Neural Basis of Perception

Question 1

What are Neurons?
(Neuron)

Answer 1

Neurons are cells receiving and transmitting information in the nervous system

Question 2

How is the activity of a single neuron measured?
(Neuron)

Answer 2

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

Question 3

What are synapses?
(Neuron)

Answer 3

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)

Question 4

What are receptors?
(Neuron)

Answer 4

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

Question 5

How are visual representations of the world created?
(Eye)

Answer 5

1. We look at an object
2. Light reflected by object enters the eye
3. Image of the object is focussed onto the retina

Question 6

What structural elements form the eye?
(Eye)

Answer 6

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

Question 7

What does the Retina consist of?
(Eye)

Answer 7

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

Question 8

How do photoreceptors work?
(Eye)

Answer 8

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

Question 9

What are the differences between rods and cones?
(Eye)

Answer 9

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

Question 10

How are rods and cones distributed in the retina?
(Eye)

Answer 10

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)

Question 11

How do ganglion cells transmit the signals?
(Eye)

Answer 11

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)

Question 12

How do the Ganglion cells receptive field work?
(Eye)

Answer 12

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

Question 13

Trough what steps goes the information flow from the eye to the brain?
(Eye)

Answer 13

1. Retina
2. Ganglion Cell
3. Lateral Geniculate Nucleus (LGN)
4. Striate Cortex (primary visual cortex)
5. Higher-level visual areas

=> not just one “vision-area”

Question 14

What is the Lateral Geniculate Nucleus (LGN)?
(Eye)

Answer 14

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

Question 15

What is the striate cortex?
(Eye)

Answer 15

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

Question 16

What cell types are in the striate cortex?
(eye)

Answer 16

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

Question 17

What does it mean when cells in the striate cortex are end-stopped?
(Eye)

Answer 17

=> some cells prefer bars of light of a certain length

-> length is increased beyond size of the receptive field <=> response rate is decreased

Question 18

How does the brain create complex representations?
(Eye)

Answer 18

increasingly complex signals
-> combining signals from previous steps,
-> the brain creates complex representation that can
code for…
- orientation,
- width,
- length,
- position,

Question 19

What 4 areas of the brain localize cognitive functions?
(Brain)

Answer 19

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

Question 20

What are some specialised brain areas for different stimuli?
(brain)

Answer 20

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)

Question 21

What is feature binding?
(brain)

Answer 21

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

Question 22

What are experimental measures alternative to animal studies?
(selfstudy)

Answer 22

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

Question 23

What is the Tilt Aftereffect?
(selfstudy)

Answer 23

= 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

Question 24

What is the Hermann Grid?
(selfstudy)

Answer 24

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)