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ACTIVE SENSING

ACTIVE SENSING. Lecture 1: The Senses. The senses:. Sensing:. Sensory encoding:. vision. audition. somatosensation. 10 m m. 10 m m. ~200 m m. retina. Finger pad. cochlea. What receptors tell the brain. Sensory organs consist of receptor arrays :. Sensory encoding:. vision.

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ACTIVE SENSING

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  1. ACTIVE SENSING Lecture 1: The Senses

  2. The senses:

  3. Sensing:

  4. Sensory encoding: vision audition somatosensation 10 mm 10 mm ~200 mm retina Finger pad cochlea What receptors tell the brain Sensory organs consist of receptor arrays:

  5. Sensory encoding: vision audition somatosensation 10 mm 10 mm ~200 mm retina Finger pad cochlea What receptors tell the brain Sensory organs consist of receptor arrays: Spatial organization => Spatial coding (“which receptors are activated”)

  6. Spatial coding (via passive sensing) would be sufficient had the world being continuously flashing on us and sensory sheets were u n i f o r m

  7. light is Pressure is Imprinted on the skin via mechano-receptors Imprinted on paper via carbon particles Imprinted on the retina via photo-receptors Passive sensing metaphors one could think of: the eye as a camera the skin as a carbon paper

  8. However 1. The world is not flashing and receptors are mostly sensitive to changes Receptors must move

  9. Active Sensing: Sensor organs MOVE in order to obtain information

  10. However 1. The world is not flashing 2. sensory sheets are not uniform

  11. whisker eye finger Fovea Fovea => macro movements of the sensory organ

  12. Sensor motion is required for • Foveation • Sensing stationary environment • Without sensor motion sensation is limited to moving or flashing objects

  13. How sensor motion constrains sensory coding?

  14. Eye movements during fixation backward!

  15. Eye movements during fixation

  16. sensory encoding: vision audition somatosensation 10 mm 10 mm ~200 mm retina Finger pad cochlea What receptors tell the brain Sensory organs consist of receptor arrays: Spatial organization => Spatial coding (“which receptors are activated”) Movements => Temporal coding (“whenare receptorsactivated”)

  17. Some similarities between vision and touch sensation

  18. Some similarities between vision and touch sensation eye Finger pad RA PC SA RAI RAII SAI SAII whisker R G B Meissner (RAI) Merkel (SAI) Ruffini (SAII) Lanceolate (RAx) free endings Receptor types

  19. Some similarities between vision and touch sensation @ 1o 5’ eye Receptors mix whisker finger

  20. Some similarities between vision and touch sensation Vision Touch SA PC R RA B G 1 10 100 1000 Frequency (Hz) Frequency (1013 Hz) Receptor filtering

  21. Some similarities between vision and touch sensation Receptor convergence / divergence Human eye: 5M cones + 120M rods --> 1M fibers Human skin: 2,500 receptors/cm2 --> 300 fibers / cm2 Rat whisker: 2,000 receptors --> 300 fibers Human ear: 3,000 hair cells --> 30,000 fibers

  22. Some similarities between vision and touch sensation Receptors Ganglion cells Brainstem cells Thalamus Cortex Processing stations whisker eye finger Receptors Bipolar cells Ganglion cells Thalamus Cortex

  23. Some similarities between vision and touch sensation Lateral inhibition whisker eye finger Receptors Receptors Bipolar cells Ganglion cells Ganglion cells Brainstem cells

  24. Some similarities between vision and touch sensation vision 10 mm retina Spatial Encoding retina – 2D matrix of photorecetors sensitive to light changes finger tip – 2D array of mechanoreceptors sensitive to skin movement Whisker pad – 2D array of hairs sensitive to movement somatosensation ~10 mm Finger pad

  25. Some similarities between vision and touch sensation Spatial Encoding whiskers – 2D array of whiskers but ...

  26. Some similarities between vision and touch sensation Analogies Fovea: retinal fovea - finger pad - whisker pad Sensor motion: an eye - a finger - a whisker

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