A researcher suggests that Casey et al. (2011) could have improved their study's internal validity by randomly allocating the adult participants to either the 'high delayer' or 'low delayer' group.
Explain why this suggestion is impossible, and use this to explain why Casey et al.'s study is classified as a quasi-experiment.
39 exam-style questions on OCR A Level Psychology Regions of the brain, covering Sperry (1968): Split brain study and Casey et al. (2011): Neural correlates of delay of gratification. Each one has a worked solution and a mark scheme showing where the marks go.