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Code For Subjective Thresholds

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Ver 1.85.4

Hi folks
I am a self-admitted novice for any sort of coding, and seeking help in order to generate something rather advanced.

I am looking to implement a piece of code (in builder mode) for a particular block of trials. What will be shown is a prime word initially set for a visual duration of 100ms, after which, the participant presses either ‘Q’ for being able to see the prime, or ‘P’ for not seeing it.

I am looking for code that implements a 15ms reduction of this prime duration everytime Q is pressed on the subsequent trial (thus duration = 100ms trial 1, 85ms trial 2, 70ms trial 3, 55ms and so on). Eventually, the duration time will be so short that the participant will press ‘P’, indicating that they now cannot see the prime, and is thus rendered subliminal (otherwise known as stimulus onset asynchrony or subjective threshold).

It is thought that a portion of Stroop interference occurs due to failure of maintaining goal behaviour (i.e. the goal of responding as quickly as possible to Stroop words). I want to see if goal-relevant prime words (i.e. quick hurry fast speedy express and rapid) subliminally presented may facilitate task performance.

Finally to add, after this threshold establishment block of trials, the participant proceeds to practice blocks, and then to the experimental block…
fixation cross -> prime word -> backward mask -> stroop word, loop

The prime word’s duration should be determined by whatever the duration time was last set, back in the threshold trials (thus at the point that participant could no longer consciously see the word). Their threshold time is carried over to the experimental trial basically.

I know this is a very big ask, and a lengthy question. I have taken time to adapt the staircase method, and other means, but it appears very difficult to generate code specifically for this, at least for me. This may benefit anyone looking to do subliminal priming tasks as well. I am a beginner I admit, but ambitious! I just want to know if this is possible, and any code anyone may know of to get me going (in builder mode).

(p.s. if the participant keeps spamming Q, eventually prime duration in the beginning will reach 0ms, at which point, the experiment could close down).

Kind Regards Guys,
Anthony

Before attacking the software side of things, you need to understand the (current) hardware limitations. Your screen (except in very specific circumstances) updates at a fixed rate, typically at 60 Hz for regular LCDs, although gaming-oriented LCDs might run at 144 Hz. In the 60 Hz case, this implies that any stimulus duration must be a multiple of 1000 ms / 60, or ~16.666 ms. So you can have a stimulus that lasts 100 ms (== 6 screen refreshes), or 83.33 ms (== 5 screen refreshes), 66.66 ms, and so on, but not arbitrary durations like 85 ms or 70 ms.

Hey Michael

I’m grateful for your insight , I do actually recall reading this on psych org, that the ms duration must be specific in order to correspond to the monitor refresh adjustment, as opposed to a steady 15 increase.

I used 15 ms intervals for my undergraduate design on E Prime , though I had a programmer come to add the necessary code for this. Back then however, I was not aware of the hardware specifics…