12-week lecture series on "the neural basis of consciousness" by Prof Nao Tsuchiya. Given to 3rd year undergraduate level. No prerequisites. Contents: 1) What is our peripheral experience? - A closer look with color, motion, and metacognition 2) What neural mechanisms underlie the transmission of visual input from the eyes to the brain? 3) What is a receptive field of a neuron? 4) What are the key properties of V1 (the primary visual cortex)? 5) What are the implications of the properties of V1 for conscious phenomenology? 6) What are the visual pathways from the eyes to the brain, and its implication for blindsight?

1. Week 5
Neural basis of consciousness:
Eyes, early visual system and
consciousness
Prof Nao Tsuchiya
Twitter: @conscious_tlab
Email: naotsugu.tsuchiya@monash.edu
Facebook: Naotsugu Tsuchiya

2. Recap of Wk 4
Nonconscious processing under (sandwich) masking
Behavioral validation of conscious visibility and
invisibility of the stimuli
Neuronal and behavioral evidence of nonconscious
visual processing

3. Recap of Wk 4
Blindsight in monkeys:
What neural mechanisms
explain blindsight?
Metacognitive accuracy as a way to discriminate conscious
from nonconscious processing.
Structure of the eye
Do we see color outside of the fovea?

4. In Wk 5,
We will
● explain the properties of visual cortex, in particular V1,
and discuss the implication for our color vision at the
periphery, and
● explain the neural mechanisms of blindsight, while going
through the early visual systems and alternative
pathways.

5. Learning Objectives
To be able to answer the following questions:
What is our peripheral experience?
A closer look with color, motion, and metacognition
What neural mechanisms underlie the transmission of
visual input from the eyes to the brain?
What is a receptive field of a neuron?

6. Learning Objectives
What are the key properties of V1 ---
the primary visual cortex?
What are the implications of the properties
of V1 for conscious phenomenology?
What are the visual pathways from the eyes to the brain,
and its implication for blindsight?
QFC Chapter (3), 4, 8 (Chapter 5-7 are optional reading)

7. Recap: Demonstration in Week 4
If you have not completed, please participate in the survey for
Week 4!
Closer look at peripheral experience

8. Recap: Demonstration in Week 4
If you have not completed, please participate in the survey for
Week 4!
Closer look at peripheral experience

9. Metacognition of your peripheral experience
Closer look at peripheral experience
1) Prepare a set of playing
card suit.
2) Pick a card with the back
side facing to you.
3) Move the card to the place
where you think you can
identify the identity of the
card.
4) Flip it. See if you can
identify it

10. Please try it by yourself!
Closer look at peripheral experience
Then, answer the moodle
question for “metacognition
on your peripheral vision”

11. Is consciousness sparser than we think?
“we still see far less than we think we do” (Do we?)
Cohen et al 2016 TICS
Closer look at peripheral experience

12. Peripheral experience of color vs motion - 1
Closer look at peripheral experience
1) Now, do the same thing again, but
relax the condition. Estimate where
you can “see” the color of the card.
2) Flip the card.
3) Now, locate the card where you
cannot see the color of the card. Then
move it yourself OR better if you ask
people to move it. Can you see its
motion?

13. Peripheral experience of color vs motion - 2
Closer look at peripheral experience
1) Ask another person to move the card
from very periphery and say STOP
when you START seeing the motion
of the card.
2) Can you identify the color and the
number of the card there?

14. Please try it by yourself!
Closer look at peripheral experience

15. Is consciousness sparsar than we think?
“we still see far less than we think we do” (Do we?)
Cohen et al 2016 TICS
Closer look at peripheral experience

16. Let’s hear what Dennett says (2020, Jan)
Daniel Dennett - one of the most
influential philosophers.
https://www.youtube.com/watch?v
=8yZw4wxvnVQ
Mindscape by Sean Carroll
Closer look at peripheral experience

17. Summary
Experience in the periphery is … controversial.
Please answer the questions for “metacognition on your
peripheral vision” in Moodle.

19. Roles of eye movements in conscious vision
(Unlikely) hypothesis 1: You
actually do NOT see color in
the periphery BECAUSE OF
the lower density of cones at
the periphery.
But, somehow, we feel color
in the periphery. WHY?
Eye movements and consciousness

20. Roles of eye movements in conscious vision
[(Unlikely) explanation]
Because we move eyes to see color
in the periphery! We are unaware that
we are seeing color at the fovea!
[Fact!] We move the eyes ~3 times per
second.
Eye movements and consciousness

21. Puzzles of eye movements & conscious vision
You move your eyes roughly 3 times per second.
Q1. Are you normally aware of the eye movements?
Q2. Can you become aware of when eye movements
happen if you pay attention to it?
---> Hinting at the relation between attention and
consciousness
Q3. During eye movements, can you see things?
Eye movements and consciousness

22. Eye movements & conscious vision
Demo
Part 1) Face to your friend (or record your face with videos).
Can you see the quick movements of the eyes?
Part 2) Go in front of the mirror. Look at your own left eye.
Then move your eyes to fixate on your own right eye. Can
you see the quick movements of the eyes?
Eye movements and consciousness

23. Saccades suppresses conscious vision
Saccadic suppression:
Eye movements and consciousnessIdrees 2020 Nat Comm

24. Ultra rapid eye movements can be possible...
Eye movements and consciousness

25. How can we reduce the eye movement confound?
1. Measure eye movements (can be tedious)
Or
2. Present stimuli for a brief period (<250ms)
3. Present them in a random timing and position
Then, any saccade towards the stimulus makes the
vision blurry. And any incoming signal is strongly
attenuated!
Eye movements and consciousness

26. Let’s revisit Ariel’s task
Link to the Ariel’s color similarity task
Eye movements and consciousness

27. Summary (not conclusive at the moment)
Are we fooled to experience color in the periphery because of
(nonconscious) eye movements?
Brief presentation of peripheral stimuli can address this
question.
(Sidenote - but important)
We cannot see well during saccades (saccadic suppression)
Eye movements and consciousness

29. What are the neuronal mechanisms that are
responsible for (peripheral) vision?
Eye to brain - RF
We will
● explain the properties visual systems from eyes to V1
and discuss the implication for our color vision at the
periphery.

30. Entry to the visual system: Eye
Eye to brain - RF

31. Recording neuronal activity from retinal ganglion cells
Eye to brain - RF

32. Receptive field of a RGC
Eye to brain - RF

33. Size of RGC and
the extent of the
dendrites
-> Extent of RF!
Eye to brain - RF

34. What does this mean for our fovea/peripheral vision?
Retina LGN V1
Eye to brain - RF

35. Neurons that respond to peripheral visual inputs …
… reflect inputs from cones over wider areas thana those that
respond to foveal visual inputs.
And this convergence effect becomes stronger for the
neurons at more periphery.
Assuming color qualia arise from higher areas, BIG and
uniform surface CAN evoke stronger color qualia
Eye to brain - RF

36. What does this mean for our fovea/peripheral vision?
Retina LGN V1
Eye to brain - RF

37. If the same sized object is projected to retina…
Neurons at the fovea have a better spatial resolution.
Collecting inconsistent color information at the periphery
predicts more blunt responses of neurons responsible for
color qualia at the periphery.
But this is not the same thing as “we cannot see any color at
the periphery”!
Eye to brain - RF

38. Summary
Retinal ganglion cells have a receptive field that looks like
annulus and send visual inputs to lateral geniculate nucleus
through spikes (all or none).
Some are sensitive to onset, others are sensitive to offset of
visual stimuli.
Receptive fields of RGC scales as eccentricity - implications
for conscious phenomenology in fovea vs periphery
Eye to brain - RF

40. What are the neuronal mechanisms that are
responsible for (peripheral) vision? --- Part 2
V1 properties and phenomenology
We will
● explain the properties visual systems, focusing on V1,
and discuss the implication for our color vision at the
periphery.

41. Neuronal structure in cortex: I
Any cortical area is composed of
5-6 layers in a vertical dimension.
Neurons in each layer tend to have
similar connectivity patterns, which
is utilized to …
V1 properties and phenomenology

42. … to derive cortical hierarchy
Felleman 1991 Cereb Cor
V1 properties and phenomenology

43. Neuronal structure in cortex: II
The higher in the hierarchy a
neuron locates,
1) the bigger the size of the
receptive field becomes, and
2) the more complicated the
property of the RF becomes.
V1 properties and phenomenology

44. Neuronal structure in cortex: III
Along the surface (horizontally) the RF properties tend to be
similar among neurons (columnar structure).
In V1, ocular dominance
and orientation are
clearly clustering.
There are other features
that cluster too.
V1 properties and phenomenology

45. (A bit of preview for the next week)

46. How does a visual image map to V1?
Important concepts:
Retinotopy
Cortical magnification
V1 properties and phenomenology

47. How does a visual image map to V1?
Very important!
V1 properties and phenomenology

48. How does a visual image map to V1?
?
?
V1 properties and phenomenology

49. How does a visual image map to V1?
Outside Retina
Left V1
Be careful. Many web resources are
WRONG about this basic...
Left V1 Right V1
V1 properties and phenomenology

50. What are the implications for conscious vision?
Why do we not see images upside down?
Why do we not see images in a distorted way?
What we experience is not the mirror image (a simplistic
“representation”) of the world. How come?
Fovea is hugely enlarged in V1. In the end, are we actually
not seeing much of the periphery?
V1 properties and phenomenology

51. Summary
Cortex is vertically layered and it is horizontally organized in a
columnar fashion.
At the higher hierarchy, the receptive field of a neuron
becomes bigger in size and more complex in its property.
Cortical magnification and retinotopy presents the first step to
the Hard problem. What is the link between neurons and
phenomenology?
V1 properties and phenomenology

52. Summary
Cortical representation of the fovea is huge in V1. Up to 2.5
dva corresponds to ~20-25% of V1. 10 dva to 50%.
What does this mean about our “impression” of
consciousness in the periphery?
But, is V1 really responsible for conscious vision? (next week)
These are important topics, which we will be coming back
again in the next lectures.
V1 properties and phenomenology

54. What are the neuronal mechanisms that are
responsible for blindsight?
Blindsight and visual pathways
Keys to explain
Lack of visual phenomenology
Presence of certain behaviors:
Eye movement to an object
Localization of an object

55. V1 lesion should block
all visual pathways…?
Felleman 1991 Cereb Cor Blindsight and visual pathways

56. Actually, there is an
alternative pathway!
Blindsight and visual pathways

57. Actually, there is an
alternative pathway!
~90% of RGC projects to
LGN (in primates)
~10% of RGC projects to
superior colliculus
Blindsight and visual pathways

58. An alternative pathway from retina to the cortex
SC: Superior colliculus
(important for eye movements
and attention)
Amygdala: important (?) for fear
reaction (and experience?)
Pessoa 2010 Nat Rev Neuro
Blindsight and visual pathways

59. Long-term effects of V1 lesion on anatomy
Cowey 2009 Exp Brain Res
At least 10 pathways:
1 dorsal Lateral Geniculate Nucleus
2 Inferior Pulvinar (PI)
3 Superior Colliculus
4 PreGeniculate Nucleus
5 Olivary Nucleus
6 Nucleus of the Optic Tract
7-9 M/L/DTM : Medial/Lateral/Dorsal
Terminal accessory optic Nuclei
10 SupraChiasmatic Nucleus
Blindsight and visual pathways
V1 lesioned

60. Actually,... multiple pathways exist!
Pessoa 2010 Nat Rev Neuro
Blindsight and visual pathways

61. Multiple shortcuts and feedback to explain masking?
Blindsight and visual pathways

62. Spatial vs. Temporal
hierarchy in the brain
Blindsight and visual pathways

63. Dorsal vs. Ventral pathway
Vision for action, where, and
how (nonconscious?):
related to eye movements
and localization
Vision for object recognition
and what (conscious?)
Blindsight and visual pathways

64. Dorsal vs. Ventral pathway
Blindsight and visual pathways

65. Summary
Blindsight occurs when the retino-LGN-V1 pathway is
damaged.
The retino-SC-pulvinar-cortex and the retino-LGN-MT
pathways are likely to mediate the blindsight behaviors.
Q. (for the next week) If superior colliculus is important for
attentional orienting, can blindsight patients direct attention to
invisible objects?
Blindsight and visual pathways

66. Summary
Multiple pathways in vision (other modality as well) introduces
highly complex temporal hierarchy, which is unexpected from
the Felleman-Van Essen diagram.
Q. What is the role of feedforward/feedback neural activity for
conscious vision?
Blindsight and visual pathways