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Comparative Approaches > From Receptor Signal to Perception > Flashcards

From Receptor Signal to Perception Flashcards

1
Q

INTRO

A
  • linking retinal filtering of edges to perception
  • visual processing beyond retina in primate/human brain
  • human/animal colour vision
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2
Q

WHY DOES RETINA FILTER EDGES SO EARLY IN VISUAL PATHWAY?

A

RAW IMAGE PROJECTION
- receptor signals are distributed spatially in continuous/noisy patterns; threshold required to detect contrasts
PROCESSED IMAGE
- contrast edges (areas of change) contain info

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3
Q

VISUAL PROCESSING: EARLY STAGES

A
  • involve edge filtering & enhancement
  • lateral inhibition (found in centre-surroind (CS) receptive fields of many retina ganglion cells) explain hard-wired phenomena in perception ie. Herrman grid
  • we see grey dots that aren’t there; during eye movements, same part of image is viewed by foveal receptors & ganglion cells/peripheral ones
  • CS receptive fields = smallest in fovea (highest spatial resolution) & larger the further in periphery of retina they are
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4
Q

HUMAN SPATIAL CONTRAST SENSITIVITY (CSF) FUNCTION

A
  • ganglion cells w/CS receptive fields:
    1. enhance edges
    2. compresses info (only respond when in receptive field)
    3. filters info according to spatial frequencies (dif sized receptive fields/varying sensitivity across retina)
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5
Q

OWSLEY (2016); GHIM & HODOS (2006)

A
  • vision & aging
  • inter/intraspecific variations in acuity/contrast sensitivity
  • both humans (Owsley) & birds (Ghim & Hodos) have similar negative correlation between contrast sensitivity & spatial frequency
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6
Q

CROWDED VISUAL SCENES

A
  • seeing/recognising objects/mates/predators/prey = important for many tasks
  • BUT visual scenes = oft crowded (typically not monochrome); contrast enhancement of edges = important for many visual tasks
  • major tasks of visual system = segregating objects/backgrounds automatically/quickly
  • other tasks require further computations to extract info
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7
Q

EGELHAAF ET AL. (2012); KANG ET AL (2012)

A
  • spatial vision in insects = fascilitated by shaping dynamics of visual input through behavioural action
  • camoflauge through active choice of resting spot/body orientation in moths
  • insects land preferably at edge of objects
  • moths actively choose spots; vary orientation to align w/lines in background for better camoflauge against avian predators
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8
Q

HATEREN ET AL. (1990)

A
  • insects discriminate/generalise stripe patterns & recognise illusory contours
  • bees were trained w/variations of stripe pattern; each tested group learned to discriminate particular orientation of these patterns; experiment trained bees to Kanisza rectangles
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9
Q

LOOKING: PHOTORECEPTOR SIGNALS

A
  • change very quickly; are noisy
  • movements (eyes/head/body) change/stabilise gaze for very short periods of time; fast main function filtering decomposing images into elementary features in peripheral visual system layers
  • early segregation fed into parallel visual streams for unconscious/conscious visual perception
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10
Q

ACTIVELY LOOKING & SEEING: UNCONSCIOUS PERCEPTION

A
  • can be fast/slow/filtered depending on task/pathway can be invariant/selective/less noisy
  • guides fast/slow actions; analyses scenes/objects; changes are perceived via task outcomes (ie. consequence of beh response/change in internal state/top-down control (ie. gaze/conscious decision-making in humans))
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11
Q

SEEING: CONSCIOUS VISUAL PERCEPTION

A
  • in humans = stable/slow/invariant/affected by filtering BUT less selective than unconscious perception/low noise
  • only pronounced eye/head/body movements result in perceived change of viewed scene/object; conscious vision seems relevant for some specific tasks; can exert some top-down control but mostly results from processes at lvl 1/2; some = hard-wired
  • humans = difficult to generate evidence clearly separating domains 2/3
  • animals = lvl 3 studied w/brain imaging in monkeys/modelling
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12
Q

METHODOLOGICAL APPROACHES TO STUDYING SENSING/PERCEPTION

A

PSYCHOPHYSICS
NEUROANATOMY
FUNCTIONAL NEUROPHYSIOLOGY/NEUROGENETICS
THEORETICAL NEUROSCIENCE/COMPUTATIONAL MODELLING

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13
Q

METH APPROACHES: PSYCHOPHYSICS

A
  • links variation in stimulus w/changes in beh (ie. eye/body responses/verbal responses/task acquisition/execution)
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14
Q

METH APPROACHES: NEUROANATOMY

A
  • provides info about connectivity in sensory organs/brain/motor systems
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15
Q

METH APPROACHS: FUNCTIONAL NEUROPHYSIOLOGY/NEUROGENETICS

A
  • links neural response patterns to connectivity/behaviour
  • tests concepts/algorithms
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16
Q

METH APPROACHES: THEORETICAL NEUROSCIENCE/COMPUTATIONAL MODELLING

A
  • proposes concepts
  • tests mechanistic/functional hypotheses; formulates methematical algorithms to show how nerons do/may interact within/between brain areas
17
Q

THE CORTICAL PATHWAY

A
  • cortical pathway = processes image info
  • lateral geniculate nucleus (LGN) aka. thalamus
  • subcortical pathways = pretectum (mediates pupillary reflex) & superior colliculus (controls saccadic eye movements)
18
Q

THALAMUS

A
  • principal synaptic relay before sensory info reaches verebral cortex
  • high input = 10,000 ganglion axons
  • thalamus gates/modulates info flow to cortex
  • LGN = parvocellular (small cell) laminae/magnocellular (large cell) laminae
19
Q

STRUCTURE/RETINOTOPIC ORGANISATION OF PRIMARY VISUAL CORTEX

A
  • retinotopic = relative position of object in visual field is preserved in retina; also preserved in LGN & primary visual cortex
  • BUT… mape = upside down (due to focusing on lens/cornea); aka. disproportionate; more cells = devoted to processing info from fovea aka. cortical magnification
  • V1 contains large diversity of cells incl. simple/complex cells
20
Q

DETECTING OBJECTS THAT LACK CONTINUOUS EDGES

A
  • early 20th century; School of Gestalt psychology proposed shape/object perception = underpinned by processes in mind that are characterised by Gestalt laws ie. proximity/similarity (ie. in colour/size)
  • local cues/features = integrated across long distances in image into global features
  • aka. is slow! requires lot more computations/eye scannings of whole scene to make sense of world & resolve ambiguities
21
Q

RENOIR (1885)

A
  • coding of contours/boundaries analysis of objects
  • shape/positional invariance
  • contour enhancement required for object identification
  • aka. V1 = fundamentally important for conscious vision/perception
22
Q

MISHKIN, UNGERLEIDER & MACKO (1983)

A
  • what/where streams in cortical processing of visual info in primates/humans
    A. MAKING SENSE OF WORLD
  • aka. object discrimination
  • bilateral remova of area TE in inferior temporal cortex produces severe impairment on object discrimination aka. 1-trial object recognition task based on principle of non-matching to sample where monkeys familiarised first w/1 object of pair in central location then rewarded in choice test for selecting unfamiliar objects
    B. INTERACTING W/WORLD
  • aka. landmark discrimination
  • bilateral removal of posterior parietal cortex produces severe impairment on landmark discrimination
  • monkeys rewarded for choosing covered foodwell positioned randomly trial to trial
23
Q

NICHOLLS ET AL. (2011)

A
  • V1 = higher visual areas generate conscious percepts
  • parallel processing = ganglion cells receive inpit from same photoreceptors
  • serial processing = signals transmitted from photoreceptors to ganglion cells to LGN -> V1
  • parietal lobe = dorsal (where) stream; association cortex -> retinal ganglion cells
  • temporal lobe = ventral (what) stream
24
Q

DI CARLO ET AL. (2012)

A
  • macaque monkey brain object recognition/categorisation
  • discrimination (<200ms)
  • recognition of objects (also when changes in object position/size/viewpoint/visual context)
  • ventral cortical stream = critical for object recognition
  • V1-V4 = occipital lobes
  • IT = inferior temporal cortex (temporal lobes)
25
Q

HOW CAN FILTERED/DECOMPOSED ELEMENTS BE COMBINED IN BRAIN?

A
  • receptive fields in interneurons of brain can be varied in many ways to combine info provided within/between visual pathways
  • cells in serially connected layers directly/simply cause elements of perception
26
Q

CONCEPTS OF PERCEPTUAL INFO CODING

A
  • redundancy reduction/sparse coding/selective attention keep energetic cost of processing low
    1. GRANDMOTHER/GNOSTIC CELLS
  • ie. face-selective cells in interotemporal cortex of monkeys
  • sparsely coded representation of object
    2. DISTRIBUTED NETWORKS
  • represent objects by binding features coded in receptive fields across neural brain centres; form distributed representation of object
27
Q

HUMAN COLOUR VISION

A
  • originates in P pathway
  • S/M/L cones contribute to colour vision
  • fovea only contains M/L cones
  • rods mediate night vision aka. achromatic
  • V1 = primary visual cortex
  • M pathway = colour/fast/low acuity/high contrast sensitivity
  • P pathway = colour sensitive/slow/high acuity/low contrast sensitivity
28
Q

“WHERE” SYSTEM AKA. MT (V5)

A
  • motion perception
  • depth perception
  • spatial organisation
  • figure/ground segregation
29
Q

“WHAT” SYSTEM AKA. V4

A
  • object recognition
  • face recognition
  • colour perception
30
Q

COLOUR = USEFUL INFO

A
  • colour vision = ability to discriminate light stimuli by spectral content (colour cue) NOT intensity (brightness cue)
  • widespread in animals; number of photoreceptors/spectral sensitivity differs
  • ie. bees see rockrose flowers as pink/red rather than gold aka. via primary colours
31
Q

COLOUR-BLINDNESS

A
  • human colour vision polymporphism
  • most mammals have also 2 spectral types of photoreceptors ie. colour-blind humans
  • marine mammals = truly colour-blind; have only 1 spectral type of photoreceptors
32
Q

COLOUR CONSTANCY

A
  • ability to recognise colours under dif illuminations
  • sunlight = slightly colours during dusk/dawn
  • visual system compensates for such slow changes by global adaptation
  • during visual search in natural scene; visual system can also adapt quickly BUT within spatially restricted area of visual search
33
Q

LEHRER ET AL. (1988); KINOSHITA & ARIKAWA (2000)

A
  • insects have perceptial constancy/code depth from 2D retinal image
  • size constancy = honeybees can discriminate between objects based on size; motion cues provide bee’s visual world w/third dimension
  • honeybees/butterfly have colour constancy; recognise rewarded colour in Mondrian stimulus under dif coloured illuminations
34
Q

SUMMARY

A
  • sensory systems extract info from sensory cues to generate unconscious/conscious perception depending on task type/priorities for decision making/task execution in dif areas/systems of brain
  • visual/perceptual info (motion/colour hue/saturation/brightness/edges/shape/spatial & temporal patterns) = computed from photoreceptor signals; processed in various parallel working pathways hierarchically organised (aka. serial connectivity)
  • evidence generayed in research not always links perception to tasks thus studying isolated components of visual system/brain; incorporating comparative approached/ecological/evolutionary considerations (ie. by considering properties of natural visual scenes (beh & ecological needs of humans/animals) can help better understand functions/limitations of brain mechanisms

Comparative Approaches (10 decks)

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