I participated in a government research study at the local Veterans Administration hospital. I was just hooked up to machines and did not work. Do I owe anything?

The VA study I participated in was focused on reducing chronic pain through breathing exercises. I went 10 times and was paid $40 each visit for a total of $400, which included compensation for travel. I did not receive a form in the mail from the government that said I owed anything...do I owe any taxes? Thank you!