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. A cue is some organization of the data present in the signal which allows for meaningful extrapolation. For example, sensory cues include visual cues, auditory cues, haptic cues, olfactory cues and environmental cues. Sensory cues are a fundamental part of theories of perception, especially theories of appearance (how things look). Concept There are two primary theory sets used to describe the roles of sensory cues in perception. One set of theories are based on the Constructivist theory of perception, while the others are based on the Ecological theory. Basing his views on the Constructivist theory of perception, Helmholtz (1821-1894) held that the visual system constructs visual percepts through a process of unconscious inference, in which cues are used to make probabilistic inferences about the state of the world. These inferences are based on prior experience, assuming that the most commonly correct interpretation of a cue will continue to hold true. A visual percept is the final manifestation of this process. Brunswik (1903-1955) later went on to formalize these concepts 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 likelihood of correlating 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. A second set of theories was posited by Gibson (1904-1979), based on the Ecological theory of perception. These theories held that no inferences are necessary to accomplish accurate perception. Rather, the visual system is able to take in sufficient cues related to objects and their surroundings. This means that a one:one mapping between the incoming cues and the environment they represent can be made. These mappings will be shaped by certain computational constraints; traits known to be common in an organism's environment. The ultimate result is the same: a visual precept is manifested by the process. Cue combination is an active area of research in perception, that seeks to understand how information from multiple sources is combined by