Chapter 13: Occipital Lobes and Pathways

Human Neuropsychology

What is the primary function of the occipital lobe?

Vision

Where is the primary visual cortex (V1) located?

Around the calcarine sulcus

What do "blobs" in V1 process?

Color information

What do cells between the blobs in V1 process?

Form and motion

What types of stripes exist in V2 and what do they process?

Thin stripes: color, Thick stripes: form, Pale stripes: motion

What are the three main visual streams?

Dorsal stream (visual guidance of movement), Ventral stream (object perception), STS stream (object & motion perception)

What visual function is V3 specialized for?

Dynamic form (shapes of objects in motion)

What visual function is V4 specialized for?

Color processing

What visual function is V5 (MT) specialized for?

Motion processing

What happens when V1 is damaged?

People report blindness, though subcortical projections allow limited vision

What is the proposed function of the ventral stream?

Object, face, body, and landmark analysis

What is the proposed function of the dorsal stream?

Visuomotor control (eye movement, grasping, reaching, object-directed action)

What is vision for action?

Visual processing used to guide specific movements like reaching or catching

What is action for vision?

Using eye movements to selectively focus visual attention (e.g., focusing on eyes and mouth when viewing faces)

What is egocentric visual space?

Objects described relative to the observer

What is allocentric visual space?

Objects described relative to each other

What is the dorsal stream primarily responsible for?

Real-time visual control of action

What type of neurons in the parietal lobe respond only during visually guided action?

Posterior parietal visual neurons

What visual area shows activity when detecting motion?

V5 (MT)

What visual area shows activity when detecting color?

V4

What is macular sparing?

Partial vision retained in the central visual field despite cortical damage

What are scotomas?

Small blind spots in the visual field, often unnoticed

What is blindsight?

The ability to respond to visual stimuli without conscious awareness of seeing them

Which case showed recovery of some visual function due to neuroplasticity after bilateral occipital damage?

B.I.

Which patient lost all color vision after V4 damage?

J.I.

Which patient retained color imagery despite cortical blindness?

P.B.

Which patient could not perceive motion after V5 damage?

L.M.

What is visual agnosia?

Inability to recognize objects despite normal vision

What type of agnosia is the inability to perceive multiple objects simultaneously?

Simultagnosia

What type of agnosia is the inability to recognize objects despite intact perception?

Associative agnosia

What is prosopagnosia?

Inability to recognize familiar faces

What brain area is typically damaged in prosopagnosia?

Bilateral occipitotemporal junction

What is alexia?

Inability to read (damage to left fusiform gyrus/lingual area)

What is visual imagery?

Top-down activation of visual areas to mentally generate images

What brain region is associated with mental rotation of images?

Right hemisphere dorsal stream areas

the dorsal stream i sknown for the ____ function, and the ventral stream is known for the _____ function.

how, what

In copying simple line drawings, you would expdct a patient with damage to her ventral pathway to:

suceed at this task and be able to recognize the object

The what stream in vision invloves which cortical lobe?

temporal lobe

The primary visual cortex is also known as the:

striate cortex

When grasping an odd-shaped object, you would expect a patient with damage to their dorsal stream to:

succeed at this task despite being unable to describe the object

Patient D.F. has a condition known as ____, which means that she cannot use vision to properly identify and recognize objects, nut she can use vision to properly guide actions

visual form agnosia

Patients with optic ataxia, which was demonstrated by patient R.V:

cannot use vision to properly guide actions

The dorsal stream goes form the V1 in the occipital lobe to the:

parietal lobe

In the priary visual cortex, ocular dominacne columns are maximally responsive to information coming from:

one eye

A cell is maximally responsive to a stationary ring of light. This cell is MOST likely a(n):

off-center retinal ganglion cell.

The BEST stimulus for a simple cell is:

A bar of light oriented at a particular angle

True or false: The receptive field of a retinal ganglion cell has two distinct regions: an excitatory region and an inhibitory region

true

In the primary visual cortex, cells are aranged in functional columns. If one column housed neurons that responded maximally to light at 90 degrees, you would expect the neighbouring colum to respong best to light at ____ degrees.

100

true or false: The receptive fields of retinal ganglion cells are larger than the receptive fields of V1 cells

false, vice versa

one way that a hypercomplex cell is different from a complex cell is that

only the receptive field of the hypercomplex cell has an inhibitory region

the best stimulus for a complex cell is:

a bar of light oriented at a particular angle and moving in a particular direction

In the primary visual cortex, cells are arranged in functional columns where all the neurons within the column are responsive to:

a particular orientation of light

What best describes a receptive field?

a sensory region that stimulates a receptor cell or neuron

striate cortex

The primary visual cortex (area 17, V1) in the occipital lobe; has a striped appearance when stained.

dorsal stream

A visual processing pathway from the primary visual cortex to the parietal lobe; guides movements relative to objects. Compare ventral stream

ventral stream

A visual processing pathway from the primary visual cortex to the temporal cortex for object identification and perception of related movements. Compare dorsal stream.

dynamic form

The shape of objects in motion.

egocentric space

A spatial location relative to an individual’s perspective. Compare allocentric space.

allocentric space

Object location relative to another object, independent of the observer’s perspective and usually at a distance. Compare egocentric space. 

polysensory neurons

A neuron within multimodal cortex that is responsive to both visual and auditory or both visual and somatosensory input.

bitemporal hemianopia

Loss of vision in both temporal fields due to damage to the medial region of the optic chiasm that severs the crossing fibers.

homonymous hemianopia

Blindness of an entire visual field due to complete cuts of the optic tract, lateral geniculate body, or area 17 (V1).

macular sparing

A condition that occurs only after unilateral lesions to the visual cortex in which the central region of the visual field is not lost, even though temporal or nasal visual fields are lost.

quadrantanopia

Defective vision or blindness in one-fourth of the fovea (visual field).

scotomas

A small blind spot in the visual field caused by small lesions, an epileptic focus, or migraines of the occipital lobe.

infarct

An area of dead or dying tissue resulting from an obstruction of the blood vessels that normally supply the area.

blindsight

The ability of patients with visual-field defects to identify at better-than-chance levels the nature of visual stimuli that are not consciously perceived. Also called cortical blindness.

ischemia

Deficient blood flow to the brain due to functional constriction or actual obstruction of a blood vessel by a clot.

angioma

Collections of abnormal blood vessels, including capillary, venous, and arteriovenous malformations, that result in abnormal blood flow.

visual agnosia

An impairment in the recognition of visually presented objects that is not a result of a deficit in visual acuity or language.

optic ataxia

A deficit in visually guided hand movements that cannot be ascribed to motor, somatosensory, or visual-field or visual-acuity deficits.

prosopagnosia

A facial-recognition deficit not explained by defective acuity or reduced consciousness or alertness; rare in pure form and thought to be secondary to right parietal lesions or bilateral lesions.

alexia

Inability to read.

apperceptive agnosia

A broad category of visual agnosias in which elementary sensory functions appear intact but a perceptual deficit prevents object recognition.

simultagnosia

An agnosia symptom in which a person is unable to perceive more than one object at a time.

associative agnosia

Inability to recognize or identify an object, despite its apparent perception.

topographic disorientation

Following brain injury, a gross disability in finding one’s way in relation to salient environmental cues; likely due to topographic agnosia or amnesia.