User Experience Research Study means google wants to know, what users/people think about Google products and features by participating in google user research studies. 

    I don't know what is truth about this Research study or survey, but there is some rumous that "Earn $75 with Google user Experience research survey per hour". i had search over the internet but i cant find any policy of google like that.

In fact, Google give you some rewards like gift cards or some donations for your participation after complete participation. And i don't know Google make a payment in dollars to you or give you some reward.
The actual earnings and payout methods are not mentioned on Google user research site. I have collected this information(about the Google user research program) from a third party website, this may or may not be true.

Another doubt is, 
How can we get money as we haven't added our bank details.

If you want to join this survey, there are basic 3 steps:
1. Sign up
2. Participation                     
3. Rewarded(no information about the $75 on google site)

Here is the link of Google user experience research program, you can check