How the Brain Works The Facts Visually Explained by DK (z-lib.org)

BRAIN FUNCTIONS AND THE SENSES

The Visual Cortex

The Visual

Cortex

Nerve signals from the eye have to

travel all the way through the brain

before they reach the area dedicated

to decoding this information. This

area is called the visual cortex.

The structure of the cortex

The visual cortex occurs in both

brain hemispheres and is further

divided into eight main areas, each

of which has a different function

(see table, opposite). Signals travel

from the retina (see pp.66–67) via

the thalamus and lateral geniculate

nucleus to the primary visual cortex

(V1). The raw data then passes

through various vision areas,

contributing different details about

shape, color, depth, and motion

before combining to form an image.

Some areas provide information that

helps with immediate recognition of

familiar objects, others with spatial

orientation or visual-motor skills.

Stereoscopic vision

Our ability to see in 3-D—known as stereoscopic

vision—is produced by having both of our eyes

looking straight ahead and moving together.

As the eyes are slightly apart, different views

are received from each, although they overlap

to a small extent. The brain computes the spatial

information from each eye to create an overall

image, using previous experience to speed

up the processing time and fill in any gaps.

Swapping sides

At a crossover point called the optic chiasm,

nerve axons from the left side of each retina

join and continue to the left visual cortex,

and likewise with nerve axons from the right.

THALAMUS

RIGHT HEMISPHERE

LEFT^ HEMISPHER

E

LEFT^ VISUAL

CORTEX

RIGHT VISUA

C L

ORTEX

From eyeball to visual cortex

Data from the eyeball travels along the

optic nerve until it reaches the optic chiasm (see

below), where some of the data is sent to the

opposite side of the brain. Signals then travel to

the lateral geniculate nucleus, which forwards

data to the visual cortex for processing.

1

KEY

Information from the eye

Face recognition pathway

Lateral geniculate

nucleus forwards

signals from retina

to visual cortex

Lateral

geniculate

nucleus

View of object

from left eye

Half of signals travel

to same hemisphere;

other half cross over

Nerve axons split off

after lateral geniculate

nucleus and radiate to

areas of visual cortex

Optic nerves

converge at

optic chiasm

View of object

from right eye

Amygdala

processes facial

expressions

Rods and cones in

retina convert light

into nerve signals

Optic nerve carries

nerve signals to brain

Frontal lobe

provides conscious

recognition of faces

3

TH

ALAMUS

OPTIC NERVE

FACE

RECOGNITION

AREA

Recognizing faces

Features that suggest a face are

sent to the face-recognition area and

amygdala, where they are searched

for details that prompt recognition.

VIS

UA

L^ C

O

RT

EX

AMYGDALA

FRONTAL LOBE

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