Primary Outcome Measures:
- Simple Reaction Time (Attention) [ Time Frame: Single visit ]
The participant was instructed to press the 'space bar' on the laptop keyboard as quickly as possible every time an upwards pointing arrow appeared on screen. Fifty stimuli were presented with an inter-stimulus duration that varied randomly between 1 and 3.5 seconds.
- Choice Reaction Time (Attention) [ Time Frame: Single visit ]
An arrow appeared on the screen pointing to the left or to the right. Participants responded with a left or right key press corresponding to the direction of the arrow. There was a randomly varying inter-stimulus interval of between 1 and 3 seconds for a total of fifty stimuli.
- Four Choice Reaction Time (Attention) [ Time Frame: Single visit ]
A visual representation of the four direction arrow keys of a standard keyboard was presented on screen. The arrows 'lit up' at random on screen until the corresponding key press was made. In all, each arrow was the target stimulus 12 times, forming a total of 48 stimuli for this task in all.
- Numeric Working Memory (Working Memory) [ Time Frame: Single visit ]
- Alphabetic Working Memory (Working Memory) [ Time Frame: Single visit ]
Five random letters (A-Z) were presented sequentially for the participant to hold in memory. This was followed by a series of 30 probe digits (15 targets and 15 distractors) for each of which the participant indicated whether or not it had been in the original series by a simple key press. The task consisted of 3 separate trials.
- Corsi Blocks Span (Spatial Working Memory) [ Time Frame: Single visit ]
In this task nine identical blue squares appeared on screen in non-overlapping random positions. A set number of blocks changed colour from blue to red in a randomly generated sequence. Participants were instructed to repeat the sequence by clicking on the blocks using the mouse and cursor. The task was repeated five times at each level of difficulty. The sequence span increased from 4, until the participant could no longer correctly recall the sequence, resulting in a span measure of nonverbal working memory, calculated by averaging the level of the last five correctly completed trials.
- 3-back Task (Working Memory) [ Time Frame: Single visit ]
A continuous string of letters (upper and lower case; inter-stimulus interval of 2.5 seconds) was presented; 45 letters in total with 15 target pairs. For each stimulus, participants were instructed to indicate whether this was the same letter that appeared three letters before.
- Immediate Word Recall (Episodic Memory) [ Time Frame: Single visit ]
A unique set of fifteen words is presented. Words were selected at random from a large bank of words derived from the MRC Psycholinguistic Database matched for word length, frequency, familiarity and concreteness. Stimulus duration was one second, as was the inter-stimulus duration. Following word presentation, the participant was allowed 60 seconds to write down as many of the words as possible.
- Delayed Word Recall (Episodic Memory) [ Time Frame: Single visit ]
The participant was again given 60 seconds to write down as many of the words presented previously as possible.
- Word Recognition (Episodic Memory) [ Time Frame: Single visit ]
The original 15 words plus 15 distractor words were presented one at a time in a random order. For each word the participant indicated whether or not it was included in the original list of words by pressing appropriate 'yes' and 'no' keys as quickly as possible. Stimuli remained on screen until an appropriate response had been made.
Secondary Outcome Measures:
- Depression, Anxiety and Stress Scale (DASS) [ Time Frame: Single visit-90 minutes ]
The DASS is a set of three self-report scales designed to measure the negative emotional states of depression, anxiety and stress. Each of the three DASS scales contains 14 items. Subjects are asked to use 4-point (0-3) severity/frequency scales to rate the extent to which they have experienced each state over the past week. Scores for Depression, Anxiety and Stress (0-42) are calculated by summing the scores for the relevant items, with higher scores indicating higher incidence of negative emotional symptoms. A total score can be derived by adding scores from each of the subscales (0-126).