© Prentice Hall, 1999. Sensation – An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent

© Prentice Hall, 1999

Sensation – An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent the conditions that stimulated it – either inside or outside the body

Perception –A process that makes sensory patterns meaningful and more elaborate

Copyright © Allyn and Bacon 2006


The brain senses the world indirectly because the sense organs convert

stimulation into the language of the nervous system: neural impulses

Absolute threshold – Amount of stimulation necessary for a stimulus to be detected

Difference threshold – Smallest amount by which a stimulus can be changed and the difference be detected (also called just noticeable difference – JND)


The principle that the jnd for any given sense is a constant fraction or proportion of the stimulation being judged.


Weber’s law – The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low

Fechner’s law – S = k log R• S = sensation• R = stimulus• k = constant that differs for each

sensory modality


Vision: a candle flame seen from 30 miles on a clear, dark night

Hearing: the tick of a watch from 20 feet in very quiet conditions

Smell: 1 drop of perfume diffused throughout a three-room apartment


Taste: .0356 ounce of table salt in 529 quarts of water

Touch: a bee wing falling on your cheek from a height of 1 centimeter


Transduction – Transformation of one form of energy into another – especially the transformation of stimulus information into nerve impulses

Receptors –Specialized neurons that are activated by stimulation and transduce (convert) it into a nerve impulse


Sensory pathway – Bundles of neurons that carry information from the sense organs to the brain


definition: below threshold We can process some

information from stimuli too weak to recognize.

effect of subliminal stimulation: a subtle, fleeting effect on thinking


No. The goal of using subliminal advertising is to increase the likelihood that you will buy a particular product.

Research has repeatedly demonstrated that subliminal advertising cannot change an individual’s behavior.


Sensory adaptation – Loss of responsiveness in receptor cells after stimulation has remained unchanged for a while


Signal detection theory – Perceptual judgment as combination of sensation and decision-making processes


Stimulus eventStimulus event

Neural activityNeural activity

Comparison with Comparison with personal standardpersonal standard

Action (or no action)Action (or no action)


The senses all operate in much the same way, but each extracts different information

and sends it to its own specialized processing

region in the brain




wavelength

amplitude



RRooddss CC

RReecceptors:eptors: rodsrods and and ccoonneess

• 120 million120 million

• peripheryperiphery

• sensitivitysensitivity

• night visionnight vision

• 8 million8 million

• ccentralentral

• cclaritylarity

• ccolor visionolor vision

oonneess





lightlight

photo-photo-receptorsreceptors

bipolar bipolar cellscells

ganglion ganglion cellscells

LGNLGNvisual visual cortexcortex

dark adaptation: increased sensitivity of rods and cones in darknesse.g., entering a darkened room

light adaptation: decreased sensitivity of rods and cones in bright light e.g., waking up at night and turning on a bright light


hue: subjective experience of “color”

saturation (purity): vividness or richness of a hue

brightness: intensity of the light


additive color mixing: mixing lights of differing wavelengths

subtractive color mixing: mixing pigments



Trichromatic theory Opponent-process theory


There are three types of cones: red, green, and blue.

The colors we see are the result of a combination of the differing amount of light absorbed by the three types of cones.


This theory only explains the way the cones transduct color.

The trichromatic theory provides an explanation for some types of colorblindness.


monochromats: people who are totally colorblind

dichromats: people who are blind to either red-green or yellow-blue



color-sensitive ganglion cells are arranged in opposing cells: red-green, yellow-blue, blackblack-white (brightness)


The activation of one cone (at retinal level) inhibits another cone.

This theory explains color vision at the level of the ganglion cells.


Opponent-process theory may explain color afterimages:

continual viewing of red weakens the ability to inhibit green;

remove red and you see green





frequency: the number of cycles per second in a wave— primary determinant of pitch

amplitude: the magnitude (height) of a wave — primary determinant of loudness


pitch: the frequency of sound vibrations, resulting in a higher/lower tone

overtones: tones that result from sound waves that are multiples of the basic tone

timbre: the “texture” of sound


hertz (Hz): cycles per second; used to measure pitch

decibel: unit of measurement for the loudness of sounds






eardrumeardrummiddle middle

earearoval oval

windowwindow

cochlearcochlearorgan of organ of

CortiCorti


organ of organ of CortiCorti

cochlear cochlear nervenerve

medullamedulla

inferior inferior colliculuscolliculus

medial medial geniculate geniculate

nucleusnucleus

auditory auditory cortexcortex

place theory frequency theory


vibration of the basilar membrane (B.M.) at different places results in different pitches/frequencies

near the oval window (where B.M. is thinner)--higher frequencies; lower frequencies occur farther from oval window


The speed of vibration determines pitch:

The faster the vibration, the higher the pitch.


auditory neurons fire in sequence: first one, then another, then perhaps a third, and finally the first one is able to fire again


conductive hearing loss: vibrations are not transmitted effectively from the eardrum to the oval window due to a stiffening of the connections between the middle ear bones

tinnitus: constantly hearing a steady, high-pitched hum




Odorant binding protein (OBP) makes the detection of odors possible.

A nasal gland coats airborne molecules with OBP to facilitate detection by the receptors in the olfactory epithelium.



receptor receptor cellscells

olfactory olfactory bulbbulb

amygdalaamygdala

thalamusthalamushypo-hypo-

thalamusthalamustemporal temporal

lobelobe


0

10

20

30

40

50

60

70

80

90C

orre

ct id

enti

fica

tion

(%

)

Scent to be identified

coffeeleatherbubble gummustardbologna

Women have a better sense of smell than men.

The ability to smell diminishes with age. Smell acuity is greatest during early adulthood (ages 20-40).


Pheromones are chemicals produced by an animal that affects the behavior of another animal through scent.

Receptors in the vomeronasal organ detect pheromones.


Yes, humans can detect pheromones, but detection typically does not alter behavior.

Menstrual synchronicity may be the one exception.




Taste buds are the structures on the tongue that contain taste receptor cells.

An adult has about 10,000 taste buds.

Taste receptors die and are replaced every 7 days.

The number of taste buds decrease with age.



taste taste budsbuds medullamedulla thalamusthalamus

primary primary somatosensory somatosensory

cortexcortex

anterior-anterior-insular insular cortexcortex

provides specific information about muscle movement, changes in posture, and strain on muscles and joints

receptors: stretch receptors and Golgi tendon organs (provide information about stretching and contraction of individual muscles)


The sense of equilibrium and awareness of body position in space.

2 types of vestibular senses: — body rotation — gravitation and movement


relays messages about the speed and direction of body rotation

stimulus: movement of the head receptors: hair cells in the

semicircular canals


provides information about gravitation and movement forward and backward, up and down

stimulus: movement of body and/or gravity

receptors: hair cells in the vestibular sacs


Receptors in the skin provide information about:

— touch — temperature — pain


A chemical sense in which certain chemicals are released when injury (tissue damage) occurs.

These chemicals activate pain receptors.


A “gate” in the spinal cord either opens to permit pain signals traveling up small nerve fibers to reach the brain or closes to prevent their passage.



Fovea – Area of sharpest vision in the retina

Retina – Light-sensitive layer at the back of the eyeball

Photoreceptors – Light-sensitive cells in the retina that convert light energy to neural impulses

Rods – Sensitive to dimlight but not colors

Cones – Sensitive tocolors but not dim light

Optic nerve – Bundle of neurons that carries visual information from the retina to the brain


Blind spot – Point where the optic nerve exits the eye and where there are no photoreceptors

Visual cortex –Part of the brain – the occipital cortex – where visual sensations are processed


Color –Psychological sensation derived from the wavelength of visible light – color, itself, is not a property of the external world


Electromagnetic spectrum – Entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and visible light

Visible spectrum – Tiny part of the electromagnetic spectrum to which our eyes are sensitive


Color blindness – Vision disorder that prevents an individual from discriminating certain colors


Brightness – Sensation caused by the intensity of light waves


WavelengthWavelength

ColorColor

Intensity Intensity (amplitude)(amplitude)

BrightnessBrightness

The Physics of Sound• Frequency –

Number of cycles completed by a wave in a given amount of time


Low Frequency High Frequency

The Physics of Sound


High Amplitude Low Amplitude

Amplitude – Physical strength of a wave


Tympanic membrane –The eardrum


Cochlea –Where sound waves are transduced


Basilar membrane –Thin strip of tissue sensitive to vibrations

Cochlea


Auditory nerve –Neural pathway connecting the ear and the brain

Auditory cortex – Portion of the temporal lobe that processes sounds


Pitch – Sensory characteristic of sound produced by the frequency of the sound wave

Loudness – Sensory characteristic of sound produced by the amplitude (intensity) of the sound wave

Timbre – Quality of a sound wave that derives from the wave’s complexity


Conduction deafness –An inability to hear resulting from damage to structures of the middle or inner ear

Nerve deafness –An inability to hear, linked to a deficit in the body’s ability to transmit impulses from the cochlea to the brain, usually involving the auditory nerve or higher auditory processing centers


Vestibular sense –Sense of body orientation with respect to gravity

Kinesthetic sense –Sense of body position and movement of body parts relative to each other


Olfaction –Sense of smell

Olfactory bulbs –Brain sites of olfactory processing

Pheromones –Chemical signals released by organisms to communicate with other members of the species



Gustation – The sense of taste


Taste buds –Receptors for taste (primarily on the upper side of the tongue)

Touch Warmth Cold


Placebos –Substances that appear to be drugs but are not

Placebo effect –A response to a placebo caused by subjects’ belief that they are taking real drugs



Perception brings meaning to sensation, so perception

produces an interpretation of the external world, not a

perfect representation of it

Percept – Meaningful product of a perception


Feature detectors – Cells in the cortex that specialize in extracting certain features of a stimulus

Binding problem – A major unsolved mystery in cognitive psychology, concerning the physical processes used by the brain to combine many aspects of sensation to a single percept


Bottom-up processing – Analysis that emphasizes characteristics of the stimulus, rather than internal concepts

Top-down processing – Emphasizes perceiver's expectations, memories, and other cognitive factors


Perceptual constancy – Ability to recognize the same object under different conditions, such as changes in illumination, distance, or location



shape constancy: a tendency to see an object as the same shape no matter what angle it is viewed from.


figure: entity perceived to stand apart from the background

ground: background against which a figure appears


Monocular distance cue in which one object, by partially blocking another, is perceived as being closer.


The higher on the horizontal plane an object is, the farther away it appears.


Two parallel lines appear to converge at the horizon.


Objects seen at greater distances appear to be smoother and less textured.


Shadows often appear on the parts of objects that are more distant.

Illusions – Demonstrably incorrect experience of a stimulus pattern, shared by others in the same perceptual environment

Ambiguous figures – Images that are capable of more than one interpretation



Do you see or ?



The Herman Grid

Do you see small gray squares between the black squares?



Learning-based inference –View that perception is primarily shaped by learning, rather than innate factors

Perceptual set –Readiness to detect a particular stimulus in a given context



B

A

Which box is bigger, A or B?

Gestalt psychology – View that much of perception is shaped by innate factors built into the brain

Figure – Part of a pattern that commands attention

Ground – Part of a pattern that does not command attention; the background


Subjective contours – Boundaries that are perceived but do not appear in the stimulus pattern


Closure – Tendency to fill in gaps in figures and see incomplete figures as complete


SimilaritySimilarity

ProximityProximity

ContinuityContinuity

Common fateCommon fate

PrägnanzPrägnanz


ABIRD

IN THETHE HAND




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© Prentice Hall, 1999. Sensation – An early stage of perception in which neurons in a receptor create an internal pattern of nerve impulses that represent