PSY 246 Occipital lobes and networks

What is the retina

Light-senstive layer at the back of the eye that converts light into neural signals

Light passes through several layers of cells before reaching rods and cones

What forms the optic nerve?

Ganglion cells have axons that leave the retina through the optic disc that form the optic nerve which creates the blindspot

Optic Nerve vs Optic Chaism

Optic nerve = ganglion cell axons. Leave eye at optic disc

Optic Chiasm = point of crossover for half the visual projections

What is our blind spot

Where optic nerve passes through optic disc 

• Since there are no cells to detect light an optic disc, that part of retina is blind 

• We dont notice it because our brain “fills in” this spot by taking in the best guess of whats actually there based on our surroundings

What is the pathway from eye to the brian

Eye - Optic Nerve - optic chiasm - LGN - Visual Cortex

What are the two visual pathways

• Retino-geniculate-striate pathway = Eye → optic chiasm → LGN of thalamus → striate (primary visual cortex) [solid line of diagram]

  • when talking about vision, this is what its talking about

• Tectopulvinar Pathway = eye → optic chiasm → superior colliculi → lateral posterior and pulvinar nuclei of thalamus

Name the parts of the occipital lobe and their functions

• Primary Visual cortex (V1) = basic features (edges, orientation, spatial frequency)

• Secondary visual cortex (V2/V3) = form depth, binocular vision

• Association cortex (V4) = COLOUR

• Middle temporal region (V5) = Motion

What are the consequences of damage to primary visual cortex

Hemanopia = loss of vision in HALF the visual field

Scotoma = loss of vision in one point

Quadrantanopia = loss of vision to a quarter of the visual field

Compare and contrast the ventral and dorsal visual streams

Ventral Stream = “what” pathway

• Recognizes objects

• Names and functions of objects regardless of location

Dorsal stream = “Where”/”How” pathway

• Locations of objects, but not their names or functions

  • How to interact with objects

Inferotemporal cortex (IT); what visual stream is it apart of, part in the brain; what is it important for

Part of the cerebral cortex in the lower portion of temporal lobe, important for object recognitionW

What are the consequecnes of damaging inferotemporal cortex (IT)

Agnosias = inability to recognize objects

Prosopagnosia = inability to recognize faces

What do neurons in IT cortex respond and dont respond to

Dont respond well to spots or lines

Respons well to stimulus such as hands, faces, or objects

Some areas of the cortex are specialized to proccess certain types of stimuli, name the two areas mentioned in class

Parahippocampal Place Area (PPA = responds to places (pictures of houses, landmarks)

Fusiform Face Area (FFA) = respond to faces more than objects

What is Pareidolia

Seeing faces in a mbigious stimuli

(brunt toast, front of vehicles, wall plug ins)

What are the visual perceptual disorders

Damages in higher visual areas and not primary visual cortex

• Provlems with interpreting or recognizing visual information despite normal vision

Apperceptive Visual Agnosia

• Cant combine visual details into a complete image

• Cant recognize objects because they cant assemble visual features into a whole

• Basic sensory abilities (acuity, color, shape detection) are intact

“Can see that something is there but cant perceive it (naming it, saying what it is or copying it)”

Assiociative Visual Agnosia

• Impairment in linking visual perception to meaning

  • objects can be seen but not recognized

• Can copy and describe objects accurately

• Cannot identify or name objects despire normal vision and perception

What are tests for visual agnosias? AND compare how apperceptive and associative individuals differ in these tests

Tests include copying drawings, “real or not” images, or impossible objects 

• Apperceptive: struggle to tell real vs impossible because they cant form percept 

• Associative: Can tell real vs impossible but cannot recognize or name a real object

Prosopagnosia; what is it, and where is the damage located that causes this

• Impairment in recognizing familiar faces, despite normal vision

• Cannot recognize photos of their own face

• Damage to Fusiform face area in the cortex (most likely in the right)

Individuals with prosagnosia are able to identify people by

Voice

Clothing

Body image

Context

What is blindsight; where is the damage located?

Ability to respond to visual stimuli without conscious awareness of seeing them

Often due to damage in V1 

For invidiuals affected with blindsight, how do they still see

Tecto-Pulvinar Pathway

• Not all visual information relies on geniculostriate pathway

• Supports unconsious vision: Explains blindsight

What is akinetopsia

Inability to perceive motion, even though static objects are seen normally

Patients sees the world in a series of static “frames”

Caused by damage to visual area V5/MT