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PSYC2022 - Perception & Cogition > Slides Week 4 > Flashcards

Slides Week 4 Flashcards

1
Q

From Light to Neural Signals

A
  • We see objects when we detect light reflected from the through our eyes
  • A narrow band of electromagnetic radiation that can be demonstrated as a wave of a stream of photons
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2
Q

From Light to Vision

A
  • Light enters the eye throught the Pupil
  • Lens refracts light and focusses it on the back of the eye
  • Lens focuses an image on the Retina
  • Retina sends signals to brain through the Optic Nerve
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3
Q

Rods & Cones

A
  • Light is Transduced into neural energy by photoreceptors
  • Located in the Retina
  • There are two types
    • Rods
    • Cones
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4
Q

Photoreceptors - Rods

A
  • Specialised for night vision
  • Do not process colour
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5
Q

Photoreceptors - Cones

A
  • Specialise in Daytime Vision
  • Fine visual Acuity
  • Detect Colour
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6
Q

Photopic and Scotopic Vision Table

A
  • Photopic
    • relating to vision in daylight or other bright light, believed to involve chiefly the cones of the retina
    • Cone cells are nonfunctional in low visible light.
  • Scotopic
    • The vision of the eye under low-light levels
    • Produced exclusively through rod cells,
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7
Q

Photoreceptors - Horizontal and Bipolar Cells

A
  • Bipolar cells effectively transfer information from rods and cones to ganglion cells.
  • Horizontal cells introduce lateral inhibition to the dendrites
  • Horizontal cells give rise to the center-surround inhibition which is apparent in retinal receptive fields.
  • Ganglion Cells have axons that leave the retina through the Optic Disk (Blind Spot)
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8
Q

Lateral Inhibition

A
  • The capacity of an excited neuron to reduce the activity of its neighbors
  • Disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction
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9
Q

Receptive Field

A
  • The region on the retina in which stimuli influence a neuron’s firing rate
  • We can map receptive fields by recording signal from the optic nerve
    *
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10
Q

ON-Centre Ganglion Cells

A
  • Have centre-surround receptive fields
  • ON-centre ganglion cells are excited by light that falls on their centre
  • They are inhibited by light that falls in their surround.
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11
Q

OFF-centre Ganglion Cells

A
  • Inhibited when light falls in their centre
  • Excited when light falls in their surround
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12
Q

Mach Bands

A
  • Illusions created by the visual system
  • A bright or dark stripe illusion in gradiated colour scheme
  • Occurs because ganglion cells near the transitional areas have parts of their receptive fields in another shade.
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13
Q

The Path of image processing from Eyeball to Brain

A
  1. Eye
  2. Photoreceptors
  3. Bipolar Cells
  4. Retinal Ganglion Cells
  5. Lateral Geniculate Nucleus
  6. Striate Cortex
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14
Q

Flow Chart of Visual Pathways:

Retinal Ganglion Cells

A
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15
Q

What can Retinal Ganglion Cells Respond to

A
  • Respond vigorously to spots of light
  • Also respond well to certain stripes and gratings
  • Striped pattern is called a Sine Wave Grating
  • The visual system ‘samples’ the grating discretely

Ganglion Cells can detect stripes because they are sensitive to frequency and phase.

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16
Q

Flowchart of Visual Pathways:

Thalamus LGN

A
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17
Q

Lateral Geniculate Nucleus

A
  • Where axons of Retinal Ganglion Cells synapse
  • We have two LGNs
  • each is retinotopically organised
  • maps vision contralaterally to each eye
  • Have retinal radiofrequencies next to each other
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18
Q

Magnocellular Cells

A
  • also called M-cells
  • Neurons located within the Adina magnocellular layer of the lateral geniculate nucleus of the thalamus.
  • Large RF Fast Response
  • High Sensitivity
  • Process Motion
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19
Q

Parvocellular Cells

A
  • Also called P-cells
  • Neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus.
  • “Parvus” is Latin for “small”, and the name “parvocellular” refers to the small size of the cell compared to the larger magnocellular cells
  • Small RF (High Resolution)
  • Slow Response
  • Low Sensitivity
  • Process Colour
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20
Q

Koniocellular Cells

A
  • Also known as K cell is a neuron with a small cell body
  • Located in the koniocellular layer of the lateral geniculate nucleus (LGN)
  • Not fully understood
  • Process blue/yellow colour
  • Large RF
  • High contrast sensitivity
  • Low Spatial frequency
  • Projects directly onto the Extrastriate Cortex
  • Implicated in Blindsight
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21
Q

Primary Visual Cortex

A
  • Transforms visual information in the Striate Cortex or V1
  • Circular receptive fields found in Retina and LGN replaced with elongated stripe receptive fields in cortex
  • Contains about 200 Million Cortical Cells
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22
Q

Two Important features of Striate Cortex

A
  1. Retinotopic Mapping
  2. Cortical Magnification
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23
Q

Striate Cortex: Retinotopic Mapping

A

Different parts of the visual field are mapped onto different parts of the visual cortex

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24
Q

Striate Cortex: Cortidal Magnification

A
  • Proportionally much more cortex devoted to processing the fovea than the periphery
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25
Q

Fovea

A
  • A tiny pit located in the macula of the retina
  • Provides the clearest vision of all.
  • Layers of the retina spread aside to let light fall directly on the cones, the cells that give the sharpest image
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26
Q

Cortical Magnification - Visual Crowding

A
  • The harmful effect of clutter on peripheral object detection
  • Stimuli seen in isolation in peripheral vision becoes hard to detect when other stimuli are nearby

eg: child on road but much crowded traffic and clutter; can’t see the child

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27
Q

Hubel & Wiesel’s Model

A
  • Circular receptive fields in LGN transformed into elongated fields in Striate Cortex
  • A cortical neuron that responds to oriented bars of light might receive input from several retinal ganglion cells
    *
28
Q

Orientation Tuning

A
  • Tendency of neurons in Striate Cortex to respond to most bars of certain orientation
  • Response rate falls off with angular difference of bar from preferred orientiation
29
Q

Striate Cortex - Simple Cells

A
  • Respond primarily to oriented edges and gratings and they only respond to light OR dark
30
Q

Striate Cortex - Complex Cells

A
  • Also respond primarily to oriented edges and gratings
  • have a degree of spatial invariance because the respond to light AND dark
  • Receptive field cannot be mapped into fixed excitatory and inhibitory zones.
  • It will respond to patterns of light in a certain orientation within a large receptive field, regardless of the exact location.
31
Q

Striate Cortex - Hypercomplex Cells

A

Like complex cells, but prefer stimuli with an end within the RF

32
Q

How are cells organised in the Visual Cortex?

A
  • Column
    • A vertical arrangement of neurons
    • within each column all neurons have the same orientation tuning.
  • Hypercolumn
    • A block of striate cortex with cells necessary to respond to everything the visual cortex is responsible for in a part of the visual world
33
Q

Damage to the visual system

A
  • Damage can occur anywhere along the visual system and can result in a unique pattern of impairment
  • From the eye: myopia, hyperopia, astigmatism
  • To the Brain: Anto-babinski Syndrome, Neurological visual impairment without conscious awareness.
  • Charles Bonnet Syndrome: Visual hallucinations in blind individuals
34
Q

How do we perceive Depth?

A
  • Depth Cue
  • Monocular Depth Cue
35
Q

Depth Perception - Depth Cue

A

Information about the third dimension (depth) of visual space

36
Q

Depth Perception - Monocular Depth Cue

A

A depth cue that is available even when the world is viewed with one eye alone.

37
Q

Monocular Cues to Three-Dimensional Space: Occlusion

A
  • A cue to relative depth order in which one object partially obstructs the view of another
  • Sometimes Occlusion could be an accidental view of the objects in the world
38
Q

Monocular Cues to Three-Dimensional Space: Relative Size

A

All things being equal, we assume that smaller objects are farther away from us than larger objects

39
Q

Monocular Cues to Three-Dimensional Space: Relative Height

A
  • For objects touching the ground, those higher in the visual field appear to be farther away
  • In the sky above the horizon, objects lower in the visual field appear to farther away.
40
Q

Monocular Cues to Three-Dimensional Space: Familiar size

A
  • A cue based on knowledge of the typical size of objects
  • When you know the typical size of an object you can guess how far away it is based on how small it appears
  • works on cues in conjunction with the cue of relative size.
41
Q

Monocular Cues to Three-Dimensional Space: Texture Gradient

A
  • Depth cue basedon the geometric fact that items of the same size form smaller, closer spaced images the farther away they get.
  • Result from a combination of the cues of relative sizenand relative height
42
Q

Monocular Cues to Three-Dimensional Space: Aerial Perspective

A
  • Depth Cue based on implicit understanding that light is scattered by the atmosphere
  • More light is scattered when we look thorught more atmosphere
  • As such distant objects appear fainter, bluer and less distinct
43
Q

Monocular Cues to Three-Dimensional Space: Linear Perspective

A
  • lines that are parallel in three dimensional world appear to converge in a two dimensional image as they extend into the distance
    eg: a road heading off into the distance
44
Q

Monocular Cues to Three-Dimensional Space: Vanishing Point

A

The apparent point at which parallel lines receding in depth

45
Q

Monocular Cues to Three-Dimensional Space: Motion Paralax

A
  • Images closer to the observer move faster across the visual field than images further away
  • The brain uses this information to calculate the distances of objects in the environment
46
Q

Oculomotor Monocular Depth

A
  • Cues based on the ability to sense the position of our eyes and the tension in the eye muscles
  1. Accomodation
  2. Convergence
  3. Monster Illusion
47
Q

Oculomotor Monocular Depth: Accommodation

A
  • The process by which the eye changes its focus
  • The lens gets fatter as gaze is direct toward nearer objects
48
Q

Oculomotor Monocular Depth: Convergence

A
  • The ability of the two eyes to turn inwards
  • Often used on nearer objects
49
Q

Oculomotor Monocular Depth

A
  • Depth cues indicate right monster is further away
  • Both monsters subtend at the same angle on retina
  • Brain deduces right monster is bigger
  • Both monsters are the same size
50
Q

Subtend

A

Form an angle at a particular point when straight lines from its extremities are joined at that point.

51
Q

Depth Perception: Binocular Cues

A

A depth cue that relies on information from both eyes

52
Q

Depth Perception: Stereopsis

A

The perception of depth produced by the reception in the brain of visual stimuli from both eyes in combination

53
Q

Depth Perception: Horopter

A
  • Location of objects whose images lie on the corresponding points
  • The surface of zero disparity.
  • Objects on the horopter are seen as single images when viewed with both eyes.
  • Objects significantly closer to or farther away from the horopter fall on noncorresponding points in the two eyes and are seen as two images
54
Q

Depth Perception: Binocular Disparity

A
  • The differences between the two retinal images of the same scene
  • Disparity is the basis for Steropsis a vivid perception of the three dimensions of the world not avaliable with monocular vision
55
Q

Stereoblindness

A
  • An inability to make use of binocular disparity as a depth cue
  • Most infants are stereoblind before 3 months
  • Can show a sudden onset of stereopsis at 3-5 months
  • They may have acuity matching that of adults by about 6 months (birch & Petrig, 1996)
56
Q

Define Acuity

A
  • Mental acuity is sharpness of the mind
  • Things considered in determining a person’s mental acuity are memory, focus, concentration, and understanding.
57
Q

Depth Perception: Correspondence Problem

A
  • In binocular vision the problem of figuringout which bit of the image in the left eye should be matched with which bit in the right eye
58
Q

How is Stereopsis implemented in the human brain

A

Input from two eyes must converge onto the same cell

59
Q

Binocular Rivalry and Suppression

A
  • Sometimes we have different stimuli presented to the two eyes
  • How does our visual system decide what to see?
60
Q

Do you see what I see? Antorini et al., 2017

A
  • Perception depends on personality.
  • Participants in binocular rivalry studies occasionally have moments of ‘rivalry suppression’ where both images are available at once.
  • This is more likely to occur for people high on the openness personality trait
61
Q

Do you see what I see? Tulviste 2019

A
  • Visual perception depends on culture.
  • Tribes in South Africa could not perceive depth in 2D images
  • There are difference in colour, face and object processing
62
Q

Is vision of psychological interest? Jure et al., 2016

A
  • ASD is highly prevalent in blind children
  • > 30% times more likely
  • But it is underdiagnosed
63
Q

Is vision of psychological interest? Silverstein et al., 2013

A

Congenital Blindness is a protective factor for schizophrenia

64
Q

Is vision of psychological interest? Martinez et al., 2008

A
  • Schizophrenia is characterised by deficiencies along all aspects of the visual pathway, particularly the magnocellular pathway
65
Q

Is vision of psychological interest? Kaliuzhna et al., 2020

A

Research is beginning to examine whether deficits in motion perception could be responsible for many of the symptoms of schizophrenia

66
Q

Is vision of psychological Interest? Teeple et al., 2009

A
  • Visual hallucinations are common in a number of conditions including:
    • Parkinson’s (50%)
    • Dementia (20%)
    • Depression (27%)
    • Migraines (31%)

PSYC2022 - Perception & Cogition (16 decks)

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