Scientists testing people’s ability

Describe the sound of a dog barking. You might first think of it as just a noise, a sound that can not be understood. You might think that it carries no particular message, like the pounding of a hammer. But when you really stop to consider it, think about how much a dog conveys with a bark. The bark of alarm is very different from the bark of an excited hello. We decode the messages of dogs far better than we think we do. Scientists testing people’s ability to understand different types of barks played recordings of dogs barking and asked them to guess the situation that the dog was in. Listeners correctly classified the dog’s situation more than seven out of ten times, suggesting that dogs are really talking to us through their barks.

I wonder if "Scientists testing people’s ability" means "1", "2", "3", or anything else.

1. Scientists who test people’s ability

2. Scientists who tested people’s ability

3. Scientists who were testing people’s ability

If "3", I wonder if "were testing" is "past continuous" or, future in the past".