Hacker News Reader

Comment by JoeAltmaier | Hacker News Reader

Strange; the "button test" says humans take 200ms to press a button once a green light flashes.

I set that experiment up on Engineering Days at my college. Kids who put their faces right up to the light could press the button in under 30ms. The human detector response seemed to depend upon the amplitude of the neurological signal!

View on HN

30 ms doesn't seem possible. Check the Human Benchmark for statistics, the fastest ones are around 100 ms: http://www.humanbenchmark.com/tests/reactiontime/stats.php

Maybe light delay was not randomized and people were just predicting when it'd light up? I remember this kind of trickery being used in Jeopardy to beat Watson.

Another example is the Olympic sprint, where any reaction under 100 ms is considered a false start (if I read correctly): http://www.condellpark.com/kd/reactiontime.htm

100 ms is for an adult... The kids have smaller arms, hence shorter axons. Assuming that their conduction speed are similar to that of young adults, a shorter reaction time isn't surprising for young children.

[1] for adults, they decline with age, I don't know how they evolve during development

Yes, presumably there is a difference, but it's not that much. The axons that conduct motor signals to the skeletal muscles have a conductance speed of 80-120m/s [1]. In 70ms (100ms - 30ms), at 80m/s, such a signal would travel 5.6m.

[1] http://en.wikipedia.org/wiki/Axon#Motor

My guess is that when the kids' faces were right up to the light, their subconscious mind was actually doing the triggering because the light change was noticed in their peripheral vision. At my kung fu school, we train ourselves to avoid focusing our vision on the person we're fighting because acute vision is translated/filtered by the conscious mind; the tiny delays caused by the conscious mind are enough to get you killed. Acute->Conscious reaction times are far slower than Peripheral->SubConscious reactions.

You'd probably see similar results in your experiment if you had the kids stand close to the light but focus their vision just outside the perimeter of the light.

Thats really fast. Can it be result of many hours shooter computer games practice? Newly wired fast path for pressing button.

Edit: just run some reaction tests with about 0.25 avg. I see, ie. mentally identify, the signal at ~1/5 - 1/10th of that time. The rest of the time is material muscle reaction and actual mouse button movement down. So, with hand trained for the movement (my fingers can't even take a simple accord on guitar - compare to virtuosos playing musical instruments ) and good quick button i see how it can be down to ~50ms at least.

Honest question : how did you measure how long it took you to 'mentally identify' something?

it just an estimate. The motor reaction in my case is taking most of the time, around 0.2s. So the rest is the time it takes to see and identify. It is also pretty compatible with basic estimates : 10-20ms for several layers of neurons in primary visual cortex signal processing and about the same for several layers in the upper layer.

Neat. It makes sense that you'd have a fast-path for deflecting objects that are suddenly in your face.

Lots of interesting stuff here on factors affecting reaction time: http://biae.clemson.edu/bpc/bp/Lab/110/reaction.htm#Type%20o...

Your experiment must have been set up differently though - the fastest time they mention is 180msec for teenagers.

Sounds about the right amount of time for network lag.

Kids who put their faces right up to the light could press the button in under 30ms.

That seems really fast. I can't do better than 200ms on the online reaction time tests I've tried, and zooming the screen or putting my face closer doesn't seem to help.

Reply on news.ycombinator.com