The tin foil hat is a symbol of conspiracy theories. I'm guessing it goes back to some paranoid schizophrenic who believed the govt. was either targeting him with radio waves, or read his mind (real parnoids often believe things like this), so he wore tinfoil over is head to block them.
Today, people who believe the moon landings were fake or 9/11 was done by the Bush Administration, or Obama was born in Kenya, are sometimes called the 'tinfoil hat crowd'.
People who believe these crazy theories, these beliefs sometimes interfere with the their perceptions. They will simply ignore the massive preponderance of evidence that doesn't fit their worldview, and concentrate on the skimpy evidence proving it, and then claim it was proven. Ilhan Omar married her brother to become a citizen. Gays have an agenda to take over the US. All the Democratic candidates are 'socialists'. Stuff like that.
So you could say their attitudes are interfering with their perceptions, i.e. the tinfoil hat is cutting off circulation to their brains.