Vision and audition, Course 9.04Peter H. Schiller and Chris Brown, year 2006
Introduction to Course 9.04, Vision and Audition
Vision: Peter H. Schiller Audition: Chris Brown
Reading assignments
Research report
Exams
Introductions
What aspects of visual processing are we trying to understand?
Color vision
Movement pocessing
Depth perception
Object recognition
Generation of visually guided eye movements
Tools of the trade:
Psychophysics
Anatomy
Physiology
Pharmacology
Brain lesions
Imaging
The visual and oculomotor systemsPeter H. Schiller, Sep 11, 2006
Basic Wiring of the Visual System
The world seen by the two eyes
rabbit human
Seen by both eyes
Seen by left eye Seen by right eye
Seen by both eyes
Seen by left eye Seen by right eye
Figure by MIT OCW.
LGN
Cortex
Optic chiasm
Optic tectum
Fish and Amphibia
temporal nasal
opticchiasm
terminalnuclei
superiorcolliculi
NOT
LGNp
m
FRONTAL LOBE
PARIETAL LOBE
re i
ergh
h tp
hmis
eme
isft
h phele re
TEMPORAL LOBE
MT
V4
V3
V2V1
Primates left righthemifield hemifield
Horopter (Vieth-Muller circle)
fix
Basics of Retinal Connections
and Retinal Ganglion Cells
Ciliaryprocess
Retrolental space
Optic axis
Canal ofCloquet
Retina
ScleraChoroid
Lamina cribrosa
Horizontal section of the right human eye.
Nerve & sheath
Macula lutea
Fovea
Vitreous humor
Visual axis
Ora serrataCiliary epithelium
Zonule fibers
Ciliary muscleCanal of Schlemm
ConjunctivaIris
Cornea
Rectustendon
Lens
Anterior Chamber
Posterior chamberLimbal zone
Ciliary
body
Disc
Figure by MIT OCW.
Foveal cone density: 200,000/sqmm5 degrees out: 20,000/sqmm
10 degrees out: 10,000/sqmm
Fovea
Optic nerve
Human RetinaFoveal cone density: 200,000/sqmm
5 degrees out: 20,000/sqmm10 degrees out: 10,000/sqmm
Figure by MIT OCW.
Physiology of retinal ganglion cells
Recording Methods:
electrode in nerveelectrode in eye
fiber hook
optic nerve
Stimulation Methods:
direct light
on
ON cell
time
OFF cell
ON/OFF cell
reflected light
The receptive fields of three major classes of retinal ganglion cells
OFF
inhibition
ON
inhibition
ON/OFF
inhibition
ON
inhibition
Three populations of fibers
Rapid Slower Very slow
Conduction velocity in optic nerve fibers
Figure by MIT OCW.
MIDGET SYSTEM PARASOL SYSTEM
ON OFFON OFF
neuronal response profile
time
Photoreceptors
Distribution of rods and cones on the retina
Num
ber o
f rod
s or c
ones
in a
n ar
ea 0
.006
9 sq
mm
2400
2000
1600
1200
800
400
080 60 40 20 0 20 40 60 80
1.2
1.0
0.8
0.6
0.4
0.2
0
Rel
ativ
e vi
sual
acu
ity
Degrees from the foveaFovea
Distribution of rods and cones along a horizontal meridian. Parallel vertical lines represent the blindspot. Visual acuity for a high luminance as a function of retinal location is included for comparison.
Rods (number)Cones (number)Relative visualacuity in degreesfrom the fovea
Blin
d sp
ot
Figure by MIT OCW.
Some basic facts about the receptor array
1 degree = 200u on retina
Intercone distance in fovea = 2.4u (0.7 min)
200,000 cones per sq.mm. in fovea
20,000 cones per sq.mm. 5 degrees out
Thumbnail at arm's length = 1 degree
The 12 font letter "I" activates about 80 cones at 23 cm
Each rod has 1,000 disks, each with 10,000 molecules
Only 1 of 8 cones is blue. Red and green are equal.
:
Photoreceptor basics:
1. All photoreceptors hyperpolarize to light.
2. Depolarization of the photoreceptor releases glutamate.
3. Photon absorption by the photopigment results in isomerization of the chromophore from 11-cis to all-trans. This causes hyperpolarization thereby reducing neurotransmitter release.
4. Two classes of bipolars are the ON and the OFF. The synaptic junction of OFF bipolars is sign conserving; that of the ON bipolar is sign inverting.
5. The ON bipolar receptor is mGluR6. Its activation leads to closing of channels causing hyperpolarization.
Horizontal cells
Figure by MIT OCW.
A Horizontal cell with regularly arranged dendrites thatis connected to 15 cones in a cone density region of 20.
Amacrine cells
Figure by MIT OCW.
cholinergic cell
All cell
dopaminergic cell
All
Cholinergic
Dopaminergic
Electrical responses in the retina
Figure by MIT OCW.
all hyperpolarize to light
all hyperpolarize to light
some hyperpolarize and some depolarize
some give action potentials
all give action potentials
Ganglion Cells
Bipolar Cell
Receptor
Amacrine Cell
Horizontal Cell
Overview of retinal connections:
Photoeceptors all hyperpolarize to light. They produce only graded potentials. Glutamate is the neurotransmitter.
Horizontal cells all hyperpolarize tolight and produce only graded potentials.
Some bipolar cells depolarize (ON) and some hyperpolarize (OFF) to light. Bipolars produce only graded potentials.
Some amacrine cells produce actionpotentials. There are many classes including ON and OFF.
Ganglion cells produce action potentials.There are many classes including midgetand parasol that come either as ON or OFF.
Figure by MIT OCW.
R
GMGMG
FMB
IMB
A A
IDB RB
I
H
RC
R RC C C
R
Summary:1. In primates the right brain receives input from the left visual hemifield and the left brain from the right hemifield.
2. There are five major classes of retinal cells: photorecptors (rods and cones), horizontal cells, bipolar cells, amacrine cells, and retinal ganglion cells (RGC).
3. The receptive fields of RGCs have antagonistic center/surround organization.
4. There are several classes of RGCs, two of which are (a) the ON and OFF and (b) the Midget and Parasol.
5. All photoreceptors and horizontal cells hyperpolarize to light.
6. There are both hyperpolarizing and depolarizing bipolar cells.
7. Action potentials in the retina are generated only by amacrine and RGC cells.
8. The lateral geniculate nucleus of the thalamus is a laminated structure. What is segregated in the laminae varies with species.
9. The parvocellular layers receive input from the midget cells and the magnocellular layers from the parasol cells. Inputs from the left and right eyes are segregated in the laminae.
10. The receptive field properties of LGN cells are similar to those of the retinal ganglion cells.