1. ACTIVE SENSING Lecture 1: The Senses

2. The senses:

3. Sensing:

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

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

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

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

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

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

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

14. How sensor motion constrains sensory coding?

15. Eye movements during fixation backward!

16. Eye movements during fixation

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

18. Some similarities between vision and touch sensation

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

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

21. Receptor filtering SA RA PC Frequency (Hz) Touch R G B Frequency (10 13 Hz) Vision 1101001000 Some similarities between vision and touch sensation

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

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

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

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

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

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