By Dr. Ken Broda-Bahm:
If you're outside in the dark, maybe aided by a little starlight or moonlight, you can probably see your surroundings a bit dimly: You can't see everything, but hopefully you see enough that you don't stumble. Now, add a flashlight. The path you're pointing the light at is now quite bright, but everything else outside the flashlight's beam has been lost to darkness. Human perception is a lot like that flashlight: You are focusing your attention like the flashlight beam, noticing some things but only at the cost of ignoring everything else. You aren't just taking everything in. The act of noticing some things also entails the act of ignoring others. As a result, perception is selective, constructed, and decidedly not neutral.
Memory, it turns out, is the same. We like to think of our memories as a repository or bank: We store our experience, and then retrieve it later, as long as it hasn't degraded in the meantime. But new research continues to show that memory isn't like that analogy of a leaky bucket. Instead, it is more like the flashlight in the darkness: It recalls some things, but only at the cost of losing other things. Recently, a team of neuroscientists from Cambridge University (Wimber et al., 2015) published a study with the unwieldy title, "Retrieval Induces Adaptive Forgetting of Competing Memories Via Cortical Pattern Suppression." The simpler version: In order to remember some things, we need to forget other things. In one of the first studies to show this, the researchers trained participants on specific word-picture pairs. Then they used brain scans in order to map out specific activity patterns while the participant recalled those word-picture pairs. With that map in hand, the researcher next asked participants to repeatedly recall a particular word-picture pair. What they noticed is that as that memory was favored and strengthened, the other competing memories were suppressed. More simply, "Remembering a past experience can, surprisingly, cause forgetting." Because remembering induces a process that limits distraction, that selectivity serves a purpose. "This form of forgetting," they add, "is considered to be adaptive because it reduces future interference." These results, as well as the broader point, carry some important implications for how we handle that critical variable of memory in trials.