W6 - Reality Flashcards
Does detecting modulations in colour rely in output of local/distributed neurons
Not due to single neural characteristic. Distribution representation rather than relying on 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
Evidence that colour modulation is part of a distributed network: psychophysical sensitivity chromatic stimuli > neuronal senstivity
More sensitive= lower threshold level needed to identify stimulus.
M and P Pathways to Retina Cortex
M Pathways involved in luminance
P Pathways involved in colour
- Both are anatomically distinct
M pathway in Retical Cortical Expansion
Retina: Larger receptive field than P
LGN: 1-to-1 relationship between retina and LGN
V1: Principle point of expansion
P pathway in Retical Cortical Expansion
Retina: Lesser receptive field than P
LGN: Principle point of expansion
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
Study about M and P pathways
Studies in motion in purely chromatic stimuli (no luminance) reveal strange behaviour consistent with spatiotemporal interaction prior to motion extraction.
- More slowly
- Reliance on luminance for motion detection.
fMRI study about M and P Pathways
Cardinal tuning in V1
> Represents some kind of feedback, unlike the single cones of retina, whole V1 has cardinal representation.
Why is there more feedback from V1 to LGN?
Mediating factor on Parvocellular activity, and then feed back into V1
V4 vs V1
V4: Sense of Colour (taking into account cortex)
V1: Threshold & Hue
Why is there difference between representation of colour and that of cardinal space
May be due to feedback from cortex and strong connections between LG and cortex
> Basic sense of colour is not well predicted by basic properties represented by cones.
Colour discrimination: between vs within categories
Discrimination between categories is easier than discrimination within categories.
Is colour vision categorical/continous? Cropper (2013) study
Discrimination vs Categorization Task (Without colour names):
Discrimination: Highly accurate performance (i.e., responding ‘same’ only when the test colour was very similar to the reference colour)
Categorization: Everyone their own categorical structure and much as the broader
> No categorical boundary effect
What does the discrimination v categorisation task by cropper (2013) 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. It is a subjective experience/unique and consistent
What is the most common syneaesthesia
Colours (70%)
How do hallucinogens work
Mimicking active group on neurotransmitter serotonin (5H-T), which is associated with mood, sleep, appetite, psychosis.
Increasing 5H-T = Increase cortical activity = reduce inhibition
What happens when inhibition is reduced and cortical activity is increased in system
Visual and auditory hallucination
How do hallucinogens affect simple visual tasks?
Affects motion detection
- Disruptions in integrating simple isolated vectors to a coherent representation (Biological motion, flow fields, structure from motion)
Study: Carter et al. (2004) Motion Perception and Psilocyblin. What were the 2 tasks & results
- Right motion contrast sensitivity
- 2 alternative choice
- Rigid
- Can do with basic motion detector - Motion Integration sensitivity
- 2 alternative choice
- Non Rigid
- Basic motion detector must be integrated into global precept
> Only affected in Task 2. Therefore, Psilocyblin affected integration and failure to inhibit.
What is relationship between hallucinogenics and schizophrenia
Same 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. Results
Controls: Stronger contextual suppression > More vulnerable to ‘contrast’ illusion > Less accurate at judging contrast where contrasts disrupts judgement
SZ: Weaker contextual suppression > Less vulnerable to ‘contrast’ illusion > More accurate at judging contrast since contrasts does not disrupt judgement
Schizotypy (at high levels, mirrors SZ) and hallcinations
High positive schizotypy (wild day dreams, etc) linked to having hallucination-like visual experienes
Study: Partos, Cropper, & Rawlings (2016): Schizotypy and image meaning. Study and findings
Present random array of white dots and instructed dots show something meaningful
> Individuals on higher psychoticism, neuroticism, and hallucination-proneness perceived more meaningful images of complex nature of dots
High positive schizotypy score = Increased tendency to perceive complex meaning in random visual noise.
