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In psychophysics, sensory threshold is the weakest stimulus that an organism can detect. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probability curve. Methods have been developed to measure thresholds in any of the senses.
Several different sensory thresholds have been defined;
- Absolute threshold: the lowest level at which a stimulus can be detected.
- Recognition threshold: the level at which a stimulus can not only be detected but also recognised.
- Differential threshold: the level at which an increase in a detected stimulus can be perceived.
- Terminal threshold: the level beyond which a stimulus is no longer detected.
Aviation use. When related to motion in any of the possible six degrees of freedom (6-DoF), the fact that sensory thresholds exist is why it is essential that aircraft have blind-flying instruments. Sustained flight in cloud is not possible by `seat-of-the-pants' cues alone since errors build up due to aircraft movements below the pilot's sensory threshold, ultimately leading to loss of control.
- In flight simulators with motion platforms, the motion sensory thresholds are utilised in the technique known as `acceleration-onset cueing'. This is where a motion platform, having made the initial acceleration that is sensed by the simulator crew, the platform is re-set to approximately its neutral position by being moved at a rate below the sensory threshold and is then ready to respond to the next acceleration demanded by the simulator computer.
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