Chapter Four Sensation. Copyright © Houghton Mifflin Company. All rights reserved.4 - 2 Figure 4.1: Elements of a Sensory System Ear,nose Make into a

Chapter Four

Sensation

Copyright © Houghton Mifflin Company. All rights reserved. 4 - 2

Figure 4.1: Elements of a Sensory System

Ear,nose

Make into a chemical signal


The Problem of Coding

• How are physical properties coded into neural activity?

• Doctrine of Specific Nerve Energies

• Types of codes– Temporal– Spatial


Linkages: Sensation and Biological Aspects of Psychology

• Organized sensory information is called a representation.

• Shared features of representations of vision, hearing, and skin senses:– Information from each sense reaches the

cortex via the thalamus.– Representation of world is contralateral to the

part of the world being sensed.


Linkages: Sensation and Biological Aspects of Psychology (cont’d.)

• Shared features (cont’d.):– The cortex contains topographical representations of

each sense.– The density of nerve fibers in a sense organ

determines how well it is represented in the cortex.– Each region of primary sensory cortex is divided into

columns of cells that have similar properties. – Regions of cortex other than the primary areas do

additional processing of sensory information.

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Sound

• A repeated fluctuation in the pressure of air, water, or some other substance.– Produced by vibrations of an object.

• Wave: Repeated variation in pressure that spreads out in three dimensions.


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Physical Characteristics of Sound

• A waveform represents a wave in two-dimensions.

• Characteristics of Waveforms– Amplitude– Wavelength– Frequency

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Figure 4.2: Sound Waves and Waveforms


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Psychological Dimensions of Sound

• Loudness– Intensity of sound sources.

• Pitch

• Timbre

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Table 4.1: Intensity of Sound Sources


Figure 4.3: Structures of the Ear


Figure 4.4: The Cochlea


Conduction Deafness

• The three tiny bones of the middle ear are fused together.

• Prevents accurate reproduction of vibrations.

• Surgery can break bones apart or replace them with plastic ones.

• Hearing aids can also help.


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Nerve Deafness

• Results when the auditory nerve or the hair cells are damaged.

• Can be caused by extended exposure to loud noise.

• Cochlear implants can stimulate the auditory nerve.

• Hair cell regeneration as a possible treatment.


Auditory Pathways

• Auditory nerve brainstem thalamus

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

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


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

• 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.

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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.


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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.

• But how are very low frequencies coded?

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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.


Figure 4.7: Spectrum of Electromagnetic Energy


What Influences Sensations of Light?

• Light Intensity: How much energy the light contains.– Determines the brightness of light.

• Light Wavelength: The distance between peaks in light waves.– Determines what color we see.

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Figure 4.8: Major Structures of the Eye


Figure 4.9: The Lens and the Retinal Image


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 unable to discriminate color.– But more sensitive to light than cones.

• Three forms of pigments in cones provide the basis for color vision.

• Rods and cones differ in their distribution in the eye.

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Figure 4.10: Cells in the Retina


Figure 4.11: Center-Surround Receptive Fields of Ganglion Cells


Figure 4.12: The Hermann Grid


Figure 4.13: Find Your Blind Spot


Figure 4.14: Pathways from the Ganglion Cells into the Brain


Parallel Processing of Visual Properties

• Brain conducts separate kinds of analysis simultaneously on the same information.– The “what” system– The “where” system

• How are the parallel streams assembled into a unified conscious experience?


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Hierarchical Processing of Visual Information

• Individual cells in the visual cortex receive input from several LGN neurons.– Cortical cells respond to specific features of

objects in the visual field.

• Complex feature detectors can be built up from connections among simple feature detectors.– Some of cortical processing occurs in a

hierarchical fashion.


Figure 4.15: Construction of a Feature Detector

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Psychological Dimensions of Light

• Hue

• Saturation

• Brightness


Figure 4.16: The Color Circle


Figure 4.17: Matching a Color by Mixing Lights of Pure Wavelengths


Trichromatic or Young-Helmholtz Theory of Color Vision

• 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.

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Figure 4.18: Relative Responses of Three Cone Types to Different

Wavelengths of Light

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Problem with the Trichromatic Theory

• Cannot explain some aspects of color vision, such as afterimage.

• Example: Stare at the dot on the next slide for thirty seconds.

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Opponent-Process Theory of Color Vision

• Visual elements sensitive to color are grouped into three pairs.– Members of each pair oppose, or inhibit,

each other.

• Three pairs are a red-green element, a blue-yellow element, and a black-white element.

• Explains color afterimages and the phenomenon of complimentary colors.

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Synthesis and Update

• At level of photoreceptors, a slightly revised version of the trichromatic theory is correct.– Individual differences in long-wavelength

pigments.

• At the ganglion cell level, the center and surround of the receptive field are color coded.


Figure 4.20: Color Coding and Ganglion Cells

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Interaction of the Senses

• Not uncommon for senses to interact.

• Synesthesia is a more unusual mixing of senses, or dimensions within senses.


The Chemical Senses

• 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


Figure 4.23: The Olfactory System

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Olfactory System

• 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.)

• 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

• 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


Smell, Taste, and Flavor

• 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

• 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

• 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

• 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

• 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.

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Pain

• 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.

• Pain pathways• Cerebral cortex plays role in the

experience of pain.


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Figure 4.25: Pain Pathways

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Emotional Aspects of Pain

• Specific pathways carry an emotional component of the painful stimulus to several areas of the brain.

• Overall emotional response depends greatly on cognitive factors.– Knowing about the pain.– Use of pain-reducing cognitive strategies.

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Modulating Pain

• Gate Control Theory

• Natural Analgesics– Serotonin– Endorphins


Thinking Critically: Does Acupuncture Relieve Pain?

• What am I being asked to believe or accept?– Twirling a needle in the skin can relieve pain.

• What evidence is available to support the assertion?– MRI studies.– Positive results in patients treated by

acupuncture for various kinds of pain.– Acupuncture associated with release of

endorphins.

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Thinking Critically: Does Acupuncture Relieve Pain? (cont’d.)

• Are there alternative ways of interpreting the evidence?– Might simply confirm that the body’s painkilling

system can be stimulated by external means.

• What additional evidence would help to evaluate the alternatives?– More placebo-controlled studies of acupuncture.– What is the general relationship between internal

painkilling systems and external methods for stimulating them?

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Thinking Critically: Does Acupuncture Relieve Pain? (cont’d.)

• What conclusions are most reasonable?– In some circumstances, acupuncture does

relieve pain, but it is not a cure-all.– No evidence that acupuncture is better than

other painkilling procedures.– Quality of future studies of acupuncture will

determine whether acupuncture finds a more prominent place in Western medicine.

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Proprioceptive Senses

• 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

• Organs:– Vestibular sacs– Otoliths– Semicircular canals

• Neural connections to:– The cerebellum– The autonomic nervous

system– The eye muscles


Kinesthesia

• 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.

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Focus on Research Methods: The Case of the Mysterious Spells

• What was the researcher’s question?– Is there a specific brain region that, when

activated by a seizure, causes the sensation of orgasm?

• How did the researcher answer the question?– Used the case study method of research.– Studied person’s brain activity while she was

actually having a spell.

Deborah K.

added "s" to cause


Focus on Research Methods: Mysterious Spells (cont’d.)

• What did the researcher find?– EEG showed seizures in right temporal lobe.– MRI revealed small area of abnormal tissue.– Seizures stopped after removal of tissue.

• What do the results mean?– Person was having “localization-related

epilepsy.”– Right temporal lobe may play a special role in

creating the sensory experience of orgasm.


Focus on Research Methods: Mysterious Spells (cont’d.)

• What do we still need to know?– How specific is the linkage between activity in

this brain region and the sensory experience of orgasm?

– Did person continue to experience orgasms during sexual activity?

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Chapter Four Sensation. Copyright © Houghton Mifflin Company. All rights reserved.4 - 2 Figure 4.1: Elements of a Sensory System Ear,nose Make into a