Since the 1960s, psychologists have conducted experiments on the nature and limits of human multitasking. The simplest experimental design used to investigate human multitasking is the so-called
psychological refractory period effect. Here, people are asked to make separate responses to each of two stimuli presented close together in time. An extremely general finding is a slowing in responses to the second-appearing stimulus. This slowing is intuitively apparent even in certain simple game-like contexts. Researchers have long suggested that there appears to be a processing
bottleneck preventing the brain from working on certain key aspects of both tasks at the same time (e.g., ). Bottlenecking refers to the idea that because people only have a limited amount of attentional resources, the most important information is kept. Many researchers believe that the cognitive function subject to the most severe form of bottlenecking is the planning of actions and retrieval of information from memory. Psychiatrist
Edward M. Hallowell has gone so far as to describe multitasking as a "mythical activity in which people believe they can perform two or more tasks simultaneously as effectively as one." Others have researched multitasking in the area of learning.
Richard E Mayer and
Roxana Moreno studied the phenomenon of cognitive load in multimedia learning and concluded that it is difficult, if not impossible, to learn new information while engaging in multitasking.
Reynol Junco (and Shelia R Cotten ) examined how multitasking affects academic success and found that students who engaged in high levels of multitasking reported significant issues with their academic work. A more recent study on the effects of multitasking on academic performance showed that using Facebook and text messaging while studying were negatively related to student grades, while online searching and emailing were not. Some experiments have been done that demonstrate that it is possible to divide one's attention among several tasks, how successfully depends on several factors such as how much practice one has with it or the difficulty of the task. Walter Schneider and Robert Shiffrin performed an experiment in which they presented the participants with a memory set, which consists of target stimuli such as the number three. After being presented with the memory set they were rapidly shown 20 test frames which contained distractor stimuli. One of the slides they were shown contained one of the target stimuli from the memory set. With each trial, a new memory set and new test frames were presented. At the start of the experiment, participants averaged 55% in correctly identifying the target stimuli from the memory set. After 900 trials the participants were able to bring the average up to 90%. They reported that after about 600 trials the task became automatic and they were able to respond without thinking about it.
The brain's role Because the brain cannot fully focus when multitasking, people take longer to complete tasks and are predisposed to error. When people attempt to complete many tasks at one time, "or [alternate] rapidly between them, errors go way up, and it takes far longer—often double the time or more—to get the jobs done than if they were done sequentially," states Meyer. This is largely because "the brain is compelled to restart and refocus". A study by Meyer and David Kieras found that in the interim between each exchange, the brain makes no progress whatsoever. Therefore, multitasking people not only perform each task less suitably, but lose time in the process. According to a study done by
Jordan Grafman, chief of the
cognitive neuroscience section at the National Institute of Neurological Disorders and Stroke, "the most anterior part [of the brain] allows [a person] to leave something when it's incomplete and return to the same place and continue from there," while
Brodmann Area 10, a part of the brain's frontal lobes, is important for establishing and attaining long-term goals. This study further indicates that, while the brain can become adept at processing and responding to certain information, it cannot truly multitask. People have a limited ability to retain information, which worsens when the amount of information increases. For this reason, people alter information to make it more memorable, such as separating a ten-digit phone number into three smaller groups or dividing the alphabet into sets of three to five letters, a phenomenon known as
chunking. George Miller, former psychologist at
Harvard University, believes the limits to the human brain's capacity centers around "the
number seven, plus or minus two." An illustrative example of this is a test in which a person must repeat numbers read aloud. While two or three numbers are easily repeated, fifteen numbers become more difficult. The person would, on average, repeat seven correctly. Brains are only capable of storing a limited amount of information in their short-term memories. Laboratory-based studies of multi-tasking indicate that one motivation for switching between tasks is to increase the time spent on the task that produces the most reward (Payne, Duggan & Neth, 2007). This reward could be progress towards an overall task goal, or it could simply be the opportunity to pursue a more interesting or fun activity. Payne, Duggan, and Neth (2007) found that decisions to switch task reflected either the reward provided by the current task or the availability of a suitable opportunity to switch (i.e. the completion of a subgoal). A French
fMRI study published in 2010 indicated preliminary support for the hypothesis that the brain can pursue at most two goals simultaneously, one for each
frontal lobe (which has a goal-oriented area). When studying the costs of multitasking there are typically two designs for or types of multitasking that are examined, task switching and dual tasking. Task switching involves shifting one's attention from one thing to another. Dual tasking, on the other hand, is when attention is divided among multiple things at once. Studies have been done to specifically examine the brain when one is engaged in either type of multitasking. Through the use of
MRI brain scans, researchers have found that frontoparietal regions are activated which would include the
inferior frontal junction and the
posterior parietal cortex. They also found that while each type of tasking uses different mechanisms there are also some underlying mechanisms and resources that they share.
Sex differences Although some cultures believe that women are better at multitasking than men, there is little data available to support claims of a real sex difference. Most studies that do show any sex differences tend to find that the differences are
small and inconsistent. In 2013, a brain connectivity study from
Penn Medicine found major differences in men and women's neural wiring that researchers suggested indicated that sex plays a role in multitasking skills. They said that "[On] average, men are more likely better at learning and performing a single task at hand, like cycling or navigating directions, whereas women have superior memory and social cognition skills, making them more equipped for multitasking and creating solutions that work for a group." However, this study has been widely criticized because the differences could easily have been caused by increased head movement. Moreover, the link between the DTI data and behavioral performance is speculative. In 2018, a study in Norway tested everyday scenarios via videogames and found that "none of the multitasking measures (accuracy, total time, total distance covered by the avatar, a prospective memory score, and a distractor management score) showed any sex differences." A 2019 study showed that there are not significant sex differences in multi-tasking across numerous tasks. There have been attempts to produce
evolutionary explanations for the popular belief. One story told by evolutionary biologists Silverman and Eals speculated that a
sex-based division of labor into
hunters and gatherers could favor the development of a difference in men and women's cognitive abilities, based on the hunter-gatherer tasks each sex performed in the prehistoric past. This is based on the outdated belief that prehistoric men were hunters, while women were gatherers and took care of the children, and that over time, there was a
natural selection for women who could multitask, resulting in modern females being superior multitaskers. However, an attempted verification of this study found "that multiple methodological failures all bias their results in the same direction...their analysis does not contradict the wide body of empirical evidence for gendered divisions of labor in foraging societies".
Continuous partial attention Author
Steven Berlin Johnson describes one kind of multitasking: "It usually involves skimming the surface of the incoming data, picking out the relevant details, and moving on to the next stream. You're paying attention, but only partially. That lets you cast a wider net, but it also runs the risk of keeping you from really studying the fish."
Multimedia pioneer
Linda Stone coined the phrase "
continuous partial attention" for this kind of processing. Continuous partial attention is multitasking where things do not get studied in depth. Rapidly increasing technology fosters multitasking because it promotes multiple sources of input at a given time. Instead of exchanging old equipment like TV, print, and music, for new equipment such as computers, the Internet, and video games, children and teens combine forms of media and continually increase sources of input. According to studies by the Kaiser Family Foundation, in 1999 only 16 percent of time spent using media such as Internet, television, video games, telephones, text-messaging, or e-mail was combined. In 2005, 26 percent of the time these
media were used together. This increase in simultaneous media usage decreases the amount of attention paid to each device. In 2005 it was found that 82 percent of American youth use the Internet by the seventh grade in school. A 2005 survey by the
Kaiser Family Foundation found that, while their usage of media continued at a constant 6.5 hours per day, Americans ages 8 to 18 were crowding roughly 8.5 hours' worth of media into their days due to multitasking. The survey showed that one quarter to one-third of the participants have more than one input "most of the time" while watching television, listening to music, or reading. Another study compared reaction times for experienced drivers during a number of tasks, and found that the subjects reacted more slowly to brake lights and stop signs during phone conversations than during other simultaneous tasks. When talking, people must withdraw their attention from the road in order to formulate responses. Because the brain cannot focus on two sources of input at one time, driving and listening or talking, constantly changing input provided by cell phones distracts the brain and increases the likelihood of accidents.
Supertasker In 2010, a scientific study found that a small percent of the population appeared to be much better at multitasking than others, and these people were subsequently labeled "supertaskers". In 2015, another study supported the idea of supertaskers. This particular study showed that they tested people by making them drive on a driving simulator while at the same time memorizing words and solving math problems. As expected, most of the participants did much worse than their individual task test scores. The supertaskers, however, were able to multitask without major effects to their performance. ==Popular commentary on practical multitasking==