Introduction to Perception

Perception refers to the set of processes we use to make sense of all the stimuli you  encounter every second, from the glow of the computer screen in front of you to the smell of the room to the itch on your ankle. Our perceptions are based on how we interpret all these different sensations, which are sensory impressions we get from the stimuli in the world around us. Perception enables us to navigate the world and to make decisions about everything, from which T-shirt to wear or how fast to run away from a bear.

Close your eyes. What do you remember about the room you are in? The color of the walls, the angle of the shadows? Whether or not we know it, we selectively attend to different things in our environment. Our brains simply don't have the capacity to attend to every single detail in the world around us. Optical illusions highlight this tendency. Have you ever looked at an optical illusion and seen one thing, while a friend sees something completely different? Our brains engage in a three-step process when presented with stimuli: selection, organization, and interpretation.

For example, think of Rubin's Vase, a well-known optical illusion depicted below. First we select the item to attend to and block out most of everything else. It's our brain's way of focusing on the task at hand to give it our attention. In this case, we have chosen to attend to the image. Then, we organize the elements in our brain. Some individuals organize the dark parts of the image as the foreground and the light parts as the background, while others have the opposite interpretation. 

Rubin's Vase

Rubin's Vase is a popular optical illusion used to illustrate differences in perception of stimuli.

Some individuals see a vase because they attend to the black part of the image, while some individuals see two faces because they attend to the white parts of the image. Most people can see both, but only one at a time, depending on the processes described above. All stages of the perception process often happen unconsciously and in less than a second.

The Perception Process

The perceptual process is a sequence of steps that begins with stimuli in the environment and ends with our interpretation of those stimuli. This process is typically unconscious and happens hundreds of thousands of times a day. An unconscious process is simply one that happens without awareness or intention. When you open your eyes, you do not need to tell your brain to interpret the light falling onto your retinas from the object in front of you as "computer" because this has happened unconsciously. When you step out into a chilly night, your brain does not need to be told "cold" because the stimuli trigger the processes and categories automatically.

Selection

The world around us is filled with an infinite number of stimuli that we might attend to, but our brains do not have the resources to pay attention to everything. Thus, the first step of perception is the (usually unconscious, but sometimes intentional) decision of what to attend to. Depending on the environment, and depending on us as individuals, we might focus on a familiar stimulus or something new. When we attend to one specific thing in our environment—whether it is a smell, a feeling, a sound, or something else entirely—it becomes the attended stimulus.

Organization

Once we have chosen to attend to a stimulus in the environment (consciously or unconsciously, though usually the latter), the choice sets off a series of reactions in our brain. This neural process starts with the activation of our sensory receptors (touch, taste, smell, sight, and hearing). The receptors transduce the input energy into neural activity, which is transmitted to our brains, where we construct a mental representation of the stimulus (or, in most cases, the multiple related stimuli) called a percept. An ambiguous stimulus may be translated into multiple percepts, experienced randomly, one at a time, in what is called "multistable perception."

Interpretation

After we have attended to a stimulus, and our brains have received and organized the information, we interpret it in a way that makes sense using our existing information about the world. Interpretation simply means that we take the information that we have sensed and organized and turn it into something that we can categorize. For instance, in the Rubin's Vase illusion mentioned earlier, some individuals will interpret the sensory information as "vase," while some will interpret it as "faces." This happens unconsciously thousands of times a day. By putting different stimuli into categories, we can better understand and react to the world around us.

Duck or Rabbit?

In this famous optical illusion, your interpretation of this image as a duck or a rabbit depends on how you organize the information that you attend to.