I can see clearly now.
2018-10-11 15:22:28
Prelude
Today's topics
- Common principles in sensation & perception
- Case study: Vision
Basic questions
- Exteroception
- Interoception
- Response: What should I do about it?
Questions for interoception
- Tired or rested?
- Well or ill?
- Hungry or thirsty or sated?
- Stressed vs. coping?
- Emotional state?
Questions for exteroception
- Who/What is out there?
- Where is it?
Who/what
- Animate/inanimate?
- Conspecific (same species)/non?
- Threat/non?
- Familiar/un?
- Mate/non? or Friend/not?
- Food source/non?
Where
- Distance
- Proximal
- Distal
- Elevation, azimuth
- Coordinate frames
- Self/ego (left of me)
- Object (top of object)
- Allo/world (North of College)
- Where moving?
How
- What kind of response?
- External
- Internal
- Approach/avoid/freeze
- Signal/remain silent
- Manipulate
From world to brain
- How do events/entitities generate patterns that sensors can detect?
- Chemical
- Photic/electromagnetic
- Mechanical/acoustic
More than 5 sensory channels
Vision
- Electromagnetic radiation
- What is it?
- Shape, size, surface properties (color, texture, reflectance, etc.)
- Wavelength/frequency, intensity
Vision
- Where is it?
- Position: Left/right; up/down on retina
- Near/far: retinal disparity, interposition, height above horizon…
- Orientation, motion
Audition
- Vibrations in air or water
- What is it?
- Pattern of frequencies, amplitudes, durations
Audition
- Where is it?
- Left/right or up/down: Interaural time/phase, intensity differences, pinnae filtering
- Motion: Frequency shifts via Doppler effect
Chemosensation
- Chemicals in mouth, nasal cavity
- What is it?
- Mixture of chemicals
- Where is it?
- Left/right; up/down; near/far via intensity gradients
Somatosensation
- Thermal or mechanical stimulation of skin
- What is it?
- Shape, size, smoothness, mass, temperature, deformability: Pattern of stimulation
- Where it it?
- Pattern of cutaneous receptors on skin
Interoception
- Hunger/thirst
- Receptors for nutrient, fluid levels
- Energy levels
- Receptors for hormones, NTs
- ANS responses
- Temperature
- Mating interest
- Receptors for hormones, NTs
- ANS responses
Features of sensory signals
- Tonic (sustained) vs. phasic (transient) responses
- Adaptation
- Decline in sensitivity with sustained stimulation
- Most sensory systems attuned to change
- Information propagates at different speeds
Common principles
- Sensors detect repeating signals
- In space (textures)
- In time
Spatial frequency/contrast sensitivity
Frequencies in sound
Common principles
- Compare (>1) sensor for each channel
- Eyes
- Ears
- Nostrils
- Skin surface
Common principles
- Sensory neurons have "receptive fields"
- Area on sensory surface that when stimulated changes neuron's firing
Tactile receptive field
Visual receptive field
Common Principles
- Topographic maps
Retinotopic maps in visual cortex
Common principles
- Non-uniform sensitivity
Two-point touch thresholds
Acuity variations across visual field
Hearing threshold varies across frequency
Hierarchical processing
Parallel processing
Parallel processing
Case study: Vision
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
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
The biological camera
The biological camera
Parts of the eye
- Cornea - refraction (2/3 of total)
- Pupil - light intensity; diameter regulated by Iris.
- Lens - refraction (remaining 1/3; 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 reversed (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 fovea
Acuity varies across fovea
What part of the skin is like the fovea?
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
Photoreceptors 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
- From photoreceptors…
- To Bipolar cells
- <-> and Horizontal cells
- To Retinal ganglion cells
- <-> and 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
- "Oppose" one another at cellular/circuit level
From eye to brain
From eye to brain
- Retinal ganglion cells
- 2nd/II cranial (optic) nerve
- Optic chiasm (\(\chi\) - asm): Partial crossing of fibers
- Nasal hemiretina (lateral/peripheral visual field) cross
- Left visual field (from L & R retinae) -> right hemisphere & vice versa
- Lateral Geniculate Nucleus (LGN) of thalamus (receives 90% of retinal projections)
From eye to brain
- Hypothalamus
- Suprachiasmatic nucleus (superior to the optic chiasm): Synchronizes day/night cycle with circadian rhythms
- 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
- Create "stria of Gennari" (visible stripe in layer 4)
- Calcarine fissure (medial occiptal lobe) divides lower/upper visual field
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 (remember stria of Gennari?)
- Output: Layers 2-3 (to cortex), 5 (to brainstem), 6 (to LGN)
V1 has laminar, columnar organization
- Columns
- Orientation/angle
- Spatial frequency
The "accidental" discovery of oriented receptive fields in V1
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?
Next time…
- Principles of action
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.