In 1974, researchers in Canada did an experiment on two bridges. One was a high bridge that moved in the wind. The other was low and safe.

A woman asked men on each bridge some questions and gave them her phone number. More men from the scary bridge called her later. But a fast heartbeat does not always create love. It can make bad feelings stronger, too.

The "suspension bridge effect" comes from a 1974 experiment in Canada. A female interviewer approached men who were crossing either a long, swaying bridge about 70 meters above a river or a low, solid bridge. She gave each man her phone number. Nine of the 18 men on the scary bridge called her, compared with only two of the 16 men on the safe bridge. The researchers believed the men mistook their fear for attraction.

However, the men chose which bridge to cross, so braver men may simply have been more likely to call. Later studies also suggest that excitement can increase both positive and negative feelings, depending on the person.

Take a date to a haunted house, the popular advice goes. It comes from a bold 1974 field experiment near Vancouver. A female interviewer approached men as they crossed one of two bridges. One was a narrow suspension bridge swaying about 70 meters above a canyon, and the other a low, sturdy wooden bridge.

Of the men who accepted her phone number, nine of 18 from the frightening bridge called her later, compared with two of 16 from the safe one. With a male interviewer, the difference largely disappeared. The researchers called this misattribution of arousal.

The men, they argued, credited their pounding hearts to the woman, not the bridge. The study had weaknesses. The groups were small, and the men chose their own bridge, so adventurous personalities could explain the result. A 1998 meta-analysis of 33 experiments generally supported a link between arousal and attraction.

But the effect appeared even when people knew the true source of their arousal, so excitement may automatically strengthen whatever response is dominant. In that sense, arousal works like a volume knob. A 1981 study supports this. Aroused men rated an attractive woman as more attractive and an unattractive woman as less so.