Context/Background
Biological factors influence behaviour and processing systems impact our ability to resist rewarding stimuli = delaying gratification
Ability to resist temptation to reach long term goals is hard, and ability grows with age
Avoidance of risky behaviour = greater activity in frontal gyrus
Prefrontal cortex resolves interference with competing actions, and limbic regions = immediate choices and awards
Functional magnetic resonance imaging (Fmri) is a neuro-imaging procedure using MRI scans to measure brain activity by detecting blood flow changes in the brain
Aim
To investigate whether delay of gratification in childhood predicts impulse control ability in adulthood
Method
A quasi natural experiment, IV= high or low danger, DV= performance on impulse control tasks (reaction time and accuracy) in EX. 1 and performance using Fmri in EX. 2
Repeated measures because the same p's did the procedure again in their 20's and 30's
Longitudinal study, from 4-40 years old
562, 4-year-olds from Stanford’s Bing Nursery School. 155/562 were studied in their 20s. 135/562 were studied in their 30s.
Experiment 1-
59/117 participated in ex. 1, These p's were put into groups of high or low-delayers based on the delay of gratification task and self-control measures.
32 were considered high-delayers and 27 were considered low-delayers
Experiment 2
27 took part in ex. 2 using an fMRI machine (15 high-delayers and 11 low-delayers). One man was excluded from the sample for abnormally low performance
Procedure
Experiment 1
To test if 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
59 p's took part in a behavioural version of a “hot” and “cool” impulse control task.
The p's did 2 versions of the go/no-go task. The “cool” version of the task = male and female stimuli presented, one sex as a “go” stimulus to which participants were told to press a button, and the other sex as a “no-go” stimulus to which participants were told to withhold a button press.
Before the onset of each run, a screen appeared indicating which stimulus category served as the target and P's were instructed to respond as quickly and accurately as possible.
Each face appeared for 500ms, followed by a 1-s interval. A total of 160 trials were presented in random order (120 go, 40 no-go). Accuracy and reaction times were acquired in 4 runs representing each combo 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 used to examine neural correlates of delay of gratification. It was expected that low delayers= diminished activity in right prefrontal cortex + amplified activity in ventral striatum compared to high delayers. P's completed a “hot” version of the go/no-go task like ex. 1 and differences were in timing and number of trials
Each face stimulus shown for 500ms, followed by an inter-trial interval ranging from 2 to 14.5s. 48 trials were presented per run in random order
The task was viewable by a rear projection screen and a Neuroscreen. A 5 button response pad recorded button responses and reaction times.
Findings
Experiment 1-
There was no effect of delay type on the reaction times of the participants and p's all performed with a high level of accuracy for the ‘go’ trials
Low + high delayers performed more accurately on ‘go’ trials. Accuracy for ‘no-go’ trials varied more, with lows committing more false alarms than highs
Low + high delayers performed comparably on the ‘cool’ task but the low delayers did worse on the ‘hot’ task than the highs, only the low delay group showed significantly worse performance for the “hot” trials compared to the ‘cool’
Overall individuals who had more difficulty delaying gratification at four years of age (low delayers) = more difficulty as adults in suppressing responses to happy faces than the high delayers.
Experiment 2 (fMRI)
Reaction times did not differ significantly the ‘go’ trials.
Accuracy for the ‘hot’ go/no go task = high for the ‘go’ trials, 98.2% correct. More variable performance in ‘no go’ trials with 12.4% of the responses = false alarms. Overall accuracy for ‘hot’ go/no-go task = high for ‘go’ trials, more varied performance compared to ‘no-go’ trials
Differences between the 2 groups in ‘no-go’ = consistent with differences in the ‘hot’ task performance in Experiment 1, low delayers =more false alarms than high
Imaging results= The ‘no-go’ vs. ‘go’ trials = different regions of the brain differentially engaged as a function of cognitive control tasks. Right inferior frontal gyrus = involved in accurately withholding a response. Low delayers =diminished use of inferior frontal gyrus for correct ‘no-go’ relative to ‘go’ trials.
The ventral striatum = difference in recruitment between high +low delayers. This region of the brain = a three-way interaction of group x trial x emotion, , with more activity to happy ‘no-go’ trials for low delayers compared to high delayers. These results = prefrontal cortex differentiates between ‘no-go’ and ‘go’ trials to a greater extent in high delayers. Ventral striatum showed exaggerated recruitment in low delayers.
Conclusions
Sensitivity to hot cues = significant role in suppressing actions towards alluring cues
Being resistant to temptation = measured by delay of gratification = stable individual differences predicting biases in frontal striatal circuitries that integrate motivational and control processes
The capacity to resist temptation varies by context = more tempting the choice, more predictive are the individual differences in ability to regulate their behaviour
Individuals at 4 have difficulty delaying gratification and continue to show reduced self control as adults
Evaluation
Validity- high control so reduced extraneous variables = more internal validity
It also reduced confounding variables and wasn't ecologically valid
Sample- only focused on 1 cultural group so ethnocentric