1. Yongchang Wang & Barrie J. Frost
Time To Collision Signaled By Neurons In The Nucleus Rotundus Of Pigeons
Yongchang Wang & Barrie J. Frost
Presented By Rukmini Chatterjee

2. Contextual Glossary Pigeon Looming Time To Collision Nucleus Rotundus
Extracellular Recordings
Tuning Curve
Peristimulus Time Histogram
Escape Response

3. Pigeon Avian species- Columbidae Also: Pliable/Naïve person
Known for: cooing voice and message carrying ability.
Renowned for: Gullibility and Military Service (World War I and II)
Awarded: Dickin Medal and Crois de Guerre (for military service)

4. Looming Time To Collision Nucleus Rotundus
Accelerating rate of magnification of the
visual angle of an approaching object
Time To Collision
Time of collision (tau) computed by manipulating variables for visual angle and rate of expansion
Nucleus Rotundus
Thalamic nucleus located in optical pathway
of bird brains known to be sensitive to motion in depth, color, luminance

5. Extracellular Recordings
Microfibers in the brain record electrical activity from surrounding neurons. Signal is amplified, filtered and classified to isolate data from specific neurons.
Spike/ AP rate is a measure of neural activity

6. Peristimulus Time Histogram
Tuning Curve
Plots the neural activity in response to a changing stimulus property. Measure of preference for particular range of stimuli.
Peristimulus Time Histogram
Align neural activity to stimulus onset time, divide relevant time into bins, count spikes in each time interval, divvy up spikes into time bins

7. Escape Response
Flight/Fight: Physiological changes in response to stress
Impending Collision predicted by Tau =
Initiate Defensive Behavior

8. Premise
Most animals show an escape response in reaction to hurtling objects. (Duh)
Tau (TTC) is an optical parameter that signals impending collision
Key Questions
Is Tau signaled by neurons?
Does Tau signal correspond with escape response?

9. Experimental Procedure
Anaesthetize pigeons (20) with ketamine
Record from neurons in nucleus rotundus
Present hurtling soccer ball in 26
directions

10. Results
24/145 cells sensitive to motion of object approaching directly along line of sight (looming sensitive)

11. Results
Approach signal always ~1 sec before collision irrespective of size and velocity of object. Time constant

12. Escape Response?
EMG data shows increased muscular activity with approach signal followed by rapid rise in heart rate

13. Conclusions DOES this signal represent Tau?
Neural signal for object approach along the line of sight
This neural signal is associated with physiological signs of escape response
The signal is found early on in the visual processing pathway (Thalamic vs. Cortical).
DOES this signal represent Tau?

14. Further Questions
Is the Tau signal the initiator of the escape response?
What other optical cues specify imminent collision? What motor machinery is engaged?
Is the neural signal evidence of direct perception?

15. Thank you. 