Occipital Lobes

Medial surface of occipital lobes

• AKA calcarine sulcus

• Contains primary visual cortex (V1)

• Separates upper and lower visual fields

Ventral surface of occipital lobes

• lingual gyrus (V2 and VP)

• Fusiform gyrus (V4)

V1

• AKA striate cortex

• 6 layers

• Primary visual cortex

• Input from LGN

• Output to all other occipital levels

V2

• output to all other occipital levels

• Goes to 3 parallel pathways

3 parallel pathways after V2

1. Output to parietal lobe (dorsal) that guides reaching

2. Output to inferior temporal lobe (ventral) that does shape identification

3. Output to superior temporal sulcus (STS) that is sensitive to tactile, auditory and visual info

V4

Responsible for colour vision

Functions

V1 → V4: responsive to colour

V1 → V2 → V5: detect movement

V1 → V2 → V3: form perception and dynamic form (shapes moving)

Achromatopsia

• V4 damage

• Loss of colour cognition

• Cannot see, imagine or recall colour

Akinetopsia

• V5 damage

• Eliminates ability to perceive objects in motion

• Believes everything teleports

Visual Agnosia

• V3 damage

• Form perception deficit

5 categories of vision

1. Visual recognition

2. Vision for action

3. Visual attention

4. Visual space

5. Action for vision

Object recognition

Specialized Areas in temporal lobe for significant info such as faces, hands, objects and places

Vision for action

• required to direct specific movements (grasping)

• Must be sensitive to target’s movement and shape

• Function of parietal visual areas in dorsal stream

Visual attention

• selective attention for specific aspects of visual input

• Parietal lobes guide movements

• Temporal lobes for object recognition

Parietal and Temporal loves are involved in

• Location of an object relative to person

• Location of an object relative to another

Action for vision

• top down processing to focus on specific features

• Many eye movements for scanning

• Not random eye movements

• When looking at face, focus on eyes and month in left visual field

Who created the terms dorsal and ventral streams?

Milner and Goodale

Dorsal stream

• on-line visual control of action; can see location, size and shape

• Visual guidance of movements for grasping

• Some neurons may take part in converting visual info into coordinates for action

Ventral stream

• object recognition

• IT inferior temporal cortex for object perception

• STS superior temporal sulcus for Visuospatial functions

STS stream

• polysensory neurons That are responsive for auditory and visual input

• Comes from parietal and temporal cortex

• Interaction between dorsal and ventral streams

Haxby and colleagues

• summary of PET studies

• Found activation for facial stimuli in temporal region and activation during location task in parietal region

• Motion deception in V5 and detection of shape in STS

Monocular blindness

• loss of sight in one eye

• Destruction of the retina/optic nerve in the eye

Bitemporal hemianopia

• loss of vision from both temporal fields

• Results from lesion to the optic chiasm severing crossing fibers

• Eg. Tumor in the optic chiasm

Nasal hemianopia

• loss of vision of one nasal field

• Lesion of the lateral chiasm

Homonymous hemianopia

• blindness of one entire visual field

• Complete cut of the optic tract, LGN or V1

macular sparing

• sparing of the central/macular region of the visual field

• Lesions of the optic tract/thalamus from cortical lesions

Quadrantanopia/hemianopia

• complete loss of vision in one quarter or one half of the fovea

• Lesion to V1

Scotomas

• small blind spots in visual field

• Small lesions to the occipital lobe

Patient BK: damage and scotoma

• dead tissue in right occipital love

• Blindsight, perceiving location without content

• Lose one quarter of fovea

• V2 intact, able to perceive colour, movement and location

Patient DB: V1 damage and blindsight

• angioma in the right calcarine fissure

• Had hemianopia

• Cortical blindness, no conscious awareness of seeing but can report movement, orientation and location of objects

Patient JI: V4 damage, loss of colour vision

• sustained a concussion and lost colour, though visual acuity at night improved

• Everything was all shades of gray

Patient LM: V5 damage and perception of movement

• bilateral posterior damage

• Loss of motion perception

• Unable to intercept moving objects by using her hand

• Could not see people moving

• Could see colour, write, read and recognize objects

Patient D

• right occipitotemporal lesion with left upper quadrantanopia

• Facial recognition deficit

• Unable to recognize people’s handwriting, including their own

• Reading and speech was intact

Apperceptive agnosia (visual form agnosia)

• failure in object recognition but basic visual functions preserved

• Bilateral damage to the lateral parts of the occipital lobes, carbon monoxide poisoning

Associative agnosia

• inability to recognize an object despite its perception

• Can copy a drawing but cannot identify it

• Lesion in anterior temporal lobe

Patient DF: occipital damage and apperceptive agnosia

• bilateral damage toLO region and unilateral in tissue of parietal and occipital lobes

• Cannot recognize drawings of objects

Patient VK: parietal damage and visuomotor guidance

• bilateral hemorrhages in the occipitoparietal regions

• Optic ataxia, deficit in guided hand movements

• Good form and colour

• Couldn’t grasp objects