PSYC 4220 Exam 2

Having eyes close

Provides brain with the best depth perception Tend to be predators (Eagle)

photopigments (visual pigment molecules)

(In the disc, visual pigment molecule) Light sensitive chemicals in photoreceptors that respond to light and assist in converting light into neural activity - 1 large protein (opsin): protein strand - 1 small molecule (retinal): place where light-sensitive retinal is attached

Rods

- 120 million - Contain photopigment Rhodopsin - very sensitive to light - Rods work best in dim light conditions -Doesn't provide the brain with any differences in wavelengths of light -Detect different levels of light and dark, not colors

Cones

- 6 million (tightly packed in fovea) - Contain photopigment lodopsin - require higher level of light - Work best in day light

outer segment

- Contains stacks of discs the part of a photoreceptor that contains photopigment molecules. This is where transduction occurs

3 kinds of lodopsin

- each react best to different types of wavelengths 1. One corresponds with blue - shorter wavelengths 2. One corresponds with green - middle wavelength 3. One corresponds with red - longer wavelengths - We have these three because too the levels of lodopsin

How many photoreceptors do we have?

126,000,000

White's illusion

A display in which two rectangles are perceived as differing in lightness even though they both reflect the same amount of light and even though the rectangle that is perceived as lighter receives more lateral inhibition than the one perceived as darker.

grandmother cell

A hypothesized type of neuron that responds only to a very specific stimulus, such as a person's grandmother.

lateral geniculate nucleus (LGN)

A structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.

Belongingness Principle

An area's appearance is influenced by the part of the surroundings that such area appears to belong to

Hermann Grid

At intersections the amount of lateral inhibition from the brighter areas is largest --> gives off a ghost-like grey image that is caused by lateral inhibition

Perceptions that are not explained by lateral inhibitions in the retina

Binary Cross display Whites Illusion

visual modules

Brain structures specialized to processes information about a particular type of stimulus

visual pigment regeneration

Chemical rejoining opsin and retinal molecule by enzymes 4-6 minutes for iodopsin >30 minuties for rhodopsin

Do rods or cones have better visual acuity?

Cones - ability to distinguish details of a visual scene

Difference between rods and cones

Rods are responsible for vision at low light levels, while cones are active at higher light levels and are capable of color vision and high spatial acuity. (opposites)

retinal

Crucial for transduction, because it is the part of the visual pigment that is sensitive to light.

Antagonistic arrangement of receptive fields (center-surround antagonism)

Detection of light/dark contrast

pukinje shift

Enhanced sensitivity to shorter wavelengths during dark adaptation - Caused by a shift from cone vision to rod vision

The center area of receptive field

Excitatory

Where was lateral inhibition discovered originally?

Eyes of a horseshoe crab

Prosopagnosia

Form of visual agnosia following damage to the temporal cortex -> patient has difficulty in recognizing the faces of familiar people

Having eyes far

Have a broad visual field to keep an eye on the environment Tend to be prey (squirrel)

Why are we more sensitive to blue colors?

It is a wavelength that is brighter to us

ganglion cells

In the retina, the specialized neurons that connect to the bipolar cells; the bundled axons of the ganglion cells form the optic nerve.

dark-adaptation process

Increase in light sensitivity that occurs in the dark - Caused by the regeneration of photopigments in rods and cones

rod monochromats

Individuals with a very rare genetic disorder in which the retina develops with rods but without cones; used in dark adaptation experiments to establish the curve for rods

What travels across the lateral plexus?

Inhibition

The outside circle of the receptive field

Inhibitory

Average LGN neuron

Receives info from eye, if excitatory sends info to the visual cortex

mapping the receptive field

Receptive fields tend to be circles in shape and circles within circles, surrounded by a peripheral region

fuisform face area (FFA)

Responds best to faces as well as contexts that apply faces which is located in the fusiform gyrus on the underside of the brain directly below the IT cortex. They interpreted this result to mean that the FFA is specialized to respond to faces as wells as when context implies a face

receptive fields of neurons in the visual system

Retina (Ganglion cells) Lateral Geniculate Nuclei (LGN) of Thalamus Visual cortex

Do rods or cones have better sensitivity?

Rods - they have a high capacity to detect weaker light because they converge much more

Do cones or rods converge more?

Rods converge much more than cones

Retina (ganglion cells)

Run along the inner surface of the retina Leave the eye as the optic nerve Circle shape

enzyme cascade

Sequence of reactions triggered by an activated visual pigment molecule that results in transduction. Ultimately this cascade will cause a change in permeability of the Na^+ channels which changes the membrane potential

Nasal (side view)

Side of the eye closer to the nose

Temporal side

Side of the eye farther from the nose

Retina with Light

Sodium channels close -> The release of inhibitory transmitters is reduced —> Activity is less inhibited - they are excitatory The bipolar cells is less inhibited—> So the signal reaches the ganglion cells in which the firing rate increases

amacrine cells

Specialized retinal cells that contact both the bipolar cells and the ganglion cells, and are especially significant in inhibitory interactions within the retina.

horizontal cells

Specialized retinal cells that contact both the receptor cells and the bipolar cells

Maximum cone sensitivity

Takes about 3 minutes to flatten out

receptive field

The area of the retina that affects the firing of a neuron in the visual system (VS) Influences the firing rate of a neuron

The higher the visual acuity....

The better resolution

off-center ganglion cell

The outside of the cell has the excitatory effect; the inside of the cell has inhibitory effect

On-center Ganglion cells

The outside of the cell has the inhibitory effect; the inside of the cell has excitatory effect

rod-cone break

The point on the dark adaptation curve at which vision shifts from cone vision to rod vision

primary visual cortex

The region of the cerebral cortex that receives information directly from the visual system; located in the occipital lobe

dark-adapted sensitivity

The sensitivity of the eye after it has completely adapted to the dark.

light-adapted sensitivity

The sensitivity of the eye when in the light-adapted state. Usually taken as the starting point for the dark adaptation curve because it is the sensitivity of the eye just before the lights are turned off.

Retina in total darkness

The sodium channels of the photoreceptor are open. —> The membrane is depolarized. —> Cones and rods are activated to their maximum active potential —> They release inhibitory transmitters which inhibits the activity of the bipolar and ganglion cells

How can lateral inhibition explain the simultaneous contrast effect?

The square (left) surrounded by white receives more inhibition. Bc the square on the left receives more inhibition it appears darker

binocular field

The visual field produced by the overlapping of the separate visual fields from each eye when the eyes are located on the front of the face

Visual cortex

The visual processing areas of cortex in the occipital and temporal lobes. Discovered they look like rectangles or squares

Binary Cross display

Triangle B seems brighter than A because it looks like Triangle A belongs to the background, which is white so it makes it seem darker, and Triangle B belongs to the Cross, which is black so it makes it seem brighter.

Isomerization

When a photon of light hits the retinal, it changes shape, so it is sticking out from the opsin. This step that triggers the transformation of the light entering the eye into electricity in the receptors.

inhibition

a condition that reduces the likelihood of firing of a neuron - when one neuron releases an inhibitory neurotransmitter onto another neuron

retinitis pigmentosa

a degeneration of the retina that is passed from one generation to the next (although not always affecting everyone in a family). This condition first attacks the peripheral rod receptors and results in poor vision in the peripheral visual field. Eventually, in severe cases, the foveal cone receptors are also attacked, resulting in complete blindness.

single dissociation

a situation in which a patient is impaired on a particular task (task A) but relatively spared on another task (task B)

center-surround receptive field

a visual receptive field with a circular center region and a surround region forming a ring around the center; stimulation of the center produces a response opposite that generated by stimulation of the surround

superior colliculus

an area involved in controlling eye movements and other visual behaviors that receives about 10 percent of the fibers from the optic nerve.

visual pigment bleaching

change in shape and separation from the opsin causes the molecule to become lighter in color

Where does visual transduction occur?

outer segment of photoreceptors

rods and cones

contain light-sensitive chemicals called visual pigments that react to light and trigger electrical signals.

temporal lobe damage

deficit in knowledge of biological categories - what pathway (perception)

distributed coding

different perceptions are signaled by the pattern of activity that is distributed across many neurons Large # of stimuli can be coded by fewer neurons

parietal lobe damage

difficult to describe relative locations of landmarks, but can describe objects, faces, and animals - where pathway (action)

Hubel and Wiesel

discovered feature detectors

bipolar cells

eye neurons that receive information from the retinal cells and distribute information to the ganglion cells

Where are cones located?

fovea

Retinal Cortical Visual Pathway

goes through the thalamus and reaches the cortex The function is to control and coordinate eye movements

The visual field

part of the environment that is being registered on the retina Larger

peripheral retina

includes all of the retina outside of the fovea, contains both rods and cones. It is important to note that although the fovea is the place where there are only cones, there are many cones in the peripheral retina.

sensory code

information contained in the firing of neurons that belong to relatively large neural networks in the brain Info go stored in the brain by the process of learning All of these are on a continuum

lateral inhibition

inhibition that is transmitted laterally across the retina by the horizontal and amacrine cells - Causes those changes to become even more noticeable than they are in physical reality

simultaneous contrast

perception of brightness/color of one area is affected by the brightness/color of an adjacent or surrounding area

opsin

long protein strand molecule, which loops back and forth across the disc membrane seven times

macular degeneration

most common in older people, destroys the cone-rich fovea and a small area that surrounds it. This creates a "blind spot" in central vision, so when a person looks at something he or she loses sight of it

Surprising findings about LGN

much more axons come back from the cortex than go to the cortex. Our brain is constantly trying to figure out what happens next, at the neural level this is possible bc the huge feedback pathways

Optic tracks

nerve pathways traveling from the optic chiasm to the thalamus, carry info to the first brain station: the LGN

sparse coding

neural coding based on the pattern of activity in small groups of neurons

optic chiasm

point at which optic nerve fibers cross in the brain

Photoreceptors

rods and cones

layers of retina

rods, cones, bipolar cells, horizontal cells, amacrine cells, ganglion cells, optic nerve fibers

How are objects represented in the nervous system?

sensory code

Mach Band Illusion

sensory system enhances perception of borders At edges, bipolar cells get differential amount of inhibition from darker area and brighter area —> makes edge stand out perceptually

detached retina

separation of the retina from the choroid in back of the eye

Edge

sudden change in the illuminosity of a visual scene

convergence

synapsing of more than one neuron onto a single neuron

blind sight

the ability to respond to visual stimuli without consciously perceiving them

Fovea

the central focal point in the retina, around which the eye's cones cluster

specificity coding

the idea that an object could be represented by the firing of a specialized neuron that responds only to that object "grandmother cell"

lateral plexus

the lateral fiber of which strings of photoreceptors with fibers that send signals to the brain are attached

Retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information

optic nerve

the nerve that carries neural impulses from the eye to the brain

The blind spot

the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there

Pitfalls to specificity coding

too many different stimuli to assign specific neurons to each one

double dissociation

when two related mental processes are shown to function independently of each other