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PSYC2020 > Lecture4 > Flashcards

Lecture4 Flashcards

1
Q

In what order does light enter the eye?

A

Passes the cornea, then pupil, then lens, then reaches the retina which converts light into neural signals & conducts them toward the CNS

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2
Q

Fovea subserves the finest:

A

Visual acuity

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3
Q

Where are light sensitive cells situated?

A

In the sensory membrane (retina)

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4
Q

What is the retina responsible for?

A

Transduction of light into neural signals

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5
Q

Explain the cross section of the retina

A

Retinal ganglion cells, amacrine, bipolar, horizontal cells, cone/rod receptors

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6
Q

What is the fovea a solution for?; How?

A

The inside out design of the retina; The layer of cell bodies & axons thin out around this area of the retina and reduce the distortion of incoming light

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7
Q

There’s high acuity in the central but not in the….

A

Peripheral

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8
Q

Light is sometimes referred to as waves of electromagnetic energy that are between…

A

380 & 760 nanometres in length

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9
Q

When illumination is high the pupils are…; so the image is….; When illumination is low the pupils…; which sacrifices….

A

Constricted; Sharper with depth of focus; Dilate to let in more light; Acuity & depth of focus

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10
Q

What are the amacrine cells & horizontal cells specialised for?

A

Lateral communication (communication across the major channels of sensory input

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11
Q

In what 2 ways do retinal neurons communicate?

A

Both chemically via synapses & electrically via gap junctions

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12
Q

What occurs at 17 degrees at the centre of the fovea?

A

there is a gap in the receptor layer called the blind spot; all axons from the ganglion cells leave the eye

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13
Q

What’s the difference between rods & cones?

A

Rods are achromatic, none are in the fovea, high convergence (many rods share a single ganglion cell), higher sensitivity to dim light & lower positional acuity; There are 3 classes of cones, they’re sensitive to colour, exclusive to the fovea, have low convergence (each cone in fovea gets a direct circuit back to visual cortex), less sensitive to dim light, high positional acuity, less ambiguity about location of stimulus

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14
Q

What’s the difference between Photopic vision and Scotopic vision?

A

Photopic is cone-mediated - predominates in good lighting, provides high acuity coloured perceptions; Scotopic is rod-mediated - predominates in dim light; lacks fine detail & colour

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15
Q

In the centre of the fovea at what point do the rods reach a maximum density?

A

20 degrees

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16
Q

Why do we measure size & eccentricity in degrees of visual angle?

A

Because the physical size of an object or the lateral separation of 2 objects does not tell us how big or separated they’ll be on the retina; all the information our brain has about the visual scene is contained in the retinal image

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17
Q

Your finger at about half an arms length is…; A 1cm wide object viewed at a distance of 57cm will subtend…

A

1 degree wide on your retina; 1 degree of visual angle

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18
Q

What is visual transduction?; How does this occur?

A

The conversion of light into neural signals; Photoreceptors contain a pigment (rhodopsin) that responds electrochemically to stimulation by light

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19
Q

Explain the process of visual transduction in darkness

A

Rhodopsin molecules are inactive, sodium channels are kept open so sodium ions flow into the rods partially depolarising them (inhibitory signals flow freely from receptor) & rods continuously release glutamate;

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20
Q

Explain the process of visual transduction in light

A

Light bleaches rhodopsin molecules, as a result sodium channels close (do not respond to neurotransmitters), sodium ions cannot enter rods so receptor cell hyperpolarises & reduces the release of glutamate, inhibition is reduced so the bipolar cell increases firing

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21
Q

Hyperpolarising is…; Depolarising is…

A

More negative - reduces neurotransmitter release; More positive - increases neurotransmitter release

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22
Q

With an increase of light absorption, photoreceptors…; ON Bipolar cells…; OFF Bipolar cells…

A

Hyperpolarise; Depolarise; Hyperpolarise

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23
Q

With a decrease of light absorption, photoreceptors…; ON Bipolar cells…; OFF Bipolar cells…

A

Depolarise; Hyperpolarise; Depolarise

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24
Q

What does the Mach bands demonstration show?

A

Lateral inhibition; Our perception of scalloped edges between borders of brightness between colours

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25
Q

What do Ommatidia receptors do?; How are they connected?

A

Absorb light; By a lateral neural network

26
Q

Explain the horseshoe crab theory in regards to the middle ommatidia receptors labelled D & E

A

Adjacent signals are inhibitory; D is intense light, E is dim; E receives a weak inhibitory signal from F and a strong inhibitory signal from D so D’s firing is accentuated

27
Q

Describe the process of transduction from the visual field of the left eye

A

Projection on left retina; crosses to right hemiretina, half to nasal, half to temporal side; axons travel down the optic nerve; at the optic chiasm, temporal side axons travel ipsilaterally & nasal side axons decussate to contralateral side; on each side they pass through optic tracts, lateral geniculate nuclei to primary visual cortex

28
Q

How do signals from the left visual field reach the right primary visual cortex?

A

Either ipsilaterally from the temporal hemiretina of the right eye or contralaterally (via the optic chiasm) from the nasal hemiretina of the left eye

29
Q

What proportion of the primary visual cortex is dedicated to the analysis of the fovea’s input?

A

about 25% (2 degrees of entire visual field)

30
Q

Explain retinotopic organisation

A

Each level of the system is organised like a map of the retina; two stimuli presented to adjacent areas of the retina excite adjacent neurons at all levels of the system

31
Q

How many layers is the Lateral Geniculate Nucleus composed of?

A

Six

32
Q

What are P channels?; What size cell bodies do they have?; Do cones or rods provide the majority of input?

A

Parvocellular neurons: top 4 layers of the lateral geniculate nucleus; they have small receptive fields, are particularly responsive to colour, fine pattern details & to stationary objects; Small; Cones

33
Q

What are M channels?; What size cell bodies do they have?; Do cones or rods provide the majority of input?

A

Magnocellular neurons: bottom 2 layers of the LGN; they have large receptive fields, are achromatic & responsive to motion; Large; Rods

34
Q

From the LGN, the M & P channels project to different sites in the lower part of….

A

Layer 4 in the Primary Visual Cortex

35
Q

What are 4 common features of the 3 stages of the retina-geniculate-striate system (i.e. from retina to LGN to Primary Visual Cortex)?

A

Fovea receptive fields are smaller than the periphery; all receptive fields are circular; all neurons are monocular (i.e. activated by 1 eye only); concentric excitatory/inhibitory regions

36
Q

What do Receptive Fields refer to?

A

Regions on the sensory organ (i.e. the retina in vision) & the features that excite or inhibit the cell. The nature of the receptive field of a cell gives clues about the cell’s function

37
Q

Receptors converge onto a particular ganglion cell or LGN. What are the responses of an On-centre cell?

A

There’s an ON response when a spot of light is shone anywhere in the centre of the field (complete illumination maximises firing) & an OFF response when shone in the periphery field (illumination of the surround minimises firing)

38
Q

What are the responses of an Off-centre cell?

A

There’s an OFF response when a spot of light is shone anywhere in the centre of the field & an ON response when shone in the periphery field

39
Q

What is the most effective way of maximising the firing of an on-centre or off-centre cell?; What does diffuse illumination of the entire receptive field do?

A

To completely illuminate either the ON area or the OFF area of its receptive field; Minimise firing (if both areas are illuminated together there is little reaction from the cell

40
Q

What are the main differences between Simple Cells & lower layer 4 neurons?;

A

The borders between the ON & OFF regions of the cortical receptive fields are straight lines/rectangular rather than circles & they respond best to bars of light in a dark field or single straight edges between light & dark areas

41
Q

When does a simple cell respond maximally or most vigorously?

A

When static bars with an appropriate orientation falls onto the ON subfield of the receptive field; they’re selectively responsive to specific patterns

42
Q

What do Simple VI cells code?; Low spatial frequency activates simple cells with…; High spatial frequency activates simple cells with…

A

Spatial Scale; Widely separated subfields; Less separated subfields

43
Q

Gradual undulations of simple cells are like…; The more undulations the….

A

Sine waves for the eye (number of times undulated from dark to light per unit of space); Higher the Spatial Frequency

44
Q

What does signalling changes from light to dark at a different spatial scale allow simple cells to do?; If we take out high spatial frequency what do we get?

A

Code information about different features: edges & texture; A blurred image - borders are less defined & texture is more prominent

45
Q

Where do complex cells reside?; When will a complex cell fire?

A

VI, layers 1-3 & 5-6; If it gets any input from its contributing simple cells

46
Q

Many complex cells receive inputs from both eyes, what is this called?; If inputs arrive from either the left or right eye what will happen?; If inputs arrive from both eyes simultaneously what happens?; What is occular dominance?

A

Binocular; The cell will increase firing; There’s a more vigorous response; Some cells favour one eye over the other & respond more vigorously to one eye

47
Q

How do some complex cells respond if similar contours fall on nearly the same positions in the 2 eyes?; What is this called?; Therefore what do complex cells underlie?

A

Well; Binocular disparity; Stereotopic depth perception

48
Q

Explain the columnar organisation of the primary visual cortex

A

Signals flow from simple to complex; functionally similar cells are grouped in VI; columns alternate in eye dominance

49
Q

In columnar organisation a block of tissue is assumed to analyse visual signals from one area to the visual field where half is dominated by…; & half by…; What is each slice of the block of tissue presumed to specialise in?

A

Right eye input; Left eye input; The analysis of straight lines in a particular orientation

50
Q

When proceeding vertically within cortical columns of VI, all neurons in a column have receptive fields in the…; What do all the simple & complex neurons in a column prefer?; In a given column, all monocular & binocular neurons are dominated by…

A

Same general area of the visual field; Straight line stimuli in the same orientation; The same eye

51
Q

When neurons proceed across a horizontal electrode track of VI cortical columns, the position of the receptive fields of the neurons…; & the preferred orientation of the neurons at the tip…; As the electrode advances, how does the tip move?

A

Shifts systematically at the tip; Also shifts systematically; Alternately through columns of right & left-eye dominance

52
Q

What does the Howard Dolman test teach us about comparisons between Monocular & Binocular view when looking at targets near & far?

A

It’s hard to tell the difference through one eye (monocular); with binocular we can compare horizontal differences & see the difference in separation; adjustments with 2 eyes are very precise compared to monocular vision

53
Q

Significant cortical mechanisms of vision & conscious awareness occur in ventral & dorsal streams of…

A

Inferotemporal Cortex & Prestriate Cortex

54
Q

What occurs if you have a left VI cortical scotoma?

A

You’ll have a blind spot in the right side of visual space

55
Q

What is Blind Sight?; Although a patient will report no conscious visual perception within the scotoma, how do they perform on visual tasks when tested?

A

A condition where the primary visual cortex is damaged & a large scotoma is present (usually covers half of visual field); Above chance on the following: judging orientation of lines they report they can’t see, correctly reaching for oriented objects, & correctly intercepting objects moving through their scotoma

56
Q

Name two possible explanations for visual task performance despite Blindsight

A

Damage to VI is not complete & some residual functionality remains; visual pathways exist that ascend to secondary visual cortex without passing through VI. These pathways may support visual abilities without conscious awareness

57
Q

Explain the “where vs. what” theory; What does this theory predict?

A

Dorsal stream specialises in visual spatial perception & Ventral stream specialises in visual pattern recognition; That damage in either area will disrupt the corresponding ability

58
Q

Explain the “control of behaviour vs. conscious perception” theory; What does this theory predict?

A

Dorsal stream specialises in visually guided behaviour & Ventral stream specialises in conscious visual perception; That damage in either area will disrupt the corresponding ability without affecting the other ability

59
Q

What deficit tests the Visual Pathway theory?; What is it?; They can distinguish between objects & faces but not…; What does this suggest?

A

Prosopagnosia; Where a patient can’t recognise faces (sometimes even their own); Between faces; There appears to be neural structures specific to faces

60
Q

What does Prosopagnosia result from?; Therefore theoretically what should be impeded in this condition?; What evidence supported this theory in an experiment recognising familiar & unfamiliar faces?

A

Damage to the Ventral stream; Conscious awareness but not control of behaviour; None of the faces were recognised but familiar faces yielded heightened galvanic skin responses (GSR is subserved by the dorsal stream, ie. control of behaviour)

PSYC2020 (11 decks)

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