2019-04-08 20:23:40
Prelude
Today's topics
- Exam 3 next Thursday, 4/11
- Warm-up
- Vision
Warm-up
Which type of muscle fiber is also a sensory organ?
- extrafusal
- intrafusal
- exteroceptive
- extrapyramidal
Which type of muscle fiber is also a sensory organ?
- extrafusal
- intrafusal
- exteroceptive
- extrapyramidal
How many synapses connect the Ia (stretch receptor) sensory afferent in a muscle to the \(\alpha\) motor neuron activating the same muscle?
- 1
- 2
- 10s
- too many to count
How many synapses connect the Ia (stretch receptor) sensory afferent in a muscle to the \(\alpha\) motor neuron activating the same muscle?
- 1
- 2
- 10s
- too many to count
Parkinson's and Huntington's disease are similar in that both affect this part of the brain.
- Spinal cord
- Primary motor cortex
- Basal ganglia
- Primary somatosensory cortex
Parkinson's and Huntington's disease are similar in that both affect this part of the brain.
- Spinal cord
- Primary motor cortex
- Basal ganglia
- Primary somatosensory cortex
Vision
How vision informs
- What's out there?
- Shape, form, color
- Where is it?
- Position, orientation, motion
Electromagnetic (EM) radiation
Features of EM radiation
- Wavelength/frequency
- Intensity
- Location/position of source
- Reflects off some materials
- Refracted (bent) moving through other materials
EM radiation provides information across space (and time)
Reflectance spectra differ by surface
Reflectance spectra
Optic array specifies geometry of environment
Color == categories of wavelength
- Eyes categorize wavelength into relative intensities within wavelength bands
- RGB ~
Red,
Green,
Blue
- Long, medium, short wavelengths
- Color is a neural/psychological construct
RGB monitors
How a camera works
The biological camera
The biological camera
Parts of the eye
- Cornea - refraction (2/3 of total)
- Pupil - light intensity; diameter regulated by the Iris.
- Lens - refraction (remaining 1/3; variable focus)
Parts of the eye
- Retina - light detection
- ~ skin or organ of Corti
- Pigment epithelium - regenerate photopigment
- Muscles - move eye, reshape lens, change pupil diameter
Eye forms image on retina
- Image inverted (up/down)
- Image reverseed (left/right)
- Point-to-point map (retinotopic)
- Binocular and monocular zones
Retinal image
Eyes views overlap
The fovea
The fovea
- Central 1-2 deg of visual field
- Aligned with visual axis
- Retinal ganglion cells pushed aside
- Highest acuity vision == best for details
Acuity varies across the retina
Acuity varies across the retina
What part of the skin is like the fovea?
Photoreceptors detect light
Photoreceptors detect light
- Rods
- ~120 M/eye
- Mostly in periphery
- Active in low light conditions
- One wavelength range
Photorceptors detect light
- Cones
- ~5 M/eye
- Mostly in center
- 3 wavelength ranges
Photoreceptors "specialize" in particular wavelengths
Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013.
How photoreceptors work
- Outer segment
- Membrane disks
- Photopigments
- Sense light, trigger chemical cascade
- Inner segment
- Synaptic terminal
- Light hyperpolarizes photoreceptor!
- The dark current
Retina
- Physiologically backwards
- How?
- Anatomically inside-out
- How?
Retina
- Physiologically backwards
- Dark current
- Anatomically inside-out
- Photoreceptors at back of eye
Retinal layers
Retinal layers
- Bipolar cells
- Horizontal cells
- Retinal ganglion cells
- Amacrine cells
Center-surround receptive fields
Center-surround receptive fields
- Center region
- Excites (or inhibits)
- Surround region
- Does the opposite
- Bipolar cells & Retinal Ganglion cells ->
- Most activated by "donuts" of light/dark
- Local contrast (light/dark differences)
What's a reddish-green look like?
What's a reddish-green look like?
Opponent processing
Opponent processing
- Black vs. white (achromatic)
- Long (red) vs. Medium (green) wavelength cones
- (Long + Medium) vs. Short cones
- Can't really see reddish-green or bluish-yellow
From eye to brain
From eye to brain
- Retinal ganglion cells
- 2nd/II cranial (optic) nerve
- Optic chiasm
- Lateral Geniculate Nucleus (LGN) of thalamus (90% of projections)
From eye to brain
- Hypothalamus
- Suprachiasmatic n.
- Superior colliculus & brainstem
LGN
LGN
- 6 layers + intralaminar zone
- Parvocellular (small cells): chromatic
- Magnocellular (big cells): achromatic
- Koniocellular (chromatic - short wavelength?)
- Retinotopic map of opposite visual field
From LGN to V1
From LGN to V1
- Via optic radiations
- Primary visual cortex (V1) in occipital lobe
Human V1
Measuring retinotopy in V1
Retinotopy in V1
- Fovea overrepresented
- Analogous to somatosensation
- High acuity in fovea vs. lower outside it
- Upper visual field/lower (ventral) V1 and vice versa
V1 has laminar, columnar organization
V1 has laminar, columnar organization
- 6 laminae (layers)
- Input: Layer 4
- Output: Layers 2-3 (to cortex), 5 (to brainstem), 6 (to LGN)
V1 has laminar, columnar organization
- Columns
- Orientation/angle
- Spatial frequency
Orientation/angle tuning
From center-surround receptive fields to line detection
Spatial frequency tuning
Low == gist || high == details 
V1 has laminar, columnar organization
- Columns
- Color/wavelength
- Eye of origin, ocular dominance
Ocular dominance columns
Ocular dominance signals retinal disparity
Beyond V1
Beyond V1
- Larger, more complex receptive fields
- Dorsal stream (where/how)
- Toward parietal lobe
- Ventral stream (what)
What is vision for?
- What is it? (form perception)
- Where is it? (space perception)
- How do I get from here to there (action control)
- What time (or time of year) is it?
References
Dougherty, R. F., V. M. Koch, A. A. Brewer, B. Fischer, J. Modersitzki, and B. A. Wandell. 2003. “Visual Field Representations and Locations of Visual Areas V1/2/3 in Human Visual Cortex.” Journal of Vision 3 (10): 1–1. doi:10.1167/3.10.1.
Panichello, Matthew F., Olivia S. Cheung, and Moshe Bar. 2013. “Predictive Feedback and Conscious Visual Experience.” Perception Science 3: 620. doi:10.3389/fpsyg.2012.00620.