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Why isn't perception a faithful representation
Perceptions are constructions by our CNS that are influenced by the nervous systems ability to learn and its dynamic integration, modulations, and flexible controls of stimuli
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Perception is heavily influenced by
top down processes
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Transduction
Transference of stimulus energy to neural firing
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transduction is accomplished by _____which are specialized according to ________
- sensory receptors
- mechanical, chemical, and thermal
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the source of sensory receptors are (4):
exteroreceptors (stimuli on body: skin, tongue) telereceptors (distant stim.: vision, audition, smell) - proprioceptors (muscles, joints, vestibular system) - interoceptors (internal organs)
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Sensory coding by 4 properties
- Modality (types of receptors)
- Position (location of receptors and pattern of firing)
- Intensity (# of neurons and frequency)
- Timing (Onset)
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Principles of Perception
- 1. Sensory receptors optimized to detect different stimuli
- 2. Sensory info is carried along labeled lines
- 3. center-surround organization
- 4. decussation of sensory fibers
- 5.topographic representation, but distorted
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different types of inputs
- optimized to detect different stimuli:
- touch
- taste
- smell
- hear
- see
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Sensory info is carried along labeled lines
- sensory info is categorized
- tactile info is perceived as its cannels through different parts of our brains
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center surround organization of the receptive field
- the way the perceptual field is organized
- the center needs to be stimulated for an excitatory effect
- peripheral surround portion has an inhibitory effect
- activity of a cell depends on what part is stimulating
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cell is at a
baseline activity so taht you can easily modulate activity.
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if you stimulate the surround
you go below baseline
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if you stimulate the center
its excitatory and you go above baseline
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if you activate both the surround and the center
you get a summed total effect
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the purpose of center surround is to
make perception more accurate- yes it comes from here and no it didnt come from here
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decussation of sensory fibers
left side is represented in the right and vice versa
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Topographic representation/but distorted
- A. Visual system: over representation of fovea
- B. Somatosensory system: over-representation of thumb, mouth, tongue
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Visual system
- Visual assocation cortex
- brain is building our visual perception
- distance is something you get from visual (auditory too)
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Sensory sytems
- 1.Visual
- 2.Auditory
- 3.Olfactory
- 4.Somatosensory
- 5.Gustatory
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Human visual system
- 1.50% of human brain is dedicated to vision
- 2. outgrowth of the brain
- 3. neural tube in ontogeny
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parts of the eye
- lens
- iris
- pupil
- anterior chamber
- cornea
- retina
- fovea
- blind spot
- optic nerve
- choroid
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Cones
respond to light of different colors, found more in fovea
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Rods
- sensitive to brightness, not colors
- found in periphery of retina
- important at night
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shooting stars at nigth
rods
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Process of Neural Transduction
- 1. After converting light into electrical signalsin their cell membranes, rods and cones transmit this information to other neurons in internal circuits in the retina for processing.
- 2. From these cells, messages go to the final retinal station, the ganglion cells, whose axons exit the eyeball at the optic disc and form the optic nerve, which contains about one million axons.
- 3. Because all the nerve fibers converge at the optic disc, no rods or cones are in this area and it forms a "blind spot"on the retina: this may be easily demonstrated
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choroid is the
thick blood cells
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retina is the
whole back lining
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fovea is the
subset of the retina that corresponds to the cetnral part of the visual field
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optic nerve is hte
nerves that come together and leave the visual field
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blind spot
the part of the visual scene that no longer has visual representation beceause there are no photoreceptors there due to the departure of the optic nerve
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nastagmis
the eyes are constantly moving so we never actually see our blind spot
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more rods in teh
periphery
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optic chiasm
where the decussation occurs and nerve fibers cross over
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optic tract
leads from the chiasm to the thalams (relay station)
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nuclei of the thalamus is the
Lateral Geniculate Nucleus (LGN)
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visual path
- optic nerve
- optic chiasm
- optic tracts
- thalamus
- LGN
- optic radiations
- higher visual areas
- primary visual cortex
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left visual field corresponds with
right visual field corresponds with
- right temporal retina
- left nasal retina
- left temporal retina
- right nasal retina
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hemifield closest to the fovea is the
right or left medial hemi fields
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hemi-field closest to the peripheral portion
lateral right and left hemi fields
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temporal hemi retina represents
contralateral hemifields medial portion
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nasal hemi retina represents
ipsilateral fields lateral portion
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the relay station for hte perceputal system is
thalamus (LGN)
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which hemi retina crosses over and where
the nasal hemi retina at the optic chiasm
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Vision is generated by photoreceptors in the ____, a layer of cells at the back of the eye.
retina,
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The information leaves the eye by way of the ___, and there is a partial crossing of axons at the ____.
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After, the axons are called the __D__. The __D_ then lead to the __E_, where all the axons must synapse.
- optic tract
- lateral geniculate nucleus,
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From there, the __E__axons fan out through the deep white matter of the brain as the __F__, which will ultimately travel to __G__, at the back of the brain.
- LGN axons
- optic radiations
- primary visual cortex
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what type of organization in V1
Columnar
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Within a cortical module:
set of orientation columns, ocular dominance columns, and blobs … all with similar receptive fieldsWithin
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study what each eye sees if there is a lesion at a certain spot! reminder!
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Receptive Field
area of the retina that when stimulated with light, changes the cells membrane potential
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Retinotopic map
neighboring cells in the retina feed information to neighboring places in their target structures
capture everything in visual scene and corresponds with different visual area
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LGN has what type of arrangement
annual and center surround arrangement for receptive field
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Receptive Field tells
: What partof the visual field does a neuron respond to?
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Selectivity tells
what kind of visual information a neuron responds to
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V1 has edge detectors
cars taht are representations of the receptive field
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Parallel processing
Different kinds of visual information are processed in parallel by different neural populations
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What makes a visual region?
- Cytoarchitecture
- Intracortical connections
- Retinotopy
- Functional properties
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Retino-collicular pathway
- • “rough and ready” vision
- • responsible for “blindsight”when main pathway is damaged
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visual cortex to parietal lobe
where/how
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visual cortex to temporal lobe
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M1
part that allows us to detect motion in the visual system
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Olfaction and Gustation
Pleasant tastes and odors of food, drink, andflowers; noxious odors of decay and danger(predators); bitter tastes of toxic substances
Chemical senses very old, perhaps the first typeof sense to evolve in cells (chemotaxis occurs inbacteria and single cells)
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if we want to know where to present stimuli and what is the selectivity process
we present bars of light in different orientations and find the preferred orientation
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if there is no light in the receptive field in a certain location
tehre is no stimulus so baseline firing
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V1 is sensitive to
bars of light of different orientations
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V4
contains cells that fire maximally for differnt types of colors
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serial-parallel processing
different regions care about differnt features(color contour, motion)
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Olfaction
- humans are microsomatic
- sense of smell relatively poor compared to other animals
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main olfaction component
glomeruli (similar to retina)
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glomeruli...
clump together and axons leaving create the olfactory buls
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olfaction is different because
does not have a relay to the thalamus
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olfactory cortices
- primary olfactory cortex
- orbitofrontal cortex (secondary olfactory area)
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odorant with high rate of absorption plus high air flow entering nostril equals
large neuronal response
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odorant with low rate of absorpotion plus low flow of air
equals large neuronal response
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smells are coded by
don't know yet but elicit spatiotemporal patterns of activation in the olfactory bulb
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anosmia
loss of sense of smell
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olfactory hallucinations can be
result of temporal lobe seizures
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odorants and tastes are part of
chemical stimulations
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tastes
- sour
- salty
- bitter
- sweet
- umami
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how are different tastes coded?
- little is known, taste nuerons broadly attuned to taste qualities
- no distint topographic map
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gustatory properties
- taste bud
- taste nueron/nerve
- tongue
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Audition
- transduction stimulti connect to neuronal response input (vibrations sound waves),
- this stimulates the timpanic membrane
- moves the fluid that moves the hair cells in cochlea to ove
- neural transductions happens in the hair cells
- axons leave through auditory nerves
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pathway audition
- auditory nerve
- cochlear nuclei
- superior oliveri nucleus
- auditory cortex
- medial geniculate nucleus
- inferior colliculus
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auditory pathways summarized
- Auditory pathway:–primary receptors (hair cells)
- •inner ear (in the cochlea: the organ of Corti)–intermediate-level relays
- •medial geniculate nucleus of thalamus
- •inferior colliculus in the brainstem–primary cortical representation
- •auditory cortex in temporal lobe–higher integrative areas
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sound characteristics
frequency and amplitude
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organization of auditory cortex
tonotopic
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