AP Sensation & Perception

What is the difference?

• Sensation: The ability to receive stimuli from the outside world.

• Perception: Your interpretation of the stimuli.

Generally speaking, sensation is universal, perception is individual

The Five Major Senses

1. Vision (sight)

2. Auditory (Hearing )

3. Olfactory (smell)

4. Gustatory (taste)

5. Tactile (touch)

Threshold

• The ability to recognize stimuli depends on whether the amount of stimuli reaches the level of threshold.

• Absolute threshold: the weakest amount of stimuli necessary for human sensory systems to recognize

• Just noticeable difference: smallest increase/decrease that a person senses the difference.

• Weber’s Law: Regardless of size, two stimuli must differ by a constant proportion for the difference to be noticed.

• Signal Detection Theory: the ability to detect stimuli depends not only on the amount of stimulus, but outside factors such as “noise” and attention.

Adaptation

• If the level of a stimulus stays constant, a person’s sensory system will be able to block out (ignore) it.

• Sensory systems will notice differences in level of stimuli.

• Focus also plays a role

Vision

• Most studied• Humans have the most complex system• Humans one of the few of the animal kingdom to see

in color• Light goes through the pupil, then reaches the lens,

which bends the light to the retina• The retina contains two types of light receptors:1. Rods (black/white, peripheral)2. Cones (color vision: each cone responds to a different

primary color)

Visual Problems: Issues of the Physical Eye

1. Myopia (nearsightedness): Focus point falls in front of the retina.

2. Hyperopia (farsightedness): focus point falls beyond the retina.

3. Presbyopia: Lens loses flexibility with age (often resulting in bifocals)

The World of Color

• Receptors known as cones allow for color vision.

Color has three components:1. Hue (light wavelength)2. Brightness (light amplitude)3. Purity (saturation)

How do We See in Color?

• Two theories combine to explain the process1. Opponent-process Theory (Ewald Hering)Some color combinations never seen together (blue-

yellow)Overexposure to one color, will create an afterimage of

the opposite colorProcess of experiencing color is excitatory and inhibitory

from a individual neuronsA positive response for one color, will elicit a negative in

another

2. Trichromatic (Young-Helmholtz) TheoryThomas Young proposed that color vision results

from the actions of three different receptors.Proposed this 70 years before the discovery of

conesFurther research by Herman von Helmholtz,

showed that three different wavelengths of light could be combined to form any visible color in the spectrum

Visual Perception

1. Gestalt: Attempting to make sense of the world around us.

2. Figure-ground:

3. Change blindness:

4. Phi phenomenon: illusion of movement (e.g. why we see films instead of individual frames)

Auditory• Vibrations of air (aka sound waves) are processed by the auditory

system into sounds• Sound is funneled into the inner ear from the pinna (outer ear) to

the eardrum, which causes the ear bones to vibrate against the cochlea. The fluid in the cochlea is sensed by tiny hairs (cilia), that send a signal to the auditory nerve which is transmitted to the brain

• Sound waves have two separate elements:1. Height (amplitude): determines volume2. Amount (frequency): determines pitch

Volume is measured in decibels

Auditory Theories

Place Theory: Proposed by Hermann von Helmholtz. Certain cilia respond to specific frequencies

Frequency Theory: Sound occurs because it generates a certain level of response with all the cilia.

Current understanding is that all cilia respond, but not at the same amounts.

Auditory Deficiencies• Deafness: The inability to hearTypes:1. Conduction: middle ear bones become rigid. Hearing aids can help2. Sensorineural: due to damage to the inner ear. Can be helped with a

cochlear implant.3. Environmental (aka “notch”): Caused by overexposure to loud noise

(85 db)4. Illness/Genetics (e.g. Helen Keller)

• Tinnitus: Ringing of the ears. The sound is internal. Results from overexposure to loud sounds

• Approximately 30,000,000 people in the U.S. are deaf/hard of hearing

The Chemical Senses:Olfaction and Gustation

• Olfaction: The sense of smellAsnomia: inability to smellLock and key theory: different receptors receive different odors.

Humans have over 350 different receptors for odor.Humans can track smells (Porter, 2007)Smell + Taste = FlavorBoth olfactory and gustatory receptors are short-lived

• Last month (9/13), neuroscientists announced research that shows that humans can distinguish ten types of odors (fragrant, woody/resinous, minty/peppermint, sweet, chemical, popcorn, lemon, fruity (non-citrus), pungent and decayed). (Castro et al, 2013)

Gustation

• Gustation : sense of taste• Contrary to long-standing theory, taste buds

are located throughout the tongue• Six basic tastes: Sweet, salty, bitter, sour,

umami, fat• What about spicy food?• Supertasters

Synesthesia

• For most people, only two senses work in concert: olfaction and gustatory

• For a rare few, their sensory systems work in a unique way (e.g. they can feel colors). This phenomena is known as synesthesia.

• Synesthesia appears to have genetic components (chromosomes 2, 5, 6, and 12:Asher), and may occur in up to 1% of the population

• May also be connected to autism (Asher)

Tactile and Minor Senses

• The largest body organ:

• Four different types of receptors: pain, pressure, heat, cold

• Vestibular• Kinesthetic

Issues in Perception

• Perception is learned, and is based on the individual’s interpretation of the sensation.

• New sensations are compared to ones experienced in the past, which is called frame of reference

• Subliminal perception: Being able to perceive stimuli below the known conscious threshold (limen). Use of this in advertising is controversial and illegal in the U.S.

Illusions and Hallucinations

• Illusion: Mistakes in perception based on real stimuli

Examples: FDR, magic• Hallucinations: Mistakes in perception based

on imaginary stimuli.Examples: LSD, delirium tremens, sleep

deprivation

Parapsychology

• Extrasensory Perception (ESP): The ability to receive stimuli outside the normal sensory system.

• Does it exist?Well…