Sensory cue

A sensory cue is a statistic or signal that can be extracted from the sensory input by a perceiver, that indicates the state of some property of the world that the perceiver is interested in perceiving. Sensory cues include visual cues, auditory cues, tactile cues, haptic cues, olfactory cues, and so on. Sensory cues play an important role in theories of perception, especially theories of appearance (how things look).

Helmholtz (1821-1894) and Brunswik (1903-1955) are two scientists who were known for cue theories. Helmholtz held that the visual system constructs visual percepts through a process of unconscious inference, in which cues are used to make probabilistic best guesses about the state of the world. For Helmholtz (and most modern perceptual scientists), a visual percept is the manifestation of this process. Brunswik formalized Helmholtz's ideas with the lens model, which breaks the system's use of a cue into two parts: the ecological validity of the cue, which is its correlation with a property of the world, and the system's utilization of the cue. In these theories, accurate perception requires both the existence of cues with sufficiently high ecological validity to make inference possible, and that the system actually utilizes these cues in an appropriate fashion during the construction of percepts.

Some examples of visual cues include:
 * The eyes' vergence angle is a distance cue
 * Changes in shading across an object provide a shape cue

Some examples of auditory cues include:
 * Interaural intensity difference (IID) is a sound-source direction cue
 * Difference in sound arrival time (interaural timing difference or ITD) is another sound-source direction cue

Cue combination is an active area of research in perception, that seeks to understand how information from multiple sources is combined by the brain to create a single perceptual experience or response. Recent cue recruitment experiments have shown that the adult human visual system can learn to utilize new cues through classical (Pavlovian) conditioning.