Chapter 4Perception

Basic Principles of Basic Principles of PERCEPTIONPERCEPTION

• Perception is the process that organizes those stimuli into meaningful objects and events and interprets them.

Sound LocalizationSound Localization– Sound localization: the ability to locate objects in space

solely on the basis of the sounds they make • Because the ears are only 6 inches apart, the time

lag between the sound reaching both ears is very short.

• Even such small time lags provide the auditory system with sufficient information to locate the sound.

Sound LocalizationSound Localization

Pitch Perception: Place TheoryPitch Perception: Place Theory

– Place theory: contends that we hear different pitches because different sound waves trigger hair cells on different places of the cochlea’s basilar membrane.

Pitch Perception: Frequency TheoryPitch Perception: Frequency Theory

– Frequency theory: contends that pitch is determined by the frequency with which the basilar membrane vibrates.

Pitch PerceptionPitch Perception

– Place theory best explains high-frequency sounds, while frequency theory best explains low-frequency sounds. Mid-frequency sounds are best explained by volley theory, a revision of frequency theory.

Visual PerceptionVisual Perception

• Organization and interpretation of incoming visual information.

Pathways from the Eyes to the Visual Pathways from the Eyes to the Visual Cortex (Left-Right Visual Fields)Cortex (Left-Right Visual Fields)

Visual Information ProcessingVisual Information Processing

• Feature Detectors– nerve cells in the

brain that respond to specific features of the stimulus

• shape• angle• movement

Stimulus

Cell’s responses

Young-Helmholz Trichromatic Young-Helmholz Trichromatic Theory of Color VisionTheory of Color Vision

• Any color can be created by combining three primary colors—red, green, and blue.

• The retina has three types of color receptors that produce the primary color sensations of red, green, and blue.

Additive and Subtractive Color MixingAdditive and Subtractive Color Mixing

Color VisionColor Vision

• Trichromatic theory: theory of color vision that proposes three types of cones: red, blue, and green

• Afterimages: images that occur when a visual sensation persists for a brief time even after the original stimulus is removed

LO 3.3 How Eyes See and How Eyes See Color

Color VisionColor Vision

• Opponent-process theory: theory of color vision that proposes four primary colors with cones arranged in pairs: red and green, blue and yellow– lateral geniculate nucleus (LGN) of

thalamus

LO 3.3 How Eyes See and How Eyes See Color

Opponent Process FlagOpponent Process Flag

Opponent Process FlagOpponent Process Flag

• Explanation: Color AfterimageStare at the white dot in the center of this oddly colored flag for about 30 seconds. Now look at a white piece of paper or a white wall. Notice that the colors are now the normal, expected colors of the American flag. They are also the primary colors that are opposites of the colors in the picture and provide evidence for the opponent-process theory of color vision.

Color BlindnessColor Blindness

• Monochrome colorblindness: a condition in which a person’s eyes either have no cones or have cones that are not working at all

• Red-green colorblindness: either the red or the green cones are not working– protanopia: lack of functioning red cones– deuteranopia: lack of functioning green cones– tritanopia: lack of functioning blue cones

LO How Eyes See and How Eyes See Color

The Ishihara Color TestThe Ishihara Color Test

The Ishihara Color TestThe Ishihara Color Test

•In the circle on the left, the number 8 is visible only to those with normal color vision. In the circle on the right, peoplewith normal vision will see the number 96, while those with red-green color blindness will see nothing but a circle of dots.

Perceptual Organization:Perceptual Organization:Necker CubeNecker Cube

• Gestalt– an organized

whole– tendency to

integrate pieces of information into meaningful wholes

Gestalt PrinciplesGestalt Principles

• Figure–Ground– the tendency to perceive objects, or

figures, as existing on a background

• Reversible Figures– visual illusions in which the figure and

ground can be reversed

LO 3.9 Gestalt Principles of Perception

Perceptual Organization

Figure – Ground

Organization of the visual field into objects (figures) and surrounding background (ground)

Gestalt PrinciplesGestalt Principles

• Similarity– the tendency to perceive things that look

similar to each other as being part of the same group

• Proximity– the tendency to perceive objects that are

close to each other as part of the same grouping

LO 3.9 Gestalt Principles of Perception

Gestalt PrinciplesGestalt Principles

• Closure– the tendency to complete figures that are

incomplete

• Continuity– the tendency to perceive things as simply

as possible with a continuous pattern rather than with a complex, broken-up pattern

LO 3.9 Gestalt Principles of Perception

Gestalt PrinciplesGestalt Principles

• Contiguity– the tendency to perceive two things that

happen close together in time as being related

LO 3.9 Gestalt Principles of Perception

Proximity Similarity

Continuity Closure Connectedness

Depth PerceptionDepth Perception

• Depth perception: the ability to perceive objects three-dimensionally

– Binocular cues: depth cues that require information from both eyes

– Monocular cues: depth cues that require information from only one eye

The Visual CliffThe Visual Cliff

Depth Perception – Binocular CuesDepth Perception – Binocular Cues

• Binocular cues- depend on use of two eyes

– retinal disparity• images from the two eyes differ • closer the object, the larger the disparity

– convergence• neuromuscular cue• two eyes move inward for near objects

Monocular CuesMonocular Cues

• Monocular cues (pictorial depth cues): cues for perceiving depth based on one eye only– linear perspective: the tendency for parallel

lines to appear to converge on each other– relative size: perception that occurs when

objects that a person expects to be of a certain size appear to be small and are, therefore, assumed to be much farther away

LO 3.10 What Is Depth Perception?

Monocular CuesMonocular Cues

• Monocular Cues (cont’d)– interposition (overlap): the assumption that

an object that appears to be blocking part of another object is in front of the second object and closer to the viewer

LO 3.10 What Is Depth Perception?

Linear PerspectiveLinear Perspective

linear perspectivelinear perspective..

Relative SizeRelative Size

Overlap or InterpositionOverlap or Interposition

Monocular Depth CuesMonocular Depth Cues

Monocular Depth Cues:Monocular Depth Cues:Height in Visual FieldHeight in Visual Field

Monocular CuesMonocular Cues

• Aerial perspective: the haziness that surrounds objects that are farther away from the viewer, causing the distance to be perceived as greater

• Texture gradient: the tendency for textured surfaces to appear to become smaller and finer as distance from the viewer increases

LO 3.10 What Is Depth Perception?

Texture gradient Texture gradient causes the viewer to causes the viewer to assume that as the texture of the assume that as the texture of the

pebbles gets finer, the pebbles are pebbles gets finer, the pebbles are getting farther away getting farther away

Notice how the larger pebbles in the Notice how the larger pebbles in the foreground seem to give way to foreground seem to give way to

smaller and smaller pebbles near the smaller and smaller pebbles near the middle of the picture. middle of the picture.

..

Texture GradientTexture Gradient

In In aerial aerial or or atmospheric perspectiveatmospheric perspective, the , the farther away something is the hazier it farther away something is the hazier it

appears because of fine particles in the appears because of fine particles in the air between the viewer and the object. air between the viewer and the object.

Notice that the road and farmhouse in the Notice that the road and farmhouse in the foreground are in sharp focus while the foreground are in sharp focus while the

mountain ranges are hazy and indistinct.mountain ranges are hazy and indistinct.

Monocular CuesMonocular Cues

• Motion parallax: the perception of motion of objects in which close objects appear to move more quickly than objects that are farther away

• Accommodation: as a monocular clue, the brain’s use of information about the changing thickness of the lens of the eye in response to looking at objects that are close or far away

LO 3.10 What Is Depth Perception?

Perceptual ConstancyPerceptual Constancy

• perceiving objects as unchanging despite changes in retinal image

• color• shape • size

Shape ConstancyShape Constancy

Size-Distance RelationshipSize-Distance Relationship

Perceptual Illusions – Ames RoomPerceptual Illusions – Ames Room

Size-Distance RelationshipSize-Distance Relationship

The MThe Müüeller-Lyer Illusioneller-Lyer Illusion

Müller-Lyer IllusionMüller-Lyer Illusion

Perceptual SetPerceptual Set

a mental predisposition to perceive one thing and not another

expectations that create a tendency to interpret sensory information in a particular way

Cultural Influence on PerceptionCultural Influence on Perception

Perceptual SetPerceptual Set

• What you see in the center is influenced by perceptual set

Would you have interpreted the Would you have interpreted the middle drawing differently if you had middle drawing differently if you had looked at the drawing of the man’s looked at the drawing of the man’s

face or the sitting woman first?face or the sitting woman first?

Perceptual SetPerceptual Set

Flying Saucers or Clouds?

There Is Little Scientific EvidenceThere Is Little Scientific Evidence for Extrasensory Perceptionfor Extrasensory Perception

• Extrasensory perception (ESP): the ability to perceive events without using normal sensory receptors

• Parapsychology: the field that studies ESP and other paranormal phenomena

There Is Little Scientific Evidence There Is Little Scientific Evidence for Extrasensory Perceptionfor Extrasensory Perception

• Types of ESP:– Mental telepathy: the ability to perceive others’

thoughts

– Clairvoyance: the ability to perceive objects or events that are not physically present

– Precognition: the ability to perceive events in the future

– Psychokinesis: the ability to control objects through mental manipulation

Is There Extrasensory Is There Extrasensory Perception?Perception?

• Extrasensory Perception– controversial claim that perception can occur

apart from normal sensory input• trickery (magician)• imagination• paranormal forces?????• Not a natural human ability

There Is Little Scientific Evidence There Is Little Scientific Evidence

for Extrasensory Perceptionfor Extrasensory Perception

• Reasons for skepticism include:– Generally, findings supporting the existence of

paranormal abilities cannot be replicated in subsequent research.

– Many published ESP studies have used flawed research methodologies or failed to detect outright fraud by those they were testing.

There Is Little Scientific Evidence There Is Little Scientific Evidence

for Extrasensory Perceptionfor Extrasensory Perception

• Until ESP phenomenon can be reliably replicated in carefully controlled scientific studies, it will remain only a highly speculative “extra-sense” to most practitioners of science.