Sensation and Perception

Sensation and Perception

• Sensation: The detection of physical energy emitted or reflected by physical objects; it occurs when energy in the external environment or the body stimulates receptors in the sense organs.

• Perception: The process by which the brain organizes and interprets sensory information.

Ambiguous Figure

• Colored surface can be either the outside front surface or the inside back surface– Cannot

simultaneously be both

• Brain can interpret the ambiguous cues two different ways

The Riddle of Separate Sensations

• Sense Receptors: Specialized neurons that convert physical energy from the environment or the body into electrical energy that can be transmitted as nerve impulses to the brain.

• Doctrine of Specific Nerve Energies: Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.

Measuring the Senses

• Absolute Threshold– The smallest quantity of physical energy that

can be reliably detected by an observer• Difference Threshold

– The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; also called Just Noticeable Difference (JND).

Signal Detection Theory• Holds that responses in a detection task depend on a

sensory process and a decision process.• These may vary with a person’s motivation, alertness,

and expectations

Hit False Alarm

MissCorrect

Rejection

Detection

PresentNot

Present

No Detection

Absolute Sensory Thresholds

• Vision: A single candle flame from 30 miles on a dark, clear night

• Hearing: The tick of a watch from 20 feet in total quiet

• Smell: 1 drop of perfume in a 3-room apartment• Touch: The wing of a bee on your cheek,

dropped from 1 cm• Taste: 1 tsp. Sugar in 2 gal. water

Absolute Sensory Thresholds

• Despite our impressive sensory skills, our senses are tuned to a narrow band of physical energies.

• Other species can detect signals that we cannot.

Sensory Adaptations

• Sensory Adaptation: The reduction or disappearance of sensory responsiveness that occurs when stimulation is unchanging or repetitious.

• Sensory Deprivation: The absence of normal levels of sensory stimulation.

Sensory Overload

• Selective Attention: The focusing of attention on selected aspects of the environment and the blocking out of others.

– Protects us from being overwhelmed

Vision

• What We See• An Eye on the World• Why the Visual System is Not a Camera• How We See Colors• Constructing the Visual World

What We See

• Hue: The dimension of visual experience specified by color names and related to the wavelength of light.

• Saturation: Vividness or purity of color; the dimension of visual experience related to the complexity of light waves.

• Brightness: Lightness and luminance; the dimension of visual experience related to the amount of light emitted from or reflected by an object (height of wave).

An Eye on the World

• Retina: Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.

• Rods: Visual receptors that respond to dim light.

• Cones: Visual receptors involved in color vision. Most humans have 3 types of cones.

• Dark Adaptation: The process by which visual receptors become maximally sensitive to light.

Structures of the Human Eye

Retinal Image

Structures of the Retina

The Visual System is Not a Camera

• Much visual processing is done in the brain.– Some cortical cells respond to lines in

specific orientations (e.g. horizontal)– Other cells in the cortex respond to other

shapes (e.g., bulls-eyes, spirals, faces)• Feature-detectors: Cells in the visual cortex that

are sensitive to specific features of the environment.

How We See Colors

• Trichromatic Theory• Opponent Process Theory

Trichromatic Theory

• T. Young (1802) & H. von Helmholtz (1852) both proposed that the eye detects 3 primary colors– Red, blue, & green

• All other colors can be derived by combining these three

Opponent-Process Theory

• A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic.

• Opponent-Process cells are inhibited by a color, and have a burst of activity when it is removed.

Constructing the Visual World

• Form Perception• Depth and Distance Perception• Visual Constancies: When Seeing is

Believing• Visual Illusions: When Seeing is

Misleading

Gestalt Principles

• Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.– Proximity– Closure– Similarity– Continuity

Depth and Distance Perception

• Binocular Cues: Visual cues to depth or distance that require the use of both eyes.– Convergence: Turning inward of the eyes,

which occurs when they focus on a nearby object

– Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

• Monocular Cues: Visual cues to depth or distance that can be used by one eye alone.

Visual Constancies

• The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce.– Shape constancy– Location constancy– Size constancy– Brightness constancy– Color constancy

Visual Illusions

• Illusions are valuable in understanding perception because they are systematic errors.– Illusions provide hints about perceptual strategies

• In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.

Fooling the Eye

• The cats in (a) are the same size

• The diagonal lines in (b) are parallel

• You can create a “floating fingertip frankfurter” by holding hands as shown, 5-10” in front of face.

See Chapter 6 Fun Slides

Hearing

• What We Hear• An Ear on the World• Constructing the Auditory World

What We Hear

• Loudness: The dimension of auditory experience related to the intensity of a pressure wave.

• Pitch: The dimension of auditory experience related to the frequency of a pressure wave.

• Timbre (pronounced “TAM-bur”): The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

Other Senses

• Taste: Savory Sensations• Smell: The Sense of Scents• Senses of the Skin• The Mystery of Pain• The Environment Within

Taste: Savory Sensations

• Papillae: Knoblike elevations on the tongue, containing the taste buds (Singular: papilla).

• Taste buds: Nests of taste-receptor cells.

Smell: The Sense of Scents

• Airborne chemical molecules enter the nose and circulate through the nasal cavity.– Vapors can also enter through the mouth and

pass into nasal cavity.• Receptors on the roof of the nasal cavity detect

these molecules.

Smell: The Sense of Scents

• Red bars show the people who could identify a substance dropped on the tongue when they were able to smell it

Smell: The Sense of Scents

• The Blue bars show the people who could identify the substance when they were not able to smell it

Senses of the Skin

• The skin senses include:– Touch– Warmth– Cold– Pain– Various others (itch and tickle)

Gate-Control Theory of Pain

• Experience of pain depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.

Neuromatrix Theory of Pain

• Theory that the matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.

The Environment Within

• Kinesthesis: The sense of body position and movement of body parts; also called kinesthesia.

• Equilibrium: The sense of balance.• Semicircular Canals: Sense organs in the

inner ear, which contribute to equilibrium by responding to rotation of the head.

Psychological and Cultural Influences on Perception

• Needs• Emotions• Expectations

– Perceptual Set: A habitual way of perceiving, based on expectations.

• Beliefs

Puzzles of Perception

• Subliminal Perception• Extrasensory Perception: Reality or

Illusion?

Extrasensory Perception

• Extrasensory Perception (ESP):– The ability to perceive something without

ordinary sensory information– This has not been scientifically demonstrated

• Three types of ESP:– Telepathy – Mind-to-mind communication– Clairvoyance – Perception of remote events

– Precognition – Ability to see future events