Chapter 2 perception

WARM-UP

There are several ways in which the brain interprets the complex flow of information from the various senses and creates perceptual experiences that go far beyond what is sensed directly.

How do we perceive the world around us?

• Look at the illustrations below. How does our visual system interpret them? With a partner try to explain why the visual system may interpret them the way it does.

a. b.

• Discuss your ideas in a brief plenary.

LISTENING

Pre-listening

You will hear a part of a lecture titled Perceptual Organization where some of the principles of perceptual organization will be discussed.

Guessing vocabulary from context

A. The items in the task below contain some important vocabulary from the lecture. Each of the terms is in boldface in the context in which you will hear it. Work with a partner. Take turns explaining what you think each word means, based on its context (or suggest a Russian equivalent). In some cases you may be able to give only a general idea, but this can still contribute to your overall understanding of the term. For example, is it a noun or a verb? Does it mean something good or something bad?

8. The Gestalt psychologists believed that the brain creates a coherent perceptual experience ____

9. In one important facet of the perceptual process, we distinguish figures from the ground against which they appear. ____

10. The figure-ground distinction refers to all our senses ____

11. there are not enough cues in a pattern to permit us to easily distinguish a figure from its ground ____

12. This is the principle behind camouflage – to make a figure blend into its background. ____

13. It is unclear which part of the stimulus is the figure and which is the ground. Examples of such reversible figures could be a vase and the silhouettes. ____

14. We tend to see whole objects and hear meaningful sounds rather than just random bits and pieces of raw sensory data. ____

2. Match the vocabulary terms in a with their definitions by writing the letters in the blanks.

1. if something is like that, it can be changed back to how it was before

2. a clear difference or separation between two similar things

3. clear and reasonable

4. happening or chosen without any definite plan, aim, or pattern

5. an action or event that is a signal for something else to happen

6. two or more things mix and become similar so that you do not notice them

7. one of several parts of someone's character, a situation etc (= aspect)

While-listening

The following is an incomplete summary of the lecture. Read the summary and think about what kinds of words or phrases might go in the blanks. Do not write anything yet.

One important way our perceptual processes work is through distinguishing (1)________figures from the (2)________ground against which they appear. The figure-ground distinction, first noted by (3)_______ ______Gestalt psychologists, refers to all our senses, not just (4)_______vision. For instance, a (5)_______ ______violin solo stands out against the “ground” of a symphony orchestra. When we use sensory information to create perceptions, we fill in the missing information, group (6)_______ ______various objects together, see (7) ______whole objects, and hear meaningful sounds.

Now listen to the lecture. Take notes in your own note-book. Remember, it is not necessary to write down everything that you hear. Use the summary in the box as a guide to help you listen for the important points.

Use your notes to complete the summary.

Compare summaries with a partner.

READING

A. You are going to read a text about how we perceive movement. Use the table below to think about the topic. What do you know about it? What mechanisms are involved in this process? Share your ideas with a partner.

Things I know about the topic	Things I don't know	Things I'm not sure about
1. 2.	1. 2.	1. 2.

B. Read the text and say if there is new information in it.

PERCEIVING MOVEMENT

The perception of movement is a complicated process involving both visual information from the retina and messages from the muscles around the eyes as they follow an object. At times, our perceptual processes play tricks on us, as we think we perceive movement when the objects we are looking at are, in fact, stationary. We must distinguish, therefore, between real and apparent movement.

Real movement refers to the physical displacement of an object from one position to another. The perception of real movement depends only in part on the movement of images across the retina of the eye. If you stand still and move your head to look around you, the images of all the objects in the room will pass across your retina. You will probably perceive all the objects as stationary. Even if you hold your head still and move only your eyes, the images will continue to pass across your retina. But the messages from the eye muscles seem to counteract those from the retina, so the objects in the room will be perceived as motionless.

The perception of real movement seems to be determined less by images moving across the retina than by how the position of objects changes in relation to a background that is perceived as stationary. When we perceive a car moving along a street, for example, we see the street, the buildings, and the sidewalk as a stationary background and the car as a moving object. Remarkably, the brain can distinguish these retinal images of an object moving against an immobile background from all the other moving images of the retina.

The perception of real movement is highly accurate. Imagine that you are watching a videotape of someone lifting a box of unknown weight. Research indicates that you would probably be able to predict the weight of the box fairly accurately, and you would probably also be able to tell if the person lifting the box was simply pretending it was heavier than it was. Moreover, there is some evidence that we may be specially equipped to detect biological movement, the movement of another human body. To demonstrate this, one researcher attached lights to various parts of a person’s body and then filmed movement of the lights in an extremely dark room. People watching the film were immediately able to tell that the lights in motion were really a human body in motion, even though they saw part of the film for only a fraction of a second.

Apparent movement occurs when we see movement in objects that are actually standing still. One form of apparent movement is referred to as the autokinetic illusion – the perceived motion created by a single stationary object. If you stand in a room that is absolutely dark except for one tiny spot of light and stare at the light for a few seconds, you will begin to see the light drift. In the darkened room, your eyes have no visible framework; there are no cues telling you that the light is really stationary. The slight movements of the eye muscles, which go unnoticed most of the time, make the light appear to move.

Another form of illusory movement is stroboscopic motion – the apparent motion created by a rapid series of still images. This form of apparent movement is illustrated best by a motion picture – which is not in motion at all. The film consists of a series of still pictures showing people and objects in slightly different positions. When the separate images are projected sequentially onto a screen at a specific rate of speed, the people and objects seem to be moving because of the rapid change of one still picture to the next.

Another common perceptual illusion, known as the phi phenomenon, occurs as a result of stroboscopic motion. When a light is flashed on at a certain point in a darkened room, then flashed off, and a second light is flashed on a split second later at a point a short distance away, most people will perceive these two separate lights as a single spot of light moving from one point to another. This perceptual process causes us to see motion in neon signs where words appear to move from one side to the other as different combinations of stationary lights are flashed on and off.