Sensation and Sensation and PerceptionPerception

Dr. shittu LAJDr. shittu LAJ

Lecture OverviewLecture Overview Experiencing SensationExperiencing Sensation Vision and AuditionVision and Audition Other types of SensesOther types of Senses Perception conceptPerception concept

• SelectionSelection• OrganizationOrganization• InterpretationInterpretation

Sensation and PerceptionSensation and Perception

Sensation – the process of receiving, Sensation – the process of receiving, converting and converting and transmitting information from the transmitting information from the

external and internal world to the external and internal world to the brainbrain

Sensation and PerceptionSensation and Perception

Perception – the process of selecting, Perception – the process of selecting, organizing and organizing and interpreting raw sensory data into interpreting raw sensory data into

useful mental representations of the useful mental representations of the worldworld

How sensation occursHow sensation occurs

Eyes, ears, skin, nose, and tongue Eyes, ears, skin, nose, and tongue and contain receptor cellsand contain receptor cells

These receptor cells receive and These receptor cells receive and process sensory information from the process sensory information from the environmentenvironment

Sensation/PerceptionSensation/Perception

Transduction: sensory receptors (eyes, Transduction: sensory receptors (eyes, ears, nose, skin, tongue) convert the ears, nose, skin, tongue) convert the stimulus into neural impulses which are stimulus into neural impulses which are sent to the brainsent to the brain

An example of transductionAn example of transduction

Receptor cells in the inner ear Receptor cells in the inner ear convert sound waves/vibrations into convert sound waves/vibrations into electrochemical signalselectrochemical signals

These signals are carried by neurons These signals are carried by neurons to the brainto the brain

Sensory ReductionSensory Reduction

Sensory reduction involves the Sensory reduction involves the filtering and analyzing of incoming filtering and analyzing of incoming sensations before sending a neural sensations before sending a neural message to the cortex.message to the cortex.

• If the If the reticular formation (located in the reticular formation (located in the brainstem)brainstem) decides that information is decides that information is important, it is passed on to alert the important, it is passed on to alert the cerebral cortex.cerebral cortex.

Sensory ThresholdsSensory Thresholds

Each sensory system has a threshold Each sensory system has a threshold level of energy that is required to activate level of energy that is required to activate that sense.that sense.

• Absolute thresholdAbsolute threshold:: The smallest amount of The smallest amount of stimulus needed to detect that the stimulus is stimulus needed to detect that the stimulus is presentpresent

• Difference thresholdDifference threshold:: The smallest change in The smallest change in amount of sensory stimulus needed for amount of sensory stimulus needed for someone to notice that changesomeone to notice that change

SensationSensation

Different people can have widely Different people can have widely varying sensory thresholds.varying sensory thresholds.

Thresholds can change within a Thresholds can change within a person over time and as a function of person over time and as a function of hormone status.hormone status.• Olfactory sensitivity during pregnancyOlfactory sensitivity during pregnancy• Ability to taste foods as we get olderAbility to taste foods as we get older

Modification of SensationModification of Sensation A key function of sensory systems is A key function of sensory systems is

to detect change within the to detect change within the environment.environment.• Movement in the peripheral aspects of Movement in the peripheral aspects of

the eye may signal food or danger.the eye may signal food or danger.• Constant pressure of an object on the Constant pressure of an object on the

skin may not be important.skin may not be important. A stimulus that moves across the skin may A stimulus that moves across the skin may

be a snake or a spider.be a snake or a spider. The skin adapts to constant pressure-rapid The skin adapts to constant pressure-rapid

and slow adaptability.and slow adaptability.

Sensory AdaptationSensory Adaptation

Sensory adaptation refers to the fact Sensory adaptation refers to the fact that repeated or constant stimulation that repeated or constant stimulation decreases the number of sensory decreases the number of sensory messages sent to the brain, which messages sent to the brain, which causes decreased sensation.causes decreased sensation.

Gate-Control Theory of PainGate-Control Theory of Pain

Theory proposed by Melzack & Wall (1965)Theory proposed by Melzack & Wall (1965) Pain sensations are processed and altered Pain sensations are processed and altered

by mechanisms within the spinal cord.by mechanisms within the spinal cord. Experience of pain depends partly on Experience of pain depends partly on

whether the neural messages get past a whether the neural messages get past a neuron in the spinal cord that can either neuron in the spinal cord that can either block messages or allow them to the brainblock messages or allow them to the brain

VisionVision External light falls on receptors within the External light falls on receptors within the

eye to generate the visual message.eye to generate the visual message. Light = electromagnetic energy that moves Light = electromagnetic energy that moves

in wavesin waves• Wavelength of light determines colorWavelength of light determines color

Anatomy of the EyeAnatomy of the Eye

Anatomy of the eyeAnatomy of the eye Cornea – tough, transparent layerCornea – tough, transparent layer Pupil – adjustable openingPupil – adjustable opening Iris – colored part of the eye; controls size of Iris – colored part of the eye; controls size of

pupilpupil Lens – transparent elastic structureLens – transparent elastic structure Retina- group of light receptors Retina- group of light receptors Optic Nerve – carries neural messages to the Optic Nerve – carries neural messages to the

brainbrain Fovea – tiny pit in the center of the retina filled Fovea – tiny pit in the center of the retina filled

with cones and responsible for sharp visionwith cones and responsible for sharp vision

PhotoreceptorsPhotoreceptors Photoreceptors are light-sensitive Photoreceptors are light-sensitive

cells found within the retina.cells found within the retina.• RodsRods are sensitive to light and not are sensitive to light and not

color; are active under low-light color; are active under low-light conditions.conditions.

• ConesCones are sensitive to color, are not are sensitive to color, are not active in low-light conditions and allow active in low-light conditions and allow for fine detail.for fine detail.

• Rods and cones use different Rods and cones use different photopigments that react to light so as photopigments that react to light so as to generate nerve potentials.to generate nerve potentials.

Retinal PhotoreceptorsRetinal Photoreceptors

Light passes through the Light passes through the retinal layers to reach retinal layers to reach the photoreceptors at the photoreceptors at the inner retinal surface.the inner retinal surface.

Photoreceptors and Photoreceptors and bipolar cells conduct bipolar cells conduct action potentials to the action potentials to the ganglion cells, which in ganglion cells, which in turn initiate action turn initiate action potentials which are potentials which are transmitted to the transmitted to the thalamus.thalamus.

Sensory CodingSensory Coding

Activation of Activation of retinal cells by retinal cells by light results in light results in action potentials action potentials that travel along that travel along neurons that neurons that project to the project to the occipital cortexoccipital cortex

AuditionAudition Receptors within the ear are tuned Receptors within the ear are tuned

to detect sound waves (changes in to detect sound waves (changes in sound pressure level).sound pressure level).• Sound waves vary in terms of:Sound waves vary in terms of:

Frequency: corresponds to pitchFrequency: corresponds to pitch AmplitudeAmplitude:: corresponds to loudness corresponds to loudness

Sound loudness is measured in Sound loudness is measured in decibels.decibels.

Sound Loudness (dB)Sound Loudness (dB)

Anatomy of the EarAnatomy of the Ear((Hammer, Anvil, Stirrup)Hammer, Anvil, Stirrup)

(Sound Waves)

Pitch and LoudnessPitch and Loudness Sound waves vibrate the basilar membrane Sound waves vibrate the basilar membrane

within the cochlea of the ear, which contains within the cochlea of the ear, which contains receptors for hearing.receptors for hearing.

• Place theory: explains how we hear high Place theory: explains how we hear high pitched sounds: different high-pitched sounds pitched sounds: different high-pitched sounds bend the basilar membrane hair cells at bend the basilar membrane hair cells at different locations in the cochlea.different locations in the cochlea.

• Frequency TheoryFrequency Theory:: explains how we hear explains how we hear lower pitched sounds: hair cells on the basilar lower pitched sounds: hair cells on the basilar membrane of the cochlea bend and fire membrane of the cochlea bend and fire action potentials at the same rate as the action potentials at the same rate as the frequency of the sound to the auditory nerve. frequency of the sound to the auditory nerve.

Hearing LossHearing Loss

There are 2 types of deafness:There are 2 types of deafness: Conduction deafness: Middle-ear deafness Conduction deafness: Middle-ear deafness

resulting from problems with transferring resulting from problems with transferring sound waves to the inner-ear.sound waves to the inner-ear.

Nerve Deafness: Inner-ear deafness Nerve Deafness: Inner-ear deafness resulting from damage to the cochlea, hair resulting from damage to the cochlea, hair cells, or auditory nerve. Disease, age, and cells, or auditory nerve. Disease, age, and exposure to loud music can cause nerve exposure to loud music can cause nerve deafness. deafness.

Olfaction – sense of smellOlfaction – sense of smell

Olfactory Receptors are embedded in a Olfactory Receptors are embedded in a mucus-coated membrane in the nose mucus-coated membrane in the nose called the olfactory epithelium. These called the olfactory epithelium. These receptors are modified neurons with receptors are modified neurons with dendrites extending out into epithelium. dendrites extending out into epithelium.

When chemical molecules in the air pass When chemical molecules in the air pass through the nose, the receptors initiate a through the nose, the receptors initiate a neural impulse which travels to the neural impulse which travels to the olfactory bulb, a structure just below the olfactory bulb, a structure just below the frontal lobes, where most olfactory frontal lobes, where most olfactory information is interpreted and sent to information is interpreted and sent to parts of the brain. parts of the brain.

Olfaction – sense of smellOlfaction – sense of smell

Lock-and-Key TheoryLock-and-Key Theory:: humans humans can smell various odors because can smell various odors because each three-dimensional odor each three-dimensional odor molecule fits into only one type of molecule fits into only one type of receptor.receptor.

Blacks have more olfactory receptors Blacks have more olfactory receptors and are more sensitive to smell than and are more sensitive to smell than the caucasiansthe caucasians

Gustation – the sense of tasteGustation – the sense of taste

Taste receptors are located on the Taste receptors are located on the tongue and are sensitive to five major tongue and are sensitive to five major tastes: salty, sweet, sour, bitter and tastes: salty, sweet, sour, bitter and umamiumami (delicious/savory; related to (delicious/savory; related to meats, fish, cheese).meats, fish, cheese).

Taste receptors respond differentially to Taste receptors respond differentially to the varying shapes of food and liquid the varying shapes of food and liquid molecules.molecules.

Gustation – sense of tasteGustation – sense of taste

Taste receptors are clustered within Taste receptors are clustered within little bumps called papillae, on the little bumps called papillae, on the surface of your tongue. surface of your tongue.

As you age you lose taste buds and As you age you lose taste buds and therefore your sensitivity to tastes therefore your sensitivity to tastes diminishes with agediminishes with age

The Body SensesThe Body Senses Skin Senses:Skin Senses: there are three basic skin there are three basic skin

sensations: touch (pressure), temperature sensations: touch (pressure), temperature and pain.and pain.

Vestibular Sense:Vestibular Sense: sense of body orientation sense of body orientation with respect to gravity and three-with respect to gravity and three-dimensional spacedimensional space• The The semicircular canalssemicircular canals provide the brain with balance provide the brain with balance

information.information. Kinesthetic Sense:Kinesthetic Sense: sensory system for body sensory system for body

posture, orientation and movementposture, orientation and movement• Kinsethetic receptorsKinsethetic receptors are found throughout the muscles, are found throughout the muscles,

joints, and tendons of the body.joints, and tendons of the body.

PerceptionPerception Perceptual processes Perceptual processes

include:include:• Selection refers to Selection refers to

choosing which of many choosing which of many stimuli that will be stimuli that will be processed.processed.

• Organization involves Organization involves collecting the information collecting the information into some pattern.into some pattern.

• InterpretationInterpretation involves involves understanding the understanding the pattern.pattern.

Perceptions can be in Perceptions can be in errorerror• Illusions are visual stimuli Illusions are visual stimuli

that are misinterpreted .that are misinterpreted .

Perception- SelectionPerception- Selection

Choosing where to direct your Choosing where to direct your attentionattention

3 factors are involved in the act of 3 factors are involved in the act of paying attention to some stimuli in paying attention to some stimuli in our environment and not to others. our environment and not to others. These factors include Selective These factors include Selective attention, Feature detection and attention, Feature detection and HabituationHabituation

SelectionSelection

Selective attention: filtering out and Selective attention: filtering out and attending only to important sensory attending only to important sensory messages.messages.

Feature detectors: specialized cells in the Feature detectors: specialized cells in the brain that respond only to certain sensory brain that respond only to certain sensory informationinformation

HabituationHabituation:: tendency of the brain to tendency of the brain to ignore environmental factors that remain ignore environmental factors that remain constantconstant

Horizontal-Vertical IllusionHorizontal-Vertical Illusion

WHICH LINE IS LONGER?

Form PerceptionForm Perception Gestaltists proposed laws of Gestaltists proposed laws of

organization that specify how people organization that specify how people perceive form.perceive form.

Figure and groundFigure and ground are basic are basic organizational themes for perception.organizational themes for perception.

• Figure is perceived as distinct from the Figure is perceived as distinct from the background.background.

• Figure is closer to the viewer than the Figure is closer to the viewer than the background.background.

Gestalt Organizational PrinciplesGestalt Organizational Principles

Perceptual ConstanciesPerceptual Constancies

Perceptual ConstancyPerceptual Constancy is the is the tendency for the environment to be tendency for the environment to be perceived as remaining the same perceived as remaining the same even with changes in sensory input.even with changes in sensory input.• Size constancySize constancy• Shape constancyShape constancy• Color constancyColor constancy• Brightness constancyBrightness constancy

Depth PerceptionDepth Perception

Depth perceptionDepth perception is the ability to perceive is the ability to perceive three-dimensional space and to accurately three-dimensional space and to accurately judge distance.judge distance.

Binocular cuesBinocular cues include retinal disparity and include retinal disparity and convergence.convergence.

Monocular cuesMonocular cues include linear perspective, include linear perspective, relative size, texture gradient, light and relative size, texture gradient, light and shadow, and parallax (difference in shadow, and parallax (difference in size/shape of an object due to its being size/shape of an object due to its being viewed from 2 disparate vantage points).viewed from 2 disparate vantage points).

Color PerceptionColor Perception Humans are able to discriminate 7 million Humans are able to discriminate 7 million

different hues.different hues. Colors convey important information:Colors convey important information:

• Ripeness of foodRipeness of food• Danger signals Danger signals

TricTrichrohromaticmatic theory theory• Eye contains 3 different color sensitive Eye contains 3 different color sensitive

elements elements Blue, green or red elementsBlue, green or red elements Trichromatic theory accounts for color mixing of Trichromatic theory accounts for color mixing of

lights.lights. OpponentOpponent--ProcessProcess theory theory

• Visual system is organized into red-green, Visual system is organized into red-green, blue-yellow and black-white units.blue-yellow and black-white units.

Theory can account for negative color afterimages.Theory can account for negative color afterimages.

InterpretationInterpretation

InterpretationInterpretation is influenced by:is influenced by:perceptual adaptationperceptual adaptationperceptual setperceptual setindividual motivationindividual motivationframe of referenceframe of reference

Subliminal PerceptionSubliminal Perception

Subliminal stimuliSubliminal stimuli are stimuli are stimuli presented below the threshold of presented below the threshold of awareness; the effect on behavior is awareness; the effect on behavior is uncertain.uncertain.

Extrasensory PerceptionExtrasensory Perception ESP refers to the ability to perceive ESP refers to the ability to perceive

stimuli that are outside the 5 stimuli that are outside the 5 sensessenses• Telepathy: the ability to read mindsTelepathy: the ability to read minds• Clairvoyance: the ability to perceive Clairvoyance: the ability to perceive

objects or events objects or events • Precognition: the ability to predict the Precognition: the ability to predict the

futurefuture• PsychokinesisPsychokinesis:: the ability to move the ability to move

objects objects