a setup where training is prohibited, for example, by swapping the response keys after every trial. Second, it is common practice to remove incorrect responses from the data set, whereas this may well contain information on the presence of association. The goal of the study is to assess a number of variants of the experimental setup and the data analysis, and assess the efficiency with respect to detecting associations.


In your thesis project you will:

1.Do a literature study covering experimental priming paradigms and the Stroop task

2.Derive three to five hypotheses of which experimental manipulations could increase efficiency

3.Create a standard stimuli set for the semantic priming Stroop task (for example, fairytales and novels)

4.Conduct an experiment to test your hypothesis

5.Conclude with respect to the research question

This thesis project can be carried out by a team of 2-3 students

Interested? Ask Martin Schmettow (


Macleod, C. M. (1991). Research on the Stroop Effect : An Integrative Review. Psychological Bulletin, 109(2), 163–203.

Mitterer, H., La Heij, W., & Van der Heijden, a H. C. (2003). Stroop dilution but not word-processing dilution: evidence for attention capture. Psychological Research, 67(1), 30–42. doi:10.1007/s00426-002-0108-3

Open Science Collaboration. (2015). Estimating the reproducibility of psychological science. Science, 349(6251), aac4716–aac4716. doi:10.1126/science.aac4716

Robinson, M. D., & Neighbors, C. (2005). Catching the mind in action: Implicit methods in personality research and assessment. In M. Eid & E. Diener (Eds.), Handbook of multimethod measurement in psychology (Vol. 7, pp. 115–125). Washington, DC, US: APA American Psychological Association.

Schmettow, M., & Keil, J. (2013). Development of an Implicit Picture Story Exercise Measuring Personal Motives for the Interaction with Technical Products. University of Twente.

Schmettow, M., Noordzij, M. L., & Mundt, M. (2013). An implicit test of UX: Individuals Differ in What They Associate with Computers. In CHI ’13 Extended Abstracts on Human Factors in Computing Systems on - CHI EA '13 (pp. 2039 – 2048). New York, New York, USA: ACM Press. doi:10.1145/2468356.2468722

Sparrow, B., Liu, J., & Wegner, D. M. (2011). Google effects on memory: cognitive consequences of having information at our fingertips. Science (New York, N.Y.), 333(6043), 776–8. doi:10.1126/science.1207745