Vision - unit 3 - physiological psychology

What cells in the retina make inhibitory connections to bipolar cells?

Horizontal cells make inhibitory connections to bipolar cells.

What is the role of ganglion cells in the visual system?

Ganglion cells' axons form the optic nerve, which carries visual information from the retina to the brain.

Where do the optic nerves from both eyes meet and partially cross over? A

he optic nerves meet and partially cross over at the optic chiasm.

What happens to visual information from the nasal half of each eye?

Visual information from the nasal half of each eye crosses to the contralateral hemisphere of the brain.

Which part of the brain do most ganglion cell axons go to?

Most ganglion cell axons go to the lateral geniculate nucleus, part of the thalamus.

What is the function of inhibitory connections in the retina?

Inhibitory connections in the retina help process contrast and sharpen the edges of images by reducing the activity of certain bipolar cells.

What is the role of the lateral geniculate nucleus in the visual system?

The lateral geniculate nucleus processes visual information and sends it to other parts of the thalamus and the occipital cortex.

How do the thalamus and occipital cortex interact in the visual system?

The thalamus and occipital cortex constantly exchange information, with the cortex sending many signals back to the thalamus.

What role do amacrine cells play in the retina?

Amacrine cells connect to bipolar cells and ganglion cells, helping to refine and integrate visual signals before they are sent to the brain through the optic nerve.

lateral inhibition

the retina’s way of sharpening contrasts to emphasize the borders of objects

What happens to the spontaneous output of rods and cones when light strikes them?

Light striking the rods and cones decreases their spontaneous output.

How do rods and cones affect bipolar cells when light decreases their output?

Rods and cones have inhibitory synapses onto bipolar cells, so when light decreases their output, it decreases their inhibitory signals, resulting in net excitation of the bipolar cells.

In the fovea, how are cones connected to bipolar cells?

In the fovea, each cone attaches to just one bipolar cell.

What is the role of horizontal cells in the retina?

Horizontal cells receive excitation from receptors and inhibit surrounding bipolar cells.

How does the inhibition from horizontal cells spread across bipolar cells?

Horizontal cells spread inhibition widely, with the strength of inhibition decreasing with distance from the horizontal cell.

What is the net effect on bipolar cell 8 when receptor 8 excites it?

Bipolar cell 8 shows net excitation because the excitatory signal from receptor 8 outweighs the inhibitory effect from the horizontal cell.

What happens to the bipolar cells adjacent to bipolar cell 8 (e.g., bipolar cells 7 and 9)?

Bipolar cells 7 and 9 are strongly inhibited by the horizontal cell and receive no excitation from receptor 8.

How does the inhibition from horizontal cells affect bipolar cells farther away (e.g., bipolar cells 6 and 10)?

Bipolar cells 6 and 10 are inhibited less by the horizontal cell compared to bipolar cells 7 and 9.

What happens to bipolar cells 6–10 when light excites receptors 6–10?

Bipolar cells 6–10 all receive the same amount of excitation from their corresponding receptors.

Why are bipolar cells 7, 8, and 9 inhibited more than bipolar cells 6 and 10?

Bipolar cells 7, 8, and 9 are inhibited from both sides, while bipolar cells 6 and 10 are inhibited from only one side.

Which bipolar cells respond the most when receptors 6–10 are excited, and why?

Bipolar cells 6 and 10 respond the most because they are inhibited the least, receiving inhibition from only one side.

What happens to bipolar cells 5 and 11 when receptors 6–10 are excited?

Bipolar cells 5 and 11 receive inhibition from the horizontal cell but no excitation from the receptors.

What is lateral inhibition?

Lateral inhibition is the reduction of activity in one neuron by activity in neighboring neurons, which helps to heighten contrast in the visual signal.

Which bipolar cells are most excited when light falls on a surface, and why?

Bipolar cells just inside the border of the lighted area (e.g., Bipolar Cells 6 and 10) are most excited because they receive excitation from receptors and less inhibition from the horizontal cell.

Why do bipolar cells 5 and 11 respond less than other bipolar cells farther from the area of excitation?

Bipolar cells 5 and 11 respond less because they receive inhibition from the horizontal cell but no excitation from the receptors.

How does lateral inhibition enhance visual contrast?

Lateral inhibition enhances visual contrast by making the edges of light and dark areas stand out more clearly, emphasizing differences and creating a sharper image.

receptive field

the area in visual space that is excited or inhibited. this is the point where light strikes the cell and other visual cells derive their receptive field from the connections they receive.

How do receptive fields change as signals move from rods and cones to higher levels in the visual system?

A rod or cone has a tiny receptive field. A small group of rods or cones connect to a bipolar cell, forming a larger receptive field. Several bipolar cells report to a ganglion cell, which has an even larger receptive field. The receptive fields of several ganglion cells converge to form the receptive field at the next level.

excitatory receptive field

the light at a particular spot excites the neuron

inhibitroy receptive field

when light at a particular spot inhibits activity

receptive field of ganglion cell

has a circular centre with an antagonistic doughnut shaped surround. That is light in the center of the receptive field might be excitatory while the surround will be inhibitory or the opposite

3 types of primate ganglion cells

• parvocellular nucleus

• magnocellular

• koniocellular

parvocellular neurons - structure, location

structure - has small cell bodies and small receptive fields

location - mostly in or near fovea

magnocellular neurons

larger cell bodies and receptive fields and distributed evely throughout the retina

koniocellular neurons

have small cell bodies like parvocellular but occur in the retina, have granular appeareance

use of parvocellular neurons

• due to its small receptive fields, they are well suited to detect visual details

• they also respond to color, wherein each neuron either gets excited by some wavelengths and inhibited by others

• high sensitivity to detail and color relates to the fact that these cells are located in or near the fovea cells, which has more no. of cones

uses of magnocellular neurons

responds strongly to movement and large overall patterns and not to color or fine details. Therefore these cells are found near the retina which is sensitive to movement but not color or details

how are the receptive fields of the cells of the lateral geniculate nucleus, a part of the thalamus

similar to the receptive fields of the ganglion cells - an excitatory or inhibitory center portion and a surrounding ring with the opposite effect.

where does most information go from the lateral geniculate nucleus

to the primary visual cortex in the occipital cortex, also known as area V1 or the striate cortex because of its striped appeareance

people having damage in V 1 face

• no conscious vision

• no visual imagery

• no visual images in their dreams

  contrast to people who lose vision due to eye damage, continue to have visual imagery and visual dreams

• blindsight

what is blindsight

It is shown by people who have a damage in area V1 and refers to the ability to respond in limited ways to visual info without perceiving it consciously

what are the 2 explanation of blindsight

• small undamaged patches in the damaged visual cortex that are not large enough to process the whole visual information but can process limited visual information

• alternate pathways wherein the thalamus which helps relay sensory info can send the visual info to other areas like parts of the temporal cortex, other than area V1 which allows ppl to respond to visual stimuli without conscious perception

who distingusihed several types of visual cortex cells

Huber and Wiesel

Explain simple cell of the visual cortex

• have fixed excitatory and inhibitory zone

• the more the light shines in the excitatory zone, the more the cell responds and the more the light shines in the inhibitory region, the less the cell responds

• receptive field is bar shaped or edge shaped and therefore responds only to horizontal and vertical orientations and not diagonals

• if you tilt the bar slightly / move left, right, up and down - then it reduces the response because the light strikes the inhibitory region

explain complex cells of visual cortex

• located in area V1 & V2

• does not have fixed inhibitory and excitatory regions

• it responds to a pattern of light in a particular orientation anywhere within its large receptive field

• responds more strongly to moving stimulus

explain end stopped cells

• aka hypercomplex cells

• similar to complex cells, but one exception - has a strong inhibitory zone at one end

• the cell responds to a bar shaped pattern of light anywhere in its broad receptive field

What do cells within a column of the visual cortex have in common?

They respond best to lines in the same orienta- tion. Also, they are similar in their preference for one eye or the other, or both equally.

feature detector

It is a neuron that detects the presence of a particular aspect of an object, such as a shape or a direction of movement

What is the effect of closing one eye early in life? What is the effect of closing both eyes?

If one eye is closed during early development, the cortex becomes unresponsive to it. If both eyes are closed, cortical cells remain somewhat responsive for several weeks and then gradually become sluggish and unselective in their responses.

strabismus / lazy eye

• aka strabismic amblyopia

• both eyes do not point in the same direction

• treatment - eye patch on the active eye, action video games requiring the use of both eyes

ventral stream

• through the temporal cortex

• aka what pathway

• identifying and recognizing objects

dorsal stream

• through the parietal cortex

• aka where pathway

• helps the motor system locate objects

What are the effects of damage to the dorsal stream (parietal cortex) on vision and spatial awareness?

People with damage to the dorsal stream (parietal cortex) have normal vision in terms of reading, recognizing faces, and describing objects. However, they struggle with spatial awareness—they can't accurately locate objects, bump into things while walking, and can't remember the arrangement of furniture in their house. They may also have difficulty knowing where parts of their body are.

What are the effects of damage to the ventral stream

People with damage to the ventral stream (temporal cortex) can see "where" objects are but not "what" they are. They cannot read, recognize faces, or identify objects by sight, but they can identify objects by touch or smell and recognize people by their voice. They can navigate around obstacles and reach out to grab objects, but they cannot make sense of visual details, such as a television program.

ow do cells in the inferior temporal cortex respond to identifiable objects and their transformations?

Cells in the inferior temporal cortex respond to identifiable objects based on the viewer's perception rather than the physical stimulus. They respond almost equally to negative or mirror images of a stimulus but not to a similar stimulus where the figure appears as part of the background. These cells continue to respond similarly despite changes in the object's position, size, and angle, indicating that they recognize different views as the same object.

visual agnosia

An inability to recognize objects despite otherwise satisfactory vision is called visual agnosia (meaning “visual lack of knowledge”). It usually re- sults from damage in the temporal cortex. Someone might be able to point to visual objects and slowly describe them but fail to recognize what they are.

face recognition brain areas

• parts of the occipital cortex

• anterior temporal cortex

• prefrontal cortex

• fusiform gyrus of the inferior temporal cortex esp the right hemisphere

Prosopagnosia

caused when there is a damage in any of the areas specializing in facial recognition, inability to recognize faces

What is the area imp for color perception

Area V4

Fns of Area V4

color constancy - allows obj to appear the same color, despite changes in the lighting

damage to Area V4

• not color blindness

• inability to recogniz color under different lighting

What are the functions of cells in area MT of the brain?

Cells in area MT respond selectively to movement at a particular speed and direction. They detect acceleration, deceleration, and absolute speed, and respond to motion in all three dimensions. Additionally, area MT responds to photographs that imply movement, such as images of people running.

What type of stimuli do cells in the dorsal part of area MST respond best to?

Cells in the dorsal part of area MST respond best to complex stimuli such as the expansion, contraction, or rotation of a large visual scene, which occurs when you move forward, backward, or tilt your head.

How do cells in the ventral part of area MST respond to movement?

Cells in the ventral part of area MST respond to an object that moves relative to its background. They receive messages from cells that record the movement of single objects and the entire background.

Motion blindness

abil- ity to see objects but impairment at seeing whether they are moving or, if so, which direction and how fast

What symptoms occur after damage limited to area MT? What may occur if MT is intact but area V1 is damaged?

Damage in area MT can produce motion blind- ness. If area MT is intact but area V1 is damaged, the person may be able to report motion direction despite no conscious identification of the moving object.