Introduction to Psychology

Sensation and Perception

Perception

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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

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)

Electromagnetic Spectrum

Details of the Human Eye

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

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

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

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

Negative Color Afterimages

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

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

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)