Study 1: It has been theorized that physical proximity to reward can lead to increases in impulsivity, but there has been no systematic study to examine this question. Using the Oculus Rift, we developed two immersive tasks to examine whether distance to reward impacts on two types of impulsivity (Figure 2). 1) Impulsive choice, an increased preference for immediate reward over a larger reward in the future, was examined using a 3D intertemporal choice task. Here, choices for smaller, immediate appetitive rewards were presented as tangible objects in space (Figure 3). Crucially, these were presented at either near (30cm) or far (360cm) distances. 2) Impulsive action, an inability to withhold a response, was examined using a 3D Go/Nogo task. Here, cues relating to Go and Nogo trials were presented using the same tangible objects in space. Crucially, both types of trials were presented at either near (30cm) or far (360cm) distances (Figure 4).
1) Results showed that impulsivity in intertemporal choice was not modulated by proximity. Participants (n = 27) did not make more choices for immediate rewards that were near compared to far. 2) Results from Experiment 2 showed that impulsivity of action was significantly modulated by proximity. Participants (n = 27) were less able to withhold their responses when objects representing Nogo trials were near compared to when they were far (Figure 5). This effect was robust even though participants slowed their reaction times for Go trials.
Findings suggest that self-control may be more likely to be compromised in an environment in which tempting cues are proximal. From an evolutionary perspective, we interpret this tendency for participants to behave more impulsively around near cues as an adaptive bias. However, viewed within a modern consumer society context, such a bias could be viewed as deleterious.
These findings have been presented at conferences. In addition, a research manuscript is in preparation to be submitted to Nature Human Behaviour.
Study 2: To follow up on the behavioural finding from Study 1, that impulsive action increases with proximity, we performed a second study which aimed to determine the neural mechanisms underlying such an effect. In this second study, we adapted the 3D Go/Nogo for use in the MRI brain scanner.
Performance of inhibitory control engages a different network to impulsive choice and includes prominent involvement of the lateral prefrontal cortex along with pre-SMA. A fronto-striatal circuit is also implicated in Go/No-go performance. We hypothesised that striatal activity would be modulated by task near/far Go/No-go manipulation.
We introduced two novel conditions such that Go and No-go trials were presented at near and far distances (Figure 6). This was made possible through stereoscopic presentation of cues through use of a ProPixx 3D Projector combined with a DepthQ polarisation modulator.
For this experiment, we used a jittered rapid-event related design to assess Go/No-go performance for near and far distances. Both Go and No-go trials were presented as tangible-seeming boxes and were associated with particular amounts of chocolate.
A total of twenty-eight participants have performed this task. We are currently using AFNI to analyse neuroimaging data. Over the next six months, findings will be written up for report in an international journal.