occipital lobe

V1 (4)

• functionally heterogeneous

• vision begins here

• outputs to V2 and specialized zone (V3-5)

• if damaged patients think they are blind

V2 (2)

• functionally heterogenous

• inputs from V1 + outputs to specialized zones

V3 (2)

• specialized zone

• form perception

• ie. people, basketball

V4 (4)

• in lingual gyrus

• primarily colour perception → also form perception

• also involved in thinking in colour → colour blind painter

• ie. blue, yellow, beige in an image

colour vision is important for (3)

1. motion

2. depth

3. location perception

V5

• motion perception

• more posterior

• ie. players moving around

geniculostriate pathway

visual info → eye → optic tract → lateral geniculate nucleus (thalamus) → striate cortex (V1) → other visual cortical areas

• defacto pathway

tectopulvinar pathway

visual info → eye → optic tract → superior collicus (midbrain) → pulvinar (thalamus) → other visual cortical areas

• usually used to locate objects

homonymous hemianopia

• blindness to one visual field (left/right) of both eyes

  • complete cut of optic tract/lateral geniculate nucleus

  • lesion to V1

quadrantanopia

• loss of vision in ¼ of visual field

• small lesion to occipital lobe

monocular blindness

• loss of sight in one eye

• destruction of retina/optic tract

bitemporal hemianopia

• loss of vision from both temporal (outer) fields

• lesion to medial part of optic chiasm

right nasal hemianopia

• loss of vision from one nasal (inner) field

• lesion to right lateral chiasm

  • same applies to left

scotoma

• loss of vision in a small area of visual field

• even smaller lesion to occipital lobe

dorsal stream (where/how)

• visual guidance of movements

• outputs to parietal lobe

ventral stream (what)

• object perception

• outputs to temporal lobe

STS stream

• visuospatial function → biological motion

• outputs to superior temporal sulcus

  • ie. watching someone walk → species specific

  • depends on proximity

• activated by shape perception

______ activates parietal region

location processing

________ activates temporal region (FFA)

facial processing

cortical blindness (blindsight)

• damage to V1

• cannot consciously perceive visual information BUT can identify above chance lvls nature of visual stimuli w/o conscious perception

achromatopsia

• loss of vision for colour

• due to lesion in V4

akinetopasia

• loss of vision for movement

  • unable to intercept moving objects

• due to lesion in V5

Visuospatial Agnosia (aka Topographical Disorientation)

• inability to find one’s way in relation of self to environment

• damage to right medial occipitotemporal region (including fusiform and lingual gyri)

  • (e.g.) patient can accurately report number of rooms in the house,

disruption of dorsal stream results in

optic ataxia

disruption of ventral stream results in (2)

• object agnosia

• prosopagnosia

object agnosia (apperceptive agnosia)

• deficit to perceive object structure/recognize object

• basic sensory functions intact (color/motion perception)

• bilateral damage to lateral parts of occipital lobes

patients with object agnosia ARE able to

1. recognize/draw objects from memory

2. guide hand movements towards objects

Lesson from DF Case → Bilateral Damage in Lateral Occipital Cortex (LO), Junction of Temporal/Parietal & Occipital Cortex

• use of visual info to guide movements to objects (dorsal stream) involves different brain areas than those used to recognize those objects (ventral stream)

simultagnosia

• type of apperceptive agnosia

• inability to perceive more than one object simultaneously

associative agnosia

• can perceive form

• cannot identify objects

  • ie. recall name of object from memory

• lesion to anterior temporal lobes (ventral stream)

apperceptive vs associative agnosia (3)

• double dissociation btw perception + memory identification for objects

• ability to perceive the structure of an object + ability to identify/label the object requires different neural structures

• evidence for different cognitive systems

prosopagnosia

• unable to recognize familiar faces (even one’s own)

• able to recognize ppl using other features (voice, hair)

• bilateral damage to fusiform face area (FFA)

fusiform face area (FFA) (3)

• strongly associated with face perception rather than general object recognition.

• Found in the inferior temporal cortex, within the ventral visual stream ("what" pathway).

  • Typically more active in the right hemisphere, but present bilaterally.

• Damage to the FFA → Prosopagnosia ("Face Blindness")

FFA stimulation patient video: what happens after sham + stimulation condition

• sham: no ∆ in perception

• stimulation condition: major ∆s in face only

Why is the sham condition important?

It ensures that the observed effects (such as face distortion or improved recognition) are truly due to stimulation of the FFA and not other confounding factors like placebo effects, expectation, or general brain stimulation.

optic ataxia (3)

• deficit in visually guided movements

• other functions intact (motor, somatosensory, visual acuity)

• damage to posterior parietal lobe

object agnosia vs object ataxia (3)

• double dissociation between dorsal and ventral streams

• ability to perceive an object and to use visual information to guide hand movements towards objects requires different neural structures

• visual experience is not unified, despite our phenomenological experience of it

calcarine sulcus

contains much of 1º cortex

• divides upper/lower halves of the visual world

parietal-occipital sulcus

• separates parietal lobe from occipital