 # Stim dur calculated by median is noisy

URL of experiment: https://gitlab.pavlovia.org/pinartoptas/timingpriors_avg

Description of the problem: I changed how I determine the duration of the next stimulus from calculating the average of the previous trials to taking the median of the previous trials by using the code below.

Here I store the time between 2 presses into a variable called reproduction1, and then save reproduction to a 6-element array called repro1_array later to be sorted.

``````var repro1_array = new Array (6);
var reproduction1;
var i = 0;
function iteration1RoutineEachFrame(trials) {
return function () {
//------Loop for each frame of Routine 'iteration1'-------
let continueRoutine = true; // until we're told otherwise
// get current time
t = iteration1Clock.getTime();
frameN = frameN + 1;// number of completed frames (so 0 is the first frame)
// update/draw components on each frame
if ((_key_resp_allKeys.length === 2)) {
key_resp.keys = _key_resp_allKeys.slice((- 1)).name;
reproduction1 = (_key_resp_allKeys.slice((- 1)).rt - _key_resp_allKeys.slice((- 2)).rt);
repro1_array[i] = reproduction1;
i = i+1;
continueRoutine = false;
}
``````

Here I calculate median and determine the stimulus duration of the next iteration by defining seed2 as the median.

``````    const arr1Sort = repro1_array.sort((a,b)=>a -b);
const len = repro1_array.length;
const mid = Math.ceil(len/2);
const median1 =
len % 2 == 0 ? (arr1Sort[mid] + arr1Sort[mid -1])/2 : arr1Sort[mid -1];
stimulus1t = (polygon.tStop - polygon.tStart);
stimulus1f = (polygon.frameNStop*frameDur - polygon.frameNStart*frameDur);

if ((ite1_count === trialNum)) {
seed2 = (median1); // used when I want median
// seed2 = (sum_ite1 / ite1_count); // used when I want average
ite1_count = 0;
sum_ite1 = 0;
}
``````

However, I noticed a seemingly systematic error while doing that. When the code calculates the median, there is a significant increase in the difference between the actual stimulus duration presented on the screen (which should be the median) and what I want to present (which is again, the median). More specifically, when the calculated median is below < 500 ms, the stimulus duration that is calculated by frameN*frameDur is much higher (~1000 ms higher). And this definitely does not happen when I’m calculating the average as the next stim dur.

I couldn’t figure out where in the code this problem lies exactly. So here I am sharing the problem briefly.

I would really really appreciate any help.

Hi all, I am waiting for a reply on the issue above. I’m pretty much stuck with my experiment at the moment cause I really cannot see where the problem is, and as I collect more data I see that this noisy calculation is the case with almost every participant.