some neurology about color specializations (meadows, 1974) axial view ipl fusiform v1

Some Neurology About Color Specializations

(Meadows, 1974)

Axial view

IPL

Fusiform

V1

GIRKIN AND MILLER

Surv Ophthalmol 45 (5) March–April

2001

Lingual and Fusiform

Gyri: Ventral Occipital Cortex

Cerebral achromatopsia or dyschromatopsia

•Following a cortical lesion, a human subject loses

specifically the ability to see the world in colour

•Appearance is ‘dirty shades of grey’

•Often accompanied by a transient inability to recognize

faces (prosopagnosia)

• No obvious loss of form vision measured by acuity

•The signals relayed to the brain are normal, but the

mechanism used to construct color appearance is defective.

Examples of dissociation – A little Neurology

• Oliver Sacks patient suffered a car accident; artist for whom color vision was lost while pattern vision was retained

• There are instances in which color vision is spared, whileform vision is lost: carbon monoxide poisoning (Wechsler, 1933); also SB and Michael May

Cortical Color Blind Perimetry(Meadows, 1978)

Intensity 1 Intensity 2

Munsell Organization

Munsell Page

Example

Farnsworth-Munsell 100 Hue Test

A method for determining color vision abnormalities and testing color discrimination. Provides reliable data which can be applied to many psychological and industrial color vision problems. The set consists of four trays containing a total of 85 removable color reference caps that have incremental hue variation on one side and are numbered on the reverse side. Color vision anomalies and color aptitude are detected by a subject's ability to place the color caps in hue order. The four trays are boxed in a wooden carrying case. Used by government and industry for over 50 years.

Color Blind Farnsworth-Munsell(Meadows, 1974)

Protanope

Deuteranope

Tritanope

(a) Cone loss (b) Cortical color blind (errors/2)

LiLi FuFu

Human Ventral

Occipital Cortex, Near

hV4, Responds

Powerfully to Color Signals; Damage Can

Cause A Hemifield Loss

of Color Perception

V3-ventralupper visual field

hV4-hemifield

Ventral Surface Human Brain

Lingual and Fusiform Gyri

(McKeefry and Zeki, 1997)

Upper and Lower Visual

Field Representation (V-Zeki)

Color Anomia(Meadows, 1978)

Infer ParietalLobule

Inferior Parietal Lobule

Classical Cone Specific Center-

Surround Hypothesis

(Hubel and Wiesel, 1966; Calkins and Sterling, 2001)

Anatomy: Midget Cell Surrounds Receive From All Cone Classes

(Calkins and Sterling)

H1 Horizontals receive non-

selective L,M input

Amacrine populations receive non-selective L,M

input

Hypothesis: Midget Cone Inputs Differ With Eccentricity

Central Peripheral

Small Bistratified

(Calkins and Sterling)

Measurements of single unit responses in visual cortex to simple

colored patterns

Let’s talk about action spectra in V4

(Zeki) Inhibitory

Excitatory

Method

Subject: WAP

Visual Sensitivity

and Opposing L-M signals: Eye-Same

Contrast (%)

Eye-Different Condition

Eye-Different

( ,0,0)L (0, ,0)M

Left eye Right eye

Eye-different condition BW WAP

JR SH

V1V2dV2vV3dV3v

PosteriorAnterior

cm

Retinotopic Areas in Human Occipital Lobe

2

-2

FM

RI

sign

al m

odul

atio

n (%

)

Time

FMRI Signal Time Course

• Measure signal contrast needed to obtain criterion signal level• Permits comparison with threshold psychophysics

Criterion

Human V1: fMRI time (L,M) Iso-response Contour

L-cone contrast (%)

M-c

one

cont

rast

0 50

fMRI

Contrast (%)

Subject: WAP

Exchange measurements are a way to begin the exploration of color signals in human cortex

(Zeki, many papers)

Color exchange principles

• Spatial structure is constant

• Achromatic (L+M+S) vs. Achromatic + Color (L-M, S – (L+M))

• Subtractive: differential responses are due to color

Time

Calcarine

Ventral surface

Color exchange ventral signal locations with respect to the visual

areas (A v. A+C)

Color exchange ventral signal locations with respect to the visual

areas (A v. A+C)

Visual area

Fovealconfluence

V1V2V3

V3BV3A

hV4V7

Ventral surface

Calcarine

We are now carrying out human-macaque comparisons using

functional MRI(Wade, Augath, Logothetis, Wandell)