What Stimuli Do Humans Respond To?

Environmental Stimuli

Environmental stimuli are all the things in the environment that a person can perceive and respond to. Think of all the stimuli that are present as a person takes a walk down the beach. The person can see the sunlight and how the waves sparkle underneath it. She can feel the sand slipping between her toes and the occasional splash of seafoam. The waves also make sounds, as do the seagulls. She can smell the salt in the air and the scent of a nearby fisherman's haul. These stimuli all correspond to the five basic senses: sight, hearing, taste, touch and smell.

Attended Stimuli

At any given moment, in any given environment, there is simply too much to take in all at once. The stimuli that we choose to attend to, or focus on varies from person to person. Some stimuli elicit reactions that were built in through millions of years of evolutionary history. Anything that may be percieved as a danger; e.g. a loud noise, a stab of pain, the color red, is more likely to be attended to than more innocuous stimuli. It is important to note that the brain is constantly taking in information that we are not consciously aware of. Imagine that you are at a cocktail party. Music is playing, coversations are abuzz all around you. While in the middle of discussing a recent movie release with a colleague, you suddenly hear your name from way across the room. You turn and notice that a couple of your co-workers are discussing a project that the three of you are working on together. Up until that point, you were totally absorbed in your own conversation and paying no attention to what your co-workers were doing. Your brain, however, was taking everything in, filtering out the unimportant stuff, until your name, a salient stimulus, was uttered.

Perception, Recognition and Reaction

As the brain takes in stimuli and decides which are important and which are not, the important pieces are further processed. Imagine we are back at the beach. The person taking a walk sees a bird. She may be afraid of birds, be an avid ornithologist or simply be curious about the type of bird. The brain has decided that the object is a salient stimulus and begins to work on translating the image into categories. First, the image is transferred from light energy into electrical energy. This electrical energy is sent to the eye where an image is formed. As she sees the image, her brain also perceives it as belonging to a member of a category of birds. It is a bird, not an aircraft and more specifically a seagull, not a pelican. She may decide to move in the direction of the bird. Maybe she will want a better look at it or to take a photo of it. Maybe she will decide to move away from the bird, perhaps to avoid a mess landing on top of her head. Not all stimulus perception leads to action, but most do.