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Sensation and Perception Samenvatting
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Samenvatting Sensation and Perception 2022:HC 1:
The five senses:
1. Vision
2. Audition
3. Taste
4. Smell
5. Touch
6. Balance - sort of
They all have a sensory organ that is related to them → these interact with something physical
in the world
Vision: the eye and the early visual pathways
- Used for shape, motion, color, depth, attention, awareness
- Is is a primary sense for humans → almost every action we take is guided by vision
Sensation: translation of physical/ external environment into pattern of neural activity (through
sensory organs)
Perception: analysis of this neural activity to understand the environment and to guide behavior
- Also the subjective experience of the outside world
- Limited by the body and the brain - Monism (mind as a part of the brain and nervous
system)
Sensation and Perception:
- Together the reflect the interactions between the sensory organs and physical properties
- This means they are dependent on the physical properties of the world
- And they are limited by the physical properties of our sensory organs → for
example we cannot look through a wall
- Evolved to help us survive and reproduce → optimized for useful representations of the
environment (influenced by interpretation)
- Dependent on limited source of attention and awareness
- How we view environment is not accurate but very useful
How to study?:
- Change physical environment - a sensory stimulus and measure the resulting behavior
or neural activity
- JND: just noticeable difference
- Difference threshold: minimum of difference a person can detect
- Put into a logarithmic function so it can be used on big numbers
- 2AFC: 2 alternative forced choice
- Give two options that fall in the category of correct vs incorrect, more vs less etc.
- Method of constant stimuli: present stimuli that you expect to give a response to
get a response
- Threshold usually at 75%
- Make the trial easier when something is wrong and harder when something is
right.
,Neural activity: (biological approach)
- Spiking activity: action potentials (measure directly from neuron)
- Synaptic activity: synaptic potentials
- LFP: local field potential → group of synchronized synaptic activity in a group of neurons
(neural processing)
- Theta = sleeping, Alpha = inhibition neural activity, Gamma = increase activity
- Oscillations: periodic motion in a regular cycle
- Action between inhibitory and excitatory neurons - INH is activated by EX but EX
inhibits INH so depolarizes - cycle
- Not necessary for perception but correlated
EEG: high temporal resolution but low spatial resolution
fMRI: low temporal resolution but high spatial resolution
- Resting oxyhemoglobin and deoxyhemoglobin are equal
- The stimulus spikes neural activity and causes the neurons to subtract the oxygen from
the blood cells
- Now there are only deoxygenated blood cells so blood rushes towards the area to
(over)compensate the deoxyhemoglobin (signal loss) which causes a signal
- So blood response follow the neural activity and this is what the BOLD records
- MUA - multi unit activity: action potential spikes (neural output)
HC 2:
People only see a certain spectrum of light:
- This depends on the wavelengths of the light
- Different colors have different wavelengths
- Something is not a color but it reflects a certain light of that color
- This can also depend on the surroundings of the object - later more
Vertebrate eye: i.e. the human eye
- Has a blind spot - part where photoreceptors come together to form the optic nerve →
leaves no room for photo receptors → cannot absorb the light so no vision
- Have lots of visual field overlap, most vision is seen by both eyes
- Need eye movements to see everything clearly
Lens: the thing in your eye that sees the environment
- Can help focus on a certain thing - far/ close
- Converges the light onto the retina
- When focussing on far away object the lens will be wider and thin
- When focussing on a near object the lens will be thick and round
- This is called accomodation of the eyes (for focus)
- Convergence: moving of the eyes more inward (for near) of outward (far away)
Human Retina: sensitive to light and color and sends info to the optic nerve
- Use degrees of the visual angle to find out the actual size of the object
- Size is measured in degree - the more further away = smaller and the more close =
bigger representation on the retina
Fovea: the highest sensitivity to details
- There are less ganglion cells so more cones are formed here
, - The cones are good at discovering details so this is used for focus vision
- The cones have small receptive fields in this area
- 1 bipolar cell connected to 1 ganglion cell connected to 1 photoreceptor
- In periphery they connect to multiple receptors and cells (double convergence)
Rod: photoreceptor that is used for peripheral vision and works better in the dark
- Insensitive to long wavelength (red)
- Mostly in periphery vision - this is why is it hard to see color in periphery, brain uses
experience to fill in the blanks
Cones: photoreceptor that is used for central vision and works best in the light
- Are small in the fovea and become bigger as they move to the side
- Processes colors
Rhodopsin: transmembrane protein sensitive to light
- Can be found in the disks of the cones and the rods
- When light hits the receptor the rhodopsin is broken down - causes cell to hyperpolarize
and stops produce of neurotransmitters (glutamate) - sodium cannot get in and
potassium cannot get out
Red cone = long wavelength = L - Cone
Green cone = medium wavelength = M - Cone
Blue cone = short wavelength = S - cone
Purkinje Shift:
- The light sensitivity of the eye shifts when it is light vs. when it is dark
- When it is light, cones are more active and here the L-cone is most sensitive (you notice
a red flower between green leaves)
- When it is dark the rods are more active which do not respond to L-cone which makes
you more sensitive to S-cone and M-cone
Dark adaptation:
- Makes a shift in visual sensitivity - from cones (light) to dark (rods)
- When it all of a sudden gets dark - cones reach maximum sensitivity to try to see in the
dark (about 7 min)
- Rhodopsin regenerated because of the dark - rods become more active and take over
Photopic vision: vision in well-lit conditions
Scotopic vision: vision where only rods are used (black and white)
Color deficiency: missing one type of color cone - color blind
Light perception: you do not perceive light but you perceive change in intensity
Photon noise: is less when there is more illumination
- Is more when it is dark - makes it harder to see something
More light on retina:
- Less photon noise
- Increasing density of photoreceptors but size decreases
- Acuity = how sharp you see
- High density of photoreceptors = high acuity
Eye movements:
- Because we do not perceive light but we perceive changes in light intensity
- Eyes need to keep moving in order to see objects
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