Lesson Notes

Lesson 4.4a Selection: Extracting Important Messages

We can’t possibly attend to everything that we see in our visual field. As a result, our brains will use different processes to help us attend to what is important.

• Through selective attention we can choose which information we want to attend to.
• Our feature detectors enable us to respond to specific incoming stimuli, which helps us make sense of what we are perceiving.
• Habituation is our brain’s ability to focus on newer information and ignore older, more constant information.

Let’s look at the example of driving a car. When you first learn(ed) how to drive, you probably tried to focus on as much of your environment as possible, for example, where the gas and brake pedals are, your turn signal, the cars to your front, side or behind you. You may not have noticed that the radio was on, let alone have a conversation with the person sitting beside you (selective attention). Your ability to know what the STOP sign looked like over a YIELD sign may have been due to feature detectors for understanding shapes (octagon or triangle). Finally, if you (or someone you know) have been driving for awhile, there may be times where you drive from your house to the store, but now you feel comfortable changing radio stations and/or carrying on a conversation with a friend (habituation).

Lesson 4.4b Organization: Form, Constancy, Depth, and Color

In this lesson you will learn that after selecting information to attend to, we need to determine how we are going to organize the information.

Form: Gestalt (meaning “whole”) principles help explain some of our perceptions of form. Principles, such as figure-ground, proximity, continuity, closure, and similarity, help us make sense of our world and organize information. For example, the figure-ground principle explains why you see black letters on a white screen (the letters will appear closer or on top of the white “paper” screen).

Constancies:  There are four types of constancy. We learn that size, shape, color, and brightness remain the same despite contrary evidence. For example, we know that an apple is red when we see it in light and know that it does not change color when the lights are off (color constancy).

Depth:  Our ability to perceive depth is important to our everyday lives. The visual cliff experiment suggests that even as young babies we are able to perceive distances (i.e. cliffs). With the help of both binocular and monocular cues we have the ability to move around our world effectively.

An example of the importance of depth perception can be found in the story of one man, who was blind at birth, was able to regain his sight with the help of an operation. Soon after the operation, he looked out the fifth story window of his hospital room and tried to walk through the window to go onto the street. Unfortunately, the man was unable to perceive depth and did not know that the parking lot was 50 feet away. Thank goodness, the nurse stopped him before he “jumped” out the window. This case is a clear example of the importance of depth perception.

Color: Color helps us organize the world by allowing us to see differences and details about objects in our environment. For example, our ability to see apples on a tree is assisted by our ability to see the difference between red (apple) and green (leaves).