PSYCH 377 Occipital Lobe

anatomy of occipital lobes

no clear division on lateral surface of brain

medial surface

• parieto-occiptial sulcus

Calcarine sulcus/fissure

• contains much of primary cortex

• separates upper + lower visual fields

ventral surface

• lingual + fusiform gyrus

• V2, VP, V4

connections of visual cortex: primary visual cortex (V1)

input from LGN (lateral geniculate nucleus)

Sends processed signals to secondary visual areas

organized with retinotopic map; Neurons with receptive fields close together in visual space have cell bodies close together in the cortex

• Analyzes edges, contrast, and motion direction

• feature detection

connections of visual cortex: secondary visual cortex (V2)

Located just anterior to V1 in the occipital lobe.

Receives direct input from V1 and passes information to other secondary areas.

Detects more complex patterns (e.g., textures, contours).

Plays a role in visual figure-ground separation.

connections of visual cortex: after V2

output to parietal lobe: dorsal stream

output to inferior temporal lobe: ventral stream

output to superior temporal sulcus: STS stream

V3

Adjacent to V2, divided into dorsal and ventral portions.

Processes form and motion.

The ventral part is involved in object shape processing

dorsal stream

visual guidance of movements

processes visual information for spatial localization and visually guided actions; spatial awareness, motion detection + analysis

where pathway

originates in the primary visual cortex (V1) in the occipital lobe and projects to the posterior parietal cortex

ventral stream

what pathway

processes visual information for object recognition, perception, projection and attaching meaning

originates in the primary visual cortex (V1) and travels along the ventral surface of the brain, extending into the temporal lobe

STS stream

visuospatial functions

movement perception

involved in social cognition and processing the dynamic aspects of social perception

multimodal sensory integration

Receives input from both the dorsal (motion) and ventral (object recognition) stream

V4

Located in the ventral occipital lobe, extending toward the temporal lobe.

Processes color and shape perception.

Essential for object recognition in the ventral stream (what pathway).

Damage can result in cerebral achromatopsia (color blindness).

role in detection of movement, depth + position

V5/MT (middle temporal area)

Part of the dorsal visual stream.

Located in the posterior temporal lobe.

Specialized for motion detection and motion perception.

Damage can cause akinetopsia (motion blindness), where objects appear as still frames rather than continuous motion.

visual functions beyond occipital lobe

vision-related areas in brain make u ~ 55% of total cortex surface area

multiple visual regions in temporal, parietal + frontal lobes

vision is not unitary; composed of many specific forms of processing

lateral occipital complex (LOC)

located within the ventral visual processing stream, specifically in the occipital and temporal cortex

visual shape perception

responds more strongly to objects than to scrambled objects or textures

has feedback connections to early visual cortex (V1/V2), suggesting that it integrates inputs from lower-level cortices to generate a global shape representation

category of vision: vision for action

parietal visual areas (dorsal stream)

reaching

ducking

catching

Processes information about where objects are in space, their movement, and how to interact with them

category of vision: action for vision

visual scanning

eye movements + selective attention

category of vision: visual recognition

related to the ventral “what” stream

temporal lobes

object recognition

category of vision: visual space

parietal + temporal lobes

spatial location

category of vision: visual attention

selective attention for specific visual input

parietal lobes guide movements + temporal lobes help in object recognition (independent attentional mechanisms)

monocular blindness

the complete or significant loss of vision in one eye while the other eye retains normal or near-normal vision

bitemporal hemianopia

visual field defect where vision is impaired in the outer half of both visual fields

• results from lesion to medial region of optic chiasm

nasal hemianopia

a loss of vision in the inner (nasal) half of each visual field

• results from lesion of lateral region of optic chiasm

homonymous hemianopia

a visual field loss in the same halves of the visual field of each eye

• results from complete cut of optic tract (beyond optic chiasm) or complete damage to LGN or V1 in one hemisphere

macular sparing

individuals with homonymous hemianopia (loss of vision in one half of the visual field) retain some vision in the central part of their visual field, specifically the macula, despite damage to the visual cortex

quadrantanopia

the loss of vision in one quadrant (one-fourth) of the visual field

• same VF loss in each eye

• contralateral to damage; ex. left damage = RHS

• results from lesion to occipital lobe in one hemisphere

scotomas

localized area of partial or complete vision loss within a normal or relatively normal visual field

• often go unnoticed due to nystagmus

case study: B.K

V1 damage + scotoma

• right infarct (dead tissue) in occipital lobe

• experienced blindsight - perceive motion + location without perceiving content

• lost ¼ of fovea, poor vision in upper left quadrant; stroke in RHS damage

• slow facial recognition

case study: D.B

V1 damage + blindsight

• angioma (abnormal grew of blood vessels) in right calcarine fissure

• hemianopia (LVF affected)

• cortical blindness - reports no conscious awareness of seeing, but can report movement + location of objects (motor action/dorsal stream)

• accurate pointing to light source locations

case study: J.I

V4 damage + loss of colour vision

• sustained concussion + suddenly lost colour vision

• specific damage to occipital cortex

• improved acuity at twilight or at night

years later, no longer remembered colour

case study: P.B

conscious colour perception in blind patient

• ischemia destroyed large area of posterior cortex - electrocuted

• can only detect presence or absence of light + has intact colour vision

• could identify + name colours, also name typical colours for objects from memory

case study: L.M

V5 (MT) damage + perception of movement

• vascular abnormality produced bilateral posterior damage

• loss of movement vision - people appeared here or there

• unable to intercept moving objects by using hand

• TMS to V5 in NI lead to inability to intercept

• V5 likely involved in both perception + action

case study: V.K

parietal damage

one half of double dissociation between ventral + dorsal stream

• bilateral hemorrhages in occipitoparietal regions

• disordered control of gaze, impaired visual attention + optic ataxia (deficit in visually guided hand movements)

• can recognize + name objects, but cannot accurately reach for objects

case study: D.F

occipital damage + visual agnosia

• bilateral damage to lateral occipital region + tissue between parietal + occipital lobes

• visual form agnosia - inability to recognize line drawings of objects

• can use visual information to guide movements, but not recognize objects

apperceptive agnosia

perceptual categorization; cannot form a percept of whole

individuals struggle to perceive and recognize object shapes and forms despite having normal visual acuity,

• often leads to difficulties in copying or identifying objects. 

• can recognize local aspects

early damage to ventral stream

associative agnosia

individuals struggle to recognize objects or faces despite having intact perception and the ability to copy or match them

• indicates a problem with associating visual information with stored knowledge

• cannot link percept to knowledge

category specific agnosia

individuals have difficulty recognizing objects within specific categories

• know all objects except those linked to a specific category

• possible memory access disorder

prosopagnosia

inability to recognize faces, even those of familiar people, while other aspects of vision and intellectual functioning remain intact

face processing + prosopagnosia: monkeys

specific features in IT (inferior temporal)

face processing + prosopagnosia: humans

posterior right hemisphere

configurational info; things in a certain configuration to identify

inversion effect