511-perception

Fun

Principles of sensation & perception

Senses as (perception/action) systems

Source: Amazon

Source: Swanson

Source: Swanson, 2005

Smartphone as metaphor

• Accelerometer
• Gyroscope
• Magnetometer
• Proximity sensor
• Ambient light sensor
• Barometer
• Thermometer
• Mic
• Camera
• Radios (Bluetooth, wifi, cellular, GPS)

http://www.phonearena.com/news/Did-you-know-how-many-different-kinds-of-sensors-go-inside-a-smartphone_id57885

Perception/action system dimensions

• Interoceptive
  • Body position, movement, posture
  • Internal status: hunger, thirst, arousal, discomfort/pain, etc.
• Exteroceptive
  • Layout of environment, contents

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?
• Animate/inanimate?
  • Conspecific (same species)/non?
  • Threat/non?
  • Familiar/un?
  • Mate/non? or Friend/not?
  • Food source/non
• Where is it?
  • Distance
    • Proximal
    • Distal
  • Elevation, azimuth
  • Coordinate frames
    • Self/ego (left of me)
    • Object (top of object)
    • Allo/world (North of College)
• Where moving?

Questions for action

• What kind of response?
  • External
    • Move body
      • Approach/avoid/freeze
      • Signal/remain silent
      • Manipulate
  • Internal
    • Change physiological state
• Speed, quality, direction of response

From world to brain

Realm	Domain
\(W\)	The world
\(B\)	The body
\(N\)	The nervous system
\(M\)	The mind

Properties of the world

• Behaviorally relevant conditions, events, and entities…
• Generate patterns…
  • Chemical
  • Photic/electromagnetic
  • Mechanical/acoustic
• That specialized sensors detect
• Neural circuitry processes

More than 5 sensory channels

• What is the energy/chemical source
• Different energy/chemical channels carry different types of information
  • What is out there
  • Where it’s located
• Information about behaviorally relevant dimensions often signalled by multiple sources

Vision

• Source: Electromagnetic radiation
  • Reflected from surfaces
• What is it?
  • Shape, size, surface properties (color, texture, reflectance, etc.)
  • Wavelength/frequency, intensity
• Where is it?
  • Position: Left/right; up/down on retina
  • Near/far: retinal disparity, interposition, height above horizon…
  • Orientation, motion

Audition

• Source: Mechanical vibrations in air or water
• What is it?
  • Pattern of frequencies, amplitudes, durations
• Where is it?
  • Left/right or up/down: Interaural time/phase, intensity differences, pinnae filtering
  • Motion: Frequency shifts via Doppler effect

Chemosensation

• Source: Chemicals in mouth, nasal cavity
• What is it?
  • Mixtures of chemicals
• Where is it?
  • Left/right; up/down; near/far via intensity gradients

Somatosensation

• Source: Thermal or mechanical stimulation (vibration/pressure) 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
  • Receptors in skin, viscera
• Mating interest
  • Receptors for hormones, NTs
  • ANS responses
• Body position & movement (proprioception)
  • Receptors in muscles, joints, skin

Features of sensory signals

Change across time

• Tonic (sustained) vs. phasic (transient) responses
• Adaptation
  • Decline in sensitivity with sustained stimulation
  • Most sensory systems attuned to change

• Information propagates at different speeds

Detect repeating signals

• In space (textures)
• In time

Vision: Spatial frequency/contrast sensitivity

Audition: Frequencies in sound

Compare (>1) sensors located in different parts of the body

• Eyes
• Ears
• Skin surface
• Nostrils
• Tongue

“Receptive fields”

• Area on sensory surface (e.g., retina, skin) that when stimulated changes neuron’s firing

Tactile

Visual

Topographic maps

Auditory: Tonotopic maps

Visual: Retinotopic maps

Somatosensory: Somatotopic maps in S1 & M1

Sensivity non-uniform

Two-point touch thresholds

Somatosensory homunculus

Visual acuity varies

https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/AcuityHumanEye.svg/270px-AcuityHumanEye.svg.png

Hearing thresholds varies

http://auditoryneuroscience.com/

Processing hierarchical/sequential AND parallel

Case study: Vision

Properties of Electromagnetic (EM) radiation

http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg

• Wavelength/frequency
• Intensity
• Location/position of source
• Reflects off some materials
• Refracted (bent) moving through other materials
• Information across space (and time)

http://apod.nasa.gov/apod/ap140605.html

Reflectance spectra differ by surface

http://http://www.vgt.vito.be/userguide/book_1/4/42/ie42bd.gif

Optic array specifies geometry of environment

Categories of wavelength specify perception of color

• Eyes categorize wavelength into relative intensities within wavelength bands
• RGB ~ Red, Green, Blue
  • Long, medium, short wavelengths
• Color is a neural/psychological construct

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)
• Retina - light detection
  • ~ skin or organ of Corti in inner ear
• Pigment epithelium - regenerate photopigment
• Muscles - move eye, reshape lens, change pupil diameter

Geometry of retinal image

• Image inverted (up/down)
• Image reversed (left/right)
• Point-to-point map (retinotopic)
• Binocular and monocular zones

The fovea

http://www.brainhq.com/sites/default/files/fovea.jpg

• Central 1-2 deg of visual field
• Aligned with visual axis
• Retinal ganglion cells pushed aside
• Highest acuity vision == best for details
• Acuity varies from center to periphery

http://michaeldmann.net/pix_7/blndspot.gif

What part of the skin is like the fovea?

Photoreceptors in retina detect light

• Rods
  • ~120 M/eye
  • Mostly in periphery
  • Active in low light conditions
  • One wavelength range
• Cones
  • ~5 M/eye
  • Mostly in center
  • 3 wavelength ranges

https://foundationsofvision.stanford.edu/

http://cnx.org/content/col11496/1.6/

Photoreceptor physiology

• 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

http://www.retinareference.com/anatomy/

• Information flows…
  • From photoreceptors…
  • To Bipolar cells
    • <-> and Horizontal cells
  • To Retinal ganglion cells
    • <-> and Amacrine cells
  • To cerebral cortex

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)

Opponent processing

http://www.visualexpert.com/sbfaqimages/RGBOpponent.gif

• 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

• 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)
• Hypothalamus
  • Suprachiasmatic nucleus (superior to the optic chiasm): Synchronizes day/night cycle with circadian rhythms
• Superior colliculus & brainstem

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

• 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

(Dougherty et al., 2003)

• Fovea overrepresented
  • Analogous to somatosensation
  • High acuity in fovea vs. lower outside it
• Upper visual field/lower (ventral) V1 and vice versa

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)
• Columns
  • Orientation/angle
  • Spatial frequency
  • Color/wavelength
  • Eye of origin, ocular dominance

https://foundationsofvision.stanford.edu/wp-content/uploads/2012/02/dir.selective.png

From center-surround receptive fields to line detection

(Panichello, Cheung, & Bar, 2013)

Ocular dominance columns

http://www.scholarpedia.org/w/images/9/99/11-Hubel-Wiesel-model.png

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., Koch, V. M., Brewer, A. A., Fischer, B., Modersitzki, J., & Wandell, B. A. (2003). Visual field representations and locations of visual areas V1/2/3 in human visual cortex. Journal of Vision, 3(10), 1–1. https://doi.org/10.1167/3.10.1

Panichello, M. F., Cheung, O. S., & Bar, M. (2013). Predictive feedback and conscious visual experience. Perception Science, 3, 620. https://doi.org/10.3389/fpsyg.2012.00620