Module 9 & 10

Sensation and Perception

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The cow gave cola

.rat eht saw tac ehT

The cat saw the rat.

The cat was the rat.

Absolute Thresholds• The level of sensory stimulation necessary for

sensation to occur.– Vision: Candle flame seen at 30 miles on a clear

night.– Hearing: Tick of a watch under quiet conditions at

20 feet– Touch: A bee’s wing falling on you cheek from 1

centimeter (.4 inch) above.– Smell: 1 drop of perfume diffused into a three

room apartment– Taste: 1 teaspoon of sugar in 2 gallons of water.

Difference Threshold• The minimum difference that a person

can detect between two stimuli.

• Just noticeable difference

Signal Detection Theory• Set of formulas and principles that predict when

we will detect the presence of a faint stimulus amid background stimulation.– Detection depends on qualities of the stimulus, the

environment, and the person who is detecting.

• Three Variables:– Stimulus Variable: how bright is the blip on the radar

screen

– Environmental Variables: how much distracting noise is there in the room with the radar equipment

– Organismic Variables: is the operator properly trained and motivated.

Sensory Adaptation

Diminished sensitivity as a result of constant simulation.

Selective Attention

Focusing conscious awareness on a particular stimulus to the exclusion of

others.

Sensation

The process of receiving information from the environment.

Vision• Dominates human senses.• Light

– White Light: light as it originates from the sun or a bulb before it is broken into different frequencies.

– Color is seen because light bounces off objects at different frequencies.

– The eye has different receptors for different wave lengths.

– Wave lengths are based on the texture and solidity of what they hit.

Electromagnetic Energy• An energy spectrum that includes X-rays, radar, and

radio waves, among other things. A small portion of this spectrum includes visible light energy, which can be detected by the eye.

• Two Characteristics Determines What We See:– Length of the wave determines color

• Hue: The color of light, determined by the wavelength of light energy

– Amplitude of the wave (height) determines brightness

• Taller is brighter.

Parts of the Eye• Cornea: clear outer covering of the

eye, behind which is a fluid.• Iris: a colored circular muscle that

opens and closes, forming larger and smaller circles to control the amount of light getting into the eye.

• Lens: the part of the eye that focuses an image on the retina.

Parts of the Eye• Pupil: The opening in the eye.

– Psychological factors that control iris muscles.• Smaller when disgusted• Larger when

– Really like something or someone– Afraid– Strong emotional arousal

• Retina: Back of the eye, which contains millions of receptors for light.

Parts of the Eye• Rods: A visual receptor most sensitive to

violet-purple wave length; very sensitive for nigh vision; “sees” only black and white.

• Cones: a visual receptor that responds during daylight; “”sees” color.– Red range

• Rods are on the side and cones in the middle of the retina.

Differences Between the Cone and Rod Receptors

Cones

• Number 6 million• Location in Retina Center

– (fovea)

• Color Sensitive? Yes• Sensitivity I dim light?

Low• Ability to detect sharp

detail (acuity)? High

Rods

• Number 120 million• Location in Retina Edge

– (periphery)

• Color Sensitive? No• Sensitivity in dim Light?

High• Ability to detect sharp

detail (acuity)? Low

Rods and Cones• Bipolar Cells: cells that form the middle layer in the

retina. Bipolar cells gather information from the rods and cones and pass it on to the ganglion cells.

• Ganglion Cells: the top layer in the retina. Ganglion cells receive information from the bipolar cells and transmit it through their axon, which together form the optic nerve.

• Optic Nerve: the nerve that carries visual information from the eye to the occipital lobes of the brain.– Blind Spot: the point at which the optic nerve travels

through the retina to exit the eye. The lack of receptor rods and cones at this point creates a small blind spot.

Color Blindness• Inability to perceive certain colors, such

as red and green.– 8% Males– .05 % Females

• Red and Green cones do not work

• Truly color blind people are very rare

Afterimage• Image that remains after stimulation of

the retina has ended. Cones not used fire to bring the visual system back in balance.

Hearing

Audition: the sense of hearing.

Characteristics of Sound• Pitch: How high or low a sound is

• Timbre: the complexity of a sound

• Intensity: how loud a sound is

• Decibels: a measure of how loud a sound is (its intensity)

The Structure of the Ear• Eardrum: a piece of skin stretched over the

entrance to the ear; vibrates sound• Cochlea: A snail-shaped part of the ear, filled

with fluid and small hairs that vibrate to incoming sound

• Hair-cells: receptor cells for hearing found in the cochlea

• Cilia: Hairlike extensions on cells• Auditory nerve: bundle of nerves carrying

sound to the brain

Hearing• Sound waves go to the eardrum where

vibration is started. This vibration causes the cochlea to vibrate where cilia are located. Cilia are tuned to receive different frequency movements of hare that cause electrical impulses to go through the auditory nerve to the brain.

• How strong and when a sound arrives at one ear is contrasted by the brain with the same thing from the other ear. Difference help us locate where sound is coming from

Cutaneous Senses ( Touch)

• Cutaneous Receptors: Nerve receptors in the skin that respond to pressure, temperature, or pain– Records pressure– Changes in temperature– Remain active continuously to record an injury or

poison– Can fire for hours and hours after accidents

Smell• Olfaction: the sense of smell• Odor is hard to explain in words but when

associated with emotional events. We never forget it.

• Odor can recreate strong emotional memories.

• Olfactory Bulb: units that receive odor molecules and communicate their nature to the brain

Smell• Cilia in the nose collect molecules of odor

which send and electrical impulse to the olfactory bulb which generates a “code” that is sent to the brain for interpretation.

• Smell is most critical in eating. More than taste

• Pheromones: odor chemicals that communicate a message– Animals have them. Not sure if humans do.

Taste• Taste receptors: chemical receptors on the

tongue that decode molecules of food or drinks to identify them

• Types– Salt– Sweet– Sour – Bitter

• Work the same as cones

Salt• Necessary for survival

– Operates nerve cells– Keeps body chemistry in balance– Used for muscle contraction

• Children crave salt and it tampers with age until really old it re-opens

Sugar (sweet)

• Necessary for energy

• Newborns can taste at one day old

• Too little sugar makes a person tremble, feel faint, and causes mental confusion

• The desire for something sweet is built in

Sourness and Bitterness Detectors

• Bitterness - Poisons - no odor

• Sourness - Food gone bad - odor

Body Senses• Kinesthetic sense: the system for

sensing the position and movement of individual body parts.

• Vestibular sense: the system for sensing body orientation and balance, located in semicircular canals of the inner ear.

Perception• The process of organizing and interpreting

sensory information– Bottom-up process: Information processing

that focuses on the raw material entering through our eyes, ears, and other organs of sensation.

– Top-up Process: Information processing that focuses on other expectations and experiences I interpreting incoming sensory information

Gestalt

The “whole,” or the organizational patterns, that we tend to perceive.

The Gestalt psychologists emphasized that the whole is greater than the sum

of its parts.

Figure-Ground Relationships

• Figure-ground: the organization of the visual field into objects that stand out from their surroundings.

Grouping Principles: the perceptual tendency to organize stimuli into

understandable groups

• Similarity: a perceptual cue that involves grouping like thins together

• Proximity: a perceptual cue that involves grouping together things that are near one another

• Closure: the process of filling in the missing details of what is viewed

Depth Perception

The ability to see in three dimensions and judge distance

Example:• Visual Cliff: an apparatus used to demonstrate depth

perception

Binocular Depth Cues: depth cues that require the use of both eyes

• Retinal Disparity: The difference between the image provided by the two retinas– When the images are brought together in the brain, they provide

the sense of depth

• Convergence: the tension in the eye muscles when the eyes track inward to focus on objects close to the viewer– Short distance

Monocular Depth Cues: Depth cues that require the use of only one eye

• Relative Size: If an object of known size appears large, it is probably close, and if an object appears small, it is probably distant

• Relative Motion: Apparent slowness indicates an object is distant

• Interposition: Closer objects partially obstruct the view of more distant objects

• Relative Height: distant objects appear higher in a your field of vision that closer objects do

Monocular Depth Cues• Texture Gradient: how rough or smooth

objects appear– Gradient: Different level of textures we can see at

different distances

• Relative Clarity: Distant objects are less clear than near by objects are

• Linear Perspective: Parallel lines seem to draw together in the distance

Motion Perception• Stoboscopic motion

• Phi phenomenon

Perceptual Constancies: perceiving the size, shape , and lightness of an object as

unchanging, even as the retinal image of the object changes.

• Size Constancy: the ability to retain the size of an object regardless of where it is located.

• Shape Constancy: The ability to perceive an object as having the same shape regardless of the angle at which it is seen

• Lightness Constancy: The ability to see an object as having a constant level of lightness no matter how the lighting conditions change

Perceptual Set

A mental predisposition to perceive something one way and not another

Schemas: concepts or mental frameworks that organize and interpret information

Context

The setting or environment in which we interpret sensory stimuli

Illusions

In accurate perception