Lec 3: Perception Lec 4: Visual System Readings: Sacks & McCloskey
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| Perception | the means by which info acquired from the environment via the sense organs is transformed into experiences
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| stages in perception | distal stimulus > proximal stimulus > percept
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| distal stimulus | the thing at a distance from you in the world you are trying to perceive
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| proximal stimulus | the pattern that the distal stimulus projects on to our sensory organs
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| percept | our mental representation
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| lack of correspondence | when the percept does not correspond to the distal stimulus
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| paradoxical correspondance | when the proximal stimulus does not correspond to the distal stimulus, but the percept does
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| perceptual constancy | our perception of an objects features remains constant even when viewpoint (and proximal stimulus) changes
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| size constancy | perception of size doesn't change with distance
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| color constancy | perception of color doesn't change with light
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| shape constancy | perception of shape doesn't change with angle
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| Direct perception (stimulus theory) | environment provided all necessary cues
our brains are pre-wired to pick up cues
stimulus information is almost always unambiguous
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| constructivism | perception uses data from the world and our prior knowledge and expectations
sensory information is often ambiguous (must rely on knowledge/expectations)
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| bottom-up processing | processing that is driven by the external stimulus, rather than internal knowledge
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| direct perception claims that perception is purely | ...bottom-up
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| top-down processing | processing that is driven by knowledge & expectations
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| constructivism claims that perception is | both a bottom-up and top-down process
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| depth perception | the distal stimulus is 3D but the proximal stimulus on the retina is 2D yet the perceptual experience is 3D
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| depth perception is an example of | ...paradoxical correspondance
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| examples of monocular depth cues are | linear perspective, shape, relative size, interposition, shadows, accommodation
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| monocular depth cues | can see depth cues with only 1 eye
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| examples of binocular depth cues are | retinal disparity
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| interposition | if something is close to you it will obstruct our view of what is behind it
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| binocular depth clues | can see depth cues with both eyes
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| ganglion cell layer is comprised of | ... ganglion cells
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| bipolar cell layer is comprised of | ... amacrine cells, bipolar cells, horizontal cells
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| photoreceptor layer is comprised of | photoreceptors (rods and cones)
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| rods and cones are | photoreceptors
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| rods detect | brightness
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| cones detect | colors
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| what kind of reaction takes place inside photoreceptors when exposed to light | photo-chemical reaction
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| cones are concentrated in the | ... fovea
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| color vision problems are because what photoreceptor isn't working properly | cones
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| electrical potential is | the potential to do work
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| threshold | potential must get above a threshold level for neuron to fire
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| firing | generating an action potential
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| all-or-none | action potential always has the same strength. either you get all of if (if above threshold) or none of it
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| propagation | once past threshold, active process (ion pumping) propagates action potential down axon
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| refractory period | short period after firing before neuron can fire again. used to restore the neuron back to resting state & "recode" ions
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| neural transmission | when one neuron fires it can cause neighboring cells to fire or prevent them from doing so so signal can move from one cell to another
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| neurons communicate by sending neurotransmitters across synapses which is triggered by | an action potential when it reaches an axon's end
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| neural transmission is | electrochemical
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| neural transmission involves | an electrical action potential within cells and a chemical neurotransmitter between cells
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| when neurotransmitter is released into synapses | it binds to receptors on target neuron
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| excitatory neurotransmitters | increases the potential & brings it closer to firing
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| inhibitory neurotransmitters | decreases the potential & keeps it from firing
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| summation | if combined effects at all synapses take potential across axon above threshold, then neuron will fire an action potential
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| on-center, off-surround cells | turns on when light is in the center, and turns off when light is surrounding the center
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| off-center, on-surround | turns off when light is in the center & turns on when light is in the surrounding area
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| center-surround organization | are antagonistic & tend to cancel each other out
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| functions of center-surround organization | point detection, edge detection, light-on-dark or dark-on-light
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| lateral geniculate | composed of magnocellular & parvocellular cell layers
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| magnocellular cells | have a transient response (lasting only a short period of time) and large receptive field, and track movement/location
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| parvocellular cells | have a sustained response (maintained at length without interruption or weakening), small receptive field and track patterns/color/form
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| functions of a simple cell | responds to a bar of light, specific orientation, specific retinal position
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| functions of a complex cell | edges, movement, responds to bars of light that are moving
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| hypercomplex cells responds to | very specific shapes, corners, gaps
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| edge detection | edges in images correspond to edges of real-life objects, offer depth cues, allow parts of 3D objects to be identified
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| dorsal "where" pathway | goes from the occipital lobe to parietal lobe
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| ventral "what” pathway | goes from occipital lobe to temporal lobe
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| positron emission tomography | mental activity leads to neural activity which causes blood flow, which leads to more radioactive tracer and more positrons emitted
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| a spatial (where) task should activate | occipital and parietal regions
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| an object (what) task should activate | occipital and temporal regions
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| there is not a grandmother cell | a neuron that has a very specific receptive cell that only fires when you are hearing/seeing/thinking of your grandma
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| the sacks reading described Dr. P who | could not recognize faces & would often mistake inanimate objects as being people, could not see the whole picture only details, difficulties with lefties & visual field deficits, could not make a cognitive judgement but could produce cognitive hypotheses
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| McCloskey reading focused on A.H. a | women with impairment in localizing objects from vision
severe/drastic impairment when asked to reach for objects in her visual field
reached for objects with ballistic movement
impairment in up/down & left/right localization
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| ballistic movement | without changing direction in mid movement
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| the ability to identify objects even when mislocalizing them | adds to evidence that location & identity are processed separately in the visual system
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| errors in a reflection across a vertical/horizontal axis suggests | that visual location representations have multiple components & some may be correct while others are incorrect
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| transient subsystem | specialized for processing rapidly changing visual stimuli
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| sustained subsystem | specialized for processing steady, long-duration, stationary stimuli
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| visual allochiria | an object present in 1 visual half-field is perceived at the corresponding point in the opposite half-field
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| visual allochiria is a rare symptom associated with | parietal or Pareto-occipital pathology
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| if an illusory image is palinoptic then it is | persisting after stimulus was no longer in view
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| in visual disorientation a person | can recognize objects even when can't localize the objects
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| visual disorientation doesn't have a | reflection across a vertical/horizontal axis
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| visual allochiria & disorientation can occur | with acquired brain damage
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| if visual representations are inaccurate in capturing properties | people will see a different visual scene than the real scene
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