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Brain&Behavior Ch 7
Vision: From Eye to Brain
| Term | Definition |
|---|---|
| retina | a layer of tissue in the back of the eye with several layers of neurons |
| Transduction | the process of converting one form of energy into another – e.g., turning light into neural signals |
| The eye has ________-like features | camera |
| cornea | a transparent outer layer on the eyeball that focuses and bends the light (refraction) to form images on the retina |
| The lens further focuses light using the ________ _________ in the eye to adjust the focus by changing the shape of the lens | Ciliary muscles |
| The convex shape of the eye does what? | distorts the image we see, flipping it upside down and reversed when the image hits the retina. |
| Contraction of the ciliary muscles causes nearer or farther images to come into focus—the process of ___________ | accommodation |
| Myopia | or nearsightedness, is difficulty seeing distant objects and develops if the eyeball is too long, causing images to form in front of the retina |
| As the eye ages, the lens becomes less _______ and cannot adjust to near object (i.e., farsighted vision) | elastic |
| Eye movement is controlled by three pairs of _________ _________ attached to the boney process in the eye socket | extraocular muscles |
| The first stages of visual processing begin in the retina, which contains several cell types: (4) | photoreceptors, bipolar cells, horizontal cells, and amacrine cells |
| Photoreceptors | sensory neurons that detect light |
| What are the two types of photoreceptors in the retina? | rods and cones |
| Rods respond to... | all light; primary neurons for night vision (most active at low light) |
| Cones respond to... | cells respond to different light wavelengths creating color vision |
| Bipolar cells—receive input from ____________ and synapse on ________ cells whose axons form the ______ _______, which carries information to the brain | photoreceptors, ganglion, optic nerve |
| Horizontal cells in the retina do what? | contact photoreceptors and bipolar cells |
| Amacrine cells do what?` | contact bipolar and ganglion cells (inhibitory role) |
| All cell types except _________ cells generate graded potentials, affecting each other through the graded release of neurotransmitters | ganglion |
| Ganglion cells do what? | fire action potentials |
| Rods and cones correspond to two systems: | scotopic system and photopic system |
| scotopic system | (rods)—works in dim light but is insensitive to color |
| There is ________ in the scotopic system as information from many rods converges onto each ganglion cell | convergence |
| Photopic system | (cones)—requires more light (higher threshold) and allows color vision |
| Both rods and cones have _____ that capture light particles – quanta, or photons | discs |
| The discs contain specific _________ receptor molecules (G-protein coupled receptors highly sensitive to photons) | photopigment |
| In rods, the pigment in the photoreceptor is _________ | rhodopsin (Cones have different photopigment receptor molecules) |
| Rods and cones are both stimulated by ______ | light (Rods require less light than cones) |
| At rest (in darkness) both rods and cones do what? | continually release neurotransmitter |
| Light triggers graded _____________ | hyperpolarization |
| in response, photoreceptor releases less ____________ | neurotransmitter |
| Size of hyperpolarization determines what? | amount of neurotransmitter released |
| The visual system responds over a wide range of ______ __________ using different mechanisms: | light intensities |
| Adjustments to the size of the ______ (the opening in the iris) are one type of response to different light intensities | pupil |
| When there is bright illumination, the pupil constricts (gets smaller) which is controlled by the ____________ division of the autonomic system | parasympathetic |
| When there is low light, the pupil dilates (gets larger) which is controlled by the ____________ division of the autonomic system | sympathetic |
| Range fractionation | uses different photoreceptors to handle different intensities; low – rods, high – cones |
| photoreceptor adaptation | each photoreceptor adjusts its level of sensitivity to match the average ambient level of light |
| Ultimately, the visual system concerned with ___________ in light, not absolute level of illumination | DIFFERENCES |
| Visual acuity | a measure of how much detail we see and is sharper in the center of the visual field (fovea) |
| The fovea in the center region of the ______ | retina |
| fovea- cones | high density of smaller, tightly-packed cones with high acuity but low sensitivity to light |
| fovea- rods | Rods are absent in the fovea |
| Rods are numerous in the ________ with high sensitivity to dim light but low acuity | periphery |
| Rods and cones vary in ____ and _________ across the retina | size and density |
| As with somatosensory cells in the back versus the lips, retinal cells in fovea and periphery have different __________ _______ | receptive fields |
| Another reason why the fovea has high acuity is because there are fewer ___________ to the light reaching the photoreceptors | obstructions |
| Optic disc | where blood vessels and ganglion cell axons leave the eye; creating a blind spot |
| Blind spot is due to what? | lack of photoreceptors in the optic disc |
| “_____ __________” fill in missing information so that we perceive an uninterrupted scene | Brain systems |
| Neural _______ travel from the retina to several brain regions | signals |
| Ganglion cell axons conduct ______ _________ to send information to the brain | action potentials (for the first time in retina not graded) |
| The axons make up the optic nerve, which eventually reaches the _________ _______ | occipital cortex |
| The optic nerves cross the midline at the optic ______, and are then known as the optic ______ | chiasm, tract |
| Most axons in the optic tract reach cells in the _______ __________ ________, the visual part of the thalamus | lateral geniculate nucleus (LGN) |
| Axons of LGN neurons form the optic _________ & terminate in the _______ _______ ________ of the occipital cortex | radiations, primary visual cortex (V1) |
| V1 is also called the ______ cortex due to its striped appearance in cross sections | striate |
| Each stripe, or striation, corresponds to converging ________ input | binocular |
| Visual areas outside of V1 are called __________ ______ | extrastriate cortex |
| The whole area that one sees is the ______ _______ | visual field |
| The retina represents a 2D map of the visual field, as a topographic projection, creating a _________ map | retonotopic |
| Much of the topographic projection of the visual field corresponds to the _____, giving high visual acuity | fovea |
| Retinotopic mapping makes it possible to predict a _______, or perceptual gap (region of blindness), due to injury | scotoma |
| Within a cortical scotoma person reports not being able to see, but still processes some visual information – __________ | blindsight |
| Blindsight describes what? | the inability to consciously perceive visual cues, yet be able to make visual discrimination |
| receptive field of retinal cells: Receptive field is ________ in fovea and periphery | different |
| Foveal has ______ and _______ cones leading to _______ receptive fields (better acuity) | more and smaller cones leading to smaller receptive fields |
| Periphery has ______ and ______ cones leading to _______ receptive fields (worse acuity) | larger and fewer cones leading to larger receptive fields |
| receptive field of retinal cells: Bipolar cells that connect photoreceptors to retinal ganglion cells respond differently to change in what? | neurotransmitter release |
| At rest, photoreceptors steadily release the excitatory neurotransmitter ________ | glutamate |
| What effect does glutamate have on bipolar cells? | Glutamate depolarizes one group of bipolar cells and hyperpolarizes another (Depends on the type of glutamate receptor they have) |
| At rest, rods and cones continually release ____________ | neurotransmitter |
| Size of ___________ determines amount of neurotransmitter released | hyperpolarization |
| When a photoreceptor is stimulated by light, it releases ____ excitatory glutamate. | less |
| glutamate _______ on-center bipolar cells and ________ off-center bipolar celss | inhibits, excites |
| glutamate inhibits on-center bipolar cells. What effect does this have on them? | they become depolarized and subsequently release glutamate. |
| glutamate excites off-center bipolar cells. What effect does this have on them? | they become hyperpolarized and release less glutamate. |
| On-center bipolar cells: turning ___ light in the center of the field excites the cells because they receives less glutamate and are depolarized; glutamate normally inhibits on-center bipolar cells | on |
| Off-center bipolar cells: turning ___ light in the center of the field excites the cells because they receive more glutamate and are depolarized; glutamate normally excites off-center bipolar cells | off |
| next, bipolar cells release glutamate, which always depolarizes ________ _____ | ganglion cells |
| Like bipolar cells, the receptive fields of retinal ganglion cells are concentric—a circular central area (center) with a ring around it, the ________ | surround |
| The center and its surround are always ____________ | antagonistic |
| On-center bipolar cells excite ___-center ganglion cells, when light is turned on | on |
| Off-center bipolar cells excite ___-center ganglion cells, when light is turned off | off |
| lateral inhibition | a process in which sensory receptor cells inhibit information from neighboring receptor cells, producing an effect of contrast at the edges of regions |
| lateral inhibition: Bipolar cells that relay information from photoreceptors to ganglion cells also ______ one another. | inhibit. When one bipolar cell is active it inhibits its neighbors |
| Lateral inhibition creates the experience of _____… even when they are not there. | edges |
| Receptive field is made up of the number of ________ cells that synapse on a single _______ ________ _________ cell | ganglion, Lateral Geniculate Nucleus (LGN) |
| About __% of macaque cortex is dedicated to visual processes; and __% in of human cortex is visual | 55%, 30% |
| Hubel & Wiesel (Nobel Med 1981) hierarchical model of visual cortex: | complex receptive fields are built from inputs from simpler ones |
| LGN neurons send their axons to ________ or _______ Cortical cells | Simple or Complex |
| LGN neurons (center/surround) send axons to __ | V1 |
| V1 cells require what? | more-specific, elongated stimuli |
| Simple cortical cells respond to what? | (also called bar or edge detectors) respond to an edge or bar of a specific width, orientation, and location |
| Complex cortical cells respond to what? | also respond to a bar of a particular width and orientation, but may be located anywhere in the preferred visual field (slightly more flexible/receptive than simple cells) |
| Researchers at work: What was Hubel and Wiesel's hypothesis? | that cells at higher levels of the visual system respond to progressively more complex stimuli |
| How did they test the hypothesis? | they attached a microelectrode to a cat's visual cortex and projected stimulus on the screen, then they compared receptive fields of neurons at each level to see how they related to one another |
| results: visual cells in the LGN | have concentric receptive fields and responds to light in the center of the cell's field |
| results: visual cells in the cerebral cortex (simply cortical cell) | shows orientation specificity (responded strongly when the stimulus was a vertical line) |
| results: visual cells in the cerebral cortex (complex cortical cell) | sensitive to motion: may respond only to motion in a particular direction (responded strongly only when the stimulus moves down) |
| conclusion: | neurons at each level of the visual system combine input from neurons at lower levels to make progressively more complex receptive fields |
| The spatial-frequency model says that the visual system analyzes the number of what? | light-dark (or color) cycles per degree of visual space |
| _________ neurons are optimized to detect light-dark cycles and respond maximally to repeating bars of light | Cortical |
| cortical cells respond even better to _________ patterns of light than to single bars of light | repeating |
| From area V1, axons extend to other cortical areas involved in perception of form: (3) | V2, V4, and the inferior temporal lobe (The receptive fields of these areas can be even more complex than V1 ) |
| __ is adjacent to V1 and has similar receptive fields | V2 |
| Some area V4 cells have strong responses to... (3) | concentric and radial stimuli and to color |
| The inferior temporal (IT) visual cortex responds to... | complex forms, sometimes combined with color and texture |
| IT: The complex receptive fields probably develop through __________ ane ___________ | experience and learning |
| Prefrontal cortex has some neurons that respond only to ______ | faces |
| All neurons in V5 (medial temporal area or MT) respond to _______ stimuli | moving |
| Damage to area MT in both hemispheres can lead to _________ | Akinetopsia (motion blindness) |
| Damage to color areas (such as V4) in only one hemisphere can result in a loss of... | color perception to one side of visual space (Achromatopsia) |
| Color Perception Stage1: ______ is created by the visual system as we detect differences in the wavelike movement (frequency of vibrations) of photons through space | Color |
| Differences in ________ cause us to perceive different colors, within a certain range | wavelength |
| faster vibration corresponds to the color _____ and slower vibration corresponds to the color _____ | blue, red |
| The colors we see are based on what wavelengths an object ________ and _________ | absorbs and reflects |
| An object’s color depends on which wavelengths are ________; the other colors are absorbed | reflected |
| Three dimensions of color perception: | brightness, hue, and saturation |
| brightness | varies from dark to light |
| hue | varies throughout all colors – usually what people mean by “color” |
| saturation | varies from full colors (saturated) to gray (paler) |
| To understand color perception we must understand ______ | cones |
| Color perception involves receptor cells with different ___________ | sensitivities |
| The trichromatic hypothesis of color perception (von Helmholtz) proposed what three things? | -Three different types of cones -Each responds to a different part of the spectrum -Each has a separate pathway to the brain |
| Color is recognized on the basis of which receptors are _________ | activated |
| The opponent-process hypothesis of color perception (Hering) proposed what two things? | -Four unique hues and four opposed pairs of colors -three physiological processes with opposed positive and negative value are the basis of color vision |
| Turns out that both the trichromatic hypothesis and the opponent-process hypothesis are partially correct and are part of current color vision theory which proposes what two things? | -Cones contain one of three pigments, together called opsins -These cells have overlapping but different peaks of sensitivity (in fact 2 of the 3 cone types respond to almost any wavelength) |
| Even peaks are not as far apart as Helmholz predicted, and do not necessarily line up with a specific _____. | color |
| None of the cones peak at the color ____ | red |
| Most objects stimulate at least _#_ types of cones | two |
| The nervous system compares the _______ of ___________ across receptor types and extracts more color information | degree of activation |
| Cones are not ______ detectors, rather they are wavelength detectors. | COLOR, wavelength (They are named for peak area of sensitivity along the spectrum of light, not hue) |
| Short (S): peak sensitivity at _#_ nm (nanometers) | 420 |
| Medium (M): peak sensitivity at _#_ nm | 530 |
| Long (L): peak sensitivity at _#_ nm | 560 |
| Some insects and birds are able to detect colors outside of the human range; made possible by a ___ cone (ultraviolet) | 4th cone (ultraviolet) |
| Most mammalian species have some color vision Differences are due to the types of __________ and the number of cone _____________ present | photopigments, photoreceptors |
| We most likely evolved 3 cones from 2, one on the __ Chromosome (M and L) and one on Chromosome _#_ (S) | X, 7 |
| colorblindness is more prominent in ______ | males |
| Why is colorblindness more prominent in males? | Genes encoding for photopigments are carried on the X chromosomes – in females a normal copy can compensate for a defective gene |
| Color Perception Stage2: Most ganglion cells and LGN cells fire in response to some __________ and are inhibited by others | wavelengths |
| A spectrally opponent (or color-opponent) cell has what? | opposite firing responses to different regions of the spectrum |
| +L/–M cell is stimulated above _#_ nm and inhibited at shorter wavelengths | 600 |
| ____________ are caused by spectral opponency | afterimages (caused by fatigue to cones, causing the brain, which is comparing different cones, to perceive the opponent color) |
| Spectrally opponent ganglion cells receive input from 2-3 different types of cones, through ________ cells | bipolar |
| Ganglion cells record the __________ in stimulation of these cones (excitatory or inhibitory), and respond to __________ in the corresponding range | difference, wavelengths |
| Spectrally opponent cells still cannot be called color cells because of what two things? | -They also send outputs to higher circuits for detection of form, depth, and motion -Their peak wavelength sensitivities do not correspond to wavelengths we see as the principal hues |
| Other ganglion cells are stimulated or inhibited by M and L cones, and detect _________ or __________ | brightness or darkness |
| Most important role of color perception is for understanding what? | which parts of a complex image belong to one object or another |
| Color Perception Stage3: Some ________ ________ _________ cells contribute to perception of color | spectrally opponent cortical |
| Perceptually opponent cells respond to what? | differences in color that we perceive; unlike LGN cells that respond to differences in types of cones |
| Visual cortical region V4 is rich in _____-sensitive cells | color (Blue, green, yellow, red…perceiving hue; important for color constancy ) |
| Two main processing streams originate in primary visual cortex: (2) | ventral processing stream and |
| A ventral processing stream, for identifying ________ | objects (what) |
| A dorsal stream for assessing the _________ of objects and guiding our movement toward them | the location of objects (where) |
| Damage to either processing stream can result in __________ | impairment |
| An optic ______ can cause difficulty in using vision to reach for an object | ataxia |
| Damage to the ventral stream causes problems in what? | in identifying objects |
| Visual neuroscience can be applied to alleviate visual _________ | deficiencies |
| Myopia develops if the eyeball does what? | grows too long, causing the eye to focus images in front of the retina |
| What could be the cause of Myopia? | Environmental factors such as indoor lighting. (Children who spend more time outdoors have a lower rate of myopia ) |
| Misalignment of the eyes (lazy eye) can lead to amblyopia, which is what? | reduced visual acuity not caused by optical or retinal damage |
| amblyopia: The primary visual cortex _________ information from one eye and it becomes functionally blind | suppresses |
| amblyopia: The eye muscles can be surgically adjusted to achieve better __________ | alignment |
| amblyopia: how can vision be preserved in both eyes? | If the weak eye is used regularly with the good eye covered |
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cmccartney2
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