Apparatus and Stimuli

5.4.2.1 fNIR Device

The fNIR device (fNIR Devices, Ptotmac, MD, USA) used in this experiment belongs to the ‘Continuous Wave’ family of NIRS devices. Continuous wave fNIR uses light sources that emit light at a constant frequency and amplitude. The fNIR device consists of a 16-channel forehead sensor pad, an

fNIR imaging control device and a computer with software for storing and analysing the fNIR data. The forehead sensor pad consists of 4 light sources (730nm/850nm dual wavelength LED) with an inter-optode distance of 25cm, as well as 10 light detectors (silicon photodiode with integrated trans-impedance preamp). The fNIR imaging control device sends power to the forehead sensor and then receives the data from the sensor, which it then sends to the computer for processing. The software for recording and analysing the fNIR data is the Cognitive Optical Brain Imaging (COBI) Studio (fNIR Devices, Ptotmac, MD, USA). The software utilises a modified Beer-Lambert Law in order to calculate changes in oxygenated and deoxygenated haemoglobin values relative to a pre- recorded baseline. Hb and HbO2 values are calculated every 0.5s (2Hz sampling rate) relative to a pre-recorded baseline at each of the light detectors, with the light sources activating sequentially at both wavelengths every half-second. The device is capable of recording haemodynamic activity at cortical depths of 1-2cm.

5.4.2.2 General Instructions

A set of general instructions was used to explain the overall structure and purpose of the three tasks and can be found in Appendix 5.1.

5.4.2.3 WCST

For the WCST, the apparatus and stimuli included: a computer running e-prime, a computer keyboard and the visual stimuli used for the WCST. The order in which the participants completed the tasks was fully counterbalanced. Standardised instructions were provided that contained detailed instructions explaining what each of the WCST entailed and what the participants would be required to do (Appendix 5.2). The computer keyboard was modified by placing orange stickers over the ‘X’, ‘C’, ‘B’ and ‘N’ buttons, as these were the response buttons for the WCST (i.e. the far left button was for choosing the far left reference card). Participants were required to use their left hand for ‘X’ and ‘C’ and their right for ‘B’ and ‘N’. The visual WCST stimuli were the same as those used by Lie et al. (2006). The stimuli consisted of 4 reference cards at the top of the screen that remained in the same location and order for every trial. The reference cards

differed in terms of shape, colour and number of objects on the cards themselves. These objects were triangles, circles or stars. Below the reference cards was the stimulus card. During conditions A and B the stimulus card was a variant of the reference cards (via any combination of colour, shape or number). There were a total of 60 possible stimulus cards. For the HLB, the stimulus card was an exact replica of one of the reference cards. There were a total of 4 stimulus cards for the HLB. The order in which the stimulus cards were presented was randomised in each of the conditions. The stimulus dimension that changed (i.e. the colour, shape or number) was also randomised.

5.4.2.4 CBT

For the CBT task, the apparatus and stimuli included: a computer running E-prime, a keyboard and the visual stimuli for the CBT tasks. Standardised instructions were provided which contained detailed instructions explaining what each of the CBT entailed and what the participants would be required to do (Appendix 5.3). The task stimuli followed the design originally used by Corsi (1972), with the experimental procedure matching that of Toepper et al. (2010). This consisted of a black (RGB 0 0 0) Corsiboard, with claret red (RGB 163 163 163) blocks placed upon the Corsiboard. Target blocks appeared in natural red (RGB 255 0 0), while BST distractor blocks appeared in yellow (RGB 255 255 0). Response blocks were coloured grey (RGB 163 163 163) with yellow letters ‘L’ and ‘R’ displayed upon them. Each of the blocks measured 3x3cm. A fixation cross was also used. This was placed at the centre of the screen, in black on a white (RGB 255 255 255) background. The task types, sequences, and spatial locations of the target blocks and response option blocks was fully counterbalanced and randomised. The tasks were run using e-prime. A button response pad was connected to the computer and used for making responses to the response blocks. The left button corresponded to the ‘L’ block while the right button corresponded to the ‘R’ block.

5.4.2.5 COWAT

The COWAT used: a computer running E-prime, a voice recorder and a set list of words for the control condition. Standardised instructions were provided

which contained detailed instructions explaining what each of the COWAT entailed and what the participants would be required to do. These instructions were based upon those that are used in standardised versions of the COWAT (Spreen and Strauss, 1998) and can be seen in Appendix 5.4. The voice recorder was used so that the participant’s responses could be analysed using the method of Troyer and Moscovitch (1997). Each of the four letters used (‘F’, ‘A’, ‘R’ and ‘S’) had a set list of words that were used in the reading condition (Condition A). The words were presented in a random order on the computer monitor, with a fixation cross appearing in between the presentation of the words. The words were written in black letters on a white background. These words were collected as part of a pilot study conducted on 20 participants; in order to collect common words produced beginning with the letters used for this COWAT. A total of 48 words were used for Condition A, 12 words for each letter. Condition A was run using e- prime. The list of words used can be seen in Condition A can be found in Appendix 5.5.