Berk Mirza on secondment


I have completed my secondment in Durham University, Department of Psychology in three separate visits (over four weeks). My dates of stay were: from 10th to 15th December 2017, from 14th to 19th January 2018 and from 11th to 26th February 2018.

This secondment report contains the partial results from the study that I held in Durham University. The rest of the results (questionnaires, computational modelling and EEG results) will be analysed in full in the next months.

Introduction

In this project the choice behaviour of healthy human subjects and the concurrent electroencephalography (EEG) signals are registered as they performed the patch-leaving task. The patch leaving paradigm consists of several different environments called patches. Each patch has a limited amount of resource and these resources decline over time. Essentially, the rate at which the resources decline is different for each patch. The question in this task is to decide when to leave the current patch and enter another one in order to maximise the reward over time.

Patch leaving task:

There are three patches (purple, orange and blue) with unique reward probability decline rates. The reward probability under these patches decline as one stays in a patch. Leaving a patch resets the reward probability to 1. The reward probability then declines with a rate depending on the patch as one stays. However, leaving has a cost, and this is to spend one time step in a reward free environment.

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Fig 1. Reward probability in each patch

 

The motivation for this study is to investigate different kinds of impulsive behaviour using the patch leaving paradigm. Here, we define impulsive behaviour as acting more on the immediate reward and not maximising the reward in the long run.

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Fig 2. Cognionics Quick-20 dry eeg headset

The behavioural choices of the subjects were registered by keyboard button presses. The EEG signals were acquired using Cognionics Quick-20 dry eeg headset.

 

Objectives:

The objectives of this study were:

  1. i) to run a behavioural and an EEG study using the patch leaving paradigm
  2. ii) to analyse the behavioural responses and the choice behaviour of the participants

 

Activities:

An ethics application was submitted prior to running this study. This study has received ethical approved by the Durham University Psychology Department Ethics Sub-committee (REF: 17/15).

All the participants that took part in this study gave written consent. The participants were administered UPPS-P impulsive behaviour questionnaire, WAIS-IV Digit span task and Test of premorbid functioning (TOPF). After the questionnaires the participants were asked to sit comfortably on a chair as the EEG cap was placed over their heads. After performing the patch leaving task, the participants were debriefed and compensated £15 in cash.

 

Results:

In this study 14 subjects (5 male and 9 female) have been recruited. The age of the participants was between 18 and 27, with mean 20.7 years and standard deviation 2.6 years.

The behavioural results of this study are shown in Fig 3. The top left panel of Fig 3. shows that there is a negative correlation between the time spent in a patch and the rate at which the reward probability declines under a patch (i.e. participants stayed longer in the purple patch where the rate of decline in the reward probability is slowest). Moreover the participants responded faster when the reward probability declines slower under a patch (see top right panel of Fig 3). The bottom panel in Fig 3 shows that the participants did have different preferences about how often they should leave a patch. While some participants preferred to stay more on the purple patch (see subject 1 and 7) others preferred to stay more on the blue patch (see subject 2 and 13). These results show that the variability between people who performed this task in terms of the time spent in different patches.

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Fig 3. Behavioural results on the patch leaving paradigm

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