Archives for September 2006

Professor Robert Galambos is an iconic figure in Neurosciences. Along with six other faculty, he was instrumental in establishing the first academic neurosciences department in the world at UCSD. He was elected to the National Academy of Sciences in 1960. He is most widely known for his co-discovery of the phenomenon of echolocation in bats.

I had the incredible good fortune of listening to his talk at UCSD. At an age that is nearing 91, he is still amazingly sharp and full of energy. He described joint work with G. Juhasz’s group. A key idea is that eye fixates on different aspects of the visual scene at rate of 3 fixations/second. Each fixation causes retina to transmit an optic nerve signal that lasts 300ms. The amazing fact is that 300ms seems to be a constant. Different stimuli, different mental states of animal, different duration of stimuli, or different magnitude of stimuli do not seem to affect this number! This was established via experiments in rats.

In humans, he described the following experiment. A red LED is flashed followed by inter stimulus interval (ISI) followed by a green LED. Four cases are observed:

1. When ISI is less than 60 ms, the subject sees a single flash of orange color.
2. When ISI is in range 61-90ms, the subject sees a smaller flash followed by another larger flash — both are orange in color.
3. When ISI is in range 91-290ms, the subject sees a smaller red flash followed by a larger green flash.
4. When ISI is 300ms or more, the subject sees a red flash followed by a green flash of equal durations.

He argued how these observations can be used to demystify a whole range of psychological phenomena. For example, each saccade (the blur between two fixations) is 40 ms. Above data may explain why we never see it (so called saccadic suppression).

He proposed that the principle of retina is "create the briefest possible optic nerve volley that includes all information in a scene, and send it off to cortex at the highest possible rate."

At the very end, he raised several intriguing questions: (a) If optic nerve volley is 300ms, how do we perceive motion when pictures are flashed at the rate of 24 Hz? (b) Observe that when ISI is less than 90 ms, the subject perceives orange. Why? 

W. Grey Walter, a British physiologist, in 1950 and 1951, published two Scientific American articles describing his wonderful Machina Speculatrix (fondly known as Grey Walter’s "turtle").

Walter’s turtles represent a milestone in the conception and design of intelligent machines, and a second generation turtle is preserved at the Smithsonian Institution. Walter Grey’s turtles have inspired Rodney Brooks amongst many others in their quest for building intelligent machines. Walter Freeman has referred to Grey Walter as "Godfather of truly intelligent machines".

A turtle’s brain was built with two valves, two mechanical relays, and two capacitors. On the movement side, a turtle was equipped with three wheels and two motors. One motor powered the front wheel whereas other helped steer the front wheel. On the sense side, a turtle had two receptors. One internal "touch" receptor provided the ability to detect if it had hit an obstacle or an incline — in which case it would stop, back up, and try to navigate around the obstacle. Other external receptor was a photocell. A turtle searched for "moderate level illumination" of where the precise threshold changed with the amount of charge left in its batteries. It was housed in a brightly lit hutch which it found aversive when its batteries were charged and attractive when the batteries were running out. A turtle had an internal status light that went on when it was turning. If it saw its own light in a mirror or a light of another turtle, it would engage in a remarkable turning and backing behavior.

References:

1. Walter J Freeman, W.Grey Walter: Biographical Essay. Encyclopedia of Cognitive Science(2003) 4: 537-539.
2. Michael Gasperi’s Machina Speculatrix page.
3. W. Grey Walter, The Living Brain, W. W. Norton, New York, 1963.
4. W. Grey Walter, An Imitation of Life, Scientific American, pp. 42-45. May 1950.
5. W. Grey Walter, A Machine that Learns, Scientific American, pp. 60-63, Aug 1951.

"Computer giant IBM will build the world’s most powerful supercomputer at a US government laboratory."

"The machine, codenamed Roadrunner, could be four times more potent than the current fastest machine, BlueGene/L, also built by IBM."

"The new computer is a "hybrid" design, using both conventional supercomputer processors and the new "cell" chip designed for Sony’s PlayStation 3."

"Roadrunner will be installed at the Los Alamos National Laboratory, New Mexico."  

"The new machine will be able to achieve "petaflop speeds," said IBM."

See original article –>

I wonder what new avenues in computational neuroscience can be opened with such computational power.  On a personal note, I would love to play on this machine!