I’m sorry to post a new thread here, but I’m still having issues with my change-detection experiment and I can’t seem to find the answers I need in order to get the study running sooner rather than later.
I’ve attached a sample of the experiment below. I need to present participants with a series of events which include the following trials: a 250 ms focal point (+), followed by a 250 ms .png image, followed by a 250 ms focal point (+), followed by a second 250 ms .png image. If participants have not responded during this time, the event should repeat (but ideally the timer should not reset). I was having issues with a “pause” on the last trial before the event restarted, but that seems to have been resolved in a previous post. Participants end the event when they detect the difference in the two images and respond
The problem that continues is that the presentation rate of each trial seems irregular, almost sporadic (each should be for 250ms). I attempted to remedy this (although i’m not clear on HOW it actually worked) by choosing the option to reset the timer on each trial. This seemed to make the presentation timing a bit more regular, but now I have to calculate the participants’ reaction time by counting in the output the number of trials they viewed (or iterations of the event) and multiplying this by 250 ms. However, as I believe it was mentioned in another thread, the cumulative time in the output is indicating that each trial is not being presented for exactly 250ms. Moreover, as the experiment progresses, the timing of the presentation seems to become more and more sporadic. How can I regulate this so that every trial is on the screen for exactly 250 ms. I can tell by running the study that this is not the case. It seems it would be due to the “stuff” going on in between trial presentation (loading the image), but either way, I need to regulate this so that my RTs are accurate. I tried to account for the load time of each image, but this varies as well - Each time I “preview” the same image, I get a different load time. Where is this time accounted for? It seems like it’s being taken out of the 250 ms for which the trial should appear on the screen, but the output seems to indicate that it is being tacked on elsewhere. How do I adjust the settings so that each trial is presented for exactly 250 ms and my output is accurately reflecting participants’ RTs?
I’m running the experiment on a 2GHz MacBook with built in 13 inch display. Some assistance is needed asap please!
Thank you.
sample.sl4 (161 KB)