A Tree of Percepts The Perception System takes the form of a Percept Tree. A Percept is an atomic classification and data extraction unit that models some aspect of the sensory inputs passed in by the Sensory System. Given a DataRecord it returns both a match probability (the BirdPercept will return the probability that a DataRecord represents the experience of seeing a bird) and, if the match is above a threshold, a piece of extracted data (such as body-space coordinates of the bird). The details of how the confidence is computed and what exact data is extracted are left to the individual percept. The percept structure might encapsulate a neural net or it might encapsulate a simple “if … then …else” clause. This freedom of form is one of the keys to making the Perception System extensible, since the system makes no assumptions about what a percept will detect, what type of data it will extract or how it will be implemented.