Stimulus

A stimulus is any change or signal in the environment that prompts a response from an organism or system. For example, touch, sound, or light can act as stimuli that trigger reactions such as pulling your hand away, blinking, or waking up. In psychology, stimuli are external or internal events that influence behavior or mental processes. Essentially, stimuli are the triggers that create a chain reaction, helping organisms perceive and respond to their surroundings effectively.