A stimulus is any object or event that elicits a response. For example, when food is presented to a lab mouse as a reward for pressing a lever, the food is a stimulus, and the mouse will likely respond by pressing the lever again. With regard to perception, stimuli can be visual (sight), auditory (sound), tactile (touch), olfactory (smell), or gustatory (taste). When we read words on a page, the text acts as a visual stimulus that excites the cells in our retina, which converts the stimuli to electrical signals and sends these signals to the brain.