Simon Flashcards
<p>What is properties of colour</p>
<p>- Interpretation of the brain</p>
<p>- Context-specific</p>
<p>What did Issac Newton found in colour</p>
<p>White light is made up up of all visible</p>
<p>What did Young and Helmholtz found in colour</p>
<p>3 receptors - Trichromacy RGB</p>
<p>What did Edwalrd Hering sugest</p>
<p>Opponency: Red-Green; Blue-Yellow.</p>
<p>First stage: trichromatic</p>
<p>Second stage: Opponent stage</p>
<p>Define neural substrate</p>
<p>Indicate a part of the nervous system underlying a behaviour or physiological state</p>
<p>Kraukskopf (1982): Aims</p>
<p>Aims: Simple colour detection (Presence or Absense binary)</p>
<p>Kraukskopf (1982): Method</p>
<p>- Small disc whose colour varied in time along an axis of opponent colour space</p>
<p>- Participants indicated test pulse visiblitybefore/after prolonged exposure to a stimulus modulated along given axis</p>
<p>- Contrast/visibility of pulse varied until "threshold" reached (75% correct)</p>
<p>What is a colour space</p>
<p>Method by which a light and colour may be represented such that its definition is unique and replicable </p>
<p>What are the 3 cones.</p>
<p>L Cones: Reds</p>
<p>M Cones: Green</p>
<p>S Cones:: Blue</p>
<p>What is the cardinal colour space</p>
<p>2 Chromatic Axes (Colour): R-G; B-Y</p>
<p>1 Achromatic Axis: Luminance</p>
<p>What is the cone's relationship to the cardinal colour space (What does S,M,L correspond to). Which one is luminance</p>
<p>Bluish Yellowishness: S - (L+M)</p>
<p>Reddish Greenishness: L-M</p>
<p>Blackish Whitishness: L+ M</p>
<p>Kraukskopf (1982): Outcome measure</p>
<p>Distance from centre = Adapted - Unadapted Threshold</p>
<p>(Bigger difference from centre = More adaptation effect)</p>
<ul> <li>If adapted someone on R-G and tested on B-Y <ul> <li>Distance from centre = 0</li> </ul> </li> <li>If adapted someone on R-G with greatereffects on tulse pulse on R-G, distance from centre <ul> <li>Distance from centre + big</li> </ul> </li></ul>
<p>Kraukskopf (1982): Results Interpretation</p>
<p>2 Chromatic and 1 Acrhomatic Axis = Opponency</p>
<p>1.) Each axis shows independent adaptability/orthogonality</p>
<ul> <li>Threshold only raised by adapting to a stimulus along the same axis (unaffected by adaptation to other axes)</li> <li>3 independent detection mechanisms mediate the transmission of spatio-chromatic information from retina to cortex</li></ul>
<p>In psychophysics, who are the subjects</p>
<p>Neurons. </p>
<p>What are cardinal neurons. Are there any?</p>
<p>Group of neurons involved in colour vision</p>
<p>No. No single "cardinal neuron"</p>
<p>What are properties of cardinal neurons (if any)</p>
<p>1.) Chromatic sensitivity clustered along cardinal axes (RG/BY): To get pattern of independent adaptability</p>
<p>2.) Adapatation/ Change in output after prolonged exposure</p>
<p>How does the visual system work</p>
<p>Photoreceptors > Horizontal > Bipolar > Retinal Ganglion Cell (Difference in sensitivity) > LGN > Cortex</p>
<p>LGN and Cortex connections</p>
<p>More V1 to LGN<br></br>LessLGN to V1</p>
<p>What are cells in the layers of the LGN</p>
<p>1.) Parvo Cellulular (P Cells) : Small</p>
<p>2.) Konio Cellulular: Medium</p>
<p>3.) Magno Cellular (M Cells): Big</p>
<p>Derrington (1984): Aim</p>
<p>Are the 3 LGN cells grouped along in cardinal axis? </p>
<p>Derrington (1984): Stimuli and Methods</p>
<p><u>Macaque LGN neuron</u></p>
<ul> <li>Coloured spot stimuli to establish receptive field <ul> <li>Examine neuronal output changes as a function of colour and luminance properties</li> <li>Modulated across 3 orthognal planes until"null response" is found</li> </ul> </li> <li>Silent substitution method</li> <li>Preferred stimulus of neuron = Orthogonal to null plane in 3D space</li></ul>
<p>What is the silent substitution method in Derington (1984)</p>
<p>Two coloured light exchange with no effect on output of neurons</p>
<p>This indicates that the neurons are inresponsive and the preferred stimulus is orthogonal (right-angle)</p>
<p>Derrington (1984): Results</p>
<p>Neurons "chromatic signature" fell into 3 subgroups.</p>
<p></p>
<p></p>
<p>Derrington (1984): Results from P Cells</p>
<p>1.) Parvo Cellular</p>
<p>Less sensitive to luminance</p>
<p>Senstivity to colour (RG or BY)</p>
<p></p>
Derrington (1984): Results from K cells
2.) Konio Cellulular: Not sure. But they have a large number of S cones (maybe augment)
Derrington (1984): Results from M Cells
3.) Magno Cellular:
Very sensitive to luminance
NO colour sensitivity.
Can Derington's (1984) study conclude cardinal properties of neurons?
Not fully.
Remember they need to fulfil 2 properties: (1) Chromatic Senstiivity (2) Adaptation
They only established chromatic signature, not adapatation
Krauskopf (1990) Aim
Replicate Derington (1984) in the cortex
Krauskopf (1990) Results
V1
- In each cortical group, lack of clustering (i.e. neurons redistributed across colour plane) suggest no cardinal signature
- Showed strong adaptation effect (Reduce output after prolonged exposure)
LGN vs V1 neurons
LGN: Cardinal colour signature but no adaptation
V1: No cardinal colour signature but adapt
What does all the findings suggest in about cardinal behaviour? Which neurons?
LGN (Chromatic Signature) + V1 (Adaptation) = Detection of presence.
Cardinal Behaviour
There is no modulation of colour. There is no "cardinal neurons" doing "cardinal behaviour". Can only be explained on the basis of a combination of LGN and cortical properties
Does detecting modulations in colour rely in output of local/distributed neurons
Distribution representation, not output of local/individual neurons
What are the 2 evidences to suggest that detecting colour modulation is part of a distributed representation
1.) Psychophysical sensitivity to chromatic stimuli far better than that of any individual neuron
2.) Different neural expansions in Magnocellular and Parvocellular pathways from retina to V1
First evidence that colour modulation is part of a distributed network:
Psychophysical sensitivity to chromatic stimuli > neuronal senstivity. What does sensitivity mean and how does it relate to threshold?
More sensitive = Lower threshold level needed to identify stimulus.
We need lower threshold to identify colour than luminance
Colour vs Motion: Neuronal Properties, Which Cells in the LGN, Feedback
Colour
- Population Neurons
- P cells
- Feedback between V1 and LGN
- Feedback takes time
- Hence, we are not very good at looking at colours move
Motion:
- Potentially single neurons
- M cells (Luminance)
- Little feedback between V1 and LGN
- Feedback takes time
- Hence, we are good at detecting luminance motion.
Second evidence that colour modulation is part of a distributed network:
M and P Pathways to Retina Cortex
M: Luminance
P: Colour
Both are anatomically distinct
M pathway in Retical Cortical Expansion
Retina: Cones in retina has larger receptive field than P
Retina to LGN: 1-to-1 relationship
LGN to V1: Principle point of expansion
P pathway in Retical Cortical Expansion
Retina: Cones in retina has smaller receptive field than P
Retina to LGN: Principle point of expansion
LGN to V1: Little (not 1-to-1) relationship between LGN and V1
Is there more feedback between: V1 to LGN, or LGN to V1
More feedback between V1 to LGN
What is require to study motion? What do studies of motion detection in chromatic stimui show?
Studies of chromatic stimuli (No Luminance): There must be some spatiotemporal interaction (movement in space and time) prior to motion extraction.
Motion detection
- Primarily on luminance
- Only in nosiy context does it rely on colour
fMRI study about M and P Pathways
- Cardinal tuning in V1 (Not evident in neurons)
- Represents some kind of feedback, unlike the single cones of retina, whole V1 has cardinal representation
- Presumably after feedback of LGN and V1
Why is there more feedback from V1 to LGN?
Mediating factor on Parvocellular activity, and then feedback into V1
- Relating to sense of colour (unique hues) and cardinal space
V4 vs V1
V4: Sense of Colour (taking into account context)
V1: Threshold and Hue
How does the unique hue axes differ from cardinal space
Unique Hue Axes
Defined around perception of colour
Cardinal Space
Defined upon detactability/excitability of observing a colour
Why is there a difference between a unique hue (our sensation/representation of colour) and that of cardinal space?
Basic sense of colour (unique hue) is not predicted by basic properties represented by cones (cardinal space)
- May be due to feedback from cortex and strong connections between LGN and cortex
Crooper et al. (2013): Colour discrimination: between vs within categories results
Discrimination between categories is easier than discrimination within categories.
Is colour vision categorical/continous? Cropper (2013) study overview
Discrimination (With colour name) vs Free-Categorization (Without colour names)
Is colour vision categorical/continous? Cropper (2013) study results from discrimination task
Discrimination: Highly accurate performance (i.e., responding ‘same’ only when the test colour was very similar to the reference colour)
Is colour vision categorical/continous? Cropper (2013) study results from categorical task
Free-Categorization: Everyone their own categorical structure and much as the broader > No categorical boundary effect
Is colour vision categorical/continous? Cropper (2013). When is colour categorical
When it included language
Is colour vision categorical/continous? Cropper (2013). Conclusion
Descripion and Action does not affect perception.
Rather, perception affects description and action
Taken together, what does all the vision studies suggest?
We still lack a predictive and quantitative model of how we see simple visual stimuli.
What is syneaesthesia
Involuntary conjoint perception across two modalities
Is synaesthesia objective?
No.
(a) Subjective/Unique
(b) Consistent
Experience
What is the most common syneaesthesia
Colours (70%)
How do hallucinogens work
Mimics NT serotonin.
Increasing 5H-T = Increase cortical activity = reduce inhibition
What is induced when inhibition is reduced and cortical activity is increased in system
Visual and auditory hallucination
Impairs high-level, not low-level, motion perception.
Define motion detection (What does it require). How do hallucinogens affect motion detection
Motion Detection (Biological motion, flow fields, structure from motion)
Hierarchical system: Requires integration from simple isolated vecotrs into coherent representation.
Disuprts integration process.
Study: Carter et al. (2004) Motion Perception and Psilocyblin. What were the 2 tasks
1. Right motion contrast sensitivity
2. Motion Integration sensitivity
What is simple motion detection
Motion Vector
- Indicates direction and speed of image in retina
- Most likely luminance, could be colour
Study: Carter et al. (2004) Motion Perception and Psilocyblin. What were results from Task 1
Right motion contrast sensitivity
- Rigid
- Dots move same direction
Results
- Can do with basic motion detection
Study: Carter et al. (2004) Motion Perception and Psilocyblin. What were results from Task 2. Conclusions from Task 1 and 2.
2. Motion Integration sensitivity
- Non Rigid
- Global
- More dots with differing movements
- Basic motion detector must be integrated into global precept
Results
- Integration critically affected
- Therefore, psilocyblin affected integration and failure to inhibit.
What is relationship between hallucinogenics and schizophrenia
Some similarities to psychosis
- In SZ patents, simple visual task requiring less integration led to better performance (due to context)
Study: Dakin et al. (2005) Contrast of central disk and SZ patients. Compare the results of SZ and controls
Controls: Worse
(a) Stronger contextual suppression
(b) Vulnerable to 'contrast' illusion
(c) Less accurate at judging contrast where contrasts disrupts judgement
SZ: Better
(a) Weaker contextual suppression
(b) Less vulnerable to 'contrast' illusion
(c) More accurate at judging contrast since contrasts does not disrupt judgement
What is schizotypy and what is it linked with?
At high levels, mirrors SZ.
High positive schizotypy (wild day dreams, etc) linked to hallucinations
Study: Partos, Cropper, and Rawlings (2016): Schizotypy and image meaning. Study Overview
Present random array of white dots and instructed dots show something meaningful .
Study: Partos, Cropper, and Rawlings (2016): Schizotypy and image meaning. Study Findings and Conclusion
Higher psychoticism, neuroticism, hallucination-proneness
- Perceived more meaningful images of complex nature of dots
- Therefore, schizotypy associated with perceiving complex meaning in random visual noise.
A cardinal colour space was defined on the basis of
Note: Include 3 properties
Cardinal colour space consists of two chromatic axes (colour) and one achromatic axis (luminance)
- Psychophysically orthogonal
- ‘Excitation’ stage of processing
- The axes should not be termed red-green and blue-yellow or any other colour-name as they correspond to cone excitation
- BY: S-(L+M)
- RG: L-M
- Luminance: (L+M)+S
Orthogonality in the vector representation of signal-coding confers which of the following properties upon that stage of the system?
Cardinal Colour Space
- Threshold is only raised by adapting to a stimulus along the same axis; threshold is unaffected by adapting to other two axes
- Three independent detection mechanisms mediate the transmission of spatio-chromatic information from retina to cortex
The physiological basis for cardinal colour sensitivity is found in
LGN (P Cells)
First candidates were Retinal ganglion cells
The problem with colour vision is
2 things
- Simplest visual task involving coloured stimuli cannot be explained by what we currently know about the visual system, let alone the more complex observations we make all the time
- Excitation (neural properties) and sensation (what we experience) do not align because the cardinal axis and unique hue axis do not align
The term “opponency” refers to..
- When the bipolar cells wire up to retinal ganglion cells they wire up in an opponent mechanism which contributes to the colour after image we perceive. Red-Green and Blue-Yellow
- Receptors act in opposite ways to wavelengths associated with 2 pairs of colours
- Accounts for the perception of four primary colours and afterimages (the colours perceived after the complementary colours are removed)
- Adapation by Cardinal Neurons?
What is red?
- Subjective
- Uniquely definable in terms of wavelength of photon and something that is impossible to describe what the sensation is
- Can’t describe red without using the word ‘colour’ to someone who hasn’t seen red
- L Wave Length
Neurones in the LGN cannot be the physiological substrate for the cardinal axes because..
LGN neurones have cardinal colour signatures but don’t adapt
Cardinal behaviour (independent adaptability) can only be explained on the basis of a combination of LGN and cortical properties
Neurones in primary visual cortex (V1) cannot be the physiological substrate for the cardinal axes because..
V1 neurones do not have cardinal signatures but do adapt
Cardinal behaviour (independent adaptability) can only be explained on the basis of a combination of LGN and cortical properties
The fundamental crux of the argument between Hering and Helmholtz was..
Helmholtz
- Helmholtz suggested there were three receptors, sensitive each to red, green, and blue wavelength
Hering
- 4 receptors, sensitive each to red, green, blue, and yellow wavelengths, with these wired in pairs of red-green and blue-yellow
- First stage of colour vision could be a trichromatic stage and then an opponent stage
- Note: It is not mutually exclusive
The relationship between our experience and the ensemble of neural responses mediating that experience
Ensemble of neural responses are generally distributed and do not predict our experience (Perception and sensation do not always correlate)
The cardinal space are not the mechanisms that mediate our primary sense of colour
#TheDress is an example of…
- Colour is context-dependent
- Each system (person) viewing the photo is unique, from the photoreceptor mosaic onward, and everyone does see their own version of the world
-
Different sensation and perception
Colour constancy confers what benefits upon the organism
Color constancy is an example of subjectivism and a feature of the human colour perception system which ensures that the perceived color of objects remains relatively constant under varying illumination conditions.
Colour categorisation is unique to each person, but colour discrimination remains relatively constant between people, which enables organisms to agree on colour differences despite seeing ostensibly different categorisations
In the context of the ‘local’ versus ‘distributed’ processing debate
Local processing
- Cardinal neurones would be in the retina and the LGN.
- They would be adapting nicely and they would be clustered along the axis and you would call that pinkish colour the red, greenish colour green, but we don’t.
Completely distributed
- Difficult to define fine motion. Having a distributed visual system in space and time would not be good for the detection of motion.
-
No single neuron or group of neurons with a specific role of mediating a specific sensation or experience.
The Jennifer Aniston neurone is….
- Grandmother cells that respond selectively to a stimulus such as Jennier Aniston and Halle Berry
- Hypothetical neuron that represents a complex but specific concept or object
- An extreme version of the idea of local processing (single neuron level)
A cardinal colour is….
A cardinal colour is in relation to categorised vs. discriminated colours
No common category structure in colour until we tell people to learn colour.
According to Cropper et al (2013), in the absence of good colour terms
Colour is only categorical when it includes language.
- No categorical boundary effect
- Varying and broad categories across the subjects
- Performing a different task which is unique to each individual
Everyone categorised colour uniquely, which is evidence that perception doesn’t change, but the way you describe and act on something can.
Colour vision is not necessarily a good example of categorical perception because….
- We perceive a continuum of hues
- Categorisation does not affect perception.
- Rather, perception affects categorisation
-
The cardinal axes axis failed to align with the unique hue axes. The lack of correspondence between two sets of axes implies that the perception of unique hues cannot be explained by a simple linear transformation of the cone-opponent signal.
The binding problem might not be a problem because…
- It is possible that the brain does not completely separate the components of a visual image in the first place in order to reintegrate them
- Just because we have a coherent, unitary representation of the world that we identify as our visual sensation does not mean we should expect the underlying brain function to mirror that experience and provide a single unitary neural representation
- Our experience of the world is just the product of whatever is going on in our head.
- While our survival relies on experience being coherent and congruent with our expections, that does not mean that the neural ‘image’ need look like that at all.
Trichromacy is ...
Young-Helmholtz
- The theory that there are three different channels for conveying colour information, due to the three different types of cones in the retina. These cone types respond to light wavelengths red, green, and blue.
The abbreviations L, M and S refer to what property of the cones?
First-Stage Cone Mechanisms
Property of wavelength specific cone type responds to
L - Red
M - Green
S - Blue
What aspect of the relationship between the LGN and cortical V1 suggests distributed coding may be particularly important for colour vision?
- Much feedback from V1 to the LGN in order to produce our perception of colour
