David Hume And Albert Michotte On Causation

[C]auses are a strange kind of knowledge. This was first pointed out by David Hume, the 18th-century Scottish philosopher. Hume realized that, although people talk about causes as if they are real facts -- tangible things that can be discovered -- they're actually not at all factual. Instead, Hume said, every cause is just a slippery story, a catchy conjecture, a “lively conception produced by habit.” When an apple falls from a tree, the cause is obvious: gravity. Hume's skeptical insight was that we don't see gravity -- we see only an object tugged toward the earth. We look at X and then at Y, and invent a story about what happened in between. We can measure facts, but a cause is not a fact -- it's a fiction that helps us make sense of facts.

The truth is, our stories about causation are shadowed by all sorts of mental shortcuts. Most of the time, these shortcuts work well enough. They allow us to hit fastballs, discover the law of gravity, and design wondrous technologies. However, when it comes to reasoning about complex systems -- say, the human body -- these shortcuts go from being slickly efficient to outright misleading.

Consider a set of classic experiments designed by Belgian psychologist Albert Michotte, first conducted in the 1940s. The research featured a series of short films about a blue ball and a red ball. In the first film, the red ball races across the screen, touches the blue ball, and then stops. The blue ball, meanwhile, begins moving in the same basic direction as the red ball. When Michotte asked people to describe the film, they automatically lapsed into the language of causation. The red ball hit the blue ball, which caused it to move.

This is known as the launching effect, and it's a universal property of visual perception. Although there was nothing about causation in the two-second film -- it was just a montage of animated images -- people couldn't help but tell a story about what had happened. They translated their perceptions into causal beliefs.

Michotte then began subtly manipulating the films, asking the subjects how the new footage changed their description of events. For instance, when he introduced a one-second pause between the movement of the balls, the impression of causality disappeared. The red ball no longer appeared to trigger the movement of the blue ball. Rather, the two balls were moving for inexplicable reasons.

Michotte would go on to conduct more than 100 of these studies. Sometimes he would have a small blue ball move in front of a big red ball. When he asked subjects what was going on, they insisted that the red ball was “chasing” the blue ball. However, if a big red ball was moving in front of a little blue ball, the opposite occurred: The blue ball was “following” the red ball.

There are two lessons to be learned from these experiments. The first is that our theories about a particular cause and effect are inherently perceptual, infected by all the sensory cheats of vision. (Michotte compared causal beliefs to color perception: We apprehend what we perceive as a cause as automatically as we identify that a ball is red.) While Hume was right that causes are never seen, only inferred, the blunt truth is that we can't tell the difference. And so we look at moving balls and automatically see causes, a melodrama of taps and collisions, chasing and fleeing.

The second lesson is that causal explanations are oversimplifications. This is what makes them useful -- they help us grasp the world at a glance. For instance, after watching the short films, people immediately settled on the most straightforward explanation for the ricocheting objects. Although this account felt true, the brain wasn't seeking the literal truth -- it just wanted a plausible story that didn't contradict observation.

This mental approach to causality is often effective, which is why it's so deeply embedded in the brain. However, those same shortcuts get us into serious trouble in the modern world when we use our perceptual habits to explain events that we can't perceive or easily understand. Rather than accept the complexity of a situation -- say, that snarl of causal interactions in the cholesterol pathway—we persist in pretending that we're staring at a blue ball and a red ball bouncing off each other. There's a fundamental mismatch between how the world works and how we think about the world.

-- Jonah Lehrer

from "Trials and Errors: Why Science Is Failing Us"

Quoted on Sun Mar 18th, 2012