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Biological Psychology > Vision > Flashcards

Vision Flashcards

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1
Q

LIGHT SOURCES

A
  • sun/stars/heated objects/bioluminescence
  • sunlight filtered via atmosphere; reflected from surfaces
  • light = electromagnetic energy w/wave properties (ie. light ray radiation) & charged particles (photons/quanta)
  • difs in intensity/wavelengths
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2
Q

PSYCH PROCESS REGULATION IN DAY/NIGHT

A
  • light levels detected via eye sent to SCN (suprachiasmatic nucleus) in hypothalamus
  • special ganglion cell class in retina containing photopigment melanopsin (sensitive to short wavelengths (blue light); keeps circadian clock in SCN accurately timed w/natural daily light cycles
  • pineal gland = unpaired midline structure near epithalamus; produces melatonin (from serotonin) during darkness
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3
Q

HUMANS/ANIMALS’ IMAGE-FORMING EYES

A
  • eyes evolved via gradual improvement sequence for detecting directions/forming image
  • advanced eye types evolved several times in animal kingdom
  • fossil records date back to Cambrian explosion (540mya)
  • faster movement/navigation in animals required better vision
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4
Q

VISION

A
  • detecting/interpreting electromagnetic radiation patterns observer is exposed to
  • image-forming eye/visual pathways in observer’s brain
  • moving eyes to analyse/acquire visual info
  • execution of visually-guided behs/visual memory recall
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5
Q

SEEING

A
  • conscious/unconscious visual perception detected in beh responses/described via language (in humans)
  • requires light presence in visible range of wavelength spectrum (can’t see if too dark)
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6
Q

HOW DO WE SEE?

A
  • visual field = object/person seen against background in area of space
  • retinal projection = inverted 2D image distorted by eye curvature
  • perceived image = 3D/large/upright/stable/non-distorted/colourful
  • projections onto:
    1. retina = 1d visual angle = 0.288mm (ie. thumb nail when extending arm = 1.5d)
    2. fovea = 0.6mm
    3. horizontal retina = 32mm
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7
Q

FIRST PROCESSING STEPS IN RETINA

A
  • photoreceptors/bipolar cells = graded potentials

- ganglion cells = long axons form optic nerve; action potentials

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8
Q

VISUAL PATHWAYS

A
  • projections from retina to other brain areas
    GENICULATE-STRAITE PATH
    retina -> LGN (lateral geniculate nucleus) of thalamus -> VI (primary visual cortex) -> higher visual cortex areas (90% retinal projections)
  • VI required for conscious visual experiences
    EXTRAGENICULATE PATH
    retina -> SC (superior colliculus) -> several projections to areas of higher visual cortex/pulvinar nucleus of thalamus (eye movement control/visual attention; 10% retinal projections)
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9
Q

VISUAL FUNCTIONS IN BLIND HUMANS/PRIMATES

A

STOERIG (1999)

  • VI damage causes cortical blindness (conscious vision loss); patients performed visually-guided behs (ie. grasping/pointing to object location/avoiding obstacles) correctly STATSIG
  • this is blindsight
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10
Q

LIGHT PROJECTIONS ON RETINA

A
  • vision starts w/formation/processing of images in eye
  • rod/cone cells form 2D array in retina
  • human retina = ca100m rods/4m cones/1m ganglion cells
  • 108MP (megapixel) modern camera = poor technical imitation of retina; has much larger sensor area/more sophisticated processing circuits
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11
Q

FIRST STEPS IN IMAGING PROCESSING

A
  1. Lens to focus image
  2. Aperture to control light entering (iris)
  3. Pixels to register image (photoreceptors)
  4. Filtering media (glass body/macula/pigment)
  5. Filter to protect lens (cornea)
  6. Lens cover for when not used (eye-lid)
  7. Cleaning mechanism (tears)
  8. Processing algorithms (retinal interneurons)
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12
Q

DIM-LIGHT VISION (RODS)

A
  • doesn’t use central fovea
  • acuity = proportional to receptor cell density
  • vision acuity = highest in fovea; decreases towards retina periphery
  • eye movements position fovea in visual field positions where most important = collect high-acuity info
  • at night high acuity sacrificed for sensitivity; more advantageous to have no rods in fovea
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13
Q

COPING W/CHANGING LIGHT LEVELS

A
  • duplex retina in vertebrate eye
  • cones specialised for day vision (1-100m times brighter in sunlight > moonlight)
  • rods specialised for night vision
  • both detect light in similar way (opsins/metabotropic transduction) BUT rods = ^ sensitive
  • opsin = light-sensitive protein (G-protein coupled receptor molecule) in photoreceptors’ membrane; bound to chromophore retinal (for transduction)
  • 3 functional cone classes: S-/M-/L-
  • cone opsins differ in wavelength; specific affinity to absorb light (S/M/L opsins); only one type p/cone
  • 1 functional rod class = same opsin (RHI (rhodopsin))
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14
Q

EYE MOVEMENT

A
  • saccades (jumps)/fixations (stops)
  • 2-3 saccades p/second
    YARBUS (1914-1986)
  • developed first methods to accurately measure eye movements/viewing beh
  • direct fovea to collect info about visual scene
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15
Q

CONTROLLING EYE MOVEMENT

A
  • field of view defined by position/orientation of eye ball/head/body
  • can move eyes/head separately; many animals cannot (ie. insects/birds); move head/body to see
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16
Q

STABILISING GAZE FOR BETTER VISION

A
  • movement described as combo of 3 translation/rotation directions each
  • larger/faster head movements render vision blurry when eyes can’t compensate
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17
Q

DIFFERENT EYE MOVEMENTS

A

SACCADES
- eye moves v quickly to new position between periods of gaze stabilisation (fixations) to scan scene across entire view field
SMOOTH PURSUIT MOVEMENTS
- slower; keeps moving stimulus on fovea
OPTOKYNETIC NYSTAGMUS
- brings eye back from peripheral to more central position after following large-scale moving stimulus (while head static)
VESTIBULO-OCULAR MOVEMENTS
- compensate for head movement by moving eye same distance but in opposite direction to maintain constant field of view

18
Q

ATYPICAL EYE MOVEMENT: DYSLEXIA

A

PRADO et al (2007)

  • difficulties in reading words/sentences/text
  • longer/more durations of fixations during reading; shorter saccades
  • shorter visual attention span impacts eye movement patterns
19
Q

ATYPICAL EYE MOVEMENT: SCHIZOPHRENIA

A

BENSON et al (2012)

  • difficulties tracking objects w/smooth-pursuit eye movements
  • rapid/jerky eye movements
  • complex analysis of eye movements using mathematical modelling = possibly future avenue for developing diagnostic tool
20
Q

BRAIN CIRCUIT FOR SACCADIC EYE MOVEMENTS

A
  • saccadic eye movements directed via midbrain/cortex
  • conscious control of eye movements comes from FEF (cortical frontal eye fields)
  • automatic control of eye movements comes from superior colliculus
  • both use vision input BUT also auditory/somatosensory systems
21
Q

COMPLEX VERTEBRATE RETINA STRUCTURE

A
  • functional classes of retina cells:
    1. 4 photoreceptor classes (3 cones/rods)
    2. 50-70 horizontal/bipolar/amacrine cell classes
    3. 20-30 ganglion cell classes
  • first visual processing stages:
    1. Edge detection in visual scenes.
    2. Edge enhancement in patterns.
    3. Filtering of spatial/wavelength/movement/directional info
22
Q

LATERAL INHIBITION IN RETINA

A
  • photoreceptors in retina inhibit neighbours via bipolar/horizontal cells
  • edges enhanced for better detection/object discrimination/foreground/background in visual scenes
  • if light falling on retinal neuron group = uniform, their reciprocal inhibitions cancel each other out w/o effects
  • when edge (dark/light illumination) created, cells on both sides strongly influence each other; changes signals so much stronger contrast coded than physically existing
  • more distant cells unaffected so edge perception = enhanced
23
Q

IDENTIFYING SPATIAL RELATIONSHIPS/OBJECT PROPERTIES

A
  • w/o context cues we perceive physical reflectance of surfaces carrying little info
  • edges/shadows provide context info about object spatial structure/spatial relationships between objects
24
Q

SEGRAGATED ROD/CONE-CONNECTED PATHWAYS IN RETINA

A

HORIZONTAL CONNECTIONS
- horizontal cells
- amacrine cells
VERTICAL CONNECTIONS
- fovea = 1 cone: 1 bipolar
- periphery = many cones: 1 bipolar; many bipolars: 1 ganglion/rods BUT connect to rod bipolar cells/other ganglion cell classes
- cones/rods converging on bipolar cell form its receptive field; similarly ganglion cell field formed via all converging bipolar cells

25
Q

IMPORTANT FILTERS IN RETINA TO DETECT/ENHANCE EDGES

A
  • objects can be dark against bright background/bright against dark background
26
Q

ON/OFF CENTRE CELLS FILTER VISUAL INFO

A
  • ON/OFF-centre bipolar cell = non-spiking
  • ON/OFF-centre ganglion = spiking
    OFF/ON SURROUND
  • formed by lateral inhibition from neighbouring cells (ie. cones) that surround cell representing receptive field centre
27
Q

ON/OFF CENTRE CELLS x LIGHT/DARK RATIOS

A
  • respond to light/dark ratios
  • at rest, ganglion cell fires action potentials (spikes) at spontaneous rate
  • ON-centre bipolar depolarisation -> ON-centre ganglion cell increases spike rate
  • OFF-centre bipolar cell hyperpolarises -> OFF-centre ganglion decreases spike rate
28
Q

GANGLION CELLS x UNIFORM ILLUMINATION

A
  • don’t respond
  • when light spot covers whole ON-centre, ganglion responds w/highest spike rate
  • when light ring covers all surround BUT not ON-centre, ganglion responds w/lowest/no spike rate
  • when whole receptive field equally stimulated, ganglion rests/fires w/spontaneous frequency
29
Q

INVERTED RESPONSES IN OFF-CENTRE GANGLIONS

A
  • also respond to light/dark ratios BUT not uniform illumination
  • inverted responses
  • if spot illuminates centre of OFF-centre ganglion, spike rate reduces
  • if spot illuminates ON-surround of OFF-centre ganglion cell, spikes increase
  • if whole receptive field illuminated, ganglion rests/fires spontaneously
30
Q

RETINA AS COMPLEX NEUROPILE W/MANY CIRCUITS

A
  • blind spot = exit of ganglion cell axons/optic nerve in back of eye
  • first visual path stage = photoreceptors/retinal neurons
  • retina performs first filtering/decomposition of scene; codes local/global contrasts; detects/enhances features ie. edges; lateral inhibition/vertical & horizontal connectivity from circuits needed for tasks
  • early processing circuits (ie. centre-surround receptive fields) help separate coding of visual features in parallel paths/streams in visual system
  • we don’t notice consciously most of seeing BUT paradoxically we can sometimes become aware (ie. visual illusions)
31
Q

P/M-GANGLION CELLS PROJECT TO DIFFERENT LAYERS IN LGN

A

P-GANGLION CELLS
- project to parvocellular layer in LGN
- small RFs; slower conduciton speed; high acuity; poor response to transient stimuli; colour sensitive
M-GANGLION CELLS
- project to magnocellular layer in LGN
- large RFs; higher conduction speed; motion sensitive; low acuity; no colour discrimination

32
Q

P/M-PATHWAYS FROM RETINA TO VI

A
  • p-pathway = parvocellular (small soma)
  • m-pathway = magnocellular (large soma)
  • neurons of both project to dif VI layers:
  • m-cells project -> layer 4ca
  • p-cells project -> layer 4c & 2/3 interblob
33
Q

SPATIAL LAYOUT OF RETINAL GANGLION CELL PROJECTIONS

A
  • preserved

- retinal ganglion cells project retinotopically to each LGN layer; right/left eye projections also segregated in LGN

34
Q

NEURON RESPONSES IN VI ORIENTATION COLUMNS

A
  • when recording from neurons of particular orientation column, some neurons respond to orientation columns only in small visual field part corresponding to their receptive field
  • dif to retinal ganglion cells; neurons fire at maximal spike rate when bar stimulus shows their preferred orientation
  • other VI cortical cells respond w/maximal spike rate to preferred motion direction of bars/patterns
35
Q

SIMPLE/COMPLEX CELL FUNCTIONS

A
  • analysis of contours/boundaries/objects
  • shape/positional invariance
  • contour enhancement for object identification
  • VI fundamentally important for conscious vision/perception
36
Q

VI COLUMNAR STRUCTURE

A
  • along w/6 horizontal layers, neurons in VI further segregated into functionally distinct hypercolumns
  • hypercolumn (1mm^2) composed of:
    1. 1 left & right eye ocular dominance column
    2. several orientation columns (rainbow colours) containing simple/complex cells that respond to shape orientations (ie. a bar)
    3. blobs (drawn via cylinders) = structures in layers II/III of VI involved in colour vision
  • retinotopic organisation; spatial mapping arising from projection of image onto retina preserved in VI
37
Q

2 VISUAL STREAMS IN PRIMATE/HUMAN BRAIN CORTEX

A

PARIETAL CORTEX
- dorsal stream/pathway = interacting w/world via V5/MT
INFERIOR TEMPORAL CORTEX
- ventral stream/pathway = making sense of world via V4

38
Q

V4

A

TANAKA et al (1991)

  • responds to more complex stimuli than V1/V2
  • strong responses in V4 (red/orange strongest)
  • strong responses in anterior area of inferior temporal cortex
39
Q

OBJECT RECOGNITION

A

DI CARLO et al (2012)

  • discrimination (<200ms)
  • object recognition also when object position/size/viewpoint/visual context changes
  • categorisation
  • ventral cortical stream = critical for object recognition
  • V1-V4 = occipital lobes
  • IT = inferior temporal cortex (temporal lobes)
  • colour-portion dedicated to central 10deg of visual field response latencies
40
Q

EYE-HAND CO-ORDINATIONQ

A
  • guiding hand movements requires 2 processes:
    1. Deciding which objects to interact w/.
    2. Interacting w/objects skillfully.
  • require dif info type from both dorsal/ventral streams
41
Q

SUMMARY I

A
  • retina = 1st visual processing stages (edge detection in visual scenes/edge enhancement in patterns/spatial filtering/wavelength/movement/directional info)
  • lateral inhibition in retinal cells responsible for edge enhancement (Matchband effect)
  • edges/shadows provide context info about spatial structure of objects/spatial relationships between objects
  • cones/rods converging on bipolar cell form its receptive field; cones/rods/bipolars converging to ganglion cell form ganglion’s receptive field; fields are often larger in periphery (blurrier vision via low acuity)/smaller in fovea (helps achieve highest acuity)
  • some bipolar/ganglion cell classes have centre-surround receptive field; can be ON-centre/OFF-surround (lateral inhibition from surround receptors) or OFF-centre/ON-surround (lateral inhibition from photoreceptors in centre of centre-surround receptive field)
42
Q

SUMMARY II

A
  • ganglion cells respond to light/dark rations (ie. small light dot) but not to uniform illumination
  • P/M ganglion cells project to dif layers in LGN/V1; have dif properties (receptive field sizes/conduction speed/acuity/presence/lack of colour sensitivity)
  • P/M ganglion cells project retinotopically to segregated in hypercolumns which combine orientation/ocular dominance columns for each part of visual field; all neurons in orientation column share same preference for particular orientation of bar stimulus in their receptive field; within hypercolumns orientation columns found together if they receive input from either left/right eye forming left/right eye pair ocular dominance columns in each hypercolumn
  • simple cortical cells (aka bar/edge detectors) = respond best to edge/bar of particular width/orientation/location in visual field
  • complex cortical cells = respond best -> bad/particular size/orientation anywhere in particular visual field area

Biological Psychology (21 decks)

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