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Behavioral Neuroscience Vision


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How do sensory receptors differ from neurotransmitter receptors.
sensory receptors are specialized neurons whereas, neurotransmitters bind to specialized proteins.
the process by which sensory stimuli are transduced into slow, graded receptor potentials.
sensory transduction
Sensory tranduction cause changes in membrane potentials called
Receptor potentials.
More than 5 senses. Give examples of others.
What are the wavelengths of light visible to humans? colors?
380 to 760 (violet to red)
The three dimensions of light that make a percieved color:
1.) hue- the dominant wavelength.

2.) saturation- the relative purity of a color (mixed with other WL or not)

3.) brightness- the intensity of the light
What is the relationship between frequuency of oscillations and wavelength.
They are inversely proportional. As the frequency goes up wavelengths get shorter.
For an individual to see an image it must...
be focussed on the retina.
The eyes are suspended in _____________, bony pockets in the skull. They are controlled by ______ (# of muscles) called _____________ muscles.
The eyes make three types of movement they are:
1.) Vergence movement- cooperative movement of the eyes. ensures that the image falls at retina at same place

2.) Saccadic movement- rapid, jerky movements of the eyes used in scanning.

3.) Pursuit movement- the movement of the eyes to keep a moving object on the fovea.
Changes in the thickness of the lens, accomplished by ciliary muscles to focus on distant or near objects.
Trace the anatomy of the eye as light enters.
First it enters through the protective Conjuctiva. Then the cornea, iris, pupil lens, virious humor and retina.

"Call Cristy In Places Like Venice and Rome" (???)
What are photoreceptors? how many of them? where are they found? What are the two kinds? what are they each used for?
The body has 126 million photoreceptor. they are found in the retina. there are the rods (120 million) and the cones (6 million). Rods are used for black and white vision, while cones are used for colors.
What is ironic about the ratio of rods:cones?
Though there are more rods than cones, the cones provide far more visual information. Cones recall are necessary for daytime vision (color vision).
Table 6.1


1) Found where
2) sensative to
3) provide what kind of info
4) Acuity
Central retina(in fovea) ; periphery (not in fovea)

moderate to high light; low light

Hue information; monochromatic info

Excellent acuity; poor acuity
What anatomical structure is responsible for the blind spot?
The optic disk
What is umwelt?
The idea of a perceptual world. Perception is arranged differently in differing species.
Parts of the brain adapt to suit the sensations in the animal. what is the example given in class?
Rats use olfacoty system reliably and therfore have larger olfactory bulbs in the brain than humans
VERY IMPORTANT: What is something important to remember about sensory receptors?
Most sensory receptors do not have axons. Their cell bodies synapse on dendrites or cell bodies of neurons
Three overlying processes for vision to occur.
Reception (stimulus to receptors)- absorption of physical energy (pressure on the skin will bend hair cells and raphe endings)

Transduction (receptor to neurons)- coversion of physical energy to electrochemical patterns. (generator potential, receptor potential)

Coding (neuron to brain)- one to one communication with physical system and nervous system
Early work by Johannes Muller showed that
when a neuron is excited the message it sends is always the same. "all sensory inputs result in action potentials"

Perception then, is based on which neurons are active not the degree of excitement of each. (?)
there are several layers in the retina. what are they?
Photoreceptor layer, bipolar cell layer and Ganglion cell layer
About how many bipolar cells are there in the retina?
1 million
light entering the eye strikes which of the retinal sub layers first, second and last?
Photoreception, bipolars and then ganglion cells.

Photoreceptors have synapse on bipolar cells, who have synapses on ganglion cells.
We know light travels through photoreceptors, bipolar cells and ganglion cells. What anotomical structure makes up the optic nerve?
The axons of ganglion cells.
Inputs from all photoreceptors converge at the optic nerve at the same time. how is this possible?
Outer or DISTAL receptors have higher conduction speeds than PROXIMAL receptors.
Within the photoreceptors (rods and cones) we find the lamella whose function is...
storage and release of photopigments.
photopigments consist of two parts
1. opsin (protein)
2. retinal (lipid)
Rhodopsin is a photopigment. Different photopigments have a different retinal group or opsin group?
How does rhodopsin fxn in vision.
Incoming light breaks the bonds of rhodopsin and gives rod opsin and retinal. this breaking causes changes in membrane potentials and results in glutamate (excitatory neurotransmitter) release.
How are membrane potentials in vision different than those involved in neurotransmittic release in the brain?
In the dark cationic (NA and Ca) ion channels are open by cGMP and thus RESTING POTENTIAL IS LESS POLARIZED. thus, glutemate is constantly released in the dark.

In the light, rhodopsin is split and a cascade of reactions (enzyme phosphodiesterase) causes the destruction of cGMP, the closure of ion channels, and therefore, decrease in glutemate (excitatory) response.
Low convergence in _____________ circuits. High convergence in ___________ circuits.
Cone-fed; Rod-fed
Rhodopsin is found in _________ while iodopsin is found in _______________.
Rods only. Both rods and cones.
How are photoreceptors and bipolar cells different than ganglion cells?
They do not produce action potentials, while, ganglion cells do.
Recall in the dark glutemate is released. What does glutemate do to bipolar cells?
it can hyperpolarize or depolarize the membrane.

Since either effect can be seen when light strikes a hyperpolarizing or depolarizing input can be passed to ganglion cells.
Light then has the opposite effect of ____________.

If a particular bipolar cell is hyperpolarized by glutemate (dark) then it will be depolarized when light shines.
After the optic nerve where do such signals go?
Optic nerve ----> dorsal lateral geniculate nucleus of the thalamus.
The dorsal lateral geniculate nucleus (DLGN) has 6 layers of neurons. 2 large and 4 small. therefore they are called ___________, respectively.
magnocellular layers; parvocellular layers.
Message from the DLGN pass through a pathway known as _____________________.
Optic radiations to the primary visual cortex (posterior occipital lobe) AKA STRIATE CORTEX.
An X-shaped structure, where optic nerves join together...
optic chiasm
At the optic chiasm axons from the inner retina _____________________ while axons from the outer retina ___________________.
cross through the chaism; stay on their side of the chiasm. Recall the lens inverts the image of the real world.
the portion of a visual field where visual stimuli will cause alterations in the rate of neurons firing.
Receptive fields.
Why does our periperal vision have less acuity than our foveal vision?
Receptor-to-axon relationship

Ganglion cells in the fovea are fed in by a smaller number of photoreceptors. At the periphery many photoreceptors will feed into the same ganglion cell.
What are the three types of ganglion cells discovered? how is each activated or deactivated?
On, Off, On/Off

On ganglion cells: excited by light falling in their central field and deactivated by light falling outside its central field.

Off- excited by light falling outside its central field, while deactivated by it falling inside its central field.

On/Off: briefly excited when lights are turned on or off. (reflex)
What are some of the characteristics of the different types of ganglion cells (Mago and Parvocellular)
-smaller cell body
-smaller receptive fields
-mostly in the fovea
-highly sensitive to color
-high acuity
- synapse on parvocellular cells on the lateral geniculaate nucleus.

-larger cell bodies
- larger receptive fields
- found in periphery
-lower acuity
- respond best to moving stimuli NOT color.
-important for brightness and depth preception
Axons of cells from the _______________ and _________________ project to the temporal & parietal
Primary and secondary visual cortices.
Other than the LGN there are other pathways of visual stimulation to the brain. Give both.
RSCH- Retino-superchiasmatic-hypothalamic pathway- responsible for synchronizing diurnal activities.

RT pathway- Retino-tectal: responsible for muscle movements and control of the iris and pupil size.
Photoreceptors and bipolar cells do not produce action potentials. They produce
graded potentials.
Retinal ganglion cells produce action potentials.
Very important
Since bipolar cells can either increase or decrease their release of glutamate when
light is on, some bipolar cells provide hyperpolarizing input to ganglion cells, and
some bipolar cells provide depolarizing input.
What is the role of horizontal cells?
Horizontal cells also receive input from photoreceptors.
Horizontal cells perform an integrative function, providing
lateral inhibition of surrounding cells.
What is the function of amacrine cells?
Amacrine cells respond to alterations in the intensity of light - “on/off”.
The mechanism of action of horizontal and amacrine cells is not yet fully
Amacrine and horizontal cells are part of the first ____________________.
first level of processing in the visual system
Bipolar cells have receptive fields from _____________. Ganglion cells have reveptive fields from ____________. Lateral geniculate cells have receptive fields from ____________.
Photoreceptors; Bipolar cells; Ganglion cells.
Topographic organization of the visual system
See slides Chapter 6 53-56.
Recall that Parvocellular ganglion cells are __________________ FED, whereas, Magnocellular ganglion cells are ___________________________.
Cone-fed; Rod-fed.
Horizontal cells allow us to _______________________. While, Amacrine cells allow us to ____________________.
See the borders of things. Percieve changes in lighting.
overlapping receptive fields create more...
humans and old world monkeys both have ______ forms of cones.
What is the trichromatic theory of color vision?
The idea that all colors are made of three principal colors.
what are the shortcommings of the trichromatic theory?
It does not explain why YELLOW is a primary color. Nor does it explain why some colors are easily miscible and others are not (opposites).
how does modern research show that the trichromatic theory is right?
There are in fact three types of cones (RED, Green and blue cones) which absorb different amounts of light at different wavelengths.
How many of each cones are there?
Equal number of red (46%) and green (46%) cones and far less blue (8%).
What are the genetic disorders of color vision? Where do these anomalies lie? What changes do they cause? What is believed to be the cause?
Protanopia, deuteranopia and tritanopia.

X chromosome (much more common in males)

In pROtanopia, individuals confuse red and green as their red cones are filled with green opsin.
"ROjo esta ROTO"

In DEuteranopia- these individuals also confuse red and green but its because green cones are filled with red opsin.
"verDE esta roto"

Tritanopia- rare, non X Chromosome disorder where the individual cannot see short wavelengths (blues). Something wrong with blue cones.
Where does the opponent process coding come in to play? What does it mean for color sensative retina cells?
At the retinal ganglion level, the three color (trichromatic code) gets translated into an opponent-color system.

Thus, the retina contains TWO kinds of color sensative cells: red-green and yellow-blue.
CONFUSING. There are _______ kinds of sensitivities in ganglion cells. There are ______ # of receptive fields.
2 (red opposes green and blue opposes yellow)

3 (Blue on/yellow off) (Red on/ green off) (green on/red off)
How is it we see RED?
Light penetrates the eyes, photoreceptors and bipolar cellls causing differences in membrane potential.

In the ganglion cells "red cone" best absorbs red light and excites "red on/green off" ganglion cells while inhibiting "Green on/red off" cells.
How do we see blue?
Excitation of blue on yellow off. with minor inhibition of the other two ganglion receptive fields which cancel eachother out.
How do we see yellow?
Inhibition of Blue on yellow off ganglion receptive fields. ALSO, since yellow light is best absorbed by red and green cones, they are excited in equal amounts and cancel their input... leaving Yellow.
According to opponent process, we cannot see what 2 combinations of color.
Bluish-yellow and reddish-green.
What is the cause of negative afterimages?
Afterimages are a result of fatiguing cells (after staring at red, red cones are fatigued) when you now stare at a blank page "rebound effects" occur and the neurons that were initially inhibited fire faster and those that were excited are more inhibited giving the appearance of the opposite color.
As previously mentioned info passes through photoreceptors, bipolar cells, ganglion cells, DLGN and finally the striate cortex . Where in the striate cortex do these info enter? What percentage of the striate is devoted to just the fovea.
In primates at least, info enters the striate complex in a region labelled 4c. 25% of the striate is dedicated to the fovea, though it makes up a small portion of the visual field. That is why images at the fovea are seen with the most acuity.
Recall that the vision also interprets positions by _______________________ ganglion cells.
How is the position determined by neurons?
Certain neurons fire when the stimuli is horizontal, vertical or at some oblique angle. Information from these RATES of firing and their particular settings, can be translated to a position.
An orientation-sensative neuron in the striate crotex whose receptive field is organized in OPPOSITE fashion.
Simple Cell
Still other cells responsible for orientation can also pick up on movements. These neurons still respond to a particular orientation regardless of backgrounds (especially when it moves perpendicular to its orientation).
Complex cells
A neuron in the visual cortex that responds to the presence of a line segment wth a particular orientation taht ends at a particular point within the cell's receptive field.
hypercomplex cell
Which of the last three would then be responsible for detecting the "ends of things."
Hypercomplex cell
Information that collects at the DLGN then splits and travels to different paths known as:
The ventral stream and the dorsal stream.
Where does the ventral stream end up? what information does it carry? is it the what or the where?
inferior temporal cortex

it carries THE WHAT. it is responsible for recognition of objects and people. Simple recognition occurs in the posterior segments while complex recognition occurs in the anterior of the parietal lobe.
Where does the dorsal stream end up? What message is it responsible for carrying? Does it carry the what or the where?
The dorsal stream ends up in the posterior parietal lobe. It is responsible for the spatial location information. It is responsible for the where.
Neurons that are highly responsive to movement are found where.
Outside the strait cortex (extrastriate) in the V5 position more commonly known as MT (for medial temporal).
what imputs does the MT recieve?
inputs from
-striate cortex
-other extrastriate regions
The neurons of the MT are responsible for figuring out an objects movements. What important difference do these neurons exhibit?
They are thick and heavily myelinated to have fast action potentials.
Further analysis of movement, beyond that of the MT is performed by the _______. What does it do?
MST; analyzes complex movements and optical flow (movement differences when you move your head).
Where in the brain does image stabilization take place?
The MST again as in the last slide.
How does one measure depth?
By a combination of monocular cues and binocular cues.
What are examples of the monocular cues as they pertain to depth perception.
-relative retinal size
-loss of detail in the distance
-relative movement of your head
What are examples of the binocular cues as they pertain to depth perception.
Most cells in primary visual cortex are binocular

each eye "sees" a
3-dimensional sense

mediated mainly by the magnocellular pathway

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