Sensation and PerceptionKyle Kahler and Becky Marx

Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. Perception is the process by which we organize and interpret this information. We will talk about them separately, but know that they are parts of one continuous process.

Introduction

Vocabulary:• Sensory adaptation: decreasing responsiveness to stimuli due to constant

stimulation• Difference threshold (Just noticeable difference) : the minimum difference

between two stimuli required for detection 50% of the time• Weber’s Law: the principle that, to be perceived as different, two stimuli

must differ by a constant minimum percentage (rather than a constant amount)

• Absolute Threshold: the minimum stimulus needed to detect a particular stimulus 50% of the time

• Signal detection theory: predicts how and when we detect the presence of a faint stimulus amid background noise. Assumes there is no single absolute threshold and that detection depends partly on experience, expectations, motivation, and level of fatigue

Subliminal: below one’s absolute threshold for conscious awarenessPriming: the activation, often unconsciously, of certain associations, this

predisposing one’s perception, memory, or response

Sensation

Vocabulary Continued• Bottom-up processing: analysis that begins with the sensory receptors and

works up to the brain’s integration of sensory information• Top-down processing: information processing guided by higher-level

mental processes, as when we construct perceptions drawing on our experience and expectations

• Psychophysics: the study of relationships between the physical of stimuli and our psychological experience of them

• Parallel processing: processing several aspects of a problem simultaneously

Steps of Sensation1. Acquisition: stimulus is received by sensory organ2. Transduction: stimulus or energy is converted into neural impulses our

brains can interpret 3. Primary Association: neural impulses are processed4. Secondary Association: impulses trigger other processes

Sensation

Stimulus: Light Energy• what strikes our eyes isn’t color but pulses of electromagnetic energy that

our visual system perceives as color• Light’s wavelength - the distance from one wave peak to another -

determines its hue (the color we experience)• Light’s intensity, the amount of energy in light waves (determined by

wave’s amplitude) influences brightness

Vision

1. Within the eye and Acquisition:

a. reflected light enters the eye through the cornea, which protects the eye and bends the light for focus

b. passes through the pupil (small adjustable opening) which is regulated by the iris (colored muscle surrounding pupil) which dilates or constricts in response to light intensity (or emotions)

c. then the lens focuses the rays into an image on the eye’s light-sensitive back surface (the retina which contains the rods and cones and neurons). It does this through accommodation (lens changes curvature for focus)

Vision

2. The Retina and Transductiona. The first layer of cells in the retina is

directly activated by light. The cells are cones and rods arranged in a pattern where the rods outnumber the cones (around 20 to 1) and are distributed throughout, and the cones are concentrated toward the center or fovea (retina’s area of central focus). Cones are activated by color and rods respond to black and white.

b. Light energy striking the rods and cones produces chemical changes that generate neural signals that activate bipolar cells which activate ganglion cells

c. The network of ganglion cells converge to form an optic nerve that carries information to the brain where the thalamus receives and distributes information

Vision

3. Primary Associationa. the thalamus sends the message to the visual cortices in the occipital lobe which

translates impulses into perceptual datab. feature detector neurons in visual cortex receive information and respond to a

scene’s specific features4.Secondary Associationsa. Feature detection cells pass information to other areas of the cortex where cells

respond to complex patterns like perceiving faces or housesColorYoung-Helmholtz trichromatic theory: Three types of cones detect three wavelengths

of light ( blue, green, red). Opponent- process theory: opposing retinal processes (red-green, yellow-blue) enable

color vision

Vision

Stimulus: Vibrations/Soundwaves• Frequency - Rate in which a vibration occurs that constitutes a wave.• Loudness - A sound being characterized by the amount of volume and

intensity.• Pitch - The degree of highness or lowness of a tone.• Timbre - The character of quality of a musical sound or voice distinct

from it’s pitch and intensity.

Hearing

1. Acquisitiona. Soundwaves are received through the ear canal. First, the outer ear, which collects and channels sound to the middle ear. b. The middle ear turns the vibrations into a waves using the eardrum and 3 small bones. The sound vibrates the eardrum at the same frequency and passes it onto the inner ear. c. The inner ear turns the waves into nerve impulses through the inner ear fluid which are then transferred to the brain to be perceived.

Hearing

2. Transductiona. First transduction of the sound into a nerve signal is in the cochlea, which is located in the inner ear.

b. In the inner ear, the stapes vibrates the oval window. The perilymph (an extracellular fluid inside the cochlea), transfers the vibrations to the round window.c. The round window bulges when pressure rises and deflates as pressure decreases. With all of the vibration the membranous labyrinth of the cochlea encloses the scala media which has the the receptor organ called the Corti.

Hearing

(Transduction continued, and Association)d. Inside the Corti lay inner hair cells which are the auditory receptors.The stereocilia of the hair cells are embedded into the tectorial membrane.

e. When the stereocilia are pulled in the right direction, the hair depolarizes; starting the nerve process to the auditory nerve then to the temporal lobe of the auditory cortex.f. Primary auditory cortex receivesthe vibration info from the thalamusand identifies pitch and loudness.The secondary association site is the frontal lobe.

Hearing

Touch is a mix of at least four distinct skin senses: pressure, warmth, cold, and pain. Within the skin are different types of specialized nerve endings and more than tactile stimulation is involved. We are more sensitive to an unfamiliar touch or an unexpected one.

1. Acquisition: the epidermis is a barrier. The dermis holds blood vessels and the nerves that give us our sense of touch. There are several types of receptors for pain or temperature or others. A stimulus comes in contact with skin and receptors are triggered

2. Transduction: a specific sensory neuron is triggered and the information is sent to the part of the brain associated with that stimulus. This is different for pain or pressure or other feelings.

3. Primary Association: Processing primarily occurs in the primary somatosensory area in the parietal lobe of the cerebral cortex

Information is sent from the receptors via sensory nerves, through tracts in the spinal cord and finally into the brain.

Touch or Somatosensory System

Touch or Somatosensory System

Names Function

Pacinian Corpuscle

(Mechanoreceptor)

Vibration Pressure Receptor

Meissner’s Corpuscle

(Mechanoreceptor)

Heavy Pressure Receptor

Krause Corpuscle(Thermoreceptor)

Cold Receptor

Ruffini Corpuscle(Mechanorecepto

r)

Skin Stretch/HeatReceptor

Merkel Disks(Mechanorecepto

r)

Light Touch Receptor

• Alarm system that draws our attention to a physical problem• Biological, Psychological, and sociocultural influences on pain• Phantom limb sensations - brain can misinterpret nervous system activity

that occurs in the absence of normal sensory imput• Gate- control theory: spinal cord contains a neurological gate that blocks

pain signals or allows them to pass on to the brain. The gate is opened by the activity of pain signals traveling up small nerve fibers and is closed by activity in larger fibers or by information coming from the brain.

• where body meets mind - treatable physically and psychologically

Pain

Stimulus: Food molecules• Fungiform papillae - large bumps on the tongue, receptor for taste.• The five acknowledged tastes are sweet, sour, salty, bitter, and umami.• Olfactory plays a large part in taste. What we perceive as taste is a

complex interplay of smelling and taste receptors on our tongue.• Olfactory - Sense of smell• It is a myth that different parts

of your tongue taste eachof the types of tastes.

Taste

1. Acquisitiona. From the taste buds in which you put the food, three nerves gather information about the taste: the facial nerve, the hypoglossal nerve, and the glossopharyngeal nerve. b. At the same time, the molecules of the food is being processed by the olfactory system (which we will get to in a minute).

2. Transduction and Associationa. The nerves transfer the data to the thalamus and on to the specific

area on the cerebral cortex.b. That in combination with the olfactory transduction and association process makes up what we perceive as taste.

Taste

Stimulus: Odor Molecules • Olfactory Epithelium - Tissues within the nasal cavity that are responsible

for detecting odors.• Olfactory Receptors - Detects the odor and sends a nerve impulse to the

brain.• Olfactory Bulb - Structure found within the forebrain, helps with

perception of odor.• Nasal Cavity - Inside middle of your nose, lined with mucus.• Cilia - Moves with mucus up and down the nasal trap and collects dust

from the air.

Smell

1. Acquisitiona. Molecules of an odor enter through the nasal cavity when you breath.

the olfactory epithelium extends along the upper wall of the nasal cavity

to the nasal septum while the epithelium dissolves odors with mucus.b. Odors bind with proteins that are on the receptors in the nasal cavity.

Smell

2. Transduction and Associationa. From there, the proteins will cause the olfactory cell to generate a nerve impulse which is sent to the olfactory bulb where the information gathered from the receptors.b. The information is then sent to the olfactory cortex in the temporal lobe (more specifically the uncus, entorhinal areas). The olfactory bulb is connected to the amygdala and the hippocampus.

Smell

Vocabulary:• Illusions - something that is/is likely to be wrongly perceived by the

senses.• Perceptual Adaptation - in vision, the ability to adjust to an artificially

displaced or even inverted visual field.• Perceptual Set - a mental predisposition to perceive one thing and not

another.• Extrasensory perception - reception of data not gained through the

recognized physical sense but with the mind itself.

Perception

Early 20th century, a group of german psychologists noticed that when given a cluster of sensations, we tend to organize them into a gestalt (whole, form).

When seen alone, each circle simply looks like there are some random white lines in them. But when seeing the

whole image you can see a cube, ora “whole” or a “form”.

Sensation is not simply a bottom-upprocess and perception is not simplya top-down process. Sensation and perception blend into a continuousprocess.

Perceptual Organization

Perceptual adaptation: ability to adjust based on differences that the subject may witness, particularly alterations in the visual field. For example, if an individual's visual field is altered forty five degrees left, the brain accounts for the difference allowing the individual to function normally.

Perceptual set: a mental predisposition to perceive one thing and not another. For example, we are more likely to perceive two people as looking alike if we are previously told that they are related.

Context also affects perception. Lew Kulechov showed this in his experiment on how film evokes emotion. He created three short films with one of three contexts followed by an actor with neutral expression. The audience was struck by the actor’s sadness in the film where a woman died. When the actor was eating, they thought the actor seemed thoughtful. When the actor was playing with children, they perceived him as happy.

Perceptual Interpretation

Denotes psychic abilities such as telepathy, clairaudience, and clairvoyance. Also referred to as “the sixth sense”. The study of ESP and other psychic phenomena is called parapsychology. Because of lack of evidence, theory, and experimental techniques that can provide reliable results, ESP is considered a pseudoscience.

Extrasensory Perception?