Neural Basis of Perception Flashcards
What are Neurons?
(Neuron)
Neurons are cells receiving and transmitting information in the nervous system
How is the activity of a single neuron measured?
(Neuron)
action potential
-> information is transmitted trough the axon in the form of an electrical impulse
resisting potential
-> -70 mV becomes depolarized
-> +40 mV goes into repolarization and returns to baseline after
Transmitting process
1. Dendrites receive information from other neurons
2. The celbody contains the nucleus and most cell organelles
3. Information collected by dendrites is integrated in the axon hillock, which generates action potential
4. The axon conducts action potentials away from the body of the cell
5. Axon terminals synopse with a target cell
What are synapses?
(Neuron)
Gap between axon of a presynamptic neuron and dendrided of postsynaptic neurons
There
-> electrical signal is converted into biochemical signal
(release of neurotransmatters into the synapse)
-> Neurotransmitters bind to receptors of the postsynaptic neuron
(either excitatory or inhibitory effect, triggering or inhibiting new action potential)
What are receptors?
(Neuron)
Neurons receive input from other neurons or the environment using specialized receptors
-> stimulus intensity is represented in firing rate
Low intendity = low firing rate
High intensity = high firing rate
How are visual representations of the world created?
(Eye)
- We look at an object
- Light reflected by object enters the eye
- Image of the object is focussed onto the retina
What structural elements form the eye?
(Eye)
Retina
-> light sensitive membrane in the back of the eye
-> transforms light into neural signals
optic nerve
-> transmits visual information from the retina to the brain
Fovea
-> Area at the centre of the retina
-> highest visual acuity
Periphery
-> Parts of the visual field away from the fovea
What does the Retina consist of?
(Eye)
Photoreceptors
-> Transduce light into neural signal
-> Two types: Rods and Cones
Ganglion cells
-> Neural signal is passed on to
-> transmit signal to the brain via optic nerves
optic nerves
= bundle of ganglion cells
How do photoreceptors work?
(Eye)
Function
-> transduce light into neural signal
-> carry the protein opsin that changes its shape when
struck by a photon
-> biochemical processes cause changes in the
neurotransmitters released to bipolar cells
What are the differences between rods and cones?
(Eye)
Rods
-> scotopic vision (low-light conditions)
-> do not process color
-> Multiple rods converge on the ganglion cell
(summation of several signals)
- Higher sensitivity
- Lower acuity
Cones
-> photopic vision (well-lit conditions)
-> 3 different types for light at different wavelengths (rgb)
-> Connect to a single ganglion cell
(No summation of signals)
- lower sensitivity
- higher acuity
How are rods and cones distributed in the retina?
(Eye)
Fovea
(= small part of visual field with color and “full resolution”)
-> highest visual acuity
-> highest density of cones
-> at the centre no rods
Periphery
(= away from the fovea)
-> lower visual acuity
-> fewer cones
-> primarily rods
Optic disc
(= point where optic nerve leaves the eye - away from fovea)
-> blind spot
-> no rods or cones
-> not usually noticed
(brain fills in & two eye covering for each other)
How do ganglion cells transmit the signals?
(Eye)
Final layer of the retina
-> last stop before the brain
receptors
-> information from several receptors converge at single ganglion cell
-> depending on size of receptive field
receptieve field
-> circular layer of the retina
-> size differs across retina
-> donut shape
- centre (inner circle)
- surround (ring)
How do the Ganglion cells receptive field work?
(Eye)
Donut-shaped receptive field
ON (excitatory-area)
-> shining light on ON-area
-> firing rate of the cell increases
OFF (inhibitatory-area)
-> shining light on OFF-area
-> firing rate of the cell decreases
Two-types
-> On-centre cell
(light in middle -> strongest response)
-> OFF-centre cell
(light around middle -> strongest response)
=> First coding of size and location at retina level
Trough what steps goes the information flow from the eye to the brain?
(Eye)
- Retina
- Ganglion Cell
- Lateral Geniculate Nucleus (LGN)
- Striate Cortex (primary visual cortex)
- Higher-level visual areas
=> not just one “vision-area”
What is the Lateral Geniculate Nucleus (LGN)?
(Eye)
WHAT?
-> organization of brain areas involved in visual
perception
-> follows topographical mapping
STRUCTURE?
-> same donut shaped receptive field as ganglion cells
-> receive input from them
CONNECTION?
-> Feedback connections from higher brain areas to LGN
-> visual field processed in inverse side LGN
What is the striate cortex?
(Eye)
WHAT?
-> same topogrophical mapping as LGN,
-> more than 100 times as many cells
-> cortical magnification
(much larger representation of the fovea)
FUNCTION?
-> summarize signals from LGN cells
-> LGN receptive fields form a straight line of donuts in the visual field
(converging on a single striate cortex cell)
-> Firing rate increases <=> light falls on ON-centres of all LGN cells
=> Response stronger to bars, lines and edges
What cell types are in the striate cortex?
(eye)
STRUCTURE?
-> simple cells
-> complex cells
-> end-stopped cells
simple cells
(= neurons with defined excitatory and inhibitory
receptive field regions)
-> Edge detectors
- respond strongest to to edges
(light-dark side divide)
-> stripe detectors
- respond strongest to stripes of light
(light stripe surrounded by dark stripes or invers)
complex cells
(= receptive field not clearly defined in excitatory and inhibitory receptive fields)
-> fires if light falls anywhere within the receptive field
What does it mean when cells in the striate cortex are end-stopped?
(Eye)
=> some cells prefer bars of light of a certain length
-> length is increased beyond size of the receptive field <=> response rate is decreased
How does the brain create complex representations?
(Eye)
increasingly complex signals
-> combining signals from previous steps,
-> the brain creates complex representation that can
code for…
- orientation,
- width,
- length,
- position,
What 4 areas of the brain localize cognitive functions?
(Brain)
Cerebral Cortex
(=outside layer of the brain)
-> Most cognitive functions are located in
-> 4 lobes
Temporal Lobe
(= Auditory Cortex)
-> hearing
Occipital Lobe
(= Visual Cortex)
-> seeing
Parietal Lobe
(= Somatosensory Cortex)
-> touch
-> temperature
-> pain
Fontal Lobe
(= Executive functions
= higher-level-cognition)
-> decision making
-> problem solving
What are some specialised brain areas for different stimuli?
(brain)
Fusiform Face Area (FFA)
-> faces
Parahipocampal Place Area (PPA)
-> places
Extrastriate Body Area (EBA)
-> bodies
-> body parts
=> complex concepts are not represented by single cells
(specifity coding)
=> complex concepts are represented by firing pattern
of…
- many cells (population coding)
- few cells (sparse coding)
What is feature binding?
(brain)
distributed processing
-> functions are rarely processed in just one brain area
feature binding
= combining features that are processed in seperate brain areas
-> usually unaware of this
-> distributed processing in…
- memory
- language
- decision making
What are experimental measures alternative to animal studies?
(selfstudy)
Neuroimaging
= field that uses various techniques to visualize the structure and function of the nervous system, (particularly the brain)
selective adaption
(= deminishing response of a sensory organ to a sustained or repeated stimulus)
-> casuses Fatigues
(cells selectively responding to that stimulus)
-> method to temporarily “knock out” groups of neurons without surgery
What is the Tilt Aftereffect?
(selfstudy)
= perceptual illusion of tilt as a result of adapting to a pattern of a given orientation
-> supports the idea that human neurons selectively respond to different orientations
=> shows how the brain can be studied without invasive and animal research
What is the Hermann Grid?
(selfstudy)
Effect
-> illusory “black dots” appear at intersections of white
grid lines
-> black dots disappear when fixated
Explanation
-> periphery (parafoveal)
- large receptive fields
- intersections -> strong OFF activation
(perceived as dark)
- between intersections -> less OFF activation
(perceived as light)
-> fixation (foveal)
- smaller receptive fields
- no difference in perception at/between intersections
Problem
-> illusory “black dots” disappear when using wavy lines
=> Ganglion cell explanation cannot account for that
- wavy lines don’t change firing rate
- straight lines dependency
=> phenomenon can be “localized” in the striate cortex
(without using neuroimaging or animal studies)