Science Helps Improve Eyewitness Testimony

it come out the way you want it to. The same paint looks different in different contexts.”

Certain contexts — situations where there is dim lighting, or a long viewing distance, or stress on the part of the viewer — lessen our capacity to see things accurately. In these conditions of uncertainty, the brain often fills in the gaps in perceptions, supplying missing information based on that person’s past experiences or expectations.

This capacity evolved over millions of years to aid survival, Albright says. “If you’re on the savannah and you see an ambiguous movement, it’s important that you identify what it is quickly so that you can survive. The visual brain has evolved this capacity to fill in the blanks based on our prior experiences, and most of the time it works.” 

Often it works even if it isn’t precisely accurate: If you’re crossing a street at dusk and catch the glimmer of metal out of the corner of your eye, for example, it doesn’t matter whether your mind fills in the actual blue car or a more-familiar gray one — either image will alert you to leap out of the way.

Sometimes we even knowingly let our eyes play tricks on us, as when we watch a magic act. “Performance magicians will create conditions of uncertainty, and they’ll introduce bias, and they’ll leave you with a very strong impression that you saw something that didn’t actually happen,” says Albright. “And because it’s the nature of the genre, we accept it; we know we’re being tricked. But similar things happen in our normal activities — uncertainties in the context prompt our brains to fill in the wrong information — and we’re completely unaware of it.”

Vision and Memory at a Crime Scene
Crime situations may involve factors that can hinder a viewer’s ability to perceive things accurately, such as quick viewing times and high levels of stress and fear. These conditions, and the uncertainty that results, may trigger the brain’s tendency to fill in the gaps, so that the witness has a coherent interpretation of what happened. But that coherence might come at the expense of accuracy.

Often, for example, a witness will report the presence of a weapon, and it turns out there was no weapon, Albright says. “If you’re witnessing a crime, you might have in your mind that in these kinds of circumstances, the perpetrator often will have a gun. And so