Visualizing Ethernet Speed

anthemaniac writes "In the blink of an eye, you can transfer files from one computer to another using Ethernet. And in the same amount of time, your eye sends signals to the brain. A study finds that images transferred to the brain and files across an Ethernet network take about the same amount of time." From the article: "The researchers calculate that the 100,000 ganglion cells in a guinea pig retina transmit roughly 875,000 bits of information per second. The human retina contains about 10 times more ganglion cells than that of guinea pigs, so it would transmit data at roughly 10 million bits per second, the researchers estimate. This is comparable to an Ethernet connection, which transmits information between computers at speeds of 10 million to 100 million bits per second."

Neuroscience != Computer Science

[KerberosKing]

I am not sure that thinking of signals from the eye to the brain work the same way as computer networks is very helpful. I don't think that there is the same sort of contention in a nervous system as there is in ethernet. Synapses as we understand them today do not appear to have any sort of collision detection. Neurons may have tens of thousands of other neurons that they are connected to in a many-to-one configuration and the whole process is analog, which is very different than ethernet frames. Also a single ganglion cell may send "10 million bits" of information, but the optic nerve is made of many such cells in parallel. I would not be surprised if our current estimates are wrong by at least an order of magnitude.

Neurons make my head hurt

[BilZ0r]

The OP doesn't say that a single retinal cell transmits 10 million bits a second, but that the whole eye does. On top of that, while discussion of collition detection is pointless, thinking about the information a neuronal population can encode does have some merits. Although it's relatively pointless (at least now) to compare the eye to an ethernet, it has uses in comparing different neural populations.

The problem is that getting bitrates for neuronal populations is more of an art that a science. The sum total of information passed on by a neuron can not be computed simpley by it's spiking rate. Large numbers of parameters alter the actual chemical I/O relationship of a neuron. Resting membrane potential before spiking, whether it shows short term facilitation/depression etc...

Re:collision detection

[Anonymous Coward]

Just to pedantic here, "wireless Ethernet" does not use collision detection (CSMA/CD). it uses collision avoidance (CSMA/CA - i.e. 802.11), collision mitigation (CDMA - i.e. Navini, etc...), collision prevention (TDMA, polling, and their scheduling kin - i.e. Canopy, etc...), or it's simply FDD (modern expensive point-to-point, or old-school EoAMPS).

Even current wired Ethernet versions (1G, 10G) have dropped collision detection, opting to go full-duplex exclusively. Also shared cables can now carry multiple different signals without interferance, thanks to things like DWDM.

-l

Re:Nice comparison

[SnowZero]

It's not so much compression as having variable resolution. The center of the retina has a much higher resolution than the periphery. Try to look 20 degrees away from some words and try to read them (without looking back). It takes some practice to focus your attention a different place than where you are looking, but it's not too bad once you get the hang of it. You'll notice that there is very little detail indeed beyond about 5 degrees from the center of focus. The problem with TV and monitor displays is that they don't know where the viewer(s) are looking, so they need high resolution everywhere. Thus the eye can get away with a much lower overall information rate in comparison.

I do find that 10Mb to be a little low as an estimate however, since each cell can likely provide more than 10 bits/sec of information, especially when it can fire up to 1k times per second. There is almost surely less than 1000 bits/sec/cell though, so its somewhere between 100Mb and 1Gb overall -- still ethernet speeds.

There is a only a little bit of processing/compression going on at the eye itself; Mainly some "center surround" processing that you can roughtly compare to an edge sharpening filter in an image editing program. Most of the real processing goes on in the occipital lobe in the back of your head, such as the V1 layer which is essentially a 2D computer, with edge finding at various angles for every location in the eye. That feeds into V2 and V3, which do quite a bit more processing and are a little less well understood. One interesting thing is that it seems our visual systems split up into "what" and "where" pathways that independently process the identity of objects and their position. Some individuals with localized brain injuries can tell you they see an objecy (such as a stapler), but can't tell you where it is, and vice versa with an injury to the "what" pathway. Overall the human visual system is absolutely amazing, and we have a long way to go to catch up with it.

P.S. I know a lot about the human visual system because I have done a fair amount of computer vision research, and graduated with a double major in Cognitive Psychology (aka how the brain works).

Re:Um yeah, I dunno...

[zizdodrian]

The frame rate of an eye isn't governed by the eye itself - given the transfer is analog, the frame rate is governed by what the visual cortex can handle. Which, if you have done any animation, is about 25 frames per second - a speed at which the human visual cortex cannot percieve the individual frames making up an animation.

I doubt the data transfer rate of any nerve is anywhere near the transfer speed of ethernet - I read an article once stating that human nerve tissue could transmit information at about 400 metres per second - something which ethernet stomps all over. The beauty of the brain is that it isn't restricted by raw transfer speed. What governs the speed at which the brain computes and calculates is its massively paralell connectivity. In fact, many have speculated that this connectivity is what conciousness itself arises from - it gives the brain a complexity far beyond the number of cells it actually contains.

The second thing to consider is that the brain is not limited by binary transfer - it can utilise chemicals and hormones, variable voltages, and timings to transfer information, not just on/off.

Re:Um yeah, I dunno...

[asuffield]

And you DO NOT have such resolution as your monitor.

Actually you do. However, you don't normally press your eyeball against the glass. At a distance of about .5m, which is normal, your eyes don't have sufficient resolution any more. If you move your head up close to the glass, you should be able to perceive the individual pixels. It's important to remember that there are three dimensions here. The expected viewing distance determines the necessary dpi of the viewing device.