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brief tactile stimulus
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brief tactile stimulus

by fphs13501 on Wed Mar 27, 2019 3:28 pm

For a class, I am planning to measure the speed of neural conduction. I plan to present stimuli on the arm at two different distances from the spinal cord. I have little vibratory motors that I was planning to use. The student is supposed to push a button as soon as the vibration is felt. One stimulus will be on the wrist and one on the shoulder. I was wondering if there is some other stimulus that would be briefer, more of a point in time, that I might use. The vibration is OK but I'd prefer a briefer stimulus--not a shock but something on that order of time. Thanks

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Re: brief tactile stimulus

by millercommamatt on Wed Mar 27, 2019 4:22 pm

Poke them with something pointy? You could probably use a skin conduction thing to trigger some timing.

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Re: brief tactile stimulus

by bwoollcombe on Fri Mar 29, 2019 7:33 pm

Got Audacity? Run the signal in on 1 channel, mic the vibrator on the other channel, and see the latency.
Then include (or rather subtract) the latency from the reaction time measurements.

Now you can teach indirect measurement, calibration of instruments, and all that good stuff. You will know that they're always gonna be relative measures, but that's not a big deal unless you're teaching in med school.

Then bring in your local neurologist to explain how they do it (super fun), and you're set.

In addition to wrist and shoulder, I would try the upper lip. Super fast pings.

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Re: brief tactile stimulus

by LarryP on Sat Mar 30, 2019 10:49 am

How about the sensation of a modest weight (say ~100 g/3 oz. or so), dropped into a waiting hand? The weight could be dropped by the test administrator or via a solenoid. I did something along these lines using a force-sensing resistor (FSR) e.g. https://www.adafruit.com/product/1075 on the palm of the hand. Or you could put the FSR into a glove or similar to position it consistently. There's a handy opAmp circuit in the Mfgr.'s docs that does a respectable job of linearizing the sensor's output: https://www.digikey.com/en/pdf/i/interlink-electronics/interlink-electronics-fsr-force-sensing-resistors-integration-guide

Hope this helps!
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Re: brief tactile stimulus

by fphs13501 on Mon Jul 01, 2019 1:25 pm

Thanks, everyone. I have another question about the same general demonstration. I want to randomly turn on ether of two stimuli --let's call them red and green lights--but I want them to occur only a set number of times, say 10. I can randomly turn on either of light at random but when one reaches my maximum (of 10), how do I get to present only the other one. And then stop when they both hit 10. For loops don't do it. I am toying with 'count,' and I think that will work, but I don't know how to resume the count for the other stimulus. That is, I'd sort of like it to go back to a certain line.

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Re: brief tactile stimulus

by adafruit_support_mike on Tue Jul 02, 2019 1:56 am

That's where indeterminate loops become useful:

Code: Select all | TOGGLE FULL SIZE
int x = 0;
int y = 0;

while (( x < 10 ) || ( y < 10 )) {
    if ( 10 <= x ) {
        // only do y
        y++;
        continue;
    }
    if ( 10 <= y ) {
        // only do x
        x++;
        continue;
    }
    if ( [50-50 chance] ) {
        // do x
        x++;
    } else {
        // do y
        y++;
    }
}
The 'continue' statement tells a loop to stop executing code and go immediately to the next iteration.

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