Media multitasking is the concurrent use of multiple digital media streams. Media multitasking has been associated with depressive symptoms and social anxiety by a study involving 318 participants. A 2018 review found that while the literature is sparse and inconclusive, people who do a heavy amount of media multitasking have worse performance in several cognitive domains. One of the authors commented that while the data does not "unambiguously show that media multitasking causes a change in attention and memory," media multitasking is an inefficient practice that requires "task switching" costs including "limitations in auditory and visual processing".

In many cases, media multitasking is made up of experiences that are not necessarily intended to be combined or coordinated. For example, a user may be browsing the Web, listening to music, playing video games, using e-mail, and/or talking on the phone while watching TV. More intentionally coordinated forms of media multitasking are emerging in the form of "co-active media" and particularly "co-active TV".

A touchstone 2009 study by Stanford University used experiments to compare heavy media multitaskers to light media multitaskers in terms of their cognitive control and ability to process information. Findings from the experiment include:

The researchers concluded that heavy media multitaskers are distracted by the multiple streams of media they are consuming, and that not multitasking can help with concentration. In the "bottleneck theory" of cognitive performance, the slowing down seen when people multitask is called "interference." According to this theory, people have only a limited amount of cognitive resources, which allow them to focus and complete one task at a time. When people try to do several things at once or multitask, their performance suffers a slowdown because of a "cognitive bottleneck," like a traffic jam in the brain.

Researchers tried to disprove this theory over several decades, and although they found a handful of activities that people can do simultaneously without slowing, these activities are relatively simple and so far removed from everyday human activities—that they cannot be used as support for people's ability to multitask. A team of researchers reviewed the extensive literature on multitasking and concluded that hundreds of studies show that slowing will happen when people try to multitask; in fact, many studies that were designed to show that people could multitask without interference in fact indicated the opposite. These researchers warned that when people attempt to multitask, especially when doing complex and potentially dangerous tasks (such as driving and using their cell phones to talk or text), they will always encounter the cognitive bottleneck, causing their performance to suffer in terms of speed or accuracy.

A related article, "Breadth-biased versus focused cognitive control in media multitasking behaviors," notes that the prevalence of this phenomenon leads "to a question about the required skills and expertise to function in society. A society with its ever-increasing complexity appears to move people towards juggling among multiple tasks rather than focusing on one task for a long period." The study's author suggests that further research will be necessary as the effects on society become more pronounced: "The new technologies are gearing people, especially young people who grow up with digital technologies and wired networks, toward breadth-biased information processing behavior rather than linear in-depth study behavior. Long-term exposure to media multitasking is expected to produce both positive and negative outcomes on cognitive, emotional, and social development."

Despite the research, people from younger generations report that they feel multitasking is easy, even "a way of life." They perceive themselves as good at it and spend a substantial amount of their time engaged in one form of multitasking or another (for example, watching TV while doing homework, listening to music while doing homework, or even all three things at once). By contrast, members of older generations often openly admit that they are not very good at multitasking, finding it difficult, and therefore, do not do it as often as young people.

Multitasking behavior in the workforce has been increasing steadily since the 1990s as people have easier, and therefore faster, access to information and communication through smart technologies that have become cheaper over time. Although multitasking behavior harms performance, the paradox is that organizational productivity is increasing at a high rate nonetheless. Concurrent with increased multitasking in the workforce and the subsequent rise in productivity and multitasking in general, literature has witnessed progressively more reports of increased stress, loss of focus, symptoms resembling attention deficit hyperactivity disorder (ADHD), and even a lowering of IQ.