Administration time
Up to 15 minutes

Task
The subject is presented with a 5x5 array of grey boxes on the screen, and two larger coloured panels below these boxes. The subject is instructed that they are playing a game for points, which they can win by making a correct decision about which colour is in the majority under the grey boxes. They must touch the grey boxes one at a time, which open up to reveal one of the two colours shown at the bottom of the screen. Once a box has been touched, it remains open. When the subject has made their decision about which colour is in the majority, they must touch the panel of that colour at the bottom of the screen to indicate their choice. After the subject has indicated their choice, all the remaining grey boxes on the screen reveal their colours and a message is displayed to inform the subject whether or not they were correct. The colours change from trial to trial.

There are two conditions – the fixed win condition, in which the subject is awarded 100 points for a correct decision regardless of the number of boxes opened, and the decreasing win condition, in which the number of points that can be won for a correct decision starts at 250 and decreases by 10 points for every box touched. In either condition an incorrect decision costs 100 points.

Test modes
IST has two modes:

* Fixed win-decreasing win (after practice trials, the fixed win stage precedes the decreasing win stage)
* Decreasing win-fixed win (after practice trials, the decreasing win stage precedes the fixed win stage)

Outcome measures
The eight IST outcome measures cover errors, latency, total correct trials, mean number of boxes opened per trial, and probability of the subject's decision being correct based on the available evidence at the time of the decision