I'm glad you found something that interests you! Let me address each of your questions...
EnglishRose98 wrote:I am going to hopefully find 50 test subjects, the range of ages I think is going to be from 12- 18. Is that okay? Keeping that in mind, should I do the experiment geared towards results comparing age or gender, or can I do both??
This is a good age range, and should work well for you. You may not find any effects of age, but it is worth testing! And yes, you can look at both age and gender.
EnglishRose98 wrote:The only thing is, I'm not quite sure what I'm going to have as my hypothesis.
You can make a prediction based on age, and you can make a prediction based on gender. Do you think older subjects will be more or less likely to notice the unusual event? What about boys vs. girls? You can have more than one hypothesis to represent your different predictions!
EnglishRose98 wrote:I had originally planned to ask them three questions. 1. How many passes did the people in white shirts make? 2. Did you notice anything unusual? 3. If so, what did you see?
Should I come up with any more questions?
These questions are very good. I think it's a good idea to tell the subjects at the beginning that you want them to count the number of passes the people in the white shirts make, but do not
tell them that it is a selective attention test. If you let them know it is a selective attention test, they might know to look for something unusual. You can just tell them you're testing their ability to focus on a particular part of a distracting situation. Then you can ask your all of your questions at the end of the video.
I don't think you need to ask any more questions to get the data you need.
EnglishRose98 wrote:Also, do you know of any more videos that I could use?
I did not find any other videos, but it appears the one you found is a good standard. It is a copywritten video, so make sure to contact the makers of the video to request permission to use it for your project. You can tell them that you will cite them in your report and your presentation. Alternatively, you could try to make your own video; but I don't think it's necessary to do so.
Please keep me posted! And let me know if other questions come up along the way.