Chapter 9 Flashcards
Scotoma
small blind spot
Are we consciously aware of everything we see?
no. we are only aware of part of the visual information our brain is processing
Sensory receptors
specialized cells that transduce (convert) sensory energy into neural activity
Do sensory receptors respond to all sensory energy?
nope. they respond only to a narrow band of energy within each modality’s energy spectrum
Vision
light energy is concerted into chemical energy in the photoreceptors of the retina and the chemical energy is concerted into action potentials
Auditory System
air-pressure waves are converted first into mechanical energy, which activates the auditory receptors that produce action potentials
Somatosensory system
mechanical energy activates receptor cells that are sensitive to touch, pressure or pain. Somatosensory receptors in turn generate action potentials
Taste and Olfaction
various chemical molecules carried by the air or contained in food fit themselves into receptors of various shapes to activate action potentials
Human sensory abilities
are average
Receptive field
region of the visual world that stimulates a receptor cell or neuron
Photoreceptor cells
in the eye; each one points in a slightly different direction and thus has a unique receptive field
What does the brain do with receptive fields
identify sensory information, contrast information from each receptor field, help locate sensory events in space
Optic flow
streaming of visual stimuli that accompanies an observer’s forward movement through space
Auditory Flow
change in sound heard as a person moves past a sound source or asa sound source moves past a person
Usefulness of auditory and optic flow
tell us how fast we are going, whether we are moving or if the world is moving, what direction (straight, up, down) we are moving
Receptor density
determines the sensitivity of a sensory system
Color photoreceptors
small, densely packed to make sensitive color discrimination in bright light
black-white vision receptors
larger, more scattered, extremely sensitive to light
neural relays
all receptors connect to the cortex through a sequence of 3-4 intervening neurons; can modify information at different stages –> sensory system can mediate different responses
Location of relays
varies, some in brainstem, spinal cord, neocortex
Layers of neural relays
at each level a relay allows a sensory system to produce relevant actions that define the hierarchy of our motor behavior
Perceptions of speech sounds
influenced by the facial gestures of a speaker
Sensory coding
all sensory info from all systems is encoded by action potentials that travel along peripheral nerves in the somatic nervous system until they enter the spinal cord or brain and from there on nerve tracts within the CNS
How do we differentiate sensations?
different sensations are processed at distinct regions of cortex; learn through experience to distinguish them; each sensory system has a preferential link with certain kinds of reflex movements
synesthesia
mixing of the senses
topographic map
spatially organized neural representation of the external world
How many primary cortical areas do mammals have for each sensory system?
at least 1
Sensation
registration of physical stimuli from the environment by the sensory organs
perception
subjective interpretation of sensations by the brain
What sense does the brain devote most to?
vision
Retina
light-sensitive surface at the back of the back of the eye consisting of neurons and photoreceptor cells; initiates neural activity
how does light travel into the eye?
light–> pupil –> eye–> retina at the back of the eye
photoreceptor
specialized type of retinal cell that transduces light into neural activitiy
what do the photoreceptor cells and the retina do?
translate light into action potentials, discriminate wavelengths so we can see colors, work in a range of light intensities
how do images appear on the retina?
upside down and backward
what wavelengths can we see?
400-700 nanometers; shortest are deep purple, longest red
how is the electromagnetic wavelength measured?
nanometers
sclera
forms the eyeball; the white of the eye
cornea
eye’s clear outer covering
iris
colored part; opens and closes to allow more or less light through a hole
pupil
hole
lens
focuses light
fovea
center of the retina; region of sharpest vision and has the densest distribution of photoreceptors specialized for color
optic disc
where blood vessels enter the eye and the axons that form the optic nerve leave the eye; has no receptors and thus forms the blind spot; conveys information from the eye to the brain
blind spot
region of the retina (the optic disc) where axons forming the optic nerve leave the eye and where blood vessels enter and leave; has no photoreceptors= blind
cornea & lens
both bend the light coming into the eye
normal vision
the lens focuses incoming light directly on the retina
myopia
can’t bring distant objects into clear focus because the focal point of light falls short of the retina; caused by round eyeball–> elongated or excessive curvature of the front of the cornea
hyperopia
can’t focus on nearby objects because the focal point of light falls beyond the retina; eyeball may be too short or the lens too flat
periphery
vision is not as good as in the center
papilloedema
swollen disc
optic neuritis
inflammation of the optic nerve
rod
photoreceptor specialized for functioning at low light levels; cylindrically shaped at one end, longer, more numerous
cone
photoreceptor specialized for color and high visual acuity; tapered at one end, shorter, not sensitive to dim light, less numerous
what happens when light strikes a photoreceptor?
it triggers a series of chemical reactions that lead to a change in the membrane potential (electrical charge) that leads to a change in the release of neurotransmitters onto nearby neurons
are rods and cones evenly distributed?
no; fovea only has cones, but cone density drops dramatically beyond the fovea
how many cone pigments are there?
3; each cone has one
how many total pigments do we have?
4; 3 from cones and 1 from rods
what do cone pigments respond to?
a range of frequencies
How are cones distributed?
randomly across the retina–> color perception constant across visual field
Red cone
gene carried in x chromosome
what do photoreceptors connect to?
connected to two layers of retinal neurons
first retinal layers
contains three types of cells (bipolar, horizontal, amacrine)
horizontal cells
link photoreceptors with bipolar cells
amacrine cells
link bipolar cells with the cells of the second neural layer
what is the second neural layer?
retinal ganglion cells
retinal ganglion cells
type of retinal neurons with axons that bundle at the optic disc and leave the eye to form the optic nerve
magnocellular (M) cell
large-celled visual-system neuron that is sensitive to moving; input from rods, sensitive to light not color
parvocellular (P) cell
small-celled visual-system neuron that is sensitive to form and color differences; input from cones, sensitive to color
Optic chiasm
junction of the optic nerve, one from each eye, at which the axons from the nasal (inside–nearer the nose) halves of the retinas cross to the opposite side of the brain
Do the fibers from the optic nerve enter the same side of the brain?
the left half of each optic nerve goes to the left side of the brain and the right half goes to the brain’s right side
nasal retina
the medial path of each retina crosses to the opposite side
temporal retina
lateral path, goes straight back on the same side
Geniculostriate system
projections from the retina to the lateral geniculate nucleus to the visual cortex; formed by all of the P ganglion cell axons and some M ganglion cells
striate cortex
primary visual cortex (V1) is in the occipital lobe; its striped appearance when stained gives it this name
tectopulvinar system
projections from the retina to the superior colliculus to the pulvinar (thalamus) to the parietal and temporal visual areas; eye–>tectum–> pulvinar
retinohypothalamic tract
neural route formed by axons of photosensitive retinal ganglion cells from the retina to the suprachiasmatic nucleus; allows light to entrain the rhythmic activity of the SCN; third visual pathway
are retinal ganglion cells photosensitive?
1-3% act as photoreceptors
role of photosensitive retinal ganglion cells
regulating circadian rhythms; pupillars reflex
Visual pathways
striate cortex–> temporal lobe (ventral stream) OR parietal lobe (dorsal stream)
Lateral geniculate nucleus (LGN)
in the thalamus; has 6 layers; projections from the two eyes go to different layers
Layers 2, 3, 5 of LGN
receive fibers from the ipsilateral eye
Layers 1, 4, 6 of LGN
receive fibers from the contralateral eye
Where do axons from P cells go?
layers 3-6 (parvocellular layers); process color/form
Where do axons from M cells go?
laters 1 and 2 (magnocellular layers); process information about movement
cortical column
cortical organization that represents a functional unit six cortical layers deep and approximately .5 mm square and that is perpendicular to the cortical surface
what makes up the tectopulvinar pathway?
remaining M cells; send their axons to superior colliculus (tectum)
tectum
produce orienting movements–detect the location of stimuli and shift the eyes toward stimuli
where does the superior colliculus send information?
region of the thalamus called the pulvinar
Pulvinar
two divisions; medial pulvinar (sends connections to the parietal lobe) and lateral pulvinar (sends connections to the temporal lobe)—> “Where” function
occipital lobe
composed of at least 6 different visual regions: V1, V2, V3, V3A, V4, V5
V1
striate cortex; is the primary visual cortex
extrastriate cortex
remaining visual areas (outside striate) of the occipital lobe; secondary visual cortex
primary visual cortex (V1)
striate cortex that receives input from the lateral geniculate nucleus
blob
region in the visual field that contains color-sensitive neurons, as revealed by staining for cytochrome oxidase
neurons in blobs
take part in color perceptions
neurons in interblobs
participate in form and motion perception
what happens when info arrives at V1?
info arrives from the p-cell and m-cell pathways of the geniculostriate system and is segregated into types of info (color, form, motion)
what happens when information in V1 is broken down by type?
goes from region V1 to V2–inputs remain segregated
what happens in V2?
thick strips and pale zones receive the segregated input
what happens after V2?
pathways proceed to other occipital regions and then to the parietal and temporal lobes
ventral and dorsal streams
simple records of color, form, and motion are assembled
fusiform face area (FFA)
part of temporal lobe; specialized for recognizing faces
parahippocampal place area (PPA)
part of temporal lobe; analyzes landmarks
lateral intraparietal area (LIP)
part of parietal lobe; related to eye movements
anterior intraparieta area (AIP)
part of parietal lobe; visual control of grasping
facial agnosia
prosopagnosia; damage to FFA; face blindness–the inability to recognize faces
visual field
region of the visual world that is seen by the eyes
where does information from visual fields go?
input from right visual field goes to the left hemisphere, etc.; brain can easily determine whether visual information is located to the left or right
how do retinal ganglion cells receive information?
bipolar cells from several photoreceptors
ganglion cell’s receptive field
the region of the retina on which it is possible to influence that cell’s firing
where on the retina does light hit?
light from bottom (hits top); light from top (hits bottom)
LGN
each LGN cell has a receptive field–region of the retina that influences its activity. if two adjacent retinal ganglion cells synapse on a single LGN cell, the receptive field of the LGN cell will be the sum of the two ganglion cell’s receptive fields
does the LGN projection to the striate cortex (V1) maintain spatial info?
yes
receptive field in cortex
cells in the cortex have much larger receptive fields than those of retinal ganglion cells
Jerison’s Principle of Proper Mass
sates that the amount of neural tissue responsible for a particular function is equivalent to the amount of neural processing required for that function
relationship between sensory areas and cortical representation
sensory areas that have more cortical representation provide a more-detailed creation of the external world
Cells along the midline
look at adjacent places in the visual field; collosal connections between such cells zip the two visual fields together by combing their receptive fields to overlap at the midline. the two fields become 1
excitation and inhibition
the same cell may react differently depending on the stimulus; response is selective
neurons in the retina
do not respond to shape–> only light
retinal ganglion cells
a spot of light falling in the central circle of the receptive field excites some of the cells; light falling in the periphery inhibits cell; light falling across the entire field weakly increases firing rate
on-center cells
retinal ganglion cells that are excited by light falling in the center
off-center cells
retinal ganglion cells that are excited by light falling in the periphery
luminance contrast
the amount of light reflected by an object relative to its surroundings
what do V1 cells respond to?
they are maximally excited by bars of light oriented in a particular direction rathe than by spots of light; are orientation detectors; their on/off receptive field is rectangular
simple cells
visual cortex cells that have a rectangular receptive field
hpercomplex cell
maximally responsive to moving bars but also has a strong inhibitory area at one end of its receptive field
complex cell
maximally excited by bars of light moving in a particular direction through a visual field
ocular-dominance column
functional column in the visual cortex maximally responsive to information coming from one eye
processing shape in temporal cortex
TE neurons; maximally excited by complex visual stimuli, such as faces or hands, and can be remarkably specific in their responsiveness
TE neurons
responds to complex features: has a combination of orientation, size, color, texture
how are objects represented?
by activity of many neurons with slightly varying stimulus specificity; these neurons are grouped together into a column
stimulus equivalence
recognizing an object as remaining the same despite being viewed from different orientations
Temporal lobe’s role in visual processing
not determined genetically but is subject to experience
neurons in Primary visual cortex
are not modified by experience–> genetically programmed
primary colors or light
red, blue, green
impression of colors
light of different wavelengths stimulates the three different cone receptor types in different ways–> the ratio of this activity of these receptor types creates our impression of colors
trichromatic theory
explanation of color vision based on the coding of three primary colors: red, green, and blue
what happens if all cones are equally active?
we see white
what does the trichromatic theory predict?
if we lack one type of cone receptor we cannot process as many colors as we could with all three
protanopia
lack of red cones
deuteranopia
lack of green cones
tritanopia
lack of blue cones
opponent process
explanation of color vision that emphasizes the importance of the apparently opposing pairs of colors: red versus green, blue versus yellow
color constancy
phenomenon whereby the perceived color of an object tends to remain constant relative to other colors, regardless of changes in illumination
homonymous hemianopia
blindness of an entire left or right visual field; caused by cuts in optic tract, LGN or V1
quadrantanopia
blindness of one quadrant of visual field
scotoma
small blind spot in the visual field caused by migraine or by a small lesion of the visual cortex
cells in the visual parietal cortex during anesthetia
are not active
nystagmus
constantly occurring eye motion
visual-form agnosia
inability to recognize objects or drawings of objects
achromatopsia
color agnosia
optic ataxia
deficit in the visual control of reaching and other movements
Damage to parietal cortex (dorsal stream)
can see perfectly well, yet they cannot accurately guide their movements on the basis of visual information
function of dorsal stream
guidance of movement
damage to the ventral stream
cannot see objects but can guide their movements to objects on the basis of visual information
function of ventral stream
perception of objects
