Chapter 13: The occipital lobes and networks

thin stripes

color perception

thick stripes

form information

pale stripes

motion perceptiion

v1

receives largest input from lateral geniculate nucleus of the thalamus and projecting to all other occipital regions; necessary to process and interpret visual information

v2

secondary processing location; has 3 distinct parallel pathways emerge from it

dorsal stream

parietal pathway; visual guidance of movement

ventral stream

temporal pathway; object and motion perception

STS stream

object and motion perception

v3

processes dynamic form, or the shapes of object in motion

v4

predominantely processes color info

v5

MT (middle temporal); involved in motion procession

damage to v4

only see in shades of gray and loss of color cognition

damage to v5

erases ability to preceive objects in motion; objects vanish when they move

damage to v3

affect for perception

damage to v1

patients report being blind, but smaller projectitons from subcortical areas to high visual areas providee some limited visioin

lateral occipital (LO)

object analysis

fusiform face area (FFA)

face analysis

extrastriate body area (EBA)

body analysis

fusiform body area (FBA)

body analysis

superior temporal sulcus (STS)

analysis of biological motion

superior temporal sulcus posterior (STSp)

moving body analysis

parahippocampal place area (PPA)

analysis of landmarks

lateral intraparietal sulcus (LIP)

voluntary eye movement

anterior intraparietal sulcus (AIP)

object-directed grasping

ventral intraparietal sulcus (VIP)

visuomotor guidance

parietal reach region (PRR)

visually guided reach

intraparietal sulcus (cIPS)

object-directed action

monocular blindness

destruction of the retina or optic nerve of onee eyee

bitemporal hemianopia

lesion of medial region of optic chiasm severs crossing fibers; loss of vision of both temporal fields

nasal hemianopia

lesion of laterla chiasm; loss of vision in one of nasal fieelds

homonymous hemianopia

complete cuts of optic tract, lateral geniculate body, or V1; blindness of one entire visual field

macular sparing

damage to the visual cortex spares info from central part of the visual field

scotomas

small blind spots often unnoticed because of nystagmus; brain fills in the blind spots with info from the previous position of the eyes

nystagmus

constant tiny involuntary eye movements

hemianopia affecting the right visual field

a complete lesion of area V1 in the left hemisphere

a large lesion of the lower lip of the calcarine fissure

quadrantanopia that affects most of the upper-right visual quadrant

a smaller lesion of the lower lip of the calcarine fissure

smaller injury (scotoma) 

B.K.

• V1 damage and scotoma

• Patient awoke to discover loss of vision in left visual field

• Vision returned to the lower left visual field, but not upper left field

• MRI scan revealed evidence of a stroke in the right occipital lope

• Perimetry maps regions of blindness by asking patient to detect a small lift moving against a dark background

• Shortly after stroke, unable to detect light in the area of the stroke, but could report that it had been there after researchers moved the light to a different part of the visual field (blindsight)

  • While there’s damage in V1, higher visual areas remain intact

  • Over time, some vision returned, but the scotoma remained, and form vision was still poor in upper left quadrant

D.B.

• V1 damage and blindsight

• Had surgery to remove abnormal blood vessels, which removed part of the right calcarine fissure

• Patient typically reports they see nothing in left visual field, but sometimes has a feeling that something is there; guess correctly about shape of the object

• Accurately indicates the location of stimuli and the orientation of lines they didn’t see

• Cortical blindness occurs when a patient has no conscious awareness of visual stimuli, but can accurately indicate location, directions, forms, or colors of the stimuli 

• fMRRI shows they have activity in V5 when a stimulus is moving in their blind spot, as well as activity in the prefrontal cortex 

B.I.

• more than blindsight

• Child sustained damage to occipital lobe bilaterally in first 2 weeks of life due to a genetic disorder

• At age 6, not blind

• Can recognize faces, colors, and navigate environment

  • Significant plasticity to rearrange his visual system and strengthen pathways from subcortical areas to V5

J.L.

• V4 damage and loss of color vision

• Lost color vision following car accident

• Visual acuity improved, but world appeared as shades of gary

• Lost ability to remember or imagine colors

  • Even dreamed in black and gray

P.B.

• conscious color perception

• Man electrocuted and resuscitated, resulting in significant damage to posterior cortex

• Could detect the presence of light, but otherwise blind

• retained ability to imagine colors

L.M.

• V5 damage and movement

• Following damage to area V5, unable to detect motion

• Pouring fluids was difficult because she couldn’t see the level rise in the cup

• Interacting with people disturbing bc couldn’t see them move

• Vision otherwise normal

• Case suggest the brain processes the movement of a form separate from the form itself

• Symptoms can be mimicked by applying TMS to V5/MT

D.F.

• occipital damage and visual agnosia

• Patients with CO poisoning leading to damage to area LO have visual form agnosia and can’t recognize line drawings of objects

• Patients can’t draw pics of objects when looking at them and can’t reproduce line drawings

• No difficulty reaching and grasping objects, even though they can’t recognize them

• Unable to correctly judge lines as horizontal or vertical, but can orient movements to match horizontal or vertical lines

• Results suggest dorsal stream is intact (guiding movements to a target), but the central stream isn’t (recognizing objects)

visual agnosia

the inability to recognize objects or pictures of objects; or the inabilty to draw a copy of the objects

V.K.

• parietal damage and visual guidance

• optic ataxia

• Associated with damage to posterior parietal lobe

• Patient had bilateral strokes in occipito-parietal regions

• Normal form and color vision, but couldn't reach for objects or form hand into correct shape to pick up objects

optic ataxia

deficit in visually guided movements like reaching

D and T

• higher-level visual processes

• D has a lesion to the right occipitotemporal region and has some difficulties reading, but is unable to recognize faces

  • prosopagnosia

apperceptive agnosia

• object agnosia in which the patient fails to recognize a basic feature of the object, such as color or motion

• result from bilateral damage to the lateral aspects of the occipital lobe

simultagnosia

• patient is able to perceive an object, but unable to perceive more than one object at a time

• results form bilateral damage to the lateral aspects of the occipital lobe

associative agnosia

• patient can perceive the object, but can’t recognize it

• associated with damage to ventral stream

prosopagnosia

• can’t recognize familiar faces including their own

• rely on recognition based on sound of voice, hair, or way they walk

• visual perception normal, and can differentiate between human and nonhuman faces

• bilateral damage at the occipitotemporal junction

alexia

• inability to read

• associated with damage to left fusiform gyrus and lingual area

• left hemisphere specialized to combine letters to form words

• considered visual agnosia where the patient is unable to combine parts into a whole

cortical blindness

when patient has no conscious awareness of visual stimuli but can accurately indicate location, directions, forms, or colors of the stimuli