Thursday, February 16, 2012

Human hysteresis

kw: musings, psychology

Hysteresis is the tendency of a system's behavior to depend on its history. When the history is but one of a number of influences, possibly including inherent tendencies, we can more generally say it is the tendency to take one path in one direction, and another in the reverse direction.

A well known system that exhibits hysteresis it the magnetization of a piece of iron. In this diagram, H is the applied magnetic field, and B is the magnetization of the material. The red curve shows magnetization to saturation of an initially unmagnetized piece. The point Br, where H has been reduced to zero but some amount of B remains, is the remanent magnetization, rendering the piece a (provisionally) permanent magnet. You can make a nail into a weak permanent magnet by stroking it with a stronger magnet, such as one of the Alnico magnets used for holding things to your refrigerator.

When a strong enough reverse field is applied (see the blue curve), at the point Hc, the remanent field is erased. If H is returned to zero from that point, the piece's magnetism is gone. But if you continue along the green curve, you can magnetize the piece in the opposite direction. Magnetizing, demagnetizing, and reverse magnetizing all take energy. This illustrates one reason that putting a soft magnetic material into an oscillating magnetic field causes it to heat up.

This kind of Hysteresis Curve illustrates a lagging tendency. It takes a lot of H before B gets large, and the remanent B resists changes in B until overcome by a saturating amount of H. There is a slightly analogous tendency exhibited by a person going from one place to another, when there is a choice of paths to take. Some people will take later choices, some earlier. The first ones could be said to exhibit lagging hysteresis, the others, leading hysteresis. For an example:

Suppose you live in at the location marked "Home" at lower left, and wish to walk to "Store"; and, of course, return home. The green and blue paths shown illustrate two possible ways to get there or back. There is little to distinguish them. They have the same length. Assume that there are no stop lights, just four-way stop signs at every corner (this is a neighborhood store, not in a busy locale). Are you more likely to take the "leading" route (green) or the "lagging" route (blue)? I tend to make my turns early, and take leading routes whenever possible. I suspect there are about equal numbers of people who would make either choice.

It would be an interesting sociological experiment to gather information from a large number of people, which ones turn early and which ones turn later, and try to correlate other factors in their life or character, such as optimism or introversion or gender.

People are not pieces of iron. Some people will return by the route they took initially, while others will take the alternate route to go back home. Iron can't do that. Also, there are details about this route that we don't see in a magnetic hysteresis diagram. You must cross four streets to reach your objective. By my count, there are 20 distinct ways to get from home to the store, and all have the same walking distance, but the two shown are the only ones that have only two turns. The others have either four or six turns.

To do a social psychology study that gets into that kind of detail, you'd need to equip people with recording GPS devices, and see which people always take the same route and which ones tend to vary their route, and, well, I can think of more variations, but you get the point. People are interesting, because even in a very simple setting like this, there are so many possible outcomes.

1 comment:

Steve said...

Interesting thoughts on hysteresis and human choice. I've been thinking about hysteresis and its role in human behavior. I was wondering if you have come across any studies that have looked at this. I know of some examples in physiology and I think one could say that sleep inertia is an example of the path dependent nature of the human brain. This has been shown with anesthesia and consciousness. We also know that hysteresis shows up in economic systems, but this isn't really what I'm interested in.

I suspect that the complex issues at play make hysteresis a difficult topic of study when it comes to psychology and neuroscience. You've outlined some of these issues in the post...