Chapter 05: Sensation and Perception


From Energy to Neural Impulse

Thresholds

Sensory Adaptation

Vision

The Stimulus Input: Light Energy

The Eye

Visual Information Processing

Sensation

Other Senses

Hearing

Touch

Pain

Taste

Smell

Body Position and Movement

Perception

Perceptual Organization

Form Perception

Depth Perception

Perceptual Constancy

Perception

Perceptual Interpretation

Sensory Deprivation and Restored Vision

Perceptual Adaptation

Perceptual Set

Perception

ESP

Claims of ESP

Facts of Fantasies?

Testing ESP

Sensation & Perception

How do we construct our representations of the external world?

To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation.

When we select, organize, and interpret our sensations, the process is called perception.

Sensing the World

Senses are nature’s gift that suit an organism’s needs.

A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of the human voice.

Exploring the Senses

What stimuli cross our threshold for

conscious awareness?

Psychophysics

A study of the relationship between physical characteristics of stimuli and our psychological experience with them.

Transduction

In sensation, the transformation of stimulus energy (sights, sounds, smells) into neural impulses.

Thresholds

Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time.

Subliminal Threshold

Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness.

Weber’s Law

Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = I/I.

Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.

Now you see, now you don’t

Vision

The Stimulus Input: Light Energy

The Eye

Visual Information Processing

The Stimulus Input: Light Energy

Physical Characteristics of Light

Wavelength (hue/color)

Intensity (brightness)

Wavelength (Hue)

Hue (color) is the dimension of color determined by the wavelength of the  light.

Wavelength is the distance from the peak of one wave to the peak of the next.

Wavelength (Hue)

Intensity (Brightness)

Intensity: Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

Intensity (Brightness)

The Eye

Parts of the eye

Cornea: Transparent tissue where light enters the eye.

Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.

Lens: Focuses the light rays on the retina.

Retina: Contains sensory receptors that process visual information and sends it to the brain.

The Lens

Lens:  Transparent structure behind the pupil that changes shape to focus images on the retina.

Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

Retina

Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information.

Optic Nerve, Blind Spot & Fovea

Test your Blind Spot

Photoreceptors

Bipolar & Ganglion Cells

Visual Information Processing

Feature Detection

Shape Detection

Visual Information Processing

Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

From Sensation to Recognition

Color Vision

Trichromatic theory:  Young and von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors.

Tetrachromacy

Tetrachromatic ‘Super Vision’ May Help Some Women See 100 Million Colors, Neuroscientists Say

Color Blindness

Genetic disorder in which people are blind to green or red colors.  This supports the Trichromatic theory.

Opponent Colors

The Other Senses

Hearing

Touch

Pain

Taste

Smell

Body Position and Movement

Hearing

The Stimulus Input: Sound Waves

Sound waves are compressing and expanding air molecules.

Sound Characteristics

Frequency (pitch)

Intensity (loudness)

Frequency (pitch): The dimension of frequency determined by the wavelength of sound.

Wavelength: The distance from the peak of one wave to the peak of the next.

Intensity (Loudness)

Intensity (Loudness): Amount of energy in a wave, determined by the amplitude, relates to the perceived loudness.

Loudness of Sound

The Ear

Outer Ear: Collects and sends sounds to the eardrum.

Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

Cochlea:  Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.

Localization of Sounds

Because we have two ears, sounds that reach one ear faster than the other ear cause us to localize the sound.

Localization of Sound

1. Intensity differences

2. Time differences

Time differences as small as 1/100,000 of a second can cause us to localize sound. The head acts as a “shadow” or partial sound barrier.

Touch

The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and pain.

Skin Senses

Only pressure has identifiable receptors. All other skin sensations are variations of pressure, warmth, cold and pain.

Pain

Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain.

Biopsychosocial Influences

Gate-Control Theory

Pain Control

Taste

Sensory Interaction

Smell

Smell and Memories

Body Position and Movement

Perceptual Organization

Form Perception

Depth Perception

Perceptual Constancy

Perceptual Organization

How do we form meaningful perceptions from sensory information?

We organize it. Gestalt psychologists showed that a figure formed a “whole” different from its surroundings.

Form Perception

Organization of the visual field into objects (figures) that stand out from their surroundings (ground).

Grouping

Grouping & Reality

Although grouping principles usually help us construct reality, they may occasionally lead us astray.

Depth Perception

Depth perception enables us to judge distances. Gibson and Walk  (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception.

Binocular Cues

Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” as shown in the inset.

Monocular Cues

Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away.

Monocular Cues

Interposition: Objects that occlude (block) other objects tend to be perceived as closer.

Monocular Cues

Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are lower.

Monocular Cues

Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation point, moving slower and in the same direction.

Monocular Cues

Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance.

Monocular Cues

Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away.

Perceptual Constancy

Perceiving objects as unchanging even as illumination and retinal images change.

Color Constancy

Perceiving familiar objects as having consistent color even when changing illumination filters the light reflected by the object.

Size-Distance Relationship

The distant monster (below, left) and the top red bar (below, right) appear bigger because of distance cues.

Size-Distance Relationship

Ames Room

Lightness Constancy

Perceptual Interpretation

Sensory Deprivation and Restored Vision

Perceptual Adaptation

Perceptual Set

Perceptual Interpretation

Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences.

John Locke (1632-1704) argued that we learn to perceive the world through our experiences.

Sensory Deprivation & Restored Vision

After cataract surgery, blind adults were able to regain sight. These individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle and a triangle          (Von Senden, 1932).

Facial Recognition

After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces.  Normal observers also show difficulty in facial recognition when the lower half of the pictures are changed.

Sensory Deprivation

Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars.

Perceptual Adaptation

Visual ability to adjust to an artificially displaced visual field, e.g., prism glasses.

Perceptual Set

A mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures.

Perceptual Set

Context Effects

Cultural Context

Perception Revisited

Is There Extrasensory Perception?

Perception without sensory input is called extrasensory perception (ESP). A large percentage of scientists do not believe in ESP.

Claims of ESP

Telepathy: Mind-to-mind communication. One person sending thoughts and the other receiving them.

Clairvoyance: Perception of remote events, such as sensing a friend’s house on fire.

Precognition: Perceiving future events, such as a political leader’s death.

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