Transcript 10.1 The Blind Spot

Human Ey e
Structures of the Human Eye
Anatomy of the Retina
Hyperpolarization of Photoreceptors
Without light
With light
An Unobstructed View
Structures of the Human Eye
Densities of Retinal Receptors and Visual Acuity
Lateral Inhibition in the Retina
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The Effect of Context on the Perception of
Brightness
Dot illusion
Visual Pathways in the Human Brain
The Lateral Geniculate Nucleus
Blindsight
Individuals with damage to their visual striate cortex V1 due to
accidents or strokes reported partial or total blindness.
In spite of this, when they were prompted they could "guess" with
above-average accuracy about the presence and details of objects.
Alternative pathways for visual information
Retina – Superior Colliculus – Pulvinar – Extrastriate
A person with blindsight could detect slow or fast-moving stimuli,
but was only aware of the fast ones. Visual motion information
processing in the LGN A connection from LGN to the extrastriate
visual areas V2, V3, V4 and visual motion area V5/MT
Blindsight
Blindsight in Action: What Can the Different Sub-types of Blindsight Tell Us About the Control of Visually Guided
Actions?
James Danckert, Yves Rossetti
Connections of Cones to Bipolar Cells
See Figure 10.8
Receptive Fields of Retinal Cells
Receptive Fields of Cells at Various Levels in the Cat Visual System
Circular Receptive Fields Can Be Combined to Produce Rod-Shaped
Receptive Fields
Spatial Frequencies
Visual Subsystem Pathways
Ganglion Neurons
LGN
(L/M) “Midget”
Parvocellular in
layers 3,4,5,6
Visual Cortex
Subsystem
Color
V1 layer 4C beta >V2 Thin -> V4
S(L+M) “Bistratified”
Koniocellular
Between each of the
M and P layers
Motion
Diffuse "Parasol"
Magnocellular in
layers 1, 2
V1 layer 4C -> 4B ->
V2 Thick -> V5
Dynamic Form
Diffuse "Parasol"
Magnocellular in
layers 1, 2
V1 layer 4B -> V2
Thick -> V3
Main Visual Areas in Monkey and Human Brains
Functionally identified areas of human cortex using fMRI
The retinotopic organization of the human middle temporal area MT/V5 and its cortical neighbors.
Kolster et al. (2010) J. Neurosci. 30: 9801-9820.
Visual Areas interconnections
FELLEMANN, D..J. & D.C. VAN ESSEN. 1991. Distributed hierarchical processing in the
primate cerebral cortex. Cerebral Cortex 1: 1–47.
Why are there so many visual areas... ?
COLOUR, FORM, STEREOSCOPIC DEPTH, MOTION
All require very different processing strategies
- most efficient if performed separately
The Forest Has Eyes by Bev Dolittle