W6 - Reality Flashcards
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
- ) Psychophysical sensitivity to chromatic stimuli far better than that of any individual neuron
- ) 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
- Right motion contrast sensitivity
- 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.
