Allow keyboard response during image and fixation cross until next image is shown

What are you trying to achieve?:

I have a task that is built like this: Fixation cross (3-5s) → Image (1s) → Fixation cross (3-5s) → Next image (1s) ---->etc.

Subjects have to give a keyboard response after the image. The response duration lasts until the next image appears (i.e. from the first image throughout the fixation cross time up until the second image appears)

What did you try to make it work?:

Start time for the fixation cross: 0s
Duration for the fixation cross: $jitter (i.e. 3-5s)

Start time for the image: $jitter (so that the image appears after the first fixation cross appeared, and always appears after a fixation cross)
Duration for the image: 1s

Start time for the keyboard response: $jitter
Duration for the keyboard response: $jitter

What specifically went wrong when you tried that?:

I receive a blank screen after the image, during which I can respond, and it lasts 3-5s until the fixation cross appear.
What I want: The fixation cross to immediately appear after the image, during which keyboard response is possible, without the blank screen.

Why don’t you have the fixation cross follow the image (with an extra one before the first image)?

Then you could have

Fixation cross: start 1s, duration $jitter
image: start 0s, duration 1s
keyboard: start 1s, duration $(jitter+1)