Introduction to Psychology

Perception

Psychophysics

• Sensation is the stimulation of sense organs

• Perception is the selection, organization, and interpretation of sensory input.

Thresholds• Sensory receptors are tuned to a particular form

of energy– Auditory receptors in the ear code for sound

pressure changes, not for light

• Sensory systems require a minimum amount of energy for activation (absolute threshold)– Just-noticeable difference (JND): The minimum

difference in stimulation that is just noticeable• Weber noted that the JND is a fraction of the original

stimulus intensity: the fraction is different for different senses

© 2002 John Wiley & Sons, Inc.

The Visual System• The eye detects electromagnetic radiation

(light)– Vision is functional

• Allows for detection of movement (predator or prey?)

• Allows for detection of color (ripe or spoiled?)

• Light detection is useful because:• Light travels rapidly (no delay, unlike hearing)

• Light travels in straight lines (no distortion)

• Light interacts with the surfaces of objects in the environment (is reflected or absorbed)

© 2002 John Wiley & Sons, Inc.

Electromagnetic Spectrum

© 2002 John Wiley & Sons, Inc.

Details of the Human Eye

© 2002 John Wiley & Sons, Inc.

Transduction of Light• Light travels through the retina to impinge on

photoreceptors at the back of the eye– Light bleaches a pigment contained within the

photoreceptors:• Bleaching leads to a graded receptor potential that eventually

produces an action potential in the ganglion cell

– Two types of photoreceptors• Cones: found in center of retina (fovea) and are sensitive to

fine detail and color• Rods: found in periphery of retina and are sensitive to

movement but not fine detail

© 2002 John Wiley & Sons, Inc.

Visual Pathways in Brain:“Where” versus “What”

© 2002 John Wiley & Sons, Inc.

Perception of Color

• Color is a psychological perception– Three dimensions of color:

• Hue is the apparent color of an object (blue)

• Brightness is the intensity of a color

• Saturation is the purity of the color

– Three different types of cones are found in the eye• Each is sensitive to different wavelengths of light

– S-cones: blue

– M-cones: green

– L-cones: red

© 2002 John Wiley & Sons, Inc.

Color Vision Theories

• Young-Helmholtz:– Color is explained by differential activation of 3

color elements in eye• Could not account for negative color afterimages

• Hering: Opponent-Process Theory– Colors are derived from activity of 3 antagonistic

systems• Black-white

• Red-green

• Blue-yellow

© 2002 John Wiley & Sons, Inc.

Negative Color Afterimages

Stare at the globe for 10 seconds and then look away at a white surface

© 2002 John Wiley & Sons, Inc.

Sound

• Sound waves are vibrations of molecules that travel through air.

• Amplitude - decibels

• Wavelength - frequency (cps or hertz)

• Purity - timbre

The Auditory System

• External ear – pinna, eardrum

• Middle ear – ossicles (hammer, anvil, stirrup)

• Inner ear – cochlea

• basilar membrane –hair cells

Taste: the Gustatory System

• Taste buds

• Primary tastes: sweet, sour, bitter, salty

• Perception of flavor

• Papillae: circumvallate, foliate, & fungiform

Smell: the Olfactory System

• Smell: chemical substances dissolved in mucus

• Olfactory cilia

• Olfactory nerves

• Olfactory bulb

Skin Senses

• Receptors are localized within the skin to detect physical stimuli in the outside world

• Three classes of skin receptors:– Touch: physical contact of objects with the skin– Temperature of objects– Pain: destruction of skin tissue

© 2002 John Wiley & Sons, Inc.

Pain• Pain is a source of information that relates to tissue

destruction– Force– Heat– Chemical

• Pain is a adaptive to a degree (motivates behaviors to terminate the source of the pain)

• Pain is influenced by– Cultural beliefs– Emotional states– Exogenous drugs (opiates)– Internal transmitters (endorphins)

© 2002 John Wiley & Sons, Inc.