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
2
Q
Colour in visual perception
A
It is the waves of light that corresponds to the colour perceived
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
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
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
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
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
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.
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
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
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
12
Q
3 Levels of cells found in the Lateral Geniculate of the Thalamus
A
Magnocellular Parvocellular Koniocellular
13
Q
Magnocellular Pathway
A
- This is our motion pathway for visual perception
- Has a large receptive field
14
Q
Parvocellular Pathway
A
- Pathway for processing colour
- Slow responding
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
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
- Retinotopic Mapping
- parts of the visual field map logically and systematically to the Visual Cortex
- 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
