psych 30 mt2

what visual processing takes place in the first visual area (V1) in our brain?

V1 receptive fields

orientation selectivity

how is the first visual area (V1) organized?

visual field

orientation

ocular dominance

ganglion axons connect to the brain in the _______

occipital lobe

what does V1 stand for?

striate cortex or primary visual cortex

explain the mapping of the visual fields to the sides of the retina

right visual field mapped onto the left side of the retina

left visual field mapped onto the right side of the retina

how is the spatial information from the different visual fields retained?

through nerve fibers (axons of ganglion cells in the optic nerve)

what happens at the optic chiasm?

the left ½ of the retina (right visual field) of each eye —> left side of the brain

right ½ of retina (left visual field) of each eye —> the right side of brain

make sure not to mix up visual field vs side of retina

what is the side of the retina to the outside vs the side closer to middle of face

temporal retina (outside) vs nasal retina (medial)

what is the optic tract

continuation of optic nerve but each visual field’s nerves are now combined

what is the lateral geniculate nucleus?

key sensory relay and processing center in thalamus (one in each hemisphere!)

• each side’s LGN gets input from the opposite visual field (ex - left LGN gets input from right visual field) & vice versa

• 1st synapse from eye

• 
  

what is an example of the mapping of the LGN’s different layers (contralateral, ipsilateral)

right LGN

1. left eye (ipsi)

2. right (contra)

3. right

4. left

5. right

6. left

—> each layer contains a specific part of the visual field

what is the pathway from the light to V1

photoreceptors —> bipolar cells —> retinal ganglion cells — (optic nerve —> chiasm —> optic tract) —> LGN (1st synapse from eye) — (LGN relay neuron / optic radiation) —> V1 cortical neurons (2nd synapse)

left LGN gets input from the ___ visual field

right (and vice versa)

which V1 gets input from left visual field?

right V1 (and vice versa)

right visual field from the right eye is projected to ___ LGN and ___ V1

left / left

left visual field from the right eye is projected to ___ LGN and ____ V1

right / right

what is the reasoning for optic radiation?

“radiation” refers to spreading out of axons through the white matter as they go to the occipital lobe

• do this bc each fiber follows diff anatomical route

where is the upper left visual field mapped to (brain)?

lower bank of right V1

what is retinotopy?

mapping of visual input from the retina to neurons (contralateral & inverted mapping + cortical magnification)

Fill in the blanks (mapping things to the photo)

1. optic nerve

2. optic chiasm

3. optic tract

4. lateral geniculate nucleus

5. optic radiation

6. V1 (striate cortex/primary visual cortex)

7. right

8. left

Label brain lobes

blue = frontal

yellow = parietal

green = temporal

pink = occipital

what do the following anatomical words mean:

• anterior

• posterior

• dorsal

• ventral

• medial

• lateral

• ipsilateral

• contralateral

Anterior	Toward the front of the brain
Posterior	Toward the back of the brain
Dorsal	Toward the top of the cerebral hemispheres
Ventral	Toward the bottom
Medial	Toward the midline, between the hemispheres
Lateral	Toward the outer side of the brain
Ipsilateral	On the same side
Contralateral	On the opposite side

what is a sulcus vs gyrus

sulcus = groove or valley in the cerebral cortex

gyrus = raised fold or ridge of cortex

what is calcarine sulcus and what is V1’s relation to it (and what are key regions surround it)

calcarine sulcus = prominent groove on the medial surface of the occipital lobe

• primary visual cortex (V1) lies predominantly along its upper and lower banks

—> cuneus = gyrus above CS

—> lingual gyrus = gyrus below CS

what does homonymous hemianopia mean?

losing the same half of the visual field in both eyes

Bitemporal hemianopia

losing the temporal visual fields of both eyes; it can result from central chiasmal compression because the crossing nasal retinal fibers are affected

what is the meaning/result of cortical magnification (and where is foveal vs peripheral vision mapped)

disproportionately large amount of visual cortex represents the central visual field (bc center = high acuity vision)

• foveal vision —> posterior tip of V1 (occipital pole — very back)

• peripheral vision —> farther anteriorly along V1

how do researchers map receptive fields in human brain?

uses MRI scanner to measure brain activations when participant looks at cross but images are shown at different locations in the visual field (around the cross) —> measure responses in each voxel to estimate the receptive field

what is different about the receptive fields of V1 neurons than for ganglion neurons (what are these receptive fields useful for)?

retinal ganglion neurons have center-surround receptive fields BUT V1 neurons have elongated receptive fields

• helpful for detecting edges/lines

what does the graph of orientation tuning show?

different neurons have different preferences/selectivity to different orientations (angles, skinniness, longness)

what is ocular dominance and how does it connect to binocular integration?

neurons input to V1 (pass internal layer) → @ layer 4: neurons with response preferences to either eye are generally organized/retained by alternating columns (which span through the different cortical layers)

—> after pass through, reach superficial layer (3, 2, 1) where responses from both eyes combine/converge into one binocular neuron (initial preference still maintained!)

what is the benefit of more lateral eyes as opposed to more forward facing eyes?

lateral eyes = allows for broader total field of view (better for detecting threats across wide region)

forward facing eyes (ex - humans) = greater binocular overlap (larger part of world can be viewed by both eyes simultaneously)

what is binocular disparity and what does this allow for?

binocular disparity = horizontal difference in retinal positions in features of images captured by left and right eyes

—> stereopsis / stereovision — perception of depth / distances (3D image from two different 2D images on left and right retinas)

what is the retinal disparity at the fixation point?

0 (NONE)

what is fixation and vergence

fixation = directing gaze @ particular location / object

vergence = coordinated rotation of eyes to maintain fixation at different distances

how does stereovision/stereopsis work?

process to fuse left and right 2D images to generate a 3D image

• objects @ diff depths relative to fixation produce diff disparities —> the brain interprets these differences as depth

what are the 6 ways in which you can perceive 3D and depth from monocular vision?

1. linear perspective & relative size (closer = bigger)

2. texture gradients (closer = more pronounced texture, wider spaces, etc)

3. aerial perspective (light diffraction, so farther = blurrier, dimmer, more blue)

4. 3D shape from shading

5. occlusion (infer despite things blocking)

6. motion parallax (things’ motion relative to you reveal their depth)

why do you need 2 eyes to see 3D images with red/cyan glasses?

red and cyan images = horizontally shifted (red to left)

• horizontal disparity varies across objects

—> glasses filter one of the pictures, so each eye sees a separate photo —> combine these 2 separate 2D images to form a 3D construction

binocular rivalry

what is the visual angle?

V = 2 arctan(S/2D)

• S = object size

• D = object distance

• V = visual angles