Transcript Visual Field and the Human Visual System

Cortical Functions and Their Measurement:
Vision as a Prototype
Autoradiography
2-deoxyglucose
(2-DG)
fMRI
Six Layers of Cortex
LGN input
Parvo
Magno
Classic Cytoarchitectonic Map of
Brodmann (1909)
Classic name for
visual cortex :
Areas 17, 18, 19
Some Human Cortical Visual Regions:
V1, V2, V3, V4, V5 (MT)
Visual Field and the Human Visual System
The visual field represented in its
projection to the retina demonstrates how
the lens of the eye inverts the image being
viewed. Up is inverted down and right is
represented on the left. Signals from the
right retinas (left visual field) of both eyes
travel through the optic nerve, optic tract,
and optic radiations to the primary visual
cortex in the right hemisphere. Signals
from the left retinas (right visual field) travel
to the left hemisphere. Primary visual
cortex lies in the colored area along the
calcarine sulcus. Colors show how the
different sectors of the visual fields map on
to primary visual cortex.
Receptive Fields in Retinal Bipolar and
Ganglion Cells
Receptive Fields of Lateral Geniculate
Nucleus
Primary Visual Cortex: V1,
Area 17, Striate Cortex
Receptive Fields of Lateral Geniculate
and Primary Visual Cortex
Mapping Human Striate Cortex (V1)
with Positron Emission Tomography
(PET)
•Checkerboards were used to present stimuli
to different parts of the visual fields. The
leftmost checkerboard is a foveal stimulus, the
middle one presents a stimulus close to the
fovea (parafoveal), and the rightmost one is a
peripheral stimulus that surrounds the
parafovea from 5.5 to 15°.
•Stimuli could also be presented to the upper
quadrant (e.g., rightmost stimulus) or the
lower quadrant (e.g., middle stimulus).
(Courtesy of Posner and Raichle).
PET Techniques for Studies of the
Human Visual System
Upper row: Control PET scans
(resting while looking at static fixation
point is subtracted from looking at a
flickering checkerboard stimulus
positioned 5.5° from fixation point).
Middle row: Subtraction produces a
somewhat different image for each of
5 subjects.
Bottom row: The 5 images are
averaged to eliminate noise,
producing the image at the bottom.
Checkerboard Stimuli and Calcarine
Sulcus Activation
The foveal stimulus presented in the
center of the visual field activated
calcarine cortex most posteriorly and at
the midline, the middle parafoveal
stimulus stimulated calcarine cortex
more anteriorly at the midline, and the
rightmost more peripheral stimulus
produced the most anterior activations
at the midline.
Stimulation of the upper and lower halves of
the visual field reliably produces areas of
activation below (left) and above (right) the
calcarine sulcus.
Beyond V1: Extrastriate
Cortex
Unfolded Map of Cortex of the Monkey Brain
Highlighting Extrastriate Visual Cortex
Multiple Cortical Areas Devoted to Visual Functions
David Van Essen
developed the
graphic technique of
unfolding the cortex
to better appreciate
the many areas that
contribute to vision.
Colored areas are
devoted to visual
function and brown
areas are devoted to
other functions.
Extensive Interconnections Between
Systems Identified in Primate Brain
Separation and Integration of Function
Areas of the
monkey visual
system (shown
previously on
unfolded cortex)
are heavily
interconnected.
Dorsal (“Where”) and Ventral (“What”)
Visual Streams in Monkey
Parietal (Dorsal) and Temporal
(Ventral) Processing Streams
Areas MT and V4 in the
Macaque Brain
Dorsal (“Where”) and Ventral (“What”)
Visual Streams in Human (PET)
Dorsal (where) pathway
shown in green and blue
and Ventral (what)
pathway shown in yellow
and red serve different
functions. (Courtesy of
Leslie Ungerleider).
Retinal and Thalamic Precursors of the
Dorsal and Ventral Visual Pathways
Magnocellular (dorsal)
and parvocellular
(ventral) pathways from
the retina to the higher
levels of the visual
cortex are separate at
the lower levels of the
visual system. At higher
levels they show
increasing overlap.
Retinal Ganglion Cell Inputs to the
Different Lateral Geniculate Nucleus
(LGN) Layers
The retina gives rise to streams of
information that are processed in
parallel.
LGN – showing six cellular
layers. Magnocellular
(green) and Parvocellular
(brown). Koniocellular
(pink) layers are tiny
neurons ventral to each
layer.
The Lateral Geniculate Nucleus of the
Macaque Monkey
Tissues have been
stained with Nissl to
show cell bodies, which
appear as dots. Note
the six layers and the
larger size of the cells
in the two ventral
layers. They are in the
magnocellular layers,
whereas the smaller
cells are in the four
dorsal parvocellular
layers. (Adapted from
Hubel, 1988).
PET Identification of Inferior Occipital
Region Activated by Color
Multicolor abstract display (top)
and version of the same display
in shades of gray (bottom) used
as stimuli
Activation produced by staring at colored stimuli.
Panel A shows the blood flow images before
subtraction. Panel B show activation after subtracting
responses to the gray stimuli. Panel C depicts
statistical significance of the responses. White is
highest significance. Panel D shows the location of
the most significant responses in a sagittal, coronal,
and axial view (Courtesy of Frackowiak and Zeki).
PET Identification in Humans of Cortical
Region MT for Motion Perception
A single slice shows
the location of MT
found by Frackowiak
and Zeki in London
(red squares) and
Miezen, Petersen,
and Fox in St. Louis
(green circles). The
areas of activation in
the extrastriate cortex
almost superimpose.
PET Activations of Word vs. Nonword
Stimuli
Brain shows much greater activation
as subjects look at visual words (2nd
row) than when they view a static
fixation point (top row).
Four different features of words
PET Activations of Word vs. Nonword
Stimuli
R
L
Blood flow responses in visual cortices to 4 types of stimuli. Note the prominent
responses on the right to pseudowords and words as compared to letter strings
and false fonts.
Procedure for Visual Attention Experiment
Color vs. Form vs. Motion
Subjects were given one of 5 different instructions representing the 5 conditions.
1. Passive control. “Observe the display.” 2. Divided attention. “Press a key if
any of the elements change.” 3. Focal attention. “Press a key if only color
changes.” 4. Focal attention. “Press a key only if form changes.” 5. Focal
attention. “Press a key if only motion changes.”
Visual Attention:
Color, Form, and Movement
Activation remaining
after divided condition
subtracted from each
of 3 focal attention
conditions. Red boxes
= color activation.
Yellow boxes = motion
activation. (Courtesy of
Posner and Raichle).
The Visual System,
Light/Dark Cycles, and
Circadian Rhythms
Retinohypothalamic Pathway: Visual
Input Maintains Circadian Rhythms
Pathway from retina to the suprachiasmic nucleus (SCN) carries information
about the light-dark cycle in the environment to the SCN. The size of the
SCN is enlarged for viewing. Axons from the left eye are labeled in red and
from the right eye in green. Both eyes project so diffusely to the two
overlying SCN that they are outlined in yellow. (SCN photograph courtesy
of Cynthia L. Jordan).
Consciousness and Sleep
Electroencephalography and Stages of
Arousal and Consciousness
Donald B. Lindsley
1907-2003