Janis volunteered to participate in a psychology experiment. when janis arrives to the lab she is greeted by a lab assistant standing on the other side of a counter. the lab assistant explains the informed consent and asks her to sign the form. as the lab assistant reaches for the form he drops it behind the counter. the lab assistant reaches down behind the counter to pick up the form and unbeknownst to janis another person stands up holding the form. after janis signs the form, she is asked if she noticed the change. she replies that she did not. this phenomenon is known as