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Summary Sensation & Perception part 1 + papers
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College 13-2-2020
Vision is the primary human sense
Easy to study vision:
- Easy to give any visual input to brain
- Easy image creation with computers
- We can see where eye is moving: how retina is stimulated
Dualism: mind and body are separate entities
Monism: mind is aspect of body, just like brain and nervous system
- Viewpoint course slide 18
Perception: analysis of neural activity from the senses to understand the environment
- Also: our subjective conscious experience of the outside world
- giving meaning to sensation
Sensation: a translation of the external physical environment into a pattern of neural
activity by a sensory organ
- the ability to detect pressure and turn it into a private experience.
Perception is often inaccurate
- Because it is strongly influenced by experiences and expectations
- Eyes receive more input than they can process
How to study perception:
- Psychological approach: quantitative measurements of behaviour resulting from
perception & psychophysics
Psychophysics: the scientific study of the relation between stimulus and sensation
- Uses the Just noticable difference
The Just noticeable difference:
- Increases with strength of stimuli in (non) linear way
- Logarithmic relationship: if i double the intensity, i double the JND
Good determination of perceptual threshold:
● 2-Alternative Forced Choice: giving two options and making someone choose
, ● Method of constant stimuli: slide 35
Best way: adaptive staircase slide 36/37
Biological approach:
- What are perceptions neural substrates?
- Correlate a neural activity measure with a change in the presented stimulus
Neural activities:
- Spiking activity: action potentials
- Synaptic activity: synaptic potentials
- Metabolic activity: oxygen & glucose
EEG: records the field potential from the scalp, so is non-invasive. Because of this, it
only captures very large changes in synchronized activity, and with poor spatial
resolution.
Advantages:
- Cheap
- High temporal resolution
- Moves with the subject (good for children)
- Silent (good for auditory perception)
Disadvantages:
- Poor spatial resolution
- Poor signal-to-noise ratio
- Only senses activity near the scalp (cortex)
- Slow to set up (particularly for large electrode numbers)
Functional MRI
FMRI is by far the most common neuroimaging method used in perception. Advantages:
- High spatial resolution
- Straightforward analysis/interpretation
- Safe and non-invasive
- Easy access
Disadvantages:
- Indirect measure of neural activity
, - Low signal to noise ratios
- Awkward environment
- Poor temporal resolution
Uitleg MRI: Because we are mostly made from water, our tissues contain a lot of
hydrogen atoms. In these atoms, the electron moving around the proton acts like a tiny
magnet. Normally, the orientation of these atoms is random, but a large magnetic field
can align them all in one direction. Adding a smaller magnetic field briefly in another
direction (input RF) changes this atom spin direction. When this is removed, the atom
goes back to its original orientation. This change releases energy (exit RF) that we
measure. The amount of energy released at each location determines that location’s
intensity in the image.
BOLD signal: dip location
- Reflects LFP synaptic activity
Neural activity: LFP vs MUA
MUA (multi unit activity) action potentials (spikes). Neural “output”
LFP (local field potentials)slow electrical signals and sub-threshold activity, including
synaptic activity and voltage-dependent membrane oscillation. Neural “processing”
Neural excitation: releases glutamate, causes vasodilation: increase in blood flow
Neural inhibition: releases GABA, causes vasoconstriction: decrease in blood flow
Lesion studies: het bestuderen van beschadigde delen in het brein (lesions)
- Brain damage is rarely restricted to one area → less specific problems and less
specific ties to one area and damaged perception
- More common that lesion damages whole cortex → patient goes blind
- Creating lesions in animals: done specifically
Transcranial magnitude stimulation (TMS): artificial lesions
- Changing magnetic fields to disrupt electrical activity in a specific part of the brain
→ temporarily disrupts activity in the targeted area
- First use fMRI to find area, then TMS
, College 2
4-2-2020
Something is not red, but reflects red frequencies
We can only see a small part of all wavelengths, some animals see ultraviolet
We see the part that is handig voor zoogdieren
Fish don’t need long wave frequencies (there is no light in the ocean)
Red: long wave frequencies
Blue: short wave frequencies
Surroundings make us perceive colours differently
We do not perfeice light, but contrast/changes in light
Spiders have more than 2 eyes, different sizes and shapes
Octopus eye resembles human eye more
- Difference: our receptor point to back of the head, octopus receptors point
forward
- Other differences: shape,
Binocular vision: overlapping vision of the (2) eyes
- Large binocular vision: more head movement
- We need to move our eyes more because they are at the front of our head and
close together
When light reaches our retina:
1. Ganglion cells
2. Middle layer cells
3. Receptor cells (rod/cones)
Fovea: gele vlek op netvlies, plek waar het zicht het scherpst is met meeste cones
- No rods!
con/rod cell:
- Outer segment is made of membranes: where light is absorbed
When light hits rod/cone: rhodopsin breaks down → cell hyperpolarizes: less
neurotransmitter release (so a decrease) for the proportion of the amount of light
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