Evidence in accord with the Zeigarnik Effect:
The Zeigarnik Effect is the tendency to experience intrusive thoughts about an objective that was once pursued and left incomplete (Baumeister & Bushman, 2008, pg. 122). The automatic system signals the conscious mind, which may be focused on new goals, that a previous activity was left incomplete. It seems to be human nature to finish what we start and, if it is not finished, we experience dissonance.
A study done by Greist-Bousquet and Schiffman (1992) provided evidence for the Zeigarnik Effect. In this paper, the authors stated that there is a tendency or need to complete a task once it has been initiated and the lack of closure that stems from an unfinished task promotes some continued task related cognitive effort. The cognitive effort that comes with these intrusive thoughts of the unfinished task is terminated only once the person returns to complete the task.
In their study, two groups were observed. The first group was administered a list of 10 three letter anagrams they were asked to solve. The second group was given a list of 20 three letter anagrams they were asked to solve. The first group was asked to estimate the amount of time it took them to finish solving the list after they completed it. Their estimated time was then divided by the actual time it took them to finish. The average ratio for this group was 1.109 which means they were very close to correct (Greist-Bousquet & Schiffman, 1992).
The second group was abruptly interrupted after the first 10 three letter anagrams. They were asked to estimate how much time it took them to finish the first set of 10 (they were fully aware they still had 10 more anagrams to complete). They then proceeded to finish the last 10 anagrams. They were asked again to estimate the time it took to finish the second set of 10 anagrams. For the first set of 10 anagrams, the average ratio was 1.646, which meant they overestimated how much time it took them to finish. The average ratio was 1.346 for the second set of 10 anagrams (Greist-Bousquet & Schiffman, 1992), which was fairly accurate.
The second group overestimated the time it took them to complete the task because they were disrupted. This caused them to feel frustrated and experience a form of failure. This distress and thoughts of returning to the objective may have caused them to think they were slower at finishing the first 10 anagrams.
In another study, Johnson, Mehrabian, and Weiner (1968), classified participants into three groups. Participants took the Thematic Apperception Test (TAT), which was used to measure the need for achievement, and the Test Anxiety Questionnaire (TAQ), which assesses the level of anxiety. Out of the male sample of 82 people, the top 25% scorers were labeled as having high achievement motivation, while the bottom 25% were labeled as having low achievement motivation. The middle 50% were just considered as in the middle. The group with high motivation had characteristics like engaging in achievement related activities, anticipate success, and prefer tasks of intermediate difficulty. All groups were given a test of 58 questions after being classified. Each group performed about the same as the other. However, the group with high achievement motivation proved to have a better memory for incomplete questions than the group with low motivation (Johnson et al, 1968). They were asked about their memory immediately after the test. This finding suggests that thoughts of incomplete tasks linger more than complete tasks. Having a better memory of the incomplete tasks means that thoughts of the incomplete task must have stayed present in the conscious mind. However, motivation seems to be a factor. If people are not motivated enough to finish a task, then the Zeigarnik Effect is not so strong.
In conclusion, memory is a good indicator as to whether people continue to be interrupted by thoughts of incomplete tasks. Constant thoughts of incomplete task components cause it to be retained in memory better. Interruptions that cause a person to fall behind in their objective also cause anxiety that brings about constant thoughts of unfinished business.
Baumeister, R.F., & Bushman, B.J., (2008). Social Psychology and Human Nature. United States: Thompson Wadsworth.
Greist-Bousquet, S., Schiffman, N. (1992). The effect of Task interruption and closure on perceived duration. Bulletin of the Psychonomic Society, 30(1), 9-11.
Johnson, P.B., Mehrabian, A., Weiner, B. (1968). Achievement Motivation and the Recall of Incompleted and Completed Exam Questions. Journal of Educational Psychology, 59(3), 181-185.