Key Terms Absolute threshold: The smallest stimulus level that can be detected Action: The final behavioral response (Step 7) that involves motor activities in response to a stimulus Bottom-up processing (data-based processing): Processing that is based on the stimuli reaching the receptors Categorize: To place objects into categories Cerebral cortex: A 2-mm-thick layer of the brain that contains the machinery for creating perceptions, as well as other functions, such as language, memory, emotions, and thinking Classical psychophysical methods: The three methods for measuring a threshold: the method of limits, the method of constant stimuli, and the method of adjustment Difference threshold: The smallest difference between two stimuli that enables us to tell the difference between them Distal stimulus: A stimulus that is distant, or out in the environment Electromagnetic spectrum: A band of energy ranging from gamma rays at the short-wave end of the spectrum to AM radio and AC circuits on the long-wave end Frontal lobe: Receives signals from all of the senses, and plays an important role in perceptions that involve the coordination of information received through two or more senses Grating acuity: The smallest width of lines that participants can detect Knowledge: Any information that the perceiver brings to a situation, such as prior experience or expectations Magnitude estimation: The mathematical formulas relating physical intensity and perceptual magnitude for brightness Method of adjustment: The participant adjusts the stimulus intensity continuously until they can just barely detect the stimulus Method of constant stimuli: Stimulus intensities a