1. Blindsight refers to the phenomenon where patients with damage to visual cortex demonstrate visually guided behaviors despite reporting no visual experience or perception. This suggests the existence of two visual systems - a cortical system for visual perception and a subcortical system for visual processing without awareness. 2. Evidence from studies in monkeys, rodents, and frogs support the two visual systems hypothesis, finding that lesions to visual cortex impair perception but not all visually guided behaviors, which can still be mediated by the subcortical system. 3. In humans, the dorsal visual pathway is thought to underlie blindsight by allowing visual information processing without awareness, while the ventral pathway is necessary for conscious visual experience. However, the specific

1. SOKENDAI physiology lecture course 2013
"Neuroscience of Cognition and Motor control" #8
"Neural Mechanism of Blindsight"
June 14, Friday 10:00-12:00, Myodaiji Staff Hall 2F Meeting room
Masatoshi Yoshida (NIPS and SOKENDAI, Assistant professor)
1. What is Blindsight (盲視)?
Q: What is blindsight?
• A: “The visually evoked voluntary responses of
patients with striate cortical destruction that
are demonstrated despite a phenomenal
blindness” 1
• Phenomenal consciousness can be
dissociated from visual information processing.
2. Two visual systems:
Cortical vs. Subcortical
2-1. Two visual systems in monkeys
• Bilateral lesion in V1 - first report of blindsight
in monkey 2
• Retained: visually guided reaching and
obstacle avoidance 3
2-2. Two visual systems in rodents
• Double dissociation - lesion in visual cortex
and in the superior colliculus 4
• SC for orienting 5
• Visual cortex for pattern discrimination 6
2-3. Two visual systems in frogs
• Two Visual Systems in the Frog 7
• Lesion in the optic tectum induces rewiring.
• Neocortex for obstacle avoidance
• Optic tectum for Response to preys
3. Two cortical visual systems:
Dorsal vs. Ventral
3-1. What and where pathways (Mishkin &
Ungerleider)
• The neurons in the dorsal pathway are
selective to motion and binocular disparity.
• The neurons in the ventral pathway are
selective to shape and color. 8
• Bilateral removal of area TE: Object
discrimination - Which is the unfamiliar object?
• Bilateral removal of posterior parietal cortex:
Landmark discrimination:
• Which is near to the landmark? 9
3-2. Vision for perception and vision for
action (Goodale and Milner)
• Dorsal pathway: Vision for action -
unconscious
• Ventral pathway: Vision for perception –
conscious 10
• Optic ataxia (視覚性運動失調)
• Damage in the posterior parietal cortex -
supramarginal gyrus and angular gyrus
• Orientation error does not depends on hand
but on visual field.
• Damage in the dorsal pathway affects vision
for action. 11
• Visual form agnosia (視覚失認):
• Subject DF: Bilateral damage in ventral visual
pathway (Lateral occipital area: LO)
• Very good performance in ‘posting’ task 12
• DF matched her card orientation to the slot
during the course of the movement, well before
contacting the target. 13
• Functional double dissociation
• "Visual phenomenology ... can arise only from
processing in the ventral stream ..." "
visual-processing modules in the dorsal
stream ... are not normally available to
awareness." ("The visual brain in action"
p.200-201)
14

2. 3-3. Perceptual experience in visual agnosia
• Retained color, texture perception
• Degraded form perception
• a piece of kitchen equipment” it’s got a red
part to it, a red handle” it goes down into a
silver corrugated part” the red part’s plastic
and the other part’s metal.” (When she was
handed it) “Oh, it’s a torch.” 15
• She has difficulty describing her visual
experience, only saying that objects tend to
appear ‘blurred’ and that separate elements
‘run into each other’. 13
• Yoshida's comment: She experiences color,
texture and motion of small elements. This is
the biggest difference from the experience of
blindsight. This is the strongest evidence that
V1, not the ventral pathway, is necessary for
conscious experience.
3-4. Are they really independent?
• Single-line copying task
• She draw ‘in the air’ before copying (1st trial).
• She imagined herself tracing on top of the line
and translate the image into drawing. It takes a
longer time (5-10sec).
• DF developed a strategy to overcome
perceptual deficit by visuomotor skills. 16
• Lesson learned: Perceptual task can be solved
by visuomotor skill.
• It is very important to control tasks not to
develop unexpected strategy.
4. Blindsight in human
4-1. Case reports
• G.Y. became blind in his right visual field due
to traffic accident in eight years old. He was
diagnosed as homonymous hemianopia.
• Above-chance performance in forced-choice
=> blindsight 17
• A blindsight subject in Japan
4-2. Relationship between Blindsight and
two-visual systems hypothesis
• Access to the dorsal pathway in blindsight
4-3. Affective blindsight
• Discrimination of Emotion of face (Fearfull vs.
happy) <==> Discrimination of identity of faces
18
• Alarm system in subcortical pathway 19
• Subcortical face processing 20
4-4. Plasticity in blindsight
• 2-3 months training is necessary for blindsight.
21
• DTI revealed crossed connection between
LGN and MT. 22
• DTI revealed stronger connection SC ->
Pulvinar -> Amygdala 23
5. Blindsight in monkey
5-1. Blindsight in monkeys
• Blindsight after 2-3 months training 24
• Are the monkeys really ‘blind’ to the visual
stimuli? The monkeys behaved as if it is a
No-target trial. The monkeys are ‘not able to
see’, as in human blindsight.
5-2. Neural circuit for blindsight
• Blindsight disappear after SC inactivation. 25
• MT response does not disappear after V1
lesion.
• MT response disappear after additional lesion
of SC. 26,27
• Inactivation of LGN abolishes blindsight 28
• They did not inactivate the SC. Thus they did
not reject possibility that blindsight depends
both on LGN and SC.
• Inactivation of the SGS abolishes blindsight. 29
6. Summary
The idea of two visual systems (cortical vs.
subcortical) was confirmed in various animals.
1. Dorsal and ventral visual pathways may
have different roles on unconscious and
conscious vision, or vision for action and
vision for perception.
2. Controversy over the neural circuit for
blindsight is not settled.

3. References
1. Cowey, A. & Stoerig, P. Blindsight in monkeys.
Nature 373, 247–249 (1995).
2. Humphrey, N. K. & Weiskrantz, L. Vision in
monkeys after removal of the striate cortex.
Nature 215, 595–597 (1967).
3. Humphrey, N. K. Vision in a monkey without
striate cortex: a case study. Perception 3,
241–255 (1974).
4. Schneider, G. E. Two visual systems. Science
163, 895–902 (1969).
5. Carman, L. S. & Schneider, G. E. Orienting
behavior in hamsters with lesions of superior
colliculus, pretectum, and visual cortex. Exp
Brain Res 90, 79–91 (1992).
6. Schneider, G. E. Mechanisms of functional
recovery following lesions of visual cortex or
superior colliculus in neonate and adult
hamsters. Brain Behav. Evol. 3, 295–323
(1970).
7. Ingle, D. Two Visual Systems in the Frog.
Science 181, 1053–1055 (1973).
8. Van Essen, D. C. & Gallant, J. L. Neural
mechanisms of form and motion processing in
the primate visual system. Neuron 13, 1–10
(1994).
9. Mishkin, M., Ungerleider, L. G. & Macko, K. A.
Object vision and spatial vision: two cortical
pathways. Trends in Neurosciences 6,
414–417 (1983).
10. Goodale, M. A. & Westwood, D. A. An
evolving view of duplex vision: separate but
interacting cortical pathways for perception
and action. Current Opinion in Neurobiology
14, 203–211 (2004).
11. Perenin, M. T. & Vighetto, A. Optic ataxia: a
specific disruption in visuomotor mechanisms.
I. Different aspects of the deficit in reaching
for objects. Brain 111 ( Pt 3), 643–674 (1988).
12. Goodale, M. A., Milner, A. D., Jakobson, L. S.
& Carey, D. P. A neurological dissociation
between perceiving objects and grasping
them. Nature 349, 154–156 (1991).
13. Milner, A. D. et al. Perception and action in
'visual form agnosia'. Brain 114 ( Pt 1B),
405–428 (1991).
14. Milner, D. A. & Goodale, M. A. The Visual
Brain in Action. (Oxford University Press,
2006).
15. Humphrey, G. K., Goodale, M. A., Jakobson,
L. S. & Servos, P. The role of surface
information in object recognition: studies of a
visual form agnosic and normal subjects.
Perception 23, 1457–1481 (1994).
16. Dijkerman, H. C. & Milner, A. D. Copying
without perceiving: motor imagery in visual
form agnosia. Neuroreport 8, 729–732 (1997).
17. Weiskrantz, L., Barbur, J. L. & Sahraie, A.
Parameters affecting conscious versus
unconscious visual discrimination with
damage to the visual cortex (V1). Proc Natl
Acad Sci USA 92, 6122–6126 (1995).
18. De Gelder, B., Vroomen, J., Pourtois, G. &
Weiskrantz, L. Non-conscious recognition of
affect in the absence of striate cortex.
Neuroreport 10, 3759–3763 (1999).
19. Liddell, B. J. et al. A direct
brainstem-amygdala-cortical ‘alarm’ system
for subliminal signals of fear. NeuroImage 24,
235–243 (2005).
20. Johnson, M. H. Subcortical face processing.
Nat Rev Neurosci 6, 766–774 (2005).
21. Huxlin, K. R. et al. Perceptual Relearning of
Complex Visual Motion after V1 Damage in
Humans. J Neurosci 29, 3981–3991 (2009).
22. Bridge, H., Thomas, O., Jbabdi, S. & COWEY,
A. Changes in connectivity after visual cortical
brain damage underlie altered visual function.
Brain 131, 1433–1444 (2008).
23. Tamietto, M., Pullens, P., de Gelder, B.,
Weiskrantz, L. & Goebel, R. Subcortical
Connections to Human Amygdala and
Changes following Destruction of the Visual
Cortex. Current Biology 22, 1449–1455
(2012).
24. Yoshida, M., Takaura, K., Kato, R., Ikeda, T. &
Isa, T. Striate Cortical Lesions Affect
Deliberate Decision and Control of Saccade:
Implication for Blindsight. J Neurosci 28,
10517–10530 (2008).
25. Mohler, C. W. & Wurtz, R. H. Role of striate
cortex and superior colliculus in visual
guidance of saccadic eye movements in
monkeys. Journal of Neurophysiology 40,
74–94 (1977).
26. Rodman, H. R., Gross, C. G. & Albright, T. D.
Afferent basis of visual response properties in
area MT of the macaque. I. Effects of striate
cortex removal. J Neurosci 9, 2033–2050
(1989).
27. Rodman, H. R., Gross, C. G. & Albright, T. D.
Afferent basis of visual response properties in
area MT of the macaque. II. Effects of
superior colliculus removal. J Neurosci 10,
1154–1164 (1990).
28. Schmid, M. C. et al. Blindsight depends on the
lateral geniculate nucleus. Nature 466,
373–377 (2010).
29. Kato, R., Takaura, K., Ikeda, T., Yoshida, M. &
Isa, T. Contribution of the retino-tectal
pathway to visually guided saccades after
lesion of the primary visual cortex in monkeys.
Eur J Neurosci 33, 1952–1960 (2011).