We can listen to a car radio and drive while keeping an eye on changing traffic conditions -- separate complex tasks completed without much trouble. But if two people are talking to us at the same time, our perceptual frequencies get jammed.

A new Cornell study shows that people are pretty good at perceptual multitasking -- except when multiple sources of incoming stimuli are of the same type. Morten Christiansen, associate professor of psychology, co-authored the study with Christopher Conway, a National Institutes of Health research fellow at Indiana University.

Humans learn "sequential structure from multiple sources at the same time, as long as the sensory characteristics of the sources do not overlap," Christiansen said.

Participants in the study experienced little difficulty learning complex structures streamed at them simultaneously, such as tones and colors or even tones and speech.

"However, performance dropped when the two sets of sequences were from the same perceptual class of stimuli, such as two sets of speech stimuli," said Conway. "Overall, these results show that humans have a powerful learning system that is capable of learning sequential patterns simultaneously from multiple environmental sources -- provided each source is perceived as being distinct."

The study will appear in Psychological Science in October.