Table 2 COMPASS task descriptions and scoring

Word presentation

Individual words are presented sequentially on the monitor. Stimulus duration was 1 s, as is the inter-stimulus interval.

Immediate word recall

The participant is allowed 60 s to write down as many of the words as possible.

The task is scored for number of correct answers, errors and intrusions and the resulting score is converted into a percentage

Picture presentation

Twenty line-drawings of everyday items are presented on the computer screen. Stimulus duration is 3 s, with a 1 s inter-stimulus duration.

Simple reaction time

A series of upwards pointing arrows appear in the centre of the screen with a randomly varying inter-stimulus interval between 1 and 3 s. The participant will press the space bar as quickly as possible to the on screen appearance of each stimulus.

The task is scored in Response times (recorded in milliseconds)

Choice reaction time

Arrows pointing to the left or right are presented in the centre of the screen with a randomly varying inter-stimulus interval of 1–3 s. The volunteer presses the corresponding ‘left’ or ‘right’ cursor key on the computer keyboard as quickly as possible.

The task is scored for accuracy (%) and reaction time (ms).

Numeric working memory

A series of five digits is presented on the computer screen sequentially for the participants to hold in their memory. This is followed by a series of 30 probe digits. The participants indicate whether or not the digit was from the original series by pressing corresponding keys labelled ‘yes’ and ‘no’. This is repeated three further times with different stimulus sets.

Reaction times (ms) and accuracy (% correct) are measured

Delayed word recall

Approximately 20 min after the word presentation, the participant is allowed 60 s to write down as many of the items from word presentation as possible.

The task is scored as for immediate word recall.

Delayed word recognition

Word recognition is tested by representation of the words from the original list randomly interspersed with an equal number of distracter words. Participants respond either ‘yes’ or ‘no’ by pressing corresponding key to indicate whether the word had previously been presented or not.

The task is scored for accuracy (%), and reaction time (ms).

Delayed picture recognition

Picture recognition is tested by the presentation of the original drawings and an equal number of distracters in random order. Participants respond either ‘yes’ or ‘no’ by key press in order to indicate whether the picture had been presented previously.

The task is scored for accuracy (%) and reaction time (ms).