Sensation and PerceptionChapter 8, Section 2&3

Ishihara Color Test74 - 21

Sensation becomes Perception

Psychophysics

The study of the relationships between sensory experiences and the physical stimuli that cause them

Gustav Fechner

Our Five Senses

Sight

Vision is the most studied of all the senses

Light enters eye through pupilLens focuses light on the retina in the back of the eye

Retina made up of two types of light-sensitive cells

Rods – require less light to stimulate (night vision)Cones – require more light than rods before they

respond (less of these types of cells)

Retinal cells change light energy into neuronal impulsesImpulses transmitted down optic nerve to the brainBrain interprets the impulses in the visual cortex

located in the occipital lobe at the back of the brain

Light is a form of electromagnetic radiation known collectively as the electromagnetic spectrum

An object’s color depends on which wavelengths of light reach your eye from the visible spectrum

Hearing

Sound waves from the air pass through various bones until they reach the inner ear

The inner ear contains tiny hairlike cells that change the change the waves into neuronal signals

These signals are transmitted through the auditory nerve to the brain

Taste

Chemical senseAppropriate chemical molecules must stimulate

proper receptors in the taste buds of tongueReceptors for sour, salty, bitter and sweetThis information is then relayed to the brain along

with data about texture and temperature

Smell (Olfaction)

Chemical senseAppropriate gaseous molecules must come into contact with smell receptors in the noseMolecules enter as vapors and reach special membrane in upper part of nasal passagesMessages are sent through olfactory nerve to the brain

Cilia in nasal cavity

Touch

Receptors in skin provide information about pressure, warmth, cold and pain

Sensitivity varies across body due to number of receptors located in each piece of skin

KinesthesisThe sense of movement and body position

Helps to maintain posture and balance – otherwise, movements would be jerky and uncoordinated

Absolute Threshold

The weakest amount of a stimulus that a person can detect half the time

Difference Threshold

The smallest change in a stimulus that can be detected half the time

Weber’s LawSmall changes to stimuli are more noticeable at small levels(slight change in the volume of music is more noticeable when already listening at a low level)

Small changes to stimuli are less noticeable at large levels(slight change in the volume of music is more noticeable when already listening at the highest levels)

Signal-Detection TheoryStudies relations between motivation, sensitivity, and decision making in determining the presence or absence of a stimulus

Involves recognizing some stimulus against a background of competing stimuli

Subliminal MessagesBrief auditory or visual messages that are presented below the

absolute threshold

(means there is a less than 50% chance they will be perceived)

Monocular Depth CuesHints that help us perceiving distance and depth that can be used with just one eye

Size – bigger is nearerRelative height – further away appear on higher planeLight and shadowsInterposition – when viewing overlapping images, we know the whole object is in the front Linear Perspective – parallel

lines converge when stretched into the distance

Binocular Depth CuesHints that help us perceive distance or depth that depend upon both eyes

Convergence – our eyes turn inward to look at nearby objectsRetinal disparity – eyes actually see their own, slightly different picture. A large difference = close objectSmall difference = far object

Constancy

Tendency to perceive certain objects in the same way regardless of changing angle, distance or lighting

Ames RoomUses depth cues to distort our perception

Left side of the room sits back several feet from the perceived distance

Right side of the room rises up several feet from the perceived height

Beuchet Chair

Top of the chair is off in the background

Legs of the chair is in the foreground

Standing in just the right spot, the illusion is complete

Extrasensory Perception (ESP)

The ability to gain information by some means other than the ordinary senses