I am going to make a few sentences below.

(ex) While an image of a dog appears on a screen from an overhead projector, I trace it in the air with my index finger. After 15 seconds, it is removed from the screen. Then, I start imagining it very clearly because the tracing helps me perceive it very well.

Some of my classmates think all the sentences are correct, but others think there is something wrong. Honestly, I do not see any problems. All the sentences are straightforward. I will summarize my expressions below.

(1) image of a dog on screen
(2) image off screen 15 sec after
(3) imagination starts
(4) tracing helps perception of image during imagination

Could someone please let me know if I have made any mistakes there? Thanks a lot.