In another experiment, evolutionary psychologist Geoffrey Miller quantified how sexually attractive a woman is to a man by recording the earnings of lap dancers in a strip club. And he tracked how this changed over their monthly menstruation cycle. As it turned out, men gave twice as much in tips when the dancer was ovulating (fertile) as when she was menstruating (not fertile). But the strange part is that the men weren’t consciously aware of the biological changes that attend the monthly cycle – that when she is ovulating, a surge of the hormone estrogen changes her appearance subtly, making her features more symmetrical, her skin softer, and her waist narrower. But they detected these fertility cues nonetheless.
Another real-world manifestation of implicit memory is known as the illusion-of-truth effect: you are more likely to believe that a statement is true if you have heard it before – whether or not it is actually true. In one study, subjects rated the validity of plausible sentences every two weeks. Without letting on, the experimenters snuck in some repeat sentences (both true and false ones) across the testing sessions. And they found a clear result: if subjects had heard a sentence in precious weeks, they were more likely to now rate it as trie, even if they swore they has never heard it before.
So psychologist Roy Baumeister and colleagues put it to a closer test. People were invited to watch a sad movie. Half were told to react as they normally would, while the other half were instructed to suppress their emotions. After the movie, they were all given a hand exerciser and asked to squeeze it for as long as they could. Those who had suppressed their emotions gave up sooner. Why? Because self-control requires energy, which means we have less energy available for the next thing we need to do. And that’s why resisting temptation, making hard decisions, or taking initiative all seem to draw from the same well of energy. So willpower isn’t something that we just exercise — it’s something we deplete.
In a recent experiment, men were asked to rank how attractive they found photographs of different women’s faces. The photos were eight by ten inches, and showed women facing the camera or turned in three-quarter profile. Unbeknownst to the men, in half the photos the eyes of the women were dilated, and in the other half they were not. The men were consistently more attracted to the women with dilated eyes. Remarkably, the men had no insight into their decision making.