Compensatory Tracking Task

Background

Compensatory Tracking tasks are psychomotor tests to measure eye-hand coordination and alertness. The basic task is to keep a target that is under the constant influence of invisible, outside forces (e.g. wind gushes), steady in the center of the screen using a joystick, computer mouse or stylus pen.

During and after WWII, military researchers formally differentiated "compensatory tracking" from "pursuit tracking" (Example: Pursuit Rotor Task) with the main purpose of screening and training pilots. In 1995, Scott Makeig and Keith Jolley from the Naval Health Research Center published a widely-accepted, computerized compensatory tracking task called 'COMPTRACK'. COMPTRACK was specifically designed to require continuous user input to allow for rapid fluctuations in vigilance while still being monotonous enough to encourage loss of vigilance in the first place. One main objective of COMPTRACK was further to allow for easy synchronization with external psychophysiological devices (e.g. EEG).

COMPTRACK presents its users with a target stimulus that sits in the bull's eye of an 'imaginary' hill in the center of the screen and is subject to three outside forces that move it around constantly: A buffeting force (e.g. wind turbulence) that jerks the stimulus in different directions, a slipping force that causes the target to move downhill, and last but not least the users themselves.

Millisecond's Compensatory Tracking task is intended as a simple approximation of COMPTRACK. It includes algorithms to mimic a wind force (a multi-directional force of varying strengths) as its buffeting force as well as a downhill force that pushes the target towards the edges of the screen. For example, the script uses a simple exponential decay function to approximate the speed decay based on the target's distance to the center: steep close to its apex (the bull's eye), leveling out as the slope of the 'imaginary' hill gradually becomes flat. Wind strength is sampled from an exponential function that results into five strength categories with mild wind categories being more likely than strong ones. Wind direction is constantly fine-tuned by draws from a Bernoulli distribution every 16ms with mean = 0.05 (which results in a direction change in about 5 out of 100 draws). The new direction of the wind is then simply randomly selected from 0-359 angles.

It is important to note that Millisecond's Compensatory Tracking task does not implement the actual force algorithms used by COMPTRACK, nor does it attempt to realistically approximate real-life forces.

Task Procedure

The task is to keep a small red circle in the center of the yellow 'bull's eye' located in the center of the screen. By default, the game is absolutely sized to a screen of 15cm x 15 cm (these dimensions can easily be changed). The active game canvas presents in gray on a black background.

After learning about the task and a 1 minute practice session, participants start on a 12 minute test session that is divided (under the cover) into three separate 4 minutes long testing periods (start, middle, end).

At the beginning of the test, after a random rest time period (0-500ms), the target begins to move in a randomly selected direction with a randomly selected strength away from the hill's center and possibly 'downhill' (though this is not made explicit to participants). If the participant moves the finger/stylus/mouse over the moving red circle, its position can be corrected by dragging it back to the center (when close to the center, the target is automatically placed smack into the bull's eye's center) where it again rests for about 0-500ms before the wind starts moving it around once more. However, if no movement is registered while participant has full control over target, control is lost.

Three forces constantly act on the position and speed of the target: the wind force, the downhill force and the participant. However, these three forces don't always act on the target at the same time. For example, while the target is still moving around in the yellow bull's eye, it is not subject to the downhill force yet. The downhill force starts acting on the target once it manages to leave the confines of the bull's eye. Similarly, while the target starts moving in the center of the bull's eye, it is mostly subject to the wind force and rarely reacts to a participant's input. This requires the participant to stay vigilant as the target can slip away during this time. Once the participant grabs the target, wind and downhill force stop acting on the target as long as the target is under the participant's control and the participant actively moves the target.

The target can move through six phases:

1. The target rests motionless in the bull's eye center for 0-500ms
2. The target starts moving around on the bull's eye (no downhill force; only wind force) but cannot yet be controlled by participant.
3. The target still moves around on the bull's eye (no downhill force; only wind force) and could theoretically be controlled and moved by participant.
4. If the target reaches the edges of the bull's eye, it moves with a speed that is controlled by the 'downhill' force AND wind force. Its direction is always outward but is still subject to the direction of the wind force that can fine-tune its final direction. Participant can take control of the target during this phase.
5. The target is under full control of participant who should move it back to the center of the bull's eye. If no movement is detected, control is lost.
6. This is a 'penalty' phase. When the participant tries to move the target off screen, a warning is presented for 1 second. Then the (momentarily inactive) target reappears in one of the four screen corners (largest distance to bull's eye and now in the 'valley') and starts moving again controlled by the wind force.

What it Measures

The Compensatory Tracking task measures visuomotor coordination and vigilance

Psychological domains

• Visuomotor Coordination: The ability of the brain, eyes, and body to work together on a task
• Vigilance: Ability to maintain focus on a continuous repetitive task over a long time.

Main Performance Metrics

• Target Distance to Bull's Eye Center: the mean target distance (in mm) from the the center of the screen overall and for each test period
• Recovery Duration: the mean duration in ms that participant required to return an escaped target back to the bull's eye overall and for each test period

Psychiatric Conditions

The following patient groups have been tested with Compensatory Tracking Tasks

• Parkinson’s Disease (PD)
• Schizophrenia
• Traumatic Brain Injury (TBI)
• Stroke
• Sleep Deprivation

References

Search Google Scholar for peer-reviewed, published research using the Inquisit Compensatory Tracking Task.

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Makeig, S. & Jolley, K (1995). COMPTRACK: A Compensatory Tracking Task for Monitoring Alertness. https://apps.dtic.mil/sti/html/tr/ADA311977/index.html