Physical features of environment converted to electrochemical signals to brain. Senses: physiological mechanism for converting particular environmental features into electrochemical signals. Result of physical interaction between body and world. Sensory transducers: receptors that convert physical energy from environment into neural energy. Brain"s interpretation of initial sensory signals used to represent objects and events so can be identified, stored in memory, and used in thought and action. Processing, interpretation and representation of neural signals. Sensory nerve fibers provide only link to outside world. Perceptual world different from physical because certain environmental events cannot be detected by sensory channels. Neural patterns symbols for environmental events that occur in physical world. Bottom-up processing: sensory analysis from entry level to info go to brain. Top-down processing: info processing by high-level mental processes as we construct perceptions by filtering information throughout experience and expectations. Branch of perception concerned with establishing quantitative relations and physical stimulation.