Casey, B. J., Somerville, L. H., Gotlib, I. H., Ayduk, O., Franklin, N. T., Askren, M. K., … & Glover, G. (2011). Behavioral and neural correlates of delay of gratification 40 years later. Proceedings of the National Academy of Sciences, 108(36), 14998-15003.
This is the contemporary biological psychology study which you will look at for your H167 AS OCR Psychology exam. You will also need this study for your OCR H567 A Level Psychology core studies exam.
Background
The theme of the biological psychology studies in the H167 exam is regions of the brain. This study by Casey et al., (2011) focuses on the behavioural and neural correlates of delay of gratification.
Sounds like a mouthful?
Don’t worry, it’s easier than you’d imagine.
What are the behavioural and neural correlates of delay of gratification?
Let’s cover the first part. Behavioural and neural. Behavioural simply refers to any act or response to a stimulus. Neural simply refers to brain activity.
Correlates refers to the concurrence of two or more things. In this case the concurrence of behaviours and brain activity when participants engage in delaying gratification.
Delay of gratification simply refers to the ability or act of delaying rewards. This can be done for a number of reasons. I recommend watching the following videos and readingThe Marshmallow Test: Understanding Self-control and How To Master It to gain a deeper understanding of delay of gratification.
The Marshmallow test videos:
What theory is the research based on?
Eigsti (2006) showed performance on a delay of gratification task in childhood had high predictive validity for later performance on a go/no go task.
What is a go/no go task?
A go/no go task is a cognitive task in which participants are given the instructions to respond in a particular manner to a particular type of stimulus. For example click when you see a picture of a smiling face, but not when you see a picture of a non-smiling face.
Click here for a real example: http://cognitivefun.net/test/17
This type of test measures delay of gratification because, the natural response is to click, as you may have discovered if you had a go on the above test. When you don’t click, you are delaying gratification. If participants did this whilst in an fMRI scanner, they could study the neural (brain activity) correlates of delay of gratification.
Aim of the Experiment
The aim of Casey et al., (2011) was to build upon previous research which assessed whether delay of gratification in children predicts impulse control abilities and sensitivity to alluring or social cues (happy faces in this study) at the both the behavioural and neural level when the participants were in adulthood.
Method and Design
There were a number of different factors in Casey et al. (2011). The study was longitudinal as it was conducted over a number of years with the same participants. It was also a quasi-experiment as the participants naturally fell into either high-delaying or low-delaying groups. This could not have been manipulated by the experimenter, meaning there could not be random allocation to groups and as there were two groups, it is a quasi-experiment. The study also used a correlation to consider the relationship of brain areas and behaviours during delay of gratification.
Independent variable: high delayer or low delayer. (This was naturally occurring, as the participants early in the study were found to delay gratification frequently (high delayers) or not very often (low delayers).
Dependent variables: Performance on an impulse control task (go/no go task, see above). This was measured in terms of reaction times and accuracy. Imaging from an fMRI scanner was also measured
Sample and Sampling Method
562, 4-year-olds from Stanford’s Bing Nursery School.
155 of the original 562 were studied in their 20s (1993).
135 of the original 562 were studied in their 30s (2003).
Experiment 1
59 (23 males and 36 females) out of 117 who were contacted by Casey et al. participated in experiment 1. These participants were categorised as high-delayers or low-delayers based on the delay of gratification task and self-control measures.
32 were considered high-delayers (12 male, 20 female).
27 were considered low-delayers (11 male, 16 female).
Experiment 2
Of the 59 who participated in experiment 1:
27 (13 males and 14 females) part took in experiment 2 which used an fMRI machine (15 high-delayers and 11 low-delayers). One man was excluded from the sample for abnormally low performance.
Procedure
Experiment 1
This tested whether individuals who were less able to delay gratification as children and young adults (low delayers) would, as adults in their 40s, show less impulse control in suppression of a response to “hot” relative to “cool” cues.
The 59 participants, already classified as high or low delayers, consented to take part in a behavioural version of a “hot” and “cool” impulse control task.
The participants completed two versions of the go/no-go task. The “cool” version of the task consisted of male and female stimuli which were presented, one sex as a “go” (i.e. target) stimulus to which participants were instructed to press a button, and the other sex as a “no-go” (i.e. non-target) stimulus to which participants were instructed to withhold a button press.
Before the onset of each run, a screen appeared indicating which stimulus category served as the target.
Participants were instructed to respond as quickly and accurately as possible.
Each face appeared for 500ms, followed by a 1-s interstimulus interval.
A total of 160 trials were presented per run in pseudo-randomised order (120 go, 40 no-go).
Accuracy and response latency data (reaction times) were acquired in four runs representing each combination of stimulus sex (male, female) and trial type (go, no-go).
The “hot” version of the go/no-go task was identical to the “cool” version except that fearful and happy facial expressions served as stimuli.
The tasks were presented using programmed laptop computers sent to participants’ homes.
Experiment 2
fMRI was used to examine neural correlates of delay of gratification. It was anticipated that low delayers would show diminished activity in the right prefrontal cortex and amplified activity in the ventral striatum compared to high delayers.
Participants completed a “hot” version of the go/no-go task similar to that used in Experiment 1. Differences were in timing, number of trials and apparatus.
Each face stimulus was presented for 500ms, followed by a jittered inter-trial interval ranging from 2 to 14.5s in duration (mean 5.2s).
A total of 48 trials were presented per run in pseudo-randomised order (35 go, 13 no-go).
In total, imaging data were acquired for 26 no-go trials and 70 go trials for each expression.
The task was viewable by a rear projection screen and a Neuroscreen (a screen which the participants can view from the fMRI scanner. Remember an fMRI scanner is one big electromagnet, which means metal cannot be near it.) five-button response pad recorded button responses and reaction times.
Results
Experiment 1 (Outside Scanner)
There was no effect of delay type on the reaction times of the participants.
The participants all performed with a high level of accuracy for the ‘go’ trials:
- Cool (99.8%)
- Hot (99.5%)
Low and high delayers performed with comparable accuracy on ‘go’ trials. Accuracy for ‘no-go’ trials was more variable, with low delayers committing more false alarms than high delayers.
Low and high delayers performed comparably on the ‘cool’ task but the low delayers trended toward performing more poorly on the ‘hot’ task than the high delayers; only the low delay group showed a significant decrement in performance for the “hot” trials relative to the ‘cool’ trials.
Overall therefore the go/no-go task produced differences between the delay groups only in the presence of emotional ‘hot’ cues i.e. individuals, who as a group, had more difficulty delaying gratification at four years of age (low delayers) showed more difficulty as adults in suppressing responses to happy faces than the high delayers.
Experiment 2 (fMRI)
As with the previous experiment, the reaction times did not differ significantly the ‘go’ trials.
Overall accuracy for the ‘hot’ go/no go task was high for the ‘go’ trials with 98.2% being correct. However, there was more variable performance in the ‘no go’ trials with 12.4% of the responses being false alarms.
Overall accuracy rates for the ‘hot’ go/no-go task were uniformly high for ‘go’ trials (mean 98.2% correct hits) with more variable performance to ‘no-go’ trials
Differences between the two delay groups in ‘no-go’ accuracy were consistent with the observed differences in the ‘hot’ task performance in Experiment 1, with low delayers committing more false alarms than high delayers.
Imaging results – The ‘no-go’ vs. ‘go’ trials identified candidate regions of the brain differentially engaged as a function of cognitive control tasks. – The right inferior frontal gyrus was involved in accurately withholding a response. – Compared with high delayers, low delayers had diminished recruitment of the inferior frontal gyrus for correct ‘no-go’ relative to ‘go’ trials.
The ventral striatum demonstrated significant difference in recruitment between high and low delayers. This reward-related region of the brain showed a three-way interaction of group x trial x emotion, with elevated activity to happy ‘no-go’ trials for low delayers relative to high delayers.
These results showed that the prefrontal cortex differentiated between ‘no-go’ and ‘go’ trials to a greater extent in high delayers. The ventral striatum showed exaggerated recruitment in low delayers.
Conclusions
Resistance to temptation as measured originally by a delay of gratification task is a relatively stable individual difference that predicts reliable biases in frontalstriatal circuitries that integrate motivational and control processes.
Casey et al. (2011) Evaluation
+ Casey et al (2011) used a highly controlled quasi-experiment, which reduced the delay of gratification down using a simple task to study the neural and behavioural correlates thereof. The high level of control and the reduction of the behaviour increases the internal validity of Casey et al (2011) measurements, which in turn enhances the predictive power of the study.
+ Laboratory study – the laboratory environment allows the researchers to control many aspects of the environment and experience of the participant, which reduces confounding variables and thus increases the internal validity of the study
– Ecological validity – the task which the participants had to conduct was not a task which is commonly found in real life. Nor does it address the complexity of delay of gratification in real life.
+ Temporal Validity – As this study used a longitinudal design, which measured the same participants when they were young and when they were older, the results which we see from the study are likely to be valid across different time periods. Futher, this temporal validity also suggests that the results and conclusions of the study have greater internal and predictive validity as the researchers suggest that being high or low in terms of delay of graticiation is an enduring individual difference.
Casey, B. J., Somerville, L. H., Gotlib, I. H., Ayduk, O., Franklin, N. T., Askren, M. K., … & Glover, G. (2011). Behavioral and neural correlates of delay of gratification 40 years later. Proceedings of the National Academy of Sciences, 108(36), 14998-1
Further Reading
The Marshmallow Test: Understanding Self-control and How To Master It
Psych Yogi’s Top Ten Psychology Revision Tips for the A* Student