Chapter 6: Vision Flashcards
Sensation
Process in which specialized cells of nervous system detect environmental stimuli and transduce their energy into receptor potentials
- Involved cells of nervous system that are specialized to detect stimuli from environment
Perception
Conscious experience and interpretation of info from senses
Electromagnetic spectrum
Shortest Wavelengths—> Longest Wavlengths
Gamma rays X- rays Ultraviolet rays Visible spectrum Infrared rays Radar Television and radio
Visible Spectrum
400 nm- purple
500 nm- blue
600 nm- yellow
700 nm- red
Hue
Wavelength of light
Brightness
Intensity of light
Saturation
Relative purity of light
Sensory Receptors
Specialized neuron that detects a particular category of physical events
Sensory Transduction
Process by which sensory stimuli are transduced into slow, graded receptor potential
Receptor Potential
Slow, graded electrical potential produced by receptor cell in response to physical stimulus
Retina
Neural tissue and photoreceptive cells located on inner surface of posterior portion of eye
Eyes are held in place and moved by […] attached to […]
Six extraocular muscles; sclera
Sclera
white outer coat of eye
Opaque and doesn’t permit entry of light into eye
Conjunctiva
Mucous membranes that line eyelid and fold back to attach to eye
Cornea
Outer layer
Transparent
Pupil
Regulates amount of light that enters eye
Accomodation
Changes in thickness of lens of eye, accomplished by the ciliary muscles, that focus images of near or distant objects on retina
Main part of eyes are filled with […]
Vitreous humor
Photoreceptor
One of receptor cells of retina
Transduces photic energy into electrical potential
Rod
Sensitive to light of low intensity
Cone
Maximally sensitive to one of three different wavelengths of light and hence encodes color vision
Bipolar cells
Convey info from photoreceptors to ganglion cells
- middle layer of retina
Ganglion cells
Receives visual info from bipolar cells
- Axons give rise to optic nerve
Horizontal cells
Interconnect adjacent photoreceptors and outer processes of bipolar cells
Amacrine cells
Neuron in retina that interconnects adjacent ganglion cells and inner processes of bipolar cells
We have […] rods than cones
More
[…] provide us with most of visual info about environment
Cones
Fovea
Region of retina that mediates most acute vision of birds and higher mammals
- only contains cones
Characteristics of Cones
- Most prevalent in central retina; found in fovea
- Sensitive to moderate to high levels of light
- Provide info about hue
- Provide excellent activity
Characteristics of Rods
- Most prevalent in the peripheral retina; not found in fovea
- Provide only monochromatic info
- Provide poor acuity
Optic Disk
Location of exit point from retina of fibers of ganglion cells that form optic nerve
- Responsible for blind spot
Transduction
Process by which energy from environment is converted to change in membrane potential in neuron
Photopigments are embedded in […]
Lamellae
Photopigments
Protein dye bonded to retinal, a substance derived from Vitamin A
- Responsible for transduction of visual info
Lamellae
Layer of membrane containing photopigments
- Found in rods and cones of retina - Thin plates of membrane that make up outer segment of photoreceptors
Each photoreceptor consists of outer segment connected by […] to inner segment
Cilium
Photopigment=
Photopigment= opsin+ retinal
- Opsin- class of protein that constitutes photopigments
- Retinal- chemical synthesized from Vitamin A (lipid)
Rhodopsin
Particular opsin found in cones
- Exposed to light —> breaks info into rod opsin and retinal - Triggers cascade of intracellular events that hyperpolarize photoreceptor membrane (first step in visual processing)
Receptive Field
Portion of visual field in which presentation of visual stimuli will produce an alteration in firing rate of particular neuron
- place visual stimulus must be located to produce response in neuron - location of receptive field of particular neuron depends on location of photoreceptors that provide it with visual info
Fovea and Periphery
- At periphery of retina many individual receptors converge on single ganglion cell
- Relatively large area of visual field
- Fovea contains approximately equal numbers of ganglion cells and cones
Types of Eye Movements
- Vergence Movement
- Saccadic Movement
- Pursuit Movement
Vergence Movement
Cooperative movement of eyes, which ensures that image of an object falls on identical portions of both retinas
Saccadic Movement
Rapid, jerky movement of eyes used in scanning visual scene
Pursuit Movement
Movement that eyes make to maintain an image of moving object on fovea
Optic Nerves
Bundles of axons from retinal ganglion cells exit the eye and convey info to lateral genicular nucleus
- Located at back of eye - Bundles axons of ganglion cells
Dorsal Lateral Geniculate Nucleus (LGN)
Group of cell bodies within lateral geniculate body of thalamus receives input from retina and project to primary visual cortex
Optic Chiasm
Cross- shaped connection between optic nerves, located below the base of brain, just anterior to pituitary gland
Visual Pathway
Pathway of visual processing from retina of LGN to striate and extrastriate cortical regions
- Journey of info from light detection in retina to experiencing complex visual scenes
- Photoreceptors —>LGN —> primary visual cortex (V1) —> visual association cortex (V2)
Visual Association Cortex (V2, extrastriate cortex)
Receives fibers from striate cortex and from superior colliculi and projects to inferior temporal cortex
- responsible for combining information from the striate cortex to allow an individual to perceive objects and entire visual scenes - receives info from "lower" regions and passes info to "higher" regions
Lateral Geniculate Nucleus Layers
Layers 1, 4, 6= receive input from retinal ganglion cells of contralateral (opposite) eye
Layers 2, 3, 5= receive input from ipsilateral (same side) eye
Magnocellular Layer
2 inner layers in dorsal LGN
- Transmit info necessary for perception of form, movement, depth, and small differences in brightness to V1
Parvocellular Layers
4 outer layers in dorsal LGN
- Transmit info necessary for perception of color and fine details to V1
Koniocellular Sublayer
Beneath other two types in dorsal LGN
- Transmits info from short-wavelength (“blue”) cones to V1
Striate Cortex
- First cortical region involved in combining visual info from several sources
- about 25% of striate cortex is devoted to analysis of info from fovea
- receives visual input from LGN and performs additional processing of information
- transmits information to extrastriate cortex (V2)
Dorsal Stream
System of interconnected regions of visual cortex involved in perception of spatial location, beginning with striate cortex and ending with posterior parietal cortex
- Processes where object is located - Speed and direction of movement
Ventral Stream
System of interconnected regions of visual cortex involved in perception of spatial location, beginning with striate cortex and ending with inferior temporal cortex
- Processes what an object is and its colors
Protanopia
Inherited form of defective color vision in which red and green hues are confused “red” cones are filled with “green” cone opsin
- involve genes on X chromosomes
Deuteranopia
Inherited form of defective color vision in which red and green hues are confused “green” cones are filled with “red” cone opsin
- involve genes on X chromosomes
Tritanopia
Inherited form of defective color vision in which hues with short wavelengths are confused “blue” cones are either lacking or faulty
Monochromatic vision
retina completely lacks cones
Yellow-blue ganglion cells are excited by […]
“Red” and “green” cones
Negative Afterimaging
Image seen after portion of retina is exposed to intense visual stimulus
- Consists of colors complementary to those of physical stimulus
Complementary Color
Colors that make white or gray when mixed together
Rebound Effect
When ganglion cells are excited or inhibited for prolonged period of time, they later fire faster or slower than normal
Parvocellular system receives info only from […]
“Red” and “green” cones
Addition info from […] cones transmitted through koniocellular system
“Blue”
Cells in parvocellular system
Show high spatial resolution and low temporal resolution
Cells in koniocellular system
Doesn’t provide info about fine detail
Cells in magnocellular system
Color blind
- can detect smaller contrasts - sensitive to movement - dorsal stream
Cerebral Achromatopsia
Inability to discriminate among different hues
- Caused by damage to visual association cortex - no disruption of visual acuity
Visual Agnosia
Defects in visual perception in absence of blindness
- Caused by damage to extrastriate cortex - Unable to identify common items by sight, although visual acuity remains
Lateral Occipital Complex (LOC)
Region of extrastriate cortex involved in perception of objects other than people’s bodies and faces
Prosopragnosia
Failure to recognize particular people by sight of their faces
- Congenital prosopragnosia show decreased connectivity within occipito-temporal cortex
Fusiform Face Area (FFA)
Located in inferior temporal lobe and involved in perception of faces and other complex objects that require expertise to recognize
- development of FFA is altered in people with autism spectrum disorder and Williams syndrome
Williams Syndrome
Genetic condition caused by mutation on chromosome 7
- FFA is enlarged
Monocular Vision
Perspective, relative retinal size, loss of detail through the effects of atmospheric haze, and appearance of movement
Binocular vision
Vivid perception of depth though process of stereopsis
- Most neurons in striate cortex are binocular and respond to retinal disparity - Density- sensitive neurons are found in dorsal stream
Retinal Disparity
Fact that points on objects located at different distances from observer will fall on slightly different locations on two retinas
- Provides basis for stereopsis
Dorsal Stream
Spatial perception
- damage = deficits in visually guided movements
Ventral Stream
Object perception
Posterior Parietal Cortex
Highest level of dorsal stream of V2
- involved in perception of movement and spatial location
Parietal Cortex
- Receives info from visual, auditory, somatosensory, and vestibular info
- Involved with guiding actions
Area V5/ Area MT
Contains neurons that respond to movement
- Receives input directly from striate cortex - Receives input from superior colliculus (involved in visual reflexes and eye movements)
- found in inferior temporal sulcus
Area MST receives info about […]
Movement from V5
- helps analyze optic flow
Optic Flow
Complex motion of points in visual field cause by relative movement between observer and environment provides info about relative distance of objects from observer and of relative direction of movement
Akinetopsia
Inability to perceive movement, caused by damage to area V5
[…] is involved in perceiving form from motion
Superior temporal sulcus
