This document provides an overview of sensation and perception. It discusses how sensation is the process of receiving and transmitting sensory information to the brain, while perception involves selecting, organizing, and interpreting that information. Key topics covered include the five senses (vision, audition, olfaction, gustation, and somatic senses), as well as perceptual concepts like attention, constancies, depth perception, and illusions. Sensory thresholds, adaptation, and transduction are described for visual and auditory systems. Overall, the document provides a high-level introduction to sensation and perception.

1. Sensation andSensation and
PerceptionPerception
Dr. shittu LAJDr. shittu LAJ

2. Lecture OverviewLecture Overview
 Experiencing SensationExperiencing Sensation
 Vision and AuditionVision and Audition
 Other types of SensesOther types of Senses
 Perception conceptPerception concept
• SelectionSelection
• OrganizationOrganization
• InterpretationInterpretation

3. Sensation and PerceptionSensation and Perception
 Sensation – the process of receiving,Sensation – the process of receiving,
 converting andconverting and
 transmitting information from thetransmitting information from the
external and internal world to theexternal and internal world to the
brainbrain

4. Sensation and PerceptionSensation and Perception
 Perception – the process of selecting,Perception – the process of selecting,
 organizing andorganizing and
 interpreting raw sensory data intointerpreting raw sensory data into
useful mental representations of theuseful mental representations of the
worldworld

5. How sensation occursHow sensation occurs
 Eyes, ears, skin, nose, and tongueEyes, ears, skin, nose, and tongue
and contain receptor cellsand contain receptor cells
 These receptor cells receive andThese receptor cells receive and
process sensory information from theprocess sensory information from the
environmentenvironment

6. Sensation/PerceptionSensation/Perception
 Transduction: sensory receptors (eyes,Transduction: sensory receptors (eyes,
ears, nose, skin, tongue) convert theears, nose, skin, tongue) convert the
stimulus into neural impulses which arestimulus into neural impulses which are
sent to the brainsent to the brain

7. An example of transductionAn example of transduction
 Receptor cells in the inner earReceptor cells in the inner ear
convert sound waves/vibrations intoconvert sound waves/vibrations into
electrochemical signalselectrochemical signals
 These signals are carried by neuronsThese signals are carried by neurons
to the brainto the brain

8. Sensory ReductionSensory Reduction
 Sensory reduction involves theSensory reduction involves the
filtering and analyzing of incomingfiltering and analyzing of incoming
sensations before sending a neuralsensations before sending a neural
message to the cortex.message to the cortex.
• If theIf the reticular formation (located in thereticular formation (located in the
brainstem)brainstem) decides that information isdecides that information is
important, it is passed on to alert theimportant, it is passed on to alert the
cerebral cortex.cerebral cortex.

9. Sensory ThresholdsSensory Thresholds
 Each sensory system has a thresholdEach sensory system has a threshold
level of energy that is required to activatelevel of energy that is required to activate
that sense.that sense.
• Absolute thresholdAbsolute threshold:: The smallest amount ofThe smallest amount of
stimulus needed to detect that the stimulus isstimulus needed to detect that the stimulus is
presentpresent
• Difference thresholdDifference threshold:: The smallest change inThe smallest change in
amount of sensory stimulus needed foramount of sensory stimulus needed for
someone to notice that changesomeone to notice that change

10. SensationSensation
 Different people can have widelyDifferent people can have widely
varying sensory thresholds.varying sensory thresholds.
 Thresholds can change within aThresholds can change within a
person over time and as a function ofperson 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

11. Modification of SensationModification of Sensation
 A key function of sensory systems isA key function of sensory systems is
to detect change within theto detect change within the
environment.environment.
• Movement in the peripheral aspects ofMovement 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 theConstant pressure of an object on the
skin may not be important.skin may not be important.
 A stimulus that moves across the skin mayA 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-rapidThe skin adapts to constant pressure-rapid
and slow adaptability.and slow adaptability.

12. Sensory AdaptationSensory Adaptation
 Sensory adaptation refers to the factSensory adaptation refers to the fact
that repeated or constant stimulationthat repeated or constant stimulation
decreases the number of sensorydecreases the number of sensory
messages sent to the brain, whichmessages sent to the brain, which
causes decreased sensation.causes decreased sensation.

13. 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 alteredPain sensations are processed and altered
by mechanisms within the spinal cord.by mechanisms within the spinal cord.
 Experience of pain depends partly onExperience of pain depends partly on
whether the neural messages get past awhether the neural messages get past a
neuron in the spinal cord that can eitherneuron in the spinal cord that can either
block messages or allow them to the brainblock messages or allow them to the brain

14. VisionVision
 External light falls on receptors within theExternal light falls on receptors within the
eye to generate the visual message.eye to generate the visual message.
 Light = electromagnetic energy that movesLight = electromagnetic energy that moves
in wavesin waves
• Wavelength of light determines colorWavelength of light determines color

15. Anatomy of the EyeAnatomy of the Eye

16. 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 ofIris – colored part of the eye; controls size of
pupilpupil
 Lens – transparent elastic structureLens – transparent elastic structure
 Retina- group of light receptorsRetina- group of light receptors
 Optic Nerve – carries neural messages to theOptic Nerve – carries neural messages to the
brainbrain
 Fovea – tiny pit in the center of the retina filledFovea – tiny pit in the center of the retina filled
with cones and responsible for sharp visionwith cones and responsible for sharp vision

17. PhotoreceptorsPhotoreceptors
 Photoreceptors are light-sensitivePhotoreceptors are light-sensitive
cells found within the retina.cells found within the retina.
• RodsRods are sensitive to light and notare sensitive to light and not
color; are active under low-lightcolor; are active under low-light
conditions.conditions.
• ConesCones are sensitive to color, are notare sensitive to color, are not
active in low-light conditions and allowactive in low-light conditions and allow
for fine detail.for fine detail.
• Rods and cones use differentRods and cones use different
photopigments that react to light so asphotopigments that react to light so as
to generate nerve potentials.to generate nerve potentials.

18. Retinal PhotoreceptorsRetinal Photoreceptors
 Light passes through theLight passes through the
retinal layers to reachretinal layers to reach
the photoreceptors atthe photoreceptors at
the inner retinal surface.the inner retinal surface.
 Photoreceptors andPhotoreceptors and
bipolar cells conductbipolar cells conduct
action potentials to theaction potentials to the
ganglion cells, which inganglion cells, which in
turn initiate actionturn initiate action
potentials which arepotentials which are
transmitted to thetransmitted to the
thalamus.thalamus.

19. Sensory CodingSensory Coding
 Activation ofActivation of
retinal cells byretinal cells by
light results inlight results in
action potentialsaction potentials
that travel alongthat travel along
neurons thatneurons that
project to theproject to the
occipital cortexoccipital cortex

20. AuditionAudition
 Receptors within the ear are tunedReceptors within the ear are tuned
to detect sound waves (changes into 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 loudnesscorresponds to loudness
 Sound loudness is measured inSound loudness is measured in
decibels.decibels.

21. Sound Loudness (dB)Sound Loudness (dB)

22. Anatomy of the EarAnatomy of the Ear
((Hammer, Anvil, Stirrup)Hammer, Anvil, Stirrup)
(Sound Waves)

23. Pitch and LoudnessPitch and Loudness
 Sound waves vibrate the basilar membraneSound waves vibrate the basilar membrane
within the cochlea of the ear, which containswithin the cochlea of the ear, which contains
receptors for hearing.receptors for hearing.
• Place theory: explains how we hear highPlace theory: explains how we hear high
pitched sounds: different high-pitched soundspitched sounds: different high-pitched sounds
bend the basilar membrane hair cells atbend the basilar membrane hair cells at
different locations in the cochlea.different locations in the cochlea.
• Frequency TheoryFrequency Theory:: explains how we hearexplains how we hear
lower pitched sounds: hair cells on the basilarlower pitched sounds: hair cells on the basilar
membrane of the cochlea bend and firemembrane of the cochlea bend and fire
action potentials at the same rate as theaction potentials at the same rate as the
frequency of the sound to the auditory nerve.frequency of the sound to the auditory nerve.

24. Hearing LossHearing Loss
 There are 2 types of deafness:There are 2 types of deafness:
 Conduction deafness: Middle-ear deafnessConduction deafness: Middle-ear deafness
resulting from problems with transferringresulting from problems with transferring
sound waves to the inner-ear.sound waves to the inner-ear.
 Nerve Deafness: Inner-ear deafnessNerve Deafness: Inner-ear deafness
resulting from damage to the cochlea, hairresulting from damage to the cochlea, hair
cells, or auditory nerve. Disease, age, andcells, or auditory nerve. Disease, age, and
exposure to loud music can cause nerveexposure to loud music can cause nerve
deafness.deafness.

25. Olfaction – sense of smellOlfaction – sense of smell
 Olfactory Receptors are embedded in aOlfactory Receptors are embedded in a
mucus-coated membrane in the nosemucus-coated membrane in the nose
called the olfactory epithelium. Thesecalled the olfactory epithelium. These
receptors are modified neurons withreceptors are modified neurons with
dendrites extending out into epithelium.dendrites extending out into epithelium.
 When chemical molecules in the air passWhen chemical molecules in the air pass
through the nose, the receptors initiate athrough the nose, the receptors initiate a
neural impulse which travels to theneural impulse which travels to the
olfactory bulb, a structure just below theolfactory bulb, a structure just below the
frontal lobes, where most olfactoryfrontal lobes, where most olfactory
information is interpreted and sent toinformation is interpreted and sent to
parts of the brain.parts of the brain.

26. Olfaction – sense of smellOlfaction – sense of smell
 Lock-and-Key TheoryLock-and-Key Theory:: humanshumans
can smell various odors becausecan smell various odors because
each three-dimensional odoreach three-dimensional odor
molecule fits into only one type ofmolecule fits into only one type of
receptor.receptor.
 Blacks have more olfactory receptorsBlacks have more olfactory receptors
and are more sensitive to smell thanand are more sensitive to smell than
the caucasiansthe caucasians

27. Gustation – the sense of tasteGustation – the sense of taste
 Taste receptors are located on theTaste receptors are located on the
tongue and are sensitive to five majortongue and are sensitive to five major
tastes: salty, sweet, sour, bitter andtastes: salty, sweet, sour, bitter and
umamiumami (delicious/savory; related to(delicious/savory; related to
meats, fish, cheese).meats, fish, cheese).
 Taste receptors respond differentially toTaste receptors respond differentially to
the varying shapes of food and liquidthe varying shapes of food and liquid
molecules.molecules.

28. Gustation – sense of tasteGustation – sense of taste
 Taste receptors are clustered withinTaste receptors are clustered within
little bumps called papillae, on thelittle bumps called papillae, on the
surface of your tongue.surface of your tongue.
 As you age you lose taste buds andAs you age you lose taste buds and
therefore your sensitivity to tastestherefore your sensitivity to tastes
diminishes with agediminishes with age

29. The Body SensesThe Body Senses
 Skin Senses:Skin Senses: there are three basic skinthere are three basic skin
sensations: touch (pressure), temperaturesensations: touch (pressure), temperature
and pain.and pain.
 Vestibular Sense:Vestibular Sense: sense of body orientationsense of body orientation
with respect to gravity and three-with respect to gravity and three-
dimensional spacedimensional space
• TheThe semicircular canalssemicircular canals provide the brain with balanceprovide the brain with balance
information.information.
 Kinesthetic Sense:Kinesthetic Sense: sensory system for bodysensory 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.

30. PerceptionPerception
 Perceptual processesPerceptual processes
include:include:
• Selection refers toSelection refers to
choosing which of manychoosing which of many
stimuli that will bestimuli that will be
processed.processed.
• Organization involvesOrganization involves
collecting the informationcollecting the information
into some pattern.into some pattern.
• InterpretationInterpretation involvesinvolves
understanding theunderstanding the
pattern.pattern.
 Perceptions can be inPerceptions can be in
errorerror
• Illusions are visual stimuliIllusions are visual stimuli
that are misinterpreted .that are misinterpreted .

31. Perception- SelectionPerception- Selection
 Choosing where to direct yourChoosing where to direct your
attentionattention
 3 factors are involved in the act of3 factors are involved in the act of
paying attention to some stimuli inpaying attention to some stimuli in
our environment and not to others.our environment and not to others.
These factors include SelectiveThese factors include Selective
attention, Feature detection andattention, Feature detection and
HabituationHabituation

32. SelectionSelection
 Selective attention: filtering out andSelective attention: filtering out and
attending only to important sensoryattending only to important sensory
messages.messages.
 Feature detectors: specialized cells in theFeature detectors: specialized cells in the
brain that respond only to certain sensorybrain that respond only to certain sensory
informationinformation
 HabituationHabituation:: tendency of the brain totendency of the brain to
ignore environmental factors that remainignore environmental factors that remain
constantconstant

33. Horizontal-Vertical IllusionHorizontal-Vertical Illusion
WHICH LINE IS LONGER?

34. Form PerceptionForm Perception
 Gestaltists proposed laws ofGestaltists proposed laws of
organization that specify how peopleorganization that specify how people
perceive form.perceive form.
 Figure and groundFigure and ground are basicare basic
organizational themes for perception.organizational themes for perception.
• Figure is perceived as distinct from theFigure is perceived as distinct from the
background.background.
• Figure is closer to the viewer than theFigure is closer to the viewer than the
background.background.

35. Gestalt Organizational PrinciplesGestalt Organizational Principles

36. Perceptual ConstanciesPerceptual Constancies
 Perceptual ConstancyPerceptual Constancy is theis the
tendency for the environment to betendency for the environment to be
perceived as remaining the sameperceived 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

37. Depth PerceptionDepth Perception
 Depth perceptionDepth perception is the ability to perceiveis the ability to perceive
three-dimensional space and to accuratelythree-dimensional space and to accurately
judge distance.judge distance.
 Binocular cuesBinocular cues include retinal disparity andinclude retinal disparity and
convergence.convergence.
 Monocular cuesMonocular cues include linear perspective,include linear perspective,
relative size, texture gradient, light andrelative size, texture gradient, light and
shadow, and parallax (difference inshadow, and parallax (difference in
size/shape of an object due to its beingsize/shape of an object due to its being
viewed from 2 disparate vantage points).viewed from 2 disparate vantage points).

38. Color PerceptionColor Perception
 Humans are able to discriminate 7 millionHumans are able to discriminate 7 million
different hues.different hues.
 Colors convey important information:Colors convey important information:
• Ripeness of foodRipeness of food
• Danger signalsDanger signals
 TricTrichrohromaticmatic theorytheory
• Eye contains 3 different color sensitiveEye contains 3 different color sensitive
elementselements
 Blue, green or red elementsBlue, green or red elements
 Trichromatic theory accounts for color mixing ofTrichromatic theory accounts for color mixing of
lights.lights.
 OpponentOpponent--ProcessProcess theorytheory
• 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.

39. InterpretationInterpretation
 InterpretationInterpretation is influenced by:is influenced by:
perceptual adaptationperceptual adaptation
perceptual setperceptual set
individual motivationindividual motivation
frame of referenceframe of reference

40. Subliminal PerceptionSubliminal Perception
 Subliminal stimuliSubliminal stimuli are stimuliare stimuli
presented below the threshold ofpresented below the threshold of
awareness; the effect on behavior isawareness; the effect on behavior is
uncertain.uncertain.

41. Extrasensory PerceptionExtrasensory Perception
 ESP refers to the ability to perceiveESP refers to the ability to perceive
stimuli that are outside the 5stimuli that are outside the 5
sensessenses
• Telepathy: the ability to read mindsTelepathy: the ability to read minds
• Clairvoyance: the ability to perceiveClairvoyance: the ability to perceive
objects or eventsobjects or events
• Precognition: the ability to predict thePrecognition: the ability to predict the
futurefuture
• PsychokinesisPsychokinesis:: the ability to movethe ability to move
objectsobjects