W6 - Reality Flashcards by andy Sitoh

Does detecting modulations in colour rely in output of local/distributed neurons

Distribution representation, not output of local/individual neurons

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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

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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

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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.

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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

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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

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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

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Is there more feedback between: V1 to LGN, or LGN to V1

More feedback between V1 to LGN

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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

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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

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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

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V4 vs V1

V4: Sense of Colour (taking into account context)

V1: Threshold and Hue

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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

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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

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Crooper et al. (2013): Colour discrimination: between vs within categories results

Discrimination between categories is easier than discrimination within categories.

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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.