Lab Report - Stroop

Abstract

The aim of this lab report is to explore the Stroop effect (Stroop, 1935) by comparing the performance, speed and accuracy of participants in an experiment where interference hinders their responses. Participants were 131 undergraduates of a regional university in Townsville, Australia with mean age of 23.36 years (SD 9.32). The experiment included a stimulus card which had three tasks outlined in relation to the four control colours red, green, blue and yellow and a response sheet with the correct answers for marking. For the first task, the word task, participants were required to read aloud the text printed of colours in order from right to left. Next was the coloured blocks task where participants called out aloud the blocks of colour in the order they appeared on the stimulus card from left to right. Following this was the Stroop task, participants were required to call out the colour of the text rather than the printed word, and the printed words were incongruent to the colours as described by MacLeod (1991, p. 167-168). The participants were timed and marked on the accuracy of their responses on response sheets. As predicted, participants completed the word task significantly faster than the coloured blocks task and the coloured blocks task was completed significantly faster than the Stroop task. It was concluded that the Stroop task did affect the comparison speed, but that further research was required to determine if the speed can be improved on with practice.

The aim of this lab report is to demonstrate the Stroop effect (Stroop, 1935). The Stroop effect is a demonstration of interference in which the brain experiences slower aptitude of processing because it is trying to sort through conflicting information. Stroop’s research was to determine and how best to explain the impacts of interference. The colour-word interference test Stroop (1935) completed in three experimental tasks which forms the basis of the study of this report. Each experiment introduced interference in the form of conflicting colours in relation to the word and measured the speed in which responses were provided.  

The beginnings of Stroop’s research originated from the work of James McKeen Cattell (1886) the project supervised by Wilhelm Wundt. Cattell found that objects and colours took longer to name aloud than the corresponding words took to read aloud. Cattell described this in the case of words and letters, that the cognitive association between the word and the idea of the word has been already taken place and become automatic due to common use of the word as described by MacLeod (1991, p. 163).

There have been numerous studies undertaken to demonstrate the Stroop effect and interference including for example the picture-word interference task (e.g., Babbitt, 1982; Dunbar, 1986; Smith & Magee, 1980 as cited in MacLeod, 1991, p.167). The picture-word interference task has been described by MacLeod (1991, p. 167) as “manipulation of semantic relations between word and picture” (e.g., the word knee on the picture of an arm) found increased interference whereas words that had no semantic association (e.g., the word sky on the picture of a dog) did not.

The purpose of this study is to demonstrate the Stroop test and to identify the effects of introduced interference. The three tasks within this experiment are the word task, the coloured block task and the Stroop task. The hypotheses that are being studied are whether participants will complete the word task significantly faster than the coloured blocks task (speed of processing) or whether participants will complete the coloured blocks task significantly faster than the Stroop task where interference is introduced and if there is a higher margin for error between the Stroop task and the other tasks.

Method

Participants

The sample consisted of a convenience sample of 131 undergraduate university students. There were 40 males, 90 females and 1 who did not provide a response. Participants varied in age (M 23.36 years, SD 9.32 years) and ethnicity. The experiment formed part of the students’ coursework whilst attending week 6 tutorial for subject PY1102 Exploring Psychology 2.

Materials

The materials used and issued to participants for experiment were published stimulus cards and response sheets. There are three tasks set out on the stimulus card and the response sheet which identified the correct answers to the corresponding tasks. The use of a personal mobile device or timer was also required to time each task of the experiment.

Procedure

As participants entered the class room, they were instructed to separate into groups of three. No time was permitted for participants to prepare for the experiment. Each group was provided with one stimulus card and a response sheet was issued to each individual. Participants were then asked to assign the following roles; a marker to mark the results on the response sheet, a timekeeper to time how long it takes for the responder to complete each activity and the responder to undertake the tasks on the stimulus card. All participants were asked to write down their age and sex on their response sheet prior to commencement of the experiment.

Each participant was instructed to complete the three tasks outlined on the stimulus sheet, then exchange roles until all participants had completed each role. The first activity was the word task which randomly ordered the colours red, green, blue and yellow in black text. Responders were instructed to read the text from right to left as quickly as possible whilst being timed by the timekeeper. Simultaneously to this, responses were being marked as being answered correctly or incorrectly on the response card by the marker.  Once the word task was completed, the timer was stopped by the timekeeper and the marker would note the time taken to complete the first task.

The second activity was the coloured block task where the stimulus card outlined the colours red, green, blue and yellow as blocks of colour rather than text as in the previous task. Responders were instructed to call out the colour blocks from left to right, again as quickly as possible, whilst being timed by the timekeeper and responses were marked as being correct or incorrect by the marker. On completion the time taken is noted on the response sheet.

The final activity was the Stoop task where interference was introduced. For this task the stimulus card outlined in coloured text each of the four colours previously prescribed in the preceding tasks. The colour of the text did not correspond with the colour worded; green coloured text was used for the words red, blue or yellow; red coloured text was used for the words green, blue or yellow; blue coloured text was used for the words red, green or yellow and finally yellow coloured text for the words blue, red or green. Responders were instructed to call out the colour of the text from left to right as quickly as possible whilst being timed by the timekeeper and responses being marked as correct or incorrect on the response sheet by the marker. On completion, the timekeeper stopped the timer and the time taken to complete is noted on the response sheet by the marker.