By: Laura Geggel, LiveScience Staff Writer
Published: 04/22/2015 10:39 AM EDT on LiveScience

A recent video of a sexual assault — on a crowded Florida beach, in broad daylight — raises a question: Why didn’t one of the hundreds of bystanders step in to help the victim?

Though perplexing, the phenomenon — known as the “bystander effect” — is common, experts said.

“There’s this kind of paradoxical relationship, where the more people [there are who] observe an incident, the less likely any single individual is to help,” said Peter Ditto, a professor of psychology and social behavior at the University of California, Irvine. [Understanding the 10 Most Destructive Human Behaviors]

The assault happened sometime between March 10 and March 12 in Panama City, Florida, a spring break destination for about 100,000 college students yearly, news outlets reported. The video was taken for a reason unrelated to the assault but shows four men allegedly assaulting a woman who appears to be unconscious.

The woman does not remember the assault, but she recognized herself when reporters played the video on the news, according to news reports. She contacted the authorities, and told them she recalled drinking out of another person’s water bottle that day. It’s likely the woman was drugged by contents in the drink and was then assaulted, authorities said.

There are several possible reasons why none of the hundreds of bystanders in the video came to the woman’s rescue or called the police, said Dave Schroeder, a professor of psychological science at the University of Arkansas.

Perhaps the bystanders didn’t realize that a sexual assault was happening, or decided to not intervene because they were unsure what was happening, Schroeder said.

In addition, the bystanders may have been drinking, which “clouds judgment, and may make things seem more acceptable,” Ditto said.

In cases where people cannot tell exactly what’s going on, “what people will do is look around and see what everybody else is doing, to help them define the situation,” Schroeder said. “And if no one else is doing anything, they draw the erroneous conclusion, ‘It must be OK.'”

Psychologists call this phenomenon “pluralistic ignorance,” or “the lack of wisdom of the crowd,” which can play a role in the bystander effect, Schroeder told Live Science.

People can overcome pluralistic ignorance by speaking up. If the victim is able to draw attention to the assault by yelling or screaming for help, or if someone intervenes, the crowd tends to realize something is wrong and gets involved, Schroeder said.

“As soon as one person intervenes, lots of people will intervene,” Schroeder said.

Unless someone speaks up, people within a crowd may not feel an obligation to help. This is called “diffusion of responsibility,” experts said. Even if bystanders realize an emergency is happening, people may not want to get involved. They may rationalize this by thinking, “Surely, with all of these people watching, somebody will help,” Ditto said.

That’s why it’s important for the victim, or for people who want to help, to point to specific bystanders and assign them tasks, such as calling the police, Ditto said. [10 Things You Didn’t Know About the Brain]

In this case, because the woman may have been drugged, it’s unlikely she could have called for help, Schroeder said. If a victim seems impaired, bystanders can ask if she or he is all right, Schroeder said. It can be difficult to intervene, but if schools, colleges and workplaces were to start teaching people to take responsibility for others in need of help, it could become a new norm, he said.

It’s also possible that bystanders in some situations don’t help because they fear for their safety. In that case, people could still help by yelling and drawing attention to the incident. With a large crowd, the perpetrators might stop assaulting the victim if there are enough efforts to stop it, Schroeder said. If people feel uncomfortable making a scene, they could also just call the police (which they should do anyway), he added.

It’s not always easy to step up, but it can save a lot of heartbreak later on, the experts said.

The woman plans to press charges against the perpetrators, and three have been charged so far, news outlets reported.

Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

• Top 10 Controversial Psychiatric Disorders
• Fight, Fight, Fight: The History of Human Aggression
• 5 Ways Your Cells Deal With Stress

Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

— This feed and its contents are the property of The Huffington Post, and use is subject to our terms. It may be used for personal consumption, but may not be distributed on a website.