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PSYC2022 - Perception & Cogition > Lecture Week 4 > Flashcards

Lecture Week 4 Flashcards

1
Q

What is light?

A

Light is a stream of electromagnetic radiation that can be viewed as a wave or stream of photons

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2
Q

Colour in visual perception

A

It is the waves of light that corresponds to the colour perceived

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3
Q

From light to Vision

A
  • Light enters the Pupil
  • It is then refracted by the lens
  • Changes the shape of the lens - stretch lens or allow it to bulge
  • Forces image on to the Retina - Retina contains photosensory cells
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4
Q

Photoreceptors

A
  • We have Rods and Cones
  • Significantly more Rods than Cones - Cones mostly located in Fovea
  • Rods specialised for night vision
  • Cones specialise in daytime vision, fine visual acuity and colour
  • Fovea are considered the point of focus in the Retina
  • Periphery of vision is comprised of rods
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5
Q

Pathway of light to brain

A
  • Light enters Photoreceptor Rods or Cones
  • Photoreceptor signals the Horizontal and Bipolar Cells
  • Bipolar Cells connect to Ganglion Cells
  • Ganglion Cells axons leave the Retina and project through the Optic Disc
  • Optic Disc leads to the Optic Nerve
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6
Q

Receptive Field

A
  • A region of photo cells on the retina
  • Influence firing rate to ganglion cells
  • Only process information from their specified area
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7
Q

ON-Centre Ganglion Receptive Fields

A
  • Ganglion Cells have centre surround receptive fields
  • This means when the light is falling directly to that recepetor it will fire the most.
  • If the light is off centre, then the receptor will synapse less
  • The ganglion is excited when the stimulus hits it’s centre
  • It is inhibited by light that reaches its Centre surrounds
  • The inhibitory rate for this ganglion will be higher because it wants to be in darkness
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8
Q

OFF-Center Ganglion Cells Receptive Fields

A
  • These cells are inhibited when light falls on it’s center because it wants to be in darkness
  • It is excited and synapses when light is in the surrounds of the receptive field.
  • If the entire cell is covered in light the cell rate will try to fire excitedly but is inhibited as well so synapses will be minimal and sluggish.
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9
Q

Lateral Inhibition

A
  • Also called CENTRE-Surround antagonism
  • When lateral cells receive mixed light signals then the brain perceives visual illusions
  • Due to the fact that the OFF-Surround is trying to inhibit the firing of the cell
  • Inhibition that is trying to happen when there is light or stimulation on the receptive field of that retinal ganglion cell.
  • Usually when visual field crosses shades
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10
Q

Sine Wave Grating

A
  • The eye responds vigoursly to spots of light and to stripes or gratings
  • This gives us insight into visual acuity and fine detail sight
  • This depends on the spacing of our retinal ganglion cells
  • Ganglion cells can detect stripes because they are sensitive to light frequency and phase position in receptive field
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11
Q

Visual Preferences

A
  • It has been found that our eyes have a preference to view spots and stripes
  • Passes this information to the Lateral Geniculate of the Thalamus
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12
Q

3 Levels of cells found in the Lateral Geniculate of the Thalamus

A

Magnocellular Parvocellular Koniocellular

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13
Q

Magnocellular Pathway

A
  • This is our motion pathway for visual perception
  • Has a large receptive field
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14
Q

Parvocellular Pathway

A
  • Pathway for processing colour
  • Slow responding
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15
Q

Koniocellular Pathway

A
  • We don’t know much about these yet
  • Some think it is for processing colours, in particular Bue and Yellow
  • It is interesting that some of these cells bypass (V1) the visual cortex
  • This means that if the visual cortex is damaged this part of the cortex can process other more specific things about the visual field
  • Gives us sight without the concious experience of sight - Blindsight
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16
Q

Primary Visual Cortex (V1)

A
  • There is a preference for processing stripe visual information over spot information here
  • The first part of V1 is dedicated to processing information of about a thumb width
  • As we move further along V1, it is processing a larger field of vision.
17
Q

Eccentricity

A
  • Distance in degrees from the fovea
  • Deviation of a curve or orbit from circularity.
18
Q

Striate Cortex - Features

A
  1. Retinotopic Mapping
    • parts of the visual field map logically and systematically to the Visual Cortex
  2. Cortical Magnification
    • More of the Cortex devoted to the Fovea and the rest is magnified in proportion to the periphery
19
Q

Hubel & Weisel’s Model

A
  • Circular receptive fields in the LGN transformed into elongated fields in the Striate Cortex
  • Just remember
    • Spots in the eyes
    • Stripes in the brain
20
Q

Primary Visual Cortex - Simple Cells

A
  • a cell that responds primarily to oriented edges and gratings
  • Only respond to light OR dark
  • Bars of particular orientations - Basically Edge Detectors
  • Discovered by Torsten Wiesel and David Hubel in the late 1950s.
21
Q

Primary Visual Cortex - Complex Cells

A
  • Also respond primarily to oriented edges and gratings
  • Has a degree of spatial invariance because the respond to light AND dark.
  • This means that its receptive field cannot be mapped into fixed excitatory and inhibitory zones
  • They are not fussy
22
Q

Primary Visual Cortex - Hypercomplex Cells

A
  • Very much like complex cells but have a preffered end stopping cell.
  • Provide a means for the brain to visually perceive corners and curves in the environment by identifying the ends of a given stimulus
23
Q

How are cells organised in the Visual Cortex

Orientation Columns

A
  • Organized regions of neurons that are excited by specific visual line stimuli
  • Located in the primary visual cortex (V1) and span multiple cortical layers
  • Geometry of the orientation columns are arranged in slabs that are perpendicular to the surface of the primary visual cortex.
24
Q

How cells are organised in the Visual Cortex

Hypercolumns

A
  • Also called a cortical column, macrocolumn, functional column
  • Each type of column is organised by type and is sorted into multiples of columns
  • Each millimeter of each hypercolumn is orgainsed to process anything your visual field will throw at it
25
Q

Binocular Depth Cue

A
  • Relies on information from both eyes
  • Best depth perception is given to us from both our eyes
26
Q

Stereopsis

A
  • Perception of depth produced by both eyes in combination
27
Q

Horopter

A
  • The point in the visual space where any objects on that space are going to have corresponding points on the retina
  • Can change depending on where we focus our eyes
  • Similar to a Horizon Point but is not fixed
28
Q

Binocular Disparity

A
  • Most things not on the Horopter will fall on different points on the retina field
  • Each eyes will see different images of the same scene
  • Allows us to see and experience a 3D World
    *
29
Q

Stereoblindness

A
  • The inability to use Binocular Disparity for Depth Perception
  • Babies develop Stereopsis by 3-5 months
30
Q

Stereoblindness

A
  • Inability to use Binocular Disparity as a depth cue
  • If our eyes don’t converge then we don’t develop Stereopsis
31
Q

Fusiform Face Area

A
  • meaning: spindular/spindle-shaped face area
  • Part of the human visual system that is specialized for facial recognition
  • Located in the Inferior temporal cortex (IT), in the fusiform gyrus
32
Q

Pareidolia

A

The ability to see faces in inanimate objects that don’t have faces

33
Q

Correspondence Problems

A
  • Similar to Cones of Confusion in audition
  • Due to binocular disparity there can be matching perceptions of vision that may give the visual illusion of something different
  • We base our decisions off the fovea which usually has the retinal image in both eyes
  • In addition we use relative location to discern where things actually are
34
Q

How is Stereopsis implemented in the brain

A
  • In order to have stereopsis we have to have binocular neurons
  • Input from two eyes have to converge on to one cell
  • This happens in the Striate Cortex or V1
35
Q

Binocular Rivalry

A
  • When we see two different images with each eye the eyeballs battle to decide how to perceive the object
  • They fight it out for a single percept
36
Q

Ponzo Illusion

A
  • Two people on the train tracks
  • Linear Perspective visual illusion
  • Includes conversion and angle of subtend on the retina

PSYC2022 - Perception & Cogition (16 decks)

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