Casey et al 2011 - delay of gratification

Background

The marshmallow test - investigated the ability to defer gratification (resist temptation) by asking children to wait before eating a treat

Aims

To investigate:

• whether the ability to delay is a consistent personality trait

• Whether this ability can be linked to differences in the way the brain behaves when resisting temptation

Design

• longitudinal study conducted over 40 years

• present part of study involved 2 quasi experiments, independent measures design

What is the independent variable for both experiments

Whether participants were high delayers or low delayers

Dependant variable in experiment 1

Reaction time and accuracy on go/no go tasks

Dependant variable in experiment 2

Activity in areas of the brain associated with cognitive control

Sample in experiment 1

59 participants (32 high delayers and 27 low delayers)

Sample in experiment 2

27 of the participants from experiment 1. But 1 excluded due to poor performance

Materials and apparatus

Neural and emotional faces from NimStim set of facial characteristics. Laptop in experiment 1 and fMRI scanner in experiment 2

Procedure - experiment 1

• participants tested on laptops in own home

• Participants given go/no go task. Had to press button when photo matched target (go) and not press if photo didn’t match (no go)

• Participants told to act as quickly and accurately as possible

• Photographs shown for 500 milliseconds

• 160 trials presented per run

• Participants had two ‘runs’ - a hot version with emotional faces (fearful or happy) and a cool run with neutral faces

Procedure - experiment 2

• only hot version run with 70 go and 26 no go trials

• An fMRI brain scan was used to assess brain activity during this task

Results - experiment 1

• participants who were high delayers as children were better at impulse control as adults

• No significant difference between high and low delayers in reaction time or accuracy on go trials

• On no go trials low delayers performed less well than high delayers on hot trials

• Low delayers were especially poor on happy no go trials

Results - experiment 2

• Low delayers committed more false alarms than high delayers on no go trials

• On no go trials low delayers had reduced activity in right inferior frontal cortex and more activity in ventral striatum when shown a happy face

• Three main affects, greater activation of: right inferior frontal cortex, primary motor cortex, left cerebellum

Conclusions

• adults who could delay gratification as children continue to be able to delay as adults

• Differences are apparent in both behavioural and neural levels

• There are important implications for cognitive control e.g. addiction