==Abstract==
 
==Abstract==
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This mini-game resembles the arcade games Tempest and Asteroids, and combines tests of motion coherence threshold, motor inhibition, and executive flexibility.  The player commands a spaceship that moves clockwise (left arrow key) or counterclockwise (right arrow key) around the perimeter of a circular field.  Slow-moving meteors materialise at the centre of the field and drift outward; the player must fire torpedoes (space bar) to destroy these meteors. (This ongoing task serves simply to maintain vigilance.)  Periodically, a wormhole materialises within the field.  The player can open this wormhole by moving around the circle to align with it, then connecting with the wormhole (up arrow). Connecting temporarily drains the ship's propulsion systems; the ship is locked in place in front of the wormhole as an unidentified ship begins to emerge.  This ship can be either a friend or a foe, with equal probability.  Friend and foe ships are identical in area and luminance, but differ subtly in form: one has two warp nacelles protruding, the other three.  Foes should be fired upon and destroyed before they get a chance to attack the player.  Conversely, withholding fire on a friend is rewarded by a weapons power-up which increases the player's firing rate.  (This change in firing rate alters the game tactically but does not affect measurement of reaction times.)  Friends and foes cannot be discriminated until they have emerged from the wormhole.  Thus during the opening of the wormhole the player must prepare, but not execute, a motor response.  Foes do not fire, and friends do not deliver weapons power-ups, until 800 ms after emerging.  A hit in this task is therefore defined as firing on a foe within this 800 ms interval, a miss as failing to fire on a foe within this interval, a correct rejection as withholding fire on a friend, and a false alarm as firing on a friend.  This task behaviourally measures inhibitory function, and can be used in conjunction with EEG measures to assess motor planning.
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This mini-game resembles the arcade games Tempest and Asteroids, and combines tests of motion coherence threshold, motor inhibition, and executive flexibility.  The player commands a spaceship that moves clockwise (left arrow key) or anticlockwise (right arrow key) around the perimeter of a circular field.  Slow-moving meteors materialise at the centre of the field and drift outward; the player must fire torpedoes (space bar) to destroy these meteors. (This ongoing task serves simply to maintain vigilance.)  Periodically, a wormhole materialises within the field.  The player can open this wormhole by moving around the circle to align with it, then connecting with the wormhole (up arrow). Connecting temporarily drains the ship's propulsion systems; the ship is locked in place in front of the wormhole as an unidentified ship begins to emerge.  This ship can be either a friend or a foe, with equal probability.  Friend and foe ships are identical in area and luminance, but differ subtly in form: one has two warp nacelles protruding, the other three.  Foes should be fired on and destroyed before they get a chance to attack the player.  Conversely, withholding fire on a friend is rewarded by a weapons power-up which increases the player's firing rate.  (This change in firing rate alters the game tactically but does not affect measurement of reaction times.)  Friends and foes cannot be discriminated until they have emerged from the wormhole.  Thus during the opening of the wormhole the player must prepare, but not execute, a motor response.  Foes do not fire, and friends do not deliver weapons power-ups, until 800 ms after emerging.  A hit in this task is therefore defined as firing on a foe within this 800 ms interval, a miss as failing to fire on a foe within this interval, a correct rejection as withholding fire on a friend, and a false alarm as firing on a friend.  This task behaviourally measures inhibitory function, and can be used in conjunction with EEG measures to assess motor planning.
    
Friendly and enemy forces in this game are pirates or mercenaries who have requested the player's help (to fend off the pirates). The class of ship used by each side therefore can change from one session of the game to the next.  A '''shift''' session is one in which the assignment of ship classes differs from that of the session immediately preceding.  A '''hold''' session is one in which the assignment of ship classes does not differ from that of a session immediately preceding.  Differences in reaction time and accuracy for the fire-or-withhold task between shift and hold sessions measure executive flexibility.
 
Friendly and enemy forces in this game are pirates or mercenaries who have requested the player's help (to fend off the pirates). The class of ship used by each side therefore can change from one session of the game to the next.  A '''shift''' session is one in which the assignment of ship classes differs from that of the session immediately preceding.  A '''hold''' session is one in which the assignment of ship classes does not differ from that of a session immediately preceding.  Differences in reaction time and accuracy for the fire-or-withhold task between shift and hold sessions measure executive flexibility.