Hi I'm currently reading a paper, which contains an experiment I was to re-create - is there any chance someone can explain the staircase to me?
I've had a quick Google - and I haven't really got anywhere - I'm not even sure if this falls under mathematics, if I'm honest. I've tried to break up the text a little, but I'm still super lost on this.
I can reword the question if the detail of the article is unhelpful - I just didn't want to remove something that was actually of importance
... In each trial, one eye was presented with a population of “signal” dots that all moved in the same direction (left or right).
The other eye was presented with the noise dots that moved in random directions.
The task was to indicate the motion direction of the signal dots. To measure the threshold number of signal dots required for 79% correct performance (the motion coherence threshold), the number of signal dots was varied on a trial-by-trial basis in a three-down, one-up staircase procedure with a proportional step size of 50% before the first reversal and 25% thereafter.
The starting point for each staircase was 100 signal dots and 0 noise dots.
When dots were removed from the signal population, they were added to the noise population and vice versa.
Each staircase consisted of six reversals, and the last five reversals were averaged to estimate threshold. During each threshold measurement, two staircases were randomly interleaved.
One staircase measured the motion coherence threshold when the signal dots were presented to the left eye and the other staircase measured the motion coherence threshold when signal dots were presented to the right eye.
In each case, the eye that did not see the signal dots saw the noise dots.
By randomly interleaving the staircases, participants could not tell which eye had seen the signal and which had seen the noise as the stimuli were fused. The interleaved staircase measurements lasted approximately 3 minutes ...
Anyone that has any advice or pointers are greatly welcomed :) Thanks!
100 - 3 down, 1 up - Proportional step size of 50% before the first reversal and 25% thereafter.
- 100 > right > right > right > 50 > wrong - is then 75?
- 100 > right > right > right > 50 > right > right> right> 25 > wrong - is then 31.25?
Is this how this works? Is the 25% proportional to the current, or the max?