Wednesday, 29 March 2006

Concerns raised about the use of computer animations in court

Things seem so much more predictable once they’ve happened – a flaw in our thinking that’s been dubbed the ‘hindsight bias’. It’s a particular problem in legal cases where jurors are asked to judge the extent to which a defendant should have known what was likely to happen when they took a certain decision (for example, when they decided to overtake on a bend).

Now for the first time, Neal Roese at the University of Illinois and colleagues have investigated the impact of computer animation on the hindsight bias, a topical issue given the increased use of such animations in American and UK courtrooms.

Participants were shown real-life road traffic scenarios either via dynamic computer animations, or via old-fashioned text descriptions and diagrams. Those participants who saw a complete version that ended with a serious crash were asked to discount what they’d seen and to estimate the likelihood of a crash happening from the moment the driver made an error (e.g. at the point of overtaking). Consistent with the hindsight bias, participants who’d seen the crash happen (via animation or diagram) estimated a crash was more likely to happen than participants who were only shown the early stages of the road scenario. Crucially, this hindsight bias was twice the size in the participants who saw the animation than in the participants who were shown diagrams.

Another finding came from participants who were shown an animation, or diagrams, up to the moment just before, but not including, the crash. Participants shown the animation up to this point (but not the participants shown diagrams) judged a crash was more likely to happen than any of the other participant groups, including those who’d seen the animation through to the end – a bias the researchers dubbed ‘the propensity effect’.

”The propensity effect is an entirely new phenomenon that stands alongside the hindsight bias, apparently born of the unique combination of motion perception plus an inference of propensity toward a salient end point (‘I just know it’s headed over there’)”, the researchers said.

They concluded with a warning about the implications for legal practice: “Our research indicates that the clarity of computer animation can obscure the underlying certainty of accident reconstruction, creating a biased feeling of knowing”.

Roese, N.J., Fessel, F., Summerville, A., Kruger, J. & Dilich, M.A. (2006). The propensity effect. When foresight trumps hindsight. Psychological Science, 17, 305-310.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

Link to relevant BBC news item.
Link to forensic animation company.

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