Section 4 Flashcards by Arianna Teel

Human vision is limited as we can only see between

380 - 760 nm

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Do we need light to see?

Yes. Not even nocturnal animals can see in the dark we all need some light to see

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Visual field (definition)

the amount of space that is divided by the nose

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Visual sensitivity

the neurons ability to detect

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Visual acuity

refers to detail/resolution

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Visual transduction

conversion of light energy to neural signals done by the receptors

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What is the advantage of having one eye on each side of the head?

Larger visual field

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What is the advantage of having both eyes in the front?

More visual acuity

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Binocular disparity (definition)

the difference between two retinal images helps create 3D or depth perception - needed by animals who work with tools

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Retina (definition)

has the receptors that regulate the transduction of light

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The two unique spots of the retina are

fovea - 90% of receptors here
blind spot - no receptors

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The layers of the retina (5)

photoreceptors (cones and rods) - transduction & synapse with bipolar cells
horizontal cells
bipolar cells - synapse with retinal ganglion cells
amacrine cells
retinal ganglion cells

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Why is the blind spot of the retina “blind”

no photoreceptors are found in this part of the retina

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Two types of photoreceptors and their properties

Cones:
- photopic vision
- predominant in bright lighting
- high acuity
- located in the center of retina

Rods:
- scotopic vision
- predominant in dim lighting
- high sensitivity
- located in the periphery/outer part of the retina

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Convergence ratio of cone-fed circuits

low convergence 1 cone: 1 bipolar: 1 retinol ganglion
high acuity and low sensitivity

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Convergence ratio of rod-fed circuits

high convergence 1 rod: 10 bipolar: 100 retinol ganglion
high sensitivity and low resolution

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How can we have clear and detail vision if incoming light is distorted and there is a blind spot?

the fovea, perceptual completion, and eye movements

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Fovea

allows high acuity vision due to the high density of receptors

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Perceptual completion

the brain does “tricks” and fills in information in the blind spot based on context and past experience

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Saccades

rapid eye movements; the perceived image is a sum of inputs received during the last few fixations (like quick camera snapshots)

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Scotoma

an area of blindness caused by damage in the visual cortical area; damage in cortical areas affects signal processing due to retinotopic organization

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Blindsight

the ability to see despite cortical-induced scotoma; happens due to alternative visual pathways (superior colliculus)

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What happens if images are stabilized on the retina (the eye is not moving)?

The neurons stop firing and the image begins to fade (no input = image fades); the neurons respond to change

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Differences between retinal images and photographs

photographs are exact copies while our visual system makes good “guesses”; what we see is our brain drawing on experiences and context

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The lens of the eye projects on to the retina a _____, ______, and _____ image

focused, inverted, reversed

Photoreceptors transduce light into ____

neural firing patterns

How does the brain make sense of these sequences of impulses originating from different parts of the retina?

firing patterns are transmitted to the bipolar and horizontal cells, then transmitted to the endocrine and ganglion cells before bundling in optic nerve which is the sent to the brain (gets more ordered at each level of processing so you perceive the image focused and at the right orientation)

Retina-geniculate-striate pathway

major visual information processing pathway

Visual signal from each visual field goes to the ______ hemisphere

contralateral (e.g. objects in the left visual field => brain structures in the right hemisphere)

If there is a lesion in the right optic nerve, how is vision affected?

the right eye cannot see, the left eye is not impacted

If there is a lesion in the optic chiasm, how is vision affected?

damage with contralateral pathways (the LVF of left eye cannot see and the RVF of the right eye cannot see)

If there is a lesion in the right V1, how is vision affected?

the LVF of both eyes cannot see (left nasal and right temporal)

Visual Thalamus (LGN)

main subcortical nuclei that carries visual signals to the cortex 6 layers of cells recieves 90% of retinal input

Input from each eye is ______ in the LGN

separate; monocular

Primary Visual Cortex

(also called V1 or striate) 6 layers of cells; LGN projects to layer 4 first stage of visual processing in cerebral cortex

Visual organization

Retinotopic organization disproportionate cortical representation of the fovea

Higher concentration of receptors in a retinal area is associated with

larger cortical representation and higher acuity

What is the visual receptive field?

the area of the retina that when stimulate with light, changes the cell's activity has two areas, a center and a surround, producing opposite repsonses (light in center might be excitatory with the surround inhibitory or the opposite)

Two forms of visual receptive fields

circular (RGN, LGN) rectangular (V1)

What are the properties of the on-center cell?

the on-center excites the neural firing while the off-surround inhibits firing

If light is shone in both the on-area and off-area at the same time the response is ____

weakend

What is the correlation between receptive field size and discrimination?

smaller receptive field = finer discrimination

How does the receptive field of neurons in the fovea compare to those in the periphery?

the RF of neurons in the fovea are smaller than in the periphery, allowing finer discrimination

Retinal Ganglion cells most respond to

small spots of light

Neurons in the V1 most respond to

bars of light

None of the receptors respond to

background or diffuse light; neurons respond to change/contrast

Two major classes of V1 neurons and properties

Simple cells: - respond to lines/bars of specific orientation - RF has a clear on/off area Complex cells: - larger RFs than those of simple cells - binocular - 3D vision begins here

Receptive fields of neurons in the foveal area of LGN or V1 are ____ than those in the periphery area

smaller

Contrast enhancement

mechanism in the visual system that enhances perception of brightness contrast between two areas

Perception is a _____ property

cortical

How does lateral inhibition work?

when a receptor fires, it also inhibits neighboring receptors

The Hermann Grid Illusion demonstrates

there is some lateral inhibition at the retinal level

If light alters the firing of a small group of receptors, what is the effect on the on-center bipolar cell that is directly connected to those receptors? What is the effect on the nearby cells? What causes this effect?

Excitatory; Inhibitory; Lateral Inhibition

Component theory

perception of color can be explained by different receptors (cones) in the retina

Opponent process theory

occurs at all levels of the visual system beyond receptors; opposing colors and complementary afterimage

Retinex theory

refers to the observation of color constancy and color contrast - the perception of object color is determined by its reflectance in a context

What behavioral phenomenon might have contributed to your percieved color?

color constancy and contrast

Which of the following most likely gives rise to the behavioral phenomenon of color constancy?

neural processing at the cortical level

Regions beyond the striate cortex are called

extrastriate areas

Cells in the extrastriate areas have ____ visual receptive fields

larger

Dorsal stream

where and action pathway; directing behavioral interactions with objects

Ventral stream

responsible for concious recognition (perception) of objects

Control of behavior vs. conscious perception

dorsal - directing behavioral interactions with objects ventral - responsible for conscious recognition of objects

Visual Agnosia

inability to recognize visual image

Prospagnosia

inability to recognize faces

What about the existence of different visual agnosias tell us about visual processing in the brain

there might be separate object recognition processes in the visual system

Simple and complex cells are alike in that

they are unresponsive to diffuse light

V1 neurons are most responsive to

sine-wave gratings of light in particular orientation

A patient with a lesion to the ventral stream is able to interact with an object, and yet has no conscious perception of the object. This is explained BEST by which visual pathway theory?

The "control of behavior" vs. "conscious perception" pathway

What is a valid interpretation of the “Halle Berry neuron”?

The properties of this type of neurons may reflect broader face processing patterns found within the recorded region which may relate to emotional salience, semantic processes, or facial recognition

If you forced someone to guess what an object found within his scotoma is, he may be able to guess correctly due to:

alternative visual pathways

Why can the eye, in particularly the retinal layers, be described as "inside-out"?

Light must pass through multiple cell layers before reaching the cells capable of responding to light.

From the eye, visual information first travels mostly to which of the following in the mammalian brain:

the lateral geniculate nucleus

Even though we blink and move our eyes, we do not see objects around us as disappearing or blurry momentarily. This is because of:

temporal summation across recent inputs

Compared to the scotopic system, the photopic system

has less convergence.

What does the “component theory” propose?

color perception emerges from the relative activity in three types of photoreceptors

Even though we blink and move our eyes, we do not see objects around us as disappearing or blurry momentarily. This is because of:

temporal summation across recent inputs

The visual areas are organized like _________, which refers to the fact that _________

a map of the retina; adjacent neurons have adjacent receptive fields

Information from the left visual field of the right eye will travel to

the right LGN

What best explains the disproportionate representation of the fovea in the primary visual cortex?

the high density of visual receptors in the fovea

The fovea Question options: consists exclusively of rods. creates the blind spot. is the area of the retina that has the greatest sensitivity. none of the above

none of the above

Section 4 Flashcards

Visual System (82 cards)