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KIN 653 Human Neuroscience Theory > Visual Processing > Flashcards

Visual Processing Flashcards

1
Q

What stimulus features are encoded by the photoreceptors?

A
  • colour of the ball, contours of the ball , Motion of the ball, Location Modality – light energy is transformed by receptors into an electrical signal called potential Brightness: stimulus intensity Amplitude of receptor potential -> rate of action potentials + number of neurons activated in brain (population code) Duration: time course of action potential Colour Location: conveyed through each receptors field
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2
Q

True or False: The receptor potential generated by an adequate stimulus produces a local of the sensory receptor cell.

A

True

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3
Q

True or False: Light causes depolarization

A

False, hyperpolarization

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4
Q

What is hyperpolarization of the retina?

A

reduced concentration of glutamate in the synaptic terminal

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5
Q

What is graded potential?

A

Graded potential: the amount of glutamate is proportional to the # of photons absorbed

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6
Q

What are the two types of bipolar cells and what are their functions?

A

on-center and off-center reduction in the release of glutamate from the photoreceptor has a differential effect on the activity of these cells

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7
Q

_______ of the on-center bipolar cell and an ______ in its transmitter release hyperpolarization of the off-center bipolar cell, and ______ in its transmitter release

A

depolarization, increase hyperpolarization, decrease

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8
Q

______ cells transform visual information into bursts of action potentials that travel to the brain through the optic nerve.

A

Retinal ganglion

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9
Q

Explain this image in text

A

**Action of neurotransmitter depends on the receptor it binds too

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10
Q

What are the 3 types of cones and what are there ranges of sensitivity

A

Blue 437 nm

Green 533 nm

Red 564 nm

Rod 498 nm

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11
Q

The receptive field of an individual ______ is the particular region of the sensory space (e.g., the body surface, or the visual field) in which a ______will modify the firing of that neuron.

A

sensory neuron, stimulus

For example, the receptive field of a ganglion cell in the retina of the eye is composed of input from all of the photoreceptors which synapse with it, and a group of ganglion cells in turn forms the receptive field for a cell in the brain. This process is called convergence.

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12
Q

Stimulus location is encoded with respect to the ______

A

fovea

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13
Q

True or False: Rods are located mostly at the fovea compared to cones

A

False,

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14
Q

Compare and contrast rods and cones

A

Cones

5 million

Color vision

Photopic vision

Low sensitivity

High spatial resolution

Rods

100 million

Monochromatic

Scotopic vision

High sensitivity

Low spatial resolution

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15
Q

_____ is the ability to resolve details and ______ is the responsiveness to light and ability to transmit signals

A

Acuity, Sensitivity

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16
Q

_______ A high ratio of photoreceptors to ganglion cells is required

______ A low ratio of photoreceptors to ganglion cells is required

A

Sensitivity and acuity

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17
Q

True or False: Spatial resolution proportional to the number of receptors neurons

A

True

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18
Q

Information processing at the retina, what is the vertical and lateral system?

A

vertical system: photoreceptors –> bipolar cells –> ganglion cells

lateral system: horizontal cells and amacrine cells

important role in lateral inhibition: neural interactions between adjacent regions of the retina

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19
Q

________ is when each neuron integrates sensory inputs from adjacent receptors and, using networks of inhibitory neurons, emphasizes the strongest signals:

A

Lateral inhibition

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20
Q

Explain this image in the text (A,B)

A

A: Mostly strong neurons in the center (red) of the array feel the stimulus. The receptive field of and the individual relay is neuron is larger than any of the presynaptic sensory neurons because of the convergent connections

B: Inhibition is mediated by local interneurons to the center zone where stimulus is the strongest, enhancing contrast between strong and weak stimulated relay neurons

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21
Q

What are the two major types of retinal ganglion cells?

A

Type M and Type P

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22
Q

What are the 3 characteristics of Type M receptors?

A
  • large RF (receptor fields): synapses with many bipolar cells: rods and cones – not color sensitive
  • responds with a transient, rapidly adapting response to a maintained stimulus
  • responds maximally, with high discharge rates, to stimuli moving across its receptive field
23
Q

What are the 4 characteristics of Type P ganglion cells?

A
  • Small RF: makes synaptic contact with one to a few bipolar which receive input mainly from cones
  • color-sensitive
  • produce a sustained, slowly adapting response that lasts as long as a stimulus is centered on its RF
  • produces weak responses to stimuli that move across its receptive field
24
Q

Know the differences in this image

A

Rapidly adapting receptor adapts to the change in the action potential

25
Q

What is the LGN?

A

The lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a relay center in the thalamus for the visual pathway. It receives a major sensory input from the retina.

26
Q

True or False: Only ~10% of synapses in the LGN are from the retina

A

True

27
Q

True or False: Visual field is left and right inverted and upside down

A

True

28
Q

What happens at the Optic chiasm?

A

partial decussation, only nasal fibers cross

= contralateral representation from each eye

29
Q

True or False: There is no binocular neurons on the LGN

A

True

30
Q

What are the layers of the LGN (4,5,6)

A

Input layer is layer 4

5 output spinal cord brainstem area, superior colliculus

6 is the thalamus?

31
Q

Explain picture, receptive fields in V1

A

The orientation of the line will increase the firing rate of a cortical cell in V1

32
Q

Explain this image in text

A

V1 is organized in columns which make a hypercolumn

Each column has a particular line orientation preference which is indicated on the top of each column (and color-coded)

Adjacent groups of columns have a particular ocular dominance—a preference for input from one eye or the other—as indicated at the bottom of the figure

Blobs are indicated as cubes embedded in the hypercolumn.

33
Q

What is the binding problem?

A
  • Information about form, motion, and color is carried by parallel and interacting pathways in the brain
  • Visual information must be brought together into a coherent visual image to build the perceived world (consciousness)

Synchronized firing, arrive approximately at the same time,

Can effect Attention

34
Q

Try to memorize

A
35
Q

Explain both the dorsal and ventral pathway

A

Ventral stream (object recognition, burgundy) analyzes and encodes information about the form and structure of the visual scene and objects within it, delivering information to the prefrontal cortex

Dorsal stream (where and how) in the parietal lobe analyzes and represents information about stimulus location and motion delivers this information to motor areas of the frontal cortex that controls movements of eyes, hand, and arm

36
Q

______ = eye movements, ______ no eye movement

A

Overt, Covert

37
Q

______ bottom-up based on salience

______ top-down based on task relevance

A

Exogenous, Endogenous

38
Q

What are the 3 ways responses of a cell could be changed by attention?

A
  1. Response enhancement
  2. Sharper tuning
  3. Altered tuning
39
Q

______ area contains a map of neurons (retinotopically-coded when the eyes are fixed) representing the saliency of spatial locations

Explain image

A

Lateral intraparietal (LIP)

A neuron in the LIP fires only in response to a salient stimuli

40
Q

Explain A and B

A

A: Monkey trained to make the second saccade cued object; the cell fires intensely when the first saccade brings object in the receptive field

B: trained to make the second saccade outside receptive field; the cell fires much less when the saccade brings the task-irrelevant stimulus in the receptive field

41
Q

True or False: During saccades, the images move across the retina at a high speed -> visual sensitivity is reduced: saccadic suppression

A

True, causes are:

  • Visual masking
  • Corollary discharge (efference copy)
42
Q

Explain image

A

Activity in parietal cortex neuron anticipates a change in position of its receptor field due to a saccade

The response of the cell to a stimulus in its receptive field decreases, even before a saccade (A) while its response to a stimulus in the anticipated post-saccade position of its receptive field increases (B)

43
Q

Explain this image from text

A

A corollary discharge from the motor program for saccades directs presaccade shifts in receptive field location for frontal eye field neurons.

A: saccade generation neuron comes from the superior colliculus, passes throig medial dorsal nucleus of the thalamus and terminated in FEF

B: When MD inactive, responses to stimuli currently in the RF are not affected,

Responses to stimuli in the prospective (future) RF are affected with MD inactivation

44
Q

What do alll these areas encode?

A

Medial intraparietal (MIP) area neurons encode the location of a reach target in nose-centered coordinates

Anterior intraparietal (AIP) area contains neurons responsive to shape, size, and orientation of objects to be grasped

LIP targets of eyemovents and projects to the FEF

VIP represents the face and projects to the face control area of F4

45
Q

Explain this image in text

A

Neurons in the anterior intraparietal cortex respond selectively to specific shapes

The neuron here is shown to be selective for a rectangle, therefore cause not much firing for the cylinder

46
Q

Explain this image

A

Bimodal neurons in the ventral intraparietal cortex of a monkey respond to both visual and tactile stimuli

The neuron responds to tactile stimulation of the monkeys head or a visual stimulus as the object is coming towards the head and goes away when it recedes

47
Q

Explain this image

A

(a cortical pathway for ventral pathway (object recognition))

neurons in V1 and V2 respond to bars with specific orientations and locations in the visual field. Convergent inputs from different V2 neurons enable V4 cells to signal an angle. In tur, the same thing happens with V4 and IT that respond optimally more complex to shapes like a triangle. Therefore stimulation of retina creates small representations that become more recognizable in higher cortical areas

48
Q

What are the two important properties of neurons in the ventral stream?

A

Response specificity and perceptual constancy

49
Q

What does the picture represent?

A

Response specificity

The neuron on the ITP responded selectively to faces such as the mouth and eyes, and elicited no almost no response in the scrambled version

50
Q

Explain the image

A

Perceptual constancy

A: Size constancy, object appears to be the same, even when retinal image size decreases in the visual field

B: Object appears to be the same even though there is a change in position

C: Form cue-invariance: Object appears to be the same even though there is a difference in reflectance

51
Q

Mechanisms of directed attention in the extrastriate cortex (V3, V4 etc.) Kasnter et al 2000

A

4 images were displayed once or one at a time

Larger activation in V4 for sensory interactions

Greater attention when ask to focused on one topic

52
Q

What is the attention selection mechanism?

A

PFC activity exerts a top-down influence by providing an excitatory signal that biases processing in other brain systems towards task-relevant information

•Deactivation of the lateral PFC attenuates the activity of extrastriate neurons to a behaviorally relevant cue

53
Q

explain the image

A

Circuits for visual association and recall

54
Q
A

KIN 653 Human Neuroscience Theory (5 decks)

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