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SENSATION & PERCEPTION. CHAPTERS 4 & 5 AP PSYCHOLOGY. SENSATION. How do we take in information?. A sense is a system that translates information from outside the nervous system into neural activity. Messages from senses are called sensations

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Sensation perception




How do we take in information
How do we take in information?

  • A sense is a system that translates information from outside the nervous system into neural activity.

  • Messages from senses are called sensations

    • For example, vision is the system through which the eyes convert light into neural activity. This tells the brain something about the source of the light (brightness) or about the objects from which the light is reflected (round, red, etc).

Elements of a sensory system
Elements of a Sensory System

  • Energy (light, sound waves, etc) contains info about the world

  • Accessory Structures (lens, ear, etc) modify energy.

  • Transduction- the process of converting incoming energy into neural activity through sensory receptors

  • Sensory nerves transfer the coded activity to the Central Nervous System.

  • Thalamus processes and relays the neural response (except in smell).

  • Cortex receives input and produces the sensation and perception

How does physical energy get converted into neural activity
How does physical energy get converted into neural activity?

CODING - translation of the physical properties of a stimulus into a pattern of neural activity that specifically identifies those physical properties.

Doctrine of Specific Nerve Energies - stimulation of a particular sensory nerve provides codes for that one sense, no matter how the stimulation takes place

Temporal Code - involves changes in the timing of the neurons firing. Ex: A bright light will cause some neurons in the visual system to fire faster than a dim light.

Spatial Code - the location of the firing neurons provides information about the stimulus (tells us where the sensation is coming from).


  • Sound is a repetitive fluctuation in the pressure of a medium, such as air.

    • In a place like the moon, which has almost no atmospheric medium, sound cannot exist

  • When you speak, your vocal cords vibrate, producing fluctuations in air pressure that spread as waves. A wave is a repetitive variation in pressure that spreads out in 3 dimensions.

  • Physical characteristics of sound
    Physical Characteristics of Sound

    • Amplitude- (intensity) difference in air pressure from the baseline to the peak of a wave.

    • Wavelength- the distance from one peak wave to the next.

    • Frequency- number of complete waves, or cycles, that pass by a given point in space every second. Described in a unit called hertz, (Hz). 1 cycle per second is 1 hertz

    Psychological dimensions of sound what do we actually hear
    Psychological Dimensions of SoundWhat do we actually hear?

    • Loudness- determined by amplitude. Greater amplitude = Louder sounds

    • Pitch- how high or low a tone sounds. Determined by frequency.

      • High frequency = High Pitch

      • Low Frequency = Low Pitch

    • Timbre- (pronounced “tamber”) is the quality of the sound

    The ear
    The Ear

    • Auditory accessory structures modify sound waves before information affects neural signals

      • Pinna – crumpled part of ear that funnels sound through the ear canal

      • Tympanic Membrane – eardrum – tightly stretched membrane in the middle ear where sound waves strike

      • Vibrations of the tympanic membrane are transferred through 3 tiny bones - malleus (hammer), incus (anvil), stapes (stirrup)

    Sound Waves 1

    Auditory transduction
    Auditory Transduction

    • After sound passes through the oval window, it enters the inner ear or cochlea - this is where transduction occurs

    • The basilar membrane forms the floor of this long tube

    • Sound waves bend hairs of the organ of Corti – a group of cells which rest on the membrane

    • Hair cells connect with fibers from the auditory nerve, a bundle of axons that goes into the brain

    Sound Waves 2

    Figure 4.4: The Cochlea

    Auditory pathways
    Auditory Pathways

    • Auditory nerve  brainstem  thalamus

    • The information coded in the activity of auditory nerve fibers is conveyed to the brain and processed further

    • Information is relayed from the auditory nerve to an area of the cerebral cortex called the primary auditory cortex

    • Various aspects of sound processed in different regions of auditory system.

    • Certain parts of auditory cortex process certain types of sounds.

    How we hear
    How we hear?


    Sensing pitch
    Sensing Pitch

    • Different people may experience the “same” sound as different pitches.

    • Pitch-recognition abilities influenced by genetics.

      • Cultural factors are also partly responsible for the way in which a pitch is sensed.

    Locating sounds
    Locating Sounds

    • Determined partly by the very slight difference in when sound arrives at each ear.

    • The brain also uses information about the difference in sound intensity at each ear.

    Coding intensity and frequency
    Coding Intensity and Frequency

    • The more intense the sound, the more rapid the firing of a given neuron.

    • Frequency appears to be coded in two ways: place theory and frequency-matching theory

    Coding frequency place theory
    Coding Frequency: Place Theory

    • Sounds produce waves that move down the basilar membrane.

      • Where the wave peaks depends on the frequency of the sound.

    • Hair cells at a particular place on the membrane respond most to a particular frequency.

    Coding frequency frequency matching theory
    Coding Frequency: Frequency Matching Theory

    • Firing rate of an auditory nerve matches a sound wave’s frequency.

    • Sometimes called the “volley theory” of frequency coding.


    • Light – electromagnetic radiation

    • Visible light has a wavelength from just under 400 nanometers to 750 nanometers

    • Light intensity –

      • How much energy the light contains

      • Determines the brightness of light

    • Light Wavelength –

      • The difference between peaks in light waves

      • Determines what color we see

    Physical properties of light waves

    Great amplitude

    (bright colors, loud sounds)

    Short wavelength=high frequency

    (bluish colors, high-pitched sounds)

    Long wavelength=low frequency

    (reddish colors, low-pitched sounds)

    Small amplitude

    (dull colors, soft sounds)

    Physical Properties of Light Waves

    Accessory structures of the eye
    Accessory Structures of the Eye

    • Cornea – curved, transparent layer through which light rays enter the eye

    • Pupil – opening in the eye through which light passes

    • Iris – colorful part of the eye which adjusts the amount of light entering the eye

    • Lens – bends rays, focusing them on the retina

    • Retina – Surfaces at back of the eye onto which the lens focuses light rays


    • Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina

      • Acuity- the sharpness of vision

      • Nearsightedness- condition in which nearby objects are seen more clearly than distant objects because distant objects in front of retina

      • Farsightedness- condition in which faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina

    How light enters the eye
    How Light enters the eye



    Normal Vision



    Converting light into images
    Converting Light into Images

    • Visual transduction is the conversion of light energy into neural activity.

    • Conversion done by photoreceptors in the retina.

    • Two main types of photoreceptors: Rods and cones.

    Rods and cones
    Rods and Cones

    • Rods

      • peripheral retina

      • detect black, white and gray

      • twilight or low light

    • Cones

      • near center of retina

      • fine detail and color vision

      • daylight or well-lit conditions

    Interactions in the retina
    Interactions in the Retina

    • Photoreceptor cells connect to bipolar cells and then to ganglion cells

    • Axons of the ganglion cells form the optic nerve, which extends out of the eye and into the brain

    • Each neuron of a sensory system has a receptive field – part of the retina and the region of the environment to which that cell responds

    Figure 4 12 the hermann grid
    Figure 4.12: The Hermann Grid Cells

    The cell whose receptive field includes the space at the intersection has more whiteness shining on its inhibitory surround than the cell whose receptive field is just to the right of the intersection. The output of the intersection cell will be lower than that of the one on the right, creating the impression of a shadow.

    Visual pathways
    Visual Pathways Cells

    • Axons from ganglion cells converge as a bundle of fibers called the optic nerve and exit the eyeball at one spot

    • The exit point has no photoreceptors and is insensitive to light creating a blind spot

    • About ½ the fibers of the optic nerve cross over to the opposite side of the brain at the optic chiasm (part of the bottom surface of the brain)

    Visual pathways con t
    Visual Pathways con’t Cells

    • Axons from most of ganglion cells in retina form synapses in the thalamus, in a specific region called the lateral geniculate nucleus (LGN)

    • Neurons in the LGN relay the visual input to the primary visual cortex, located in the occipital lobes in the back of the brain

    Visual representations
    Visual Representations Cells

    • Receptive fields of neurons are characterized by parallel processing and hierarchical processing

      • Parallel Processing of visual properties: Brain conducts separate kinds of analysis simultaneously on the same information.

        • The “what” system

        • The “where” system

    • Hierarchical Processing of visual properties:

      • Individual cells in the visual cortex receive input from several LGN neurons.

      • Cortical cells respond to specific features of objects in the visual field – Feature detectors

    Light Conversion

    Seeing color
    Seeing Color Cells

    • Hue – color determined by the dominant wavelength in the mixture of the light (excludes black, white, gray)

    • Saturation – purity of a color

    • Brightness – overall intensity of the wavelengths that make up light

    Visual information processing
    Visual Information Processing Cells

    • Trichromatic (three color) Theory

      • Young and Helmholtz

      • three different retinal color receptors

    Trichromatic theory of color
    Trichromatic Theory of Color Cells

    • Any color can be produced by mixing pure lights of blue, green, and red.

    • There are three types of cones, each most sensitive to particular wavelengths.

    • Ratio of the activities of the three types of cones indicates what color is sensed.

    Opponent process theory
    Opponent-Process Theory Cells

    • Ewald Hering

    • Each of the three color sensitive elements are organized as pairs, where each pair member opposes, or inhibits, the other

      • Red-Green

      • Blue-Yellow

      • Black-White

    Figure 4 20 color coding and ganglion cells
    Figure 4.20: Color Coding and CellsGanglion Cells

    The chemical senses
    The Chemical Senses Cells

    • Olfaction detects airborne chemicals

      • Our sense of smell

    • Gustation detects chemicals in solution that come into contact with receptors inside the mouth

      • Our sense of taste

    Olfactory system
    Olfactory System Cells

    • Employs about 1,000 different types of receptors.

    • Only sense that does not send its messages through the thalamus.

    • Processing in several brain regions including frontal lobe and amygdala

    • Strong relationship between olfaction and emotional memory

    Olfactory system cont d
    Olfactory System Cells(cont’d.)

    • Only sense that does not send its messages through the thalamus.

    • Pathways from olfactory bulb sends information on for further processing in several brain regions.

      • Including frontal lobe and amygdala.

    • Strong relationship between olfaction and emotional memory.

    Pheromones Cells

    • Chemicals released by one animal, and when detected by another, can shape the second animal’s behavior or physiology.

    • Role of pheromones in humans not clear

    Age sex and sense of smell

    Number Cells

    of correct


    Women and young adults

    have best sense of smell







    10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99

    Age Group

    Age, Sex and Sense of Smell

    Smell taste and flavor
    Smell, Taste, and Flavor Cells

    • Smell and taste act together to form system known as flavor.

    • Tastes and odors can prompt strong emotional responses.

    • Nutritional state can affect taste and flavor of food and motivation to eat particular foods.

    • Flavor includes other characteristics of food.

    Somatic senses and the vestibular system
    Somatic Senses and the CellsVestibular System

    • Somatosensory systems are spread throughout the body

    • Somatic senses include:

      • Skin senses of touch, temperature, and pain

      • Kinesthesia

    • Vestibular system tells the brain about the position and movement of the head

    Touch Cells

    • Energy detected is physical pressure on tissue.

    • Many nerve endings in the skin act as touch receptors.

    • Touch is both an active and passive sense.

    • Changes in touch provide most important sensory information.

    Coding of touch information
    Coding of Touch Information Cells

    • Intensity of the stimulus is coded by:

      • Firing rate of individual neurons and

      • The number of neurons stimulated.

    • Location is coded by the location of the neurons responding to the touch.

    Temperature Cells

    • Some of the skin’s sensory neurons respond to a change in temperature.

      • “Warm” and “cold” fibers

    • Sensations of touch and temperature sometimes interact.

    • Stimulation of the touch sense can have psychological and physiological effects.

    Sensation perception
    Pain Cells

    • Pain provides information about impact of world on body.

    • Information-carrying aspect of pain very similar to that of touch and temperature.

    • Two types of nerve fibers carry pain signals from skin to the spinal chord.

    • Cerebral cortex plays role in the experience of pain.

    Modulating pain
    Modulating Pain Cells

    • Gate Control Theory

      • theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain

      • “gate” opened by the activity of pain signals traveling up small nerve fibers

      • “gate” closed by activity in larger fibers or by information coming from the brain

    • Natural Analgesics

      • Serotonin

      • Endorphins

    Proprioceptive senses
    Proprioceptive Senses Cells

    • Sensory systems that provide information to the brain about:

      • The position of the body.

      • What each of part of the body is doing.

    • Vestibular sense indicates the position of the head in space and its general movements.

      • Sense of balance.

    Vestibular sense
    Vestibular Sense Cells

    • Organs:

      • Vestibular sacs

      • Otoliths

      • Semicircular canals

    • Neural connections to:

      • The cerebellum

      • The autonomic nervous system

      • The eye muscles

    Kinesthesia Cells

    • Sense that indicates where the parts of the body are with respect to one another.

      • Necessary guide for movement.

    • Kinesthetic information comes primarily from the joints as well as muscles.


    Three approaches to perception
    Three Approaches to Perception Cells

    • Computational – tries to determine the computations that a machine would have to solve perceptual problems

    • Constructivist – reality is constructed from fragments of sensory information

    • Ecological – environment contains most of the information needed to form perceptions

    Psychophysics Cells

    • Describes the relationship between the physical energy in the environment and the psychological experience of that energy

    • Absolute Threshold – the minimum detectable amount of environmental energy a sensory system can detect

    Absolute thresholds table 5 1
    Absolute Thresholds Cells Table 5.1

    Signal detection theory
    Signal-Detection Theory Cells

    • Sensitivity – a person’s ability to pick out a particular stimulus or signal

    • Response Criterion – a person’s willingness or reluctance to say that a stimulus is present

    • Signal-Detection Theory – model of our personal sensitivity and response criterion combined to determine whether or not a near-threshold stimulus has occurred

    Judging differences between stimuli
    Judging Differences Between Stimuli Cells

    • Difference Threshold or Just-Noticeable Difference (JND)

    • JND determined by two factors:

      • How much of a stimulus was there to begin with?

      • Which sense is being stimulated?

    Click the link below to see how JND impacts the consumer world:

    Weber s law
    Weber’s Law Cells

    • Weber’s Constant

    • Law States That JND = KI

      • K is the Weber’s constant for a particular sense.

      • I is the amount, or intensity, of the stimulus.

        • The smaller K is, the more sensitive a sense is to stimulus differences

    Magnitude estimation
    Magnitude Estimation Cells

    • Magnitude estimation is how our perception of stimulus intensity is related to actual stimuli strength

    • Fechner’s Law

      • Constant increases in physical energy will produce smaller increases in perceived magnitude

    • Steven’s Power Law

      • Describes a wider range of sensations

    Perceptual illusions
    Perceptual Illusions Cells

    • Illusion – incorrect perception of a stimulus

    • Delusion – a false belief

    • Hallucination – a perception in the absence of a stimulus

    Perceptual illusions1
    Perceptual Illusions Cells

    Ames room

    Perceptual illusions2
    Perceptual Illusions Cells

    Ames room

    Basic processes in perceptual organization
    Basic Processes in Perceptual Organization Cells

    • Figure-Ground Organization

      • Perceptual apparatus picks out some objects to be figures, while others are less relevant in the background

    • Grouping

      • Inherent properties of the stimulus environment lead people to group them together

        • Grouping Principles

          • Proximity--group nearby figures together

          • Similarity--group figures that are similar

          • Continuity--perceive continuous patterns

          • Closure--fill in gaps

          • Connectedness--spots, lines, and areas are seen as unit when connected

          • Synchrony – occur at the same time

          • Common region – located within some boundary

          • Connectedness – connected by other elements

    Perceptual organization
    Perceptual Organization Cells

    • Likelihood Principle

      • We perceive objects in the way that experience tells us is the most likely physical arrangement (consistent with Constructivism)

    • Simplicity Principle

      • We organize stimulus elements in a way that gives us the simplest possible perception

    Perception of location and distance
    Perception of Location and Distance Cells

    • Two-Dimensional Location – uses an equation that takes information about where an image strikes the retina and adjusts it based on information about movement of your eyes and head

      • Visual dominance – bias toward using visual information when it conflicts with information from other senses

    Depth perception
    Depth Perception Cells

    • Our ability to perceive distance, allowing people to experience the world in three-dimensions

      • Interposition – closer objects block the view of things further away

      • Relative Size – the object producing a larger image on the retina is perceived as closer

      • Height in the Visual Field – more distant objects are higher in the visual field

      • Texture Gradient – graduated change in texture – less detailed as distance increases

      • Linear Perspective – the closer together 2 converging lines are, the greater the perceived distance

      • Clarity, Color, Shadow – distant objects appear hazier

      • Motion Parallax – objects closer appear to move rapidly, while those distant appear motionless

    Figure 5 10 stimulus cues for depth perception
    Figure 5.10: Stimulus Cues for CellsDepth Perception

    Cues based on physiology
    Cues Based on Physiology Cells

    • Accommodation – muscles surrounding the lens either tighten (to focus on close objects) or relax (to focus on distant objects)

    • Convergence – each eye rotates inward to see closer objects

    • Binocular Disparity – the difference between the two retinal images of an object provides distance cues

    Perception of motion
    Perception of Motion Cells

    • Looming – a rapid expansion in the size of an image so that it fills the retina and is perceived as an approaching object

    • Stroboscopic Motion – our tendency to perceive motion through a series of flashing rapid light

    Perceptual constancy
    Perceptual Constancy Cells

    • The perception of objects as constant in size, shape and color

    • Size Constancy – occurs as objects move closer or farther away

    • Shape Constancy – occurs as an object appears the same, even though the shape of its retinal image changes

    • Brightness Constancy – occurs so that no matter how the amount of light striking an object changes, its perceived brightness remains constant

    Recognizing the perceptual world
    Recognizing the Perceptual World Cells

    • The brain analyzes the incoming pattern of the stimulus and compares that pattern to information stored in the memory

      • Top-down processing – guided by knowledge and expectations

        • Our experiences create schemas, or mental representations of what we know about the world

      • Bottom-up processing – relies on specific, detailed information from sensory receptors that are integrated and assembled into a whole

    Parallel distributed processing models pdp
    Parallel Distributed Processing Models (PDP) Cells

    • Units in a network operate parallelsimultaneously

    • Each element is connected to all other computational elements

    • Recognition occurs as a result of the simultaneous operation of connected units

    Attention Cells

    • The process of directing and focusing certain psychological resources to enhance perception, performance, and mental experience

    Articles Cells


    Illusions Cells


    Blind spot demonstration
    Blind Spot Demonstration Cells


    Jeopardy Cells


    More information on sensation and perception
    More Information on Sensation and Perception Cells


    References Cells