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Sensation and Perception

Principals of Behavior Chapter Three

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Sensation

 Sensation is the process by which we

detect and process stimuli in the environment.

 Sensation is the process by which we detect

physical energy such as light, sound and heat from the environment by specialized sensory receptors and encoding it as neural signals.

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Transduction

 The process of transforming physical energy

into neural signals via sensory signals.

 Sensory receptors cells in one the sense

• rgans ( eye) receive stimulus such as light.

If the amount of stimuli, via the light is strong enough the receptor cell (neuron) fires sending a neural signal (action potential) to the appropriate area of the brain  occipital lobe.

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Psychophysics

 The field that studies links between the

physical properties of stimuli and a person’s experience of them.

 Thresholds-as we are constantly bombarded with

energy,( x-rays, radio waves, ultraviolet and infrared light) Our senses allow only a restricted awareness of this energy as in what stimuli we can detect.

 This “restricted awareness” are called thresholds,

and they are different for each sensory system.

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Sensory Thresholds

 Absolute threshold  Difference threshold  Just noticeable Difference  Subliminal Perception

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The Visual System

 Properties of Light

 Energy is the form of light wave  Brightness-amplitude of the wave  Saturation-purity of the wave (presence of

more than one wave is less pure or saturated)

 Color-length of the wave.

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The Structure of the Eye

 Cornea-transparent protector through which light enters the eye.

Curved surface bends the light to focus at the back of th eye

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Pupil-a small adjustable opening that regulates the amount of light that enters the eye through a colored muscle called the iris.

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Lens-transparent structure behind the pupil that also focuses The cornea does most of the bending, while the lens fine tunes the focus in process called accommodation.

 accommodation –affects acuity which is the sharpness of our

vision, which can be affected by small distortions in the shape

• f the eye.

 The shape of the eye influences the focus of the image on the

retina.

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Accommodation

 Farsightedness- lens is longer and

flatter than normal and therefore unable to bring close objects into focus. Focusing the image behind the retina

 Nearsightedness-- eyeball is shorter

than normal, causing focus to later than normal and therefore objects up close appear blurred. Focusing the image in front of the retina.

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Parts of the Eye



Retina-the light sensitive outer surface of the eye, containing the receptors that begin visual processing

 receptor cells- located at the back of the

retina and converts light into a neural signal Two types of receptor cells, rods and cones.

 rods- located around the outside of the retina,

responsible for black, white & gray vision, vision in dim light, and peripheral vision.

 cones-located near the fovea, which was the

central focal point in the retina, which is responsible for color, fine detail and vision in day light.

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Photoreceptors

Receptor Cells (Rods & Cones) Bipolar Cells Ganglion Cells Optic Nerve ( axons of Bipolar cells)

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How the Eye Works

 Blind spot-is the point at which the optic

nerve leaves the eye and is called the blind spot because there are no receptors there.

 Optic nerve-the bundle of axons that

carries neural messages from each eye to the brain.

 Optic chiasm-point near the base of

the brain where some, not all of the

• ptic nerve fibers split and cross to

the other side of the brain.

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Hemispheric projection:Visual fields

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Theories of Color Perception Trichromatic Theory

 Proposed three types of cones: red, blue, green  Different shades of color correspond to different

amounts of light received by each of these three types of cones.

 Cones fire message to the occipital lobe  Combination of which cones are firing as well as

the rate of firing that determines the color perceived.

 Problem: After image

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Stare at the cross in center of the flag for 30 seconds, now stare at white wall or piece of paper

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Theories of Color Perception: Opponent Process

 Four primary colors: red, green, blue, yellow  Cones are arranged in pairs, red with green, blue

with yellow

 If one memory of the pair is stimulated, i.e. red,

the other member of the pair is turned off, i.e. green.

 Afterimage-if a person stares at a red object too

long, it weakens that members ability to inhibit the

• ther cell. So, if staring at a red image for too long,
• ne might begin to see green as an after-image.

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Auditory Conduction

 Stimulus is sound waves which consist of

compressed and expanded air.

 Sound wave-change in pressure caused when

molecules of air collide with one another and then move apart again.

 Properties of the sound waves:

 Amplitude = loudness (height of the wave)  Frequency = pitch (length of the wave)

longer-lower, shorter- higher. (Hz)

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Structure of the Ear

 Outer ear

 Pinna (Ear Flap) channels sound waves through

the auditory canal to the eardrum, which is a tight membrane that vibrates with the waves.

 Middle Ear

 consists of three tiny bones ( ossicles),the

hammer, anvil and stirrup which hit each each

• ther in a sequence that carries the vibrations

to the inner ear.

 Inner Ear

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Inner Ear

 Oval Window: Vibrations from the stirrup

• n the oval window set up another chain

reaction within the inner ear.

 Cochlea: is a fluid filled a snail like

structure to which the oval window is

• attached. Vibrations of the oval window

cause the fluid of the cochlea to begin to vibrate.

 Basilar membrane-membrane running

through the middle of the cochlea.

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Sound Conduction

 Organ of Corti-rests on top of the basilar

membrane.

 contains receptor cells in the form of hair

fibers.

 Hair fibers bend in response to the

vibrations which in turn causes the receptor cells to fire (action potential).

 Sends a neural impulse to the auditory nerve

which connects to the temporal lobe region

• f the brain.

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Theories of Pitch Perception

 Place theory-pitch perceived depends on

the place where the hair cells were stimulated on the organ of corti ( High pitch corresponds to bending of hair cells closest to the oval window).

 Frequency theory-pitch corresponds to the

how fast the basilar membrane vibrates ( the higher the pitch, the faster the vibrations).

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Volley Principle

 Volley Principal-combination of both theories.  Place theory works for pitches above 1000

Hz.

 Frequency theory works for pitch below 100

hz.

 Volley-In between, say 300 hz, groups of

neurons take turns sending the message to the brain, Group one, 100 hz, Group two, 100 hz, etc.

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Hearing Impairments

 Conduction deafness damage to the mechanical

system that conducts sound to the cochlea. (punctured eardrum or damage to the small inner bones) Hearing aid could help by amplifying vibrations.

 Nerve deafness damage to the hair cell receptors

• r associated nerves. Usually caused by disease or

something else biological.

 cochlear implant can help restore hearing via an

electronic device that translates sounds into electrical signals, which are wired into the cochlea’s nerves, conveying some information about sound to the brain.

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Touch

 Essential for Survival  Deprivation of touch in animal and human

infants leads to failure to thrive and/or death.

 Sense of touch is actually a mix of at least four distinct

skin senses:



• pressure,

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warmth,

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cold



pain.

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Pain

 Pain is essential as it is the body’s way of telling you that

something is wrong.

 People who cannot feel pain die by early adult hood

because they cannot tell when they have an infection or they are hurt .

 Pain has a strong psychological component, not easily

understood.

 No theory of pain explains all the phenomenon.  Many psychological influences on pain such as distraction or

endorphin release can modulate pain. (i.e athletes that continue to play while they are injured.)

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Gate Control Theory

 Spinal cord contains a “ gate” that either blocks pain signals

• r allows the signal to pass on to the brain.

 Gate can be closed by non-pain signals coming from the

body and by signals coming from the brain.



“Gate” not a physical structure, represents a relative balance in neural activity within the spinal cord.

 Stimulation of the pain receptors releases substance P

which activates neurons that open the spinal gates, resulting in a pain signal that is sent to the brain

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Perception of Pain

 Message sent from spinal cord to brain.  Areas of the brain, influenced by physiological

and psychological factors, interprets the pain sensation that either opens the gates further  increasing the pain, or closes the gates, thus dampening the pain.

 The activity of the gate can be closed by signals

coming from stimulation of competing signals from other skin sensations such as rubbing, which can reduce the feeling of pain.

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Taste

 Chemical sense -involves four basic sensations-

sweet, sour, salty, and bitter.

 Taste buds, which are bumps on our tongues, for

each of the four basic taste sensations.

 Taste buds contain a pore that catches food

molecules.

 Taste receptors are antenna like hairs the project

into the pore that respond to one of the four sensations.

 Taste receptors reproduce themselves every week

• r two although this diminishes with age.

 Taste is enhanced by smell. Smell + taste =

flavor.

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Olfaction (Smell)

 Chemical Sense-most primitive  Odors have power to evoke memories and feelings due

to a direct connection between olfaction and the limbic system.

 Sense of smell is activated by a complex protein in the

nasal gland called Oderant Binding Protein that binds with airborne molecules in the olfactory epithelium.

 Olfactory receptors recognize odors individually, and

respond selectively to different aromas.

 Axon fibers of receptor cells go directly to the olfactory

bulb, which in turn sends a message to the temporal lobe which records the awareness of smell.

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Perception

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Terms

 Perceptions- perceive the world through

• ur senses, however we transform

meaningless sensations into meaningful perceptions.

 Selective Attention-Our conscious

attention is selective, therefore at any one moment we focus our awareness on only a limited aspect of all that we are capable of experiencing.

 Cocktail Party Effect-the ability to attend

selectively to only one voice among many

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Perceptual Organization

 Gestalt-given a cluster of sensations, the

human perceiver organizes them into an

• rganized whole.

 Figure-ground- our first perceptual task

is to perceive any object called the figure, distinct from its surroundings, called the ground. (i.e. words on paper).

 Grouping- To bring order and form to

these basic sensations, and our minds follow certain rules.

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Grouping Rules

 Proximity- We group nearby figures together.  Similarity-- Figures similar to each other we

group together.

 Continuity- We perceive smooth continuous

patterns rather than discontinuous ones.

 Connectedness-When they are uniform and

linked we perceive spots, lines or areas as a single unit.

 Closure- the tendency to “fill in” gaps in a

stimulus so that the image makes sense.

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Depth Perception

 Seeing objects in three dimension when our

retinal images are only two dimensional. This enables us to estimate their distance.

 Monocular cues-distance cues, such as linear

perspective and overlap, available to either eye alone.

 Binocular cues-depth cues such as retinal

disparity and convergence, that depend on the use of two eyes.

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Monocular Cues

 Interposition- If one object partially blocks our view

• f another we see it as closer.

 Texture gradient-a gradual change from a coarse

distinct texture to a fine indistinct texture signals increasing distance. Far objects appear smaller and more densely packed.

 Linear perspective-parallel lines, such as railroad

tracks, appear to converge with distance. The more the lines converge, their greater their perceived distance.

 Light and Shadow- Nearby objects reflect more light

to our eyes. Thus given two identical objects, the dimmer one seems farther away.

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Binocular Cues

 Because our eyes are about 2 ½ inches

apart, our retina receive slightly different images of the world.

 Retinal disparity- When the brain

compares these two images, the difference between them is called retinal disparity and provides an important cue to the relative distance of different

• bjects.



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Motion Perception

 Our brain computes motion based partly

• n its assumption that shrinking objects

are retreating and enlarging objects are approaching.

 Phi phenomenon-when two adjacent

stationary lights blink on and off in quick succession, we perceive a single light moving back and forth between them

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Visual Illusions

 Illusions due to misleading cues in

stimuli that give rise to inaccurate or impossible perceptions.

 Escher Photos

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