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POWERPOINT PRESENTATION
FOR BIOPSYCHOLOGY,
9TH EDITION
BY JOHN P.J. PINEL
P R E PA R E D B Y J E F F R E Y W. G R I M M
WESTERN WASHINGTON UNIVERSITY
COPYRIGHT © 2014 PEARSON EDUCATION, INC.
ALL RIGHTS RESERVED.
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Chapter 7
Mechanisms of
Perception: Hearing, Touch,
Smell, Taste, and Attention
How You Know the World
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Learning Objectives
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LO1: Compare the current model of sensory system organization with the
former model.
LO2: Describe the organization of the auditory system.
LO3: Describe the organization of the somatosensory system.
LO4: Discuss 3 paradoxes of pain.
LO5: Describe the organization of the olfactory and gustatory systems.
LO6: Discuss selective attention, the cocktail party phenomenon, and
change blindness.
LO7: Describe the neural mechanisms of selective attention and one
relevant experiment.
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Principles of Sensory System
Organization
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Primary: input mainly from thalamic relay nuclei
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For example, the striate cortex receives input
from the lateral geniculate nucleus.
Secondary: input mainly from primary and
secondary cortexes within the sensory system
Association: input from more than one sensory
system, usually from the secondary sensory
cortex
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Principles of Sensory System
Organization (Con’t)
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Hierarchical Organization
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Specificity and complexity increases with each
level.
Sensation: detecting a stimulus
Perception: understanding the stimulus
Functional segregation: distinct functional
areas within a level
Parallel processing: simultaneous analysis of
signals along different pathways
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FIGURE 7.1 The hierarchical organization of the sensory
systems. The receptors perform the simplest and most general
analyses, and the association cortex performs the most
complex and specific analyses.
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FIGURE 7.2 Two models of sensory system organization: The former model was hierarchical,
functionally homogeneous, and serial; the current model, which is more consistent with the
evidence, is hierarchical, functionally segregated, and parallel. Not shown in the current
model are the many descending pathways that are means by which higher levels of sensory
systems can influence sensory input.
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Auditory System
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Natural sounds are complex patterns of
vibrations.
A Fourier analysis breaks natural sounds
down into sine waves.
There is a complex relationship between
natural sounds and perceived frequency.
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FIGURE 7.3 The relation between the
physical and perceptual dimensions of
sound.
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FIGURE 7.4 The breaking down of a sound—in this case, the
sound of a clarinet—into its component sine waves by Fourier
analysis. When added together, the component sine waves
produce the complex sound wave.
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The Ear
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Sound waves enter the auditory canal of the
ear and then cause the tympanic membrane
(the eardrum) to vibrate.
This sets in motion the bones of the middle
ear—the ossicles—which trigger vibrations of
the oval window.
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The Ear (Con’t)
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Sound Wave > Eardrum > Ossicles
(Hammer, Anvil, Stirrup) > Oval Window
Vibration of the oval window sets in motion
the fluid of the cochlea.
The cochlea’s internal membrane—the
organ of Corti—is the auditory receptor organ.
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FIGURE 7.5 Anatomy of the ear.
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The Ear (Con’t)
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The organ of Corti is composed of two
membranes.
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Basilar membrane: auditory receptors—hair
cells—are mounted here.
Tectorial membrane: rests on the hair cells
Stimulation of hair cells triggers action
potentials in the auditory nerve.
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The Ear (Con’t)
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Cochlear Coding
Different frequencies produce maximal
stimulation of hair cells at different points
along the basilar membrane.
The basilar membrane and most other
auditory system components are organized
tonotopically—that is, by frequency.
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From the Ear to the Primary
Auditory Cortex
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The axons of each auditory nerve synapse in the
ipsilateral cochlear nuclei.
From there, many projections lead to the superior
olives on both sides of the brain stem.
From there, axons project via the lateral lemniscus
to the inferior colliculi.
Axons then project from the inferior colliculi to the
medial geniculate nuclei of the thalamus.
Thalamic neurons then project to the primary
auditory cortex.
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FIGURE 7.6 Some of the pathways
of the auditory system that lead
from one ear to the cortex.
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Subcortical Mechanisms of
Sound Localization
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The lateral and medial superior olives react
to differences in what is heard by the two
ears.
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Medial: differences in arrival
Lateral: amplitude differences
Both project to the superior colliculus.
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The deep layers of the superior colliculus are laid out
according to auditory space, allowing location of sound
sources in the world; the shallow layers are laid out
retinotopically.
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Auditory Cortex
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The auditory cortex is located in the temporal
lobe.
Core region: includes primary cortex
The belt surrounds the core region.
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A band of secondary cortex
Areas of the secondary cortex outside the belt
are referred to as parabelt areas.
About ten separate areas of secondary
auditory cortex exist in primates.
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FIGURE 7.7 General location of the primary auditory cortex and areas
of secondary auditory cortex. Most auditory cortex is hidden from
view in the temporal cortex of the lateral fissure.
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Organization of Primate
Cortex
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Functional columns: cells of a column respond
to the same frequency
Tonotopic Organization
Secondary areas do not respond well to pure
tones and have not been well researched.
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What Sounds Should Be
Used to Study Auditory
Cortex?
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There is a lack of understanding of the
dimensions along which the auditory cortex
evaluates sound.
All through the cortical levels of the auditory
system, there are cells that respond to
complex sounds.
Perhaps study with pure tones is limited.
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Two Streams of Auditory
Cortex
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Auditory signals are conducted to two areas
of association cortex.
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Prefrontal cortex
Posterior parietal cortex
Anterior auditory pathway may be more
involved in identifying sounds (what).
Posterior auditory pathway may be more
involved in locating sounds (where).
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FIGURE 7.8 The hypothesized anterior and
posterior auditory pathways.
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Auditory–Visual Interactions
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There is evidence for interactions between
the auditory and visual systems.
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E.g., some posterior parietal neurons with both
visual and auditory receptive fields
Interaction in primary sensory cortices
indicate that sensory system interaction is an
early and integral part of sensory processing.
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Where Does the Perception
of Pitch Occur?
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Most auditory neurons respond to changes
in frequency rather than pitch.
One small area just anterior to the primary
auditory cortex has neurons that respond to
pitch rather than frequency.
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This may be where frequencies of sound are
converted to perception of pitch.
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Effects of Damage to the
Auditory System
Auditory cortex lesions in rats result in few
permanent hearing deficits.
Lesions in monkeys and humans hinder
sound localization and pitch discrimination.
Deafness in Humans
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Total deafness is rare, due to multiple pathways.
Two kinds: conductive deafness (damage to
ossicles) and nerve deafness (damage to
cochlea)
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Partial cochlear damage results in loss of hearing at
particular frequencies.
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FIGURE 7.9 Cochlear implant: The surgical
implantation is shown on the left, and a child
with an implant is shown on the right.
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Somatosensory System:
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Touch and Pain
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The somatosensory system is made up of
three separate and interacting systems.
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Exteroceptive: external stimuli
Proprioceptive: body position
Interoceptive: body conditions (e.g., temperature
and blood pressure)
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Cutaneous Receptors
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Free Nerve Endings
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Pacinian Corpuscles
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Temperature and pain
Adapt rapidly; large and deep; onion-like
Respond to sudden displacements of the skin
Merkel’s disks: gradual skin indentation
Ruffini endings: gradual skin stretch
Dermatome: the area of the body innervated by
the left and right dorsal roots of a given segment
of spinal cord
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FIGURE 7.10 Four cutaneous
receptors that occur in human
skin.
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Two Major Somatosensory
Pathways
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Dorsal-Column Medial-Lemniscus System
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Mainly touch and proprioception
First synapse in the dorsal column nuclei of the
medulla
Anterolateral System
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Mainly pain and temperature
Synapse upon entering the spinal cord
Three tracts: spinothalamic, spinoreticular,
spinotectal
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FIGURE 7.12 The dorsal-column
medial-lemniscus system. The
pathways from only one side of
the body are shown.
FIGURE 7.13 The anterolateral
system. The pathways from
only one side of the body are
shown.
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Cortical Areas of
Somatosensation
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Primary Somatosensory Cortex (SI)
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SII: mainly input from SI
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Postcentral gyrus
Somatotopic organization (somatosensory
homunculus); more sensitive, more cortex
Input largely contralateral
Somatotopic; input from both sides of the body
Much of the output from SI and SII goes to
the association cortex in the posterior
parietal lobe.
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FIGURE 7.14 The locations of human
primary somatosensory cortex (SI) and one
area of secondary somatosensory cortex
(SII) with the conventional portrayal of the
somatosensory homunculus. Something
has always confused me about this
portrayal of the somatosensory
homunculus: The body is upside-down,
while the head is right side up. It now
appears that this conventional
portrayal is wrong. The results of an fMRI
study suggest that the face representation
is also inverted (Servos et al., 1999).
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Effects of Damage to the
Primary Somatosensory
Cortex
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Effects of damage to the primary
somatosensory cortex are often mild.
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Likely due to numerous parallel pathways
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Somatosensory System and
Association Cortex
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The highest level of the sensory hierarchy
is made up of areas of association cortex
in the prefrontal and posterior parietal
cortex.
The posterior parietal cortex contains
bimodal neurons.
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Neurons that respond to activation of two
different sensory systems
Allow integration of visual and somatosensory
input
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Somatosensory Agnosias
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Astereognosia: inability to recognize objects
by touch
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Pure cases are rare; other sensory deficits are
usually present.
Asomatognosia: the failure to recognize parts
of one’s own body (e.g., the case of the man
who fell out of bed)
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Perception of Pain
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Despite its unpleasantness, pain is
adaptive and needed.
There exist no obvious cortical
representation of pain (although the
anterior cingulate gyrus appears to be
involved in the emotional component of
pain).
Descending pain control: pain can be
suppressed by cognitive and emotional
factors.
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Descending Pain Control
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Circuitry Identified by the Following Studies:
Electrical stimulation of the periaqueductal
gray (PAG) has analgesic effects.
PAG and other brain areas have opiate
receptors.
Existence of Endogenous Opiates (Natural
Analgesics); Endorphins
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FIGURE 7.18 Basbaum and
Fields’s (1978) model of the
descending analgesia circuit.
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Neuropathic Pain
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Neuropathic pain is severe chronic pain in
the absence of a recognizable pain
stimulus.
Neuropathic pain is likely the result of
pathology of the nervous system linked to
an injury.
Some evidence exists to suggest that
aberrant microglial cell signals trigger
neural pain pathways.
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Chemical Senses:
Smell and Taste
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Olfaction (Smell)
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Gustation (Taste)
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Detects airborne chemicals
Responds to chemicals in the mouth
Food acts on both systems to produce flavor.
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Chemical Senses:
Smell and Taste (Con’t)
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Pheremones are chemicals that influence that
behavior of conspecifics (members of the same
species).
Evidence of Human Pheromones
Changes in Olfactory Sensitivity across the
Menstrual Cycle
Synchronization of Menstrual Cycles
Sex Identification by Smell (Especially by Women)
Men can identify a woman’s menstrual stage by
smell.
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Olfactory System
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Receptor cells are embedded in the olfactory
mucosa of the nose.
There are many different kinds of receptors.
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Same kinds of receptor cells project to similar areas
of the olfactory bulb.
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Rats and mice have about 1,500.
Humans have almost 1,000.
Clusters of neurons near the surface of the olfactory bulbs
 Olfactory glomeruli
New receptor cells are created throughout life.
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Olfactory System (Con’t)
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The olfactory tract projects to several
structures of the medial temporal lobes
including the amygdala and the piriform
cortex.
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Does NOT first pass through the thalamus
Only sensory system that does this
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FIGURE 7.19 The human
olfactory system.
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Gustatory System
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There are receptors in the tongue and oral
cavity in clusters of about 50 called taste buds.
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Located around small protuberances called papillae
There are 4 (sweet, sour, salty, bitter) primary
tastes; 5th is umami, meat or savory.
Many tastes are not created by combining
primaries.
Salty and sour don’t have receptors; they
merely act on ion channels.
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Gustatory System (Con’t)
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Gustatory afferent neurons leave the mouth as
part of the 7th, 9th, and 10th cranial nerves to the
solitary nucleus of the medulla.
Projections then pass to the ventral posterior
nucleus of the thalamus.
From there, neurons project to the primary
gustatory cortex and then to the secondary
gustatory cortex.
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FIGURE 7.20 Taste receptors, taste
buds, and papillae on the surface of
the tongue. Two sizes of papillae are
visible in the photograph; only the
larger papillae contain taste buds
and receptors.
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Brain Damage and the
Chemical Senses
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Anosmia: inability to smell
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The most common cause is a blow to the head
that damages olfactory nerves.
Incomplete deficits are seen with a variety of
disorders.
Ageusia: inability to taste
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Rare due to multiple pathways carrying taste
information
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Gustatory System (Con’t)
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There is evidence for the narrow tuning of
gustatory receptors.
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Respond to only one taste
Tuning is broader in presynaptic cells and up
through the cortex.
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FIGURE 7.21 The human
gustatory system.
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Selective Attention
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Selective attention improves perception of
what is attended to and interferes with that
which is not.
Internal cognitive processes (endogenous
attention) and external events (exogenous
attention) focus attention.
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Selective Attention (Con’t)
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The cocktail party phenomenon indicates that
there is processing of information not
attended to.
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Change Blindness
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Change blindness: no memory of that
which is not attended to
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We do not appear to remember parts of a
scene that are not the focus of our attention.
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Neural Mechanisms of
Attention
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Selective attention is thought to work by
strengthening the neural responses to
attended-to aspects and by weakening the
responses to other.
For example, spatial attention can shift the
location of receptive fields (Wommelsdorf
et al., 2006).
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Simultanagnosia
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Simultanagnosia: a difficulty in attending
to more than one visual object at a time
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Typical cause: bilateral damage to the dorsal stream
(involved with localizing objects in space)
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