Chapter 4 Perception

Basic Principles of PERCEPTION Perception is the process that organizes those stimuli into meaningful objects and events and interprets them.

Sound 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 Localization

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

Pitch 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 Perception Organization and interpretation of incoming visual information.

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

Visual 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 Theory 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 Mixing

Color 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 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 Flag

Explanation: Color Afterimage Stare 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 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 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, people with normal vision will see the number 96, while those with red-green color blindness will see nothing but a circle of dots.

Perceptual Organization: Necker Cube Gestalt –an organized whole –tendency to integrate pieces of information into meaningful wholes

Gestalt 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 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 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 Principles Contiguity –the tendency to perceive two things that happen close together in time as being related LO 3.9 Gestalt Principles of Perception

ProximitySimilarity Continuity ClosureConnectedness

Depth 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 Cliff

Depth 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 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 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 Perspective

linear perspective.

Relative Size

Overlap or Interposition

Monocular Depth Cues

Monocular Depth Cues: Height in Visual Field

Monocular 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 causes the viewer to assume that as the texture of the pebbles gets finer, the pebbles are getting farther away Notice how the larger pebbles in the foreground seem to give way to smaller and smaller pebbles near the middle of the picture..

Texture Gradient

In aerial or atmospheric perspective, the farther away something is the hazier it appears because of fine particles in the air between the viewer and the object. Notice that the road and farmhouse in the foreground are in sharp focus while the mountain ranges are hazy and indistinct.

Monocular 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 Constancy perceiving objects as unchanging despite changes in retinal image color shape size

Shape Constancy

Size-Distance Relationship

Perceptual Illusions – Ames Room

Size-Distance Relationship

The Müeller-Lyer Illusion

Müller-Lyer Illusion

Perceptual 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 Perception

Perceptual Set What you see in the center is influenced by perceptual set

Would you have interpreted the middle drawing differently if you had looked at the drawing of the man’s face or the sitting woman first?

Perceptual Set Flying Saucers or Clouds?

There Is Little Scientific Evidence for 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 for 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 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 for 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 for 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.