Basic Reflexes

Every person is born with basic reflexes. You can see these in healthy babies as they move through their developmental stages and become integrated at predictable ages, into smooth movement. Some reflexes remain normally active in adults.

Every person has a startle reflex. The Psychological Review reported in 1990 that the vigor of the startle response in adults is affected by their emotional state. It can vary from an eye-blink to a full body jump.

When I am engrossed in work or some activity, I frequently have a full body jump if I'm interrupted.

Another predictable reflex is the "knee-jerk reaction" when the patellar tendon is struck by a doctor's hammer. But even here emotional state plays a role. The reliability of the knee jerk has been found to depend on the physician's bedside manner (as well as the motor skill of the person who is attempting to strike the tendon).

Within reason, reflexes are predictable.

Cultural Stereotypes

From early childhood we learn cultural norms. In the US, to turn a light on you move the switch upward. To turn it off, you move it downward. Dials moving clockwise indicates a higher degree of whatever you are controlling or reading. Up and clockwise indicate "more". to steer, directing the control to the left will turn you left - unless you're in a boat. You push down to apply a foot brake, whereas a hand brake will usually pull toward you.

This type of learning varies from culture to culture. In England, you push the switch down to turn on the light (opening the current). In Japan, you read from the back of the book to the front and left to right.

Within a culture these are predictive of behavior. When a person wants to turn on a light in the US, we can predict that he or she will move the switch up and be very surprised if it is set up the opposite way.

Design to fit Expectation

Knowledge of these predictable responses allows us to design things, tools, and controls that work the way people expect them to. When you click on a link in a web page, you expect a certain result. Suppose that instead of going to more information about the topic, or to the webpage you expected, you set off blinking lights and a siren. You would probably have a startle response!

Designing for the expected response decreases error and increases people's trust of the device. The more advanced or critical the piece of equipment, the more important this design factor is.

Designs that flout these conventional operations sometimes lead to catastrophic operator errors. Planes designed with the controls for left operations on the right side and vice versa can result in crashes unless the pilot is highly experienced.

Even elevator operation can be effected. I was in a building where the button labels were closer to the floor they didn't go with than to the one they did. I watched people make error after error the first week of occupancy. Eventually, people learned but it was not a quick process.

Elevator operation is not a critical action, but suppose these had been controls in a nuclear plant!


References: P Lang, M Bradley, and B Cuthbert. Emotion, Attention, and the Startle Reflex.Psychological Review, 1990, V97, No 3, 377-395.