College of Education

School of Continuing and Distance Education2014/2015 – 2016/2017

PSYC 441

Cognitive Psychology II

Session 5 – Theories of Perception

Lecturer: Dr. Benjamin Amponsah, Dept., of Psychology, UG, LegonContact Information: bamponsah@ug.edu.gh

Session Overview

• In this section, we will try to answer whether we see reality or what we see is guided by expectations. We will be studying three important theories of visual perception such as Gibson’s theory of Direct Perception and Gregory’s Constructivist theory of perception. A third theory of historical importance that will also be looked at is the Gestalt theory.

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Session Objectives

• At the end of the session, the student will be able to

• Discuss Gibson’s Direct perception theory

• Discuss the Greggory’s Constructivist theory

• Attempt to contrast the two theories

• Gestalt contribution to perception

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Session Outline

The key topics to be covered in the session are as follows:

• Topic One: Gibson’s Direct Perception Theory

• Topic Two: Greggory’s Constructive Theory of Perception

• Topic Three: Contrast of the Two Theories

• Topic Four: Gestalt Contribution to Perception

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Reading List

• Ashcraft, M. H. (2013). Cognition (6th edn.), London: Pearson Education Int.

• Eysenck, M. W. (2012). Fundamentals of Cognition (2ed). Psychology Press, Sussex.

• Galotti, K. M. (2017). Cognitive Psychology: In and out of the laboratory (6th edn.). Belmont, CA: Wadsworth.

• Hunt, R. R. & Ellis, H. C. (2004). Fundamentals of Cognitive Psychology (7th edn.), New York: McGraw-Hill.

• Willingham, D, B. (2013). Cognition: The thinking animal (International edn. NJ: Prentice-Hall).

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GIBSON’S DIRECT PERCEPTION THEORY

Topic One

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Theories of Perception

Do we see reality or what we see is guided by expectation?

• Three traditional theories of how we perceive the world will help us to answer the question.

1. Gibson’s theory of Direct Perception

2. Gregory’s Constructivist Theory of Perception

3. Gestalt theory

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• Gibson’s Theory of Direct Perception

• Direct perception proposes that information in the stimuli is the most important element in perception and that learning and cognition are unnecessary in perception.

• The leading proponent James Gibson (1966,1979) and his followers at Cornell University stated:

– “Direct perception assumes that the richness of the optic array just matches the richness of the world”.

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Optic Array is the pattern of light reaching the eye, which is

thought to contain all the visual information available on the

retina.

This implies that much of what we perceive about the world is

directly available in the stimulus information that strikes the

sensory system.

The idea of direct perception has gained support among

ecologically minded psychologists because it is assumed that

the stimulus contains enough information for correct perception

and does not require internal representations for

perception.

The perceiver does minimal work in perception because the

world out there offers so much information, leaving little demand

to construct perception and draw inferences.

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• According to Gibson our nervous system is perfectly attuned for detecting necessary information in the environment.

Evidence

• Evidence for Gibson’s direct perception theory can be found on how we detect distances - Depth perception.

• Depth perception can be detected in two main ways – Using either:

Monocular

or

Binocular cues

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Monocular and Binocular Vision

MONOCULAR CUES

Monocular cues are any visual cues for depth or distance perception that operates with one eye.

Example

• Cover one eye with your hand and look around.

Hold one finger in front of the opened eye.

Bring it very close to the eye.

What do you see? (shadow and blurred figure)

• The shadowing and accommodation produces a strong monocular depth cue. (Accommodation – how the eye maintains a clear image for objects at different distances).

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• Example: Shadow Monocular cue - gives rise to the awareness

that one object is in front of another object.

Shadow Monocular Depth cue has several rules.

If an object is solid, it will not allow light to pass through and will

therefore cast a shadow.

If there is only one light source, then all shadows will fall in the

same direction and the shadow will be opposite from the source

of light.

With a hole in the ground, the shadow appears on the same side

as the source.

Objects with shadows falling on them are farther away than objects casting the shadow.

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Relative Size - If an image contains

an array of similar objects that differ in

size, we interpret the smaller objects as

being farther away (smaller retinal image).

Superposition/Interpositioning which

occurs when a close object obscures

parts of a more distant object (one

object overlaps the other, which causes

us to perceive depth). Also Occlusion.

Relative Height – the object closer to

the horizon is perceived as farther away

and the object farther away from the

horizon is perceived as closer.

Linear Perspective - When parallel

lines appear to converge, they are

perceived as vanishing in distance.

More Examples of Monocular Depth Cues

Texture Gradient, which can be observed by

comparing the details of near and distant

objects: objects at a distance appear to be

smoother in appearance and more grey in

colour, while near objects have clear, sharp

colour and are more detailed.

Motion Parallax is another important cue to

depth perception and can be observed when

looking out of the window on a moving

vehicle: objects in the distance appear to

move slowly than do near objects.

Binocular Depth Cues

BINOCULAR DEPTH CUES

• Binocular cues are visual cues for depth perception that arise from the two retinal images obtained with both eyes.

Example:

• Hold a pen at arms length. Close each eye alternatively. The pen seem to swing back and forth.

1. The difference between the two retinal images, known as binocular disparity can give rise to distance.

2. Another binocular cue is binocular convergence - the movement of the eye muscles as we focus on near and distant objects can give rise to distance.

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• When an object is close to the observer, the two eyes must rotate inward (toward the nose) convergence.

• NB Convergence (eyes turn-in) is effective for distance less than 10 meters.

• When the target is farther away, the eyes rotate outward divergence.

• The two eyes are horizontally separated by the nose. The separation results in a distance of up to 6.5 cm between the pupils. Merging into one common percept is called fusion.

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Accommodation and Convergence allow us to see objects

clearly both near and far without diplopia (double vision)

Accommodation and Convergence

Summary

The visual cues discussed (monocular and binocular) are evidence of direct perception, and they are not dependent upon top-down processes.

Perception in this sense can be considered as direct decoding of information.

In general, direct perception assumes that the distal stimulus contains enough Information Apprehension.

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GREGGORY’S CONSTRUCTIVE THEORY OF PERCEPTION

Topic Two

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• Constructive theory of perception is based on the assumption that during perception we form and test hypotheses concerning percepts based on both what we sense and what we know (perceptual hypothesis).

• Perception then reflects combined effect of what comes in through our sensory system and what we have learnt about the world through experience.

• Think about how you recognize a familiar person – his features, nose, hair, etc. These features are registered by the eyes and also because you know the person to be in that locality. It’s possible to recognise him even if his features have changed.

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• From the perspective of the constructivists, though there may be changes in the pattern of original stimuli, you may still recognise your friend accurately because of unconscious inference – a process by which we spontaneously integrate information from several sources to construct a percept.

• When we look at something, we develop a perceptual hypothesis, which is based on prior knowledge. The hypotheses we develop are nearly always correct.

• In a few cases though, our perceptual hypotheses are disconfirmed by the data we perceive.

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Support for Gregory’s Theory

• SUPPORT FOR GREGORY’S THEORY

► Several studies using visual illusions provide support for Gregory’s constructive theory of perception.

• Visual illusion or an optical illusion is characterized by visually perceived images that differ from objective reality.

• This information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source.

• See examples below:

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How many legs does this elephant

have? 4, 5, 6 maybe 7?

Is this window on the

right or left of this building?

Let us focus specifically on the Müller-Lyer illusion. It

consists of two equal length parallel lines, which appear to

be different in length when one line has inwardly pointing

fins and the other has outwardly pointing fins.

Müller-Lyer Illusion

Gregory argued that the illusion occurs because it brings in

cues of our visual knowledge (experience) of the world.

Again Gregory argued that many visual illusions occur due to

misapplied constancy scaling (applying 3-D

characteristics to 2-D figure) .

An example is the Ponzo illusion, in which two horizontal lines

appear to be of unequal length when enclosed between two

converging lines.

• Remember Gibson’s Direct Perception theory,

argued strongly against the idea that perception

involves top-down processing and criticized

Gregory’s discussion of visual illusions on the

grounds that they are artificial examples and not

images found in our normal visual environments.

• The argument is interesting and we may probably

consider illusions as exceptions and might not be

that informative towards the debate.

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Are there top-down influences in Gibson’s Direct perception?

• When we consider Gibson’s Direct perception theory, there is the argument that his theory of affordances can be influenced by top-down processes such as:

» expectation,

» motivation and

» emotions.

• According to Gibson, affordances are “acts or behaviours permitted by objects, places and events”. The things offered by the environment to the organism.

• For humans, chairs afford sitting, a handle or knob affords grasping, a window affords looking through.

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• Gibson claimed that affordances of an object are also directly perceived; that is, we “see” a chair is for sitting, just made of wood. Can we really see sitting in a chair? (We can’t see except by imagination)

• We avoid crashing into walls and closed doors because such surfaces do not afford passing through and we perceive this as we move toward them.

• Lets look at ways in which affordances can be influenced by top-down processes such as expectation, motivation and emotion.

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Expectation

• Bruner and Minturn (1955) presented either letters or numbers to

their participants, and then showed them an ambiguous figure that

was a cross between B and 13.

• Participants who were shown letters perceived the figure as B,

whereas those who were shown numbers perceived 13.

• Thus, perception of an ambiguous objects can be influenced by

what one expects or anticipates.

Motivation

• Research has shown that the longer individuals are deprived of

food, the more likely they are to perceive ambiguous pictures as food-related.

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• Gilchrist and Nesberg (1952) showed that food

deprivation was associated with rating pictures of food

as being visually brighter than other pictures.

Emotion

• Lazarus and McCleary (1951) have demonstrated that

there could be emotional associations with stimuli and

that events can be influenced by our perception of them

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CONTRAST BETWEEN THE TWO THEORY

Topic Three

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• The two theories work well to explain perception but they

focus on different phases of the process.

• The direct-perception view is important for our

understanding of perception because it calls to attention

the significance of sensory stimuli, suggesting that the

processing of visual input is simple and direct and that

cognition and perception are natural and ecologically based.

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• The constructive perception theory on the other

hand is useful in understanding how sensory

impressions are comprehended by the thinking

brain.

• The theory also emphasises prior knowledge, past

experiences which are consistent with top-down

theories of recognition.

• The two theories must be seen as complementary.

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GESTALT CONTRIBUTION TO PERCEPTION

Topic Four

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Gestalt Approach to Perception

Gestalt Approach to Perception

Gestalt Theory

• In the 1930s the Gestalt psychologists, the most noted such as Koffka, Köhler and Wertheimer investigated how we perceive objects and visual forms.

• They argued that perceivers constantly search for a “good fit” between the visual image and stored memories of visual objects.

• Gestalt psychology maintains that psychological phenomena can only be understood if they were viewed as organized and structured wholes.

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– To understand their contribution to perception and pattern recognition we will discuss two of their principles:

• Form perception

• Gestalt Principles of Perceptual Organization.

FORM PERCEPTION

• Form perception helps us understand how perceivers come to recognize objects or forms.

• One important concern is to understand how we interpret stimuli (as consisting of objects that we see) from their background.

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Figure above shows a reversible figure-ground picture

– Generally, there are two distinct ways of seeing the pictures in the Figure above:

a black vase against a white background or

two white faces against a black background.

– This segregation of the whole display into objects (figure) and the background (ground) is an important process known to cognitive psychologists as form perception (the process by which the brain differentiates objects from their background).

The separation of objects from their background has important consequences. These are:

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1. The part of the display recognized as the figure will

be better remembered than whatever is interpreted

as background.

2. The background will be seen as shapeless, less

formed and farther away in space.

3. Perception is taken for granted but it’s more

complex, because what we perceive is not

completely determined by the stimulus display that

we see, it requires the perceiver’s active

participation.

Figure-ground separation is something we do everyday. E.g., we abstract the voice of a speaker from the background sound of a noisy party.

When people recover their sight after many years of blindness they commonly experience many difficulties in seeing the world as it is, but almost without exception, the figure-ground separation is achieved right from the onset of perception.

• This makes us take form perception for granted but the Gestaltists use of ambiguous figures as we have seen above show the complexity of perception.

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Gestalt Principles of Perceptual

Organization

• Gestalt Principles of Perceptual Organization

• Gestalt Psychologists also believed that perceivers follow certain laws or principles of organization in coming to their interpretation.

• They believed the brain imposes meaning on the discrete elements and that the whole is greater than the sum of its parts.

– Hence, they rejected the claim that perceivers recognize objects by identifying individual elements (bottom-up), instead, we see and recognize each object or unit as organized wholes.

– They vehemently opposed the structuralists who considered elements as the building blocks of conscious experience.

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• Example

• In one experiment by Navon (1977), the assumptions of the Gestalts were confirmed that in perceptual processing the most important features are identified first before the fine-grained details.

E.g., when the letter sssssss was used to write the letter H, subjects analyzed the H first before turning to the contents or the elements in the letter H which were the sssssss.

What then are the Gestalt principles of perceptual organization that allow us to perceive objects and events as organized wholes?

• Let us look briefly at 4 major principles:

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Principle of proximity

► The closer two figures are to each other, the more they will

tend to be grouped together perceptually. Proximity may

operate in time just as it does in space.

Principle of similarity

► There is the tendency for our perceptual system to group

figures based on their similarity.

Principle of Good Continuation

► Our visual system seems to prefer contours that continue

smoothly along their original course. This principle of

grouping is called good continuation.

This principle is used by the military for camouflage. It also

helps to camouflage animals against their natural

predators. It helps to conceal various insects from

predators who tend to see parts of the insect’s body as

continuations of the twigs on which it stands.

The line segments in the figure will generally be grouped so

that the contours continue smoothly.

As a result, segment A will be grouped with D, and C with

B, rather than A with B and C with D.

In A all subjects see two complex patterns intersected by a

horizontal line. Hardly anyone sees the hidden 4 contained

in that figure – and shown in B – despite the fact that we

have encountered 4’s much more than the two complex

patterns which are completely new.

Principle of Closure

► There is the tendency for our visual system to complete

figures that have gaps in them. The figure is seen as a

triangle despite the fact that the sides are incomplete.

There is the tendency to complete – or close – figures

that have a gap in them, as in the incomplete triangle

shown above.

• Summary

• Proximity, similarity, good continuation and closure are among the factors that determine whether we see portions of the visual world as belonging together or apart.

• Although the Gestalt theory has intuitive appeal, certain questions are raised.

• E.g., we do not know how these principles are transformed or translated into cognitive or physiological processes.

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• Their concepts are also very difficult to define.

• Despite the concerns, we still owe a lot to the

Gestaltists for helping us to understand some

processes in visual perception.

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Sample Questions

• Describe the two theories of perception – Gibson’s theory of direct perception and Greggory’s constructive theory of perception

• Define Form perception and discuss why it is an important concept in visual perception.

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References

• Gibson, J.J. (1979). The ecological approach to visual perception. Boston: Houghton Mifflin.

• Brunner, J. S. & Minturn, A. L. (1955). Perceptual identification and perceptual organization. Journal of General Psychology, 53, 21-28.

• Gilchrist, J. C. & Nesberg, L. S. (1952). Need and perceptual change in need-related objects. Journal of Experimental Psychology, 44, 369-376.

• Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 343-383.

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THANK YOU

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