We all know that multitasking while driving can have deadly consequences. In the U.S. alone, 3142 deaths and over 400,000 injuries were caused by distracted driving in 2020. In fact, texting while driving doubles your chances of being the cause of an accident. But is all driving-related multitasking this dangerous? A recent report by Mallory Terry and Lana Trick (pictured below) shows that not all multitasking is created equal.

In their paper published in the Psychonomic Society journal Attention, Perception, & Psychophysics, Terry and Trick examined how two visual tasks important for driving—tracking multiple moving objects and visual-motor coordination—interfere with one another. Interference would support a theory proposing that these two specific tasks are based on a common perceptual mechanism. Terry and Trick reasoned that if a common mechanism exists, then object tracking and touch guidance should interact in interesting ways.

To test this, Terry and Trick asked subjects to perform two simultaneous tasks on a computer tablet. For one task, subjects visually tracked the positions of a set of small animated ‘spheres’ moving in angular patterns. The number of tracked spheres ranged from 1 to 4 and a similar set of distraction spheres were also seen moving. At the end of 10 seconds, the motion of all spheres stopped, and subjects were asked to indicate which were the target spheres (by touching them on the screen). You can see an example of this display in the video below. While the task may seem very challenging at first, it is more manageable if you gaze toward the middle of the screen and follow the targets using mostly peripheral vision.

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For their other task, subjects simultaneously performed visually-guided touch with the moving spheres. As the spheres moved, some would briefly change color. When this occurred, subjects had to quickly tap those spheres with their index finger. Try the video above again, and this time touch any sphere that changes color after the motion starts. Tracking the initial spheres should be more difficult.

Importantly, the color-changing spheres were sometimes the same as those being visually tracked (as in the video above), and sometimes they were part of the distractor set, which is the case in this second video:

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Conditions were also included in which subjects performed either just the motion tracking or color tapping task on its own. These conditions were included to ensure that it was the combination of tasks that induced the interference.

Based on general multitasking effects, Terry and Trick expected that adding the color tapping task would inhibit target tracking performance (so that fewer spheres were correctly tracked). However, the important question was if the amount of inhibition would depend on whether the specific spheres were the same for both tasks. Terry and Trick hypothesized that if a link exists between visual tracking and visually-guiding touch, then motion tracking would be hindered less when the color-changing spheres were the same as those being tracked (vs. those from the distracter set). For the two videos above, the prediction would be that you would have less difficulty tracking the objects’ motions (while touching the color-changing spheres) in the first video than in the second.

In two separate experiments, Terry and Trick found exactly these results. Adding the color touching task did cause subjects to successfully track fewer moving spheres. However, when the motion tracking and touch guidance tasks involved the same spheres, less inhibition of motion tracking occurred. In fact, when subjects were asked to track just a single target that also changed color (so it was tapped), no reduction in tracking performance occurred.

Importantly, Terry and Trick included conditions to confirm that the touch aspect of the task was critical for this interaction to occur. Thus when subjects saw either the target or distractor spheres change color but were not required to touch them, little inhibition of object tracking was observed. Further, no interaction between target/distractor and object tracking performance occurred without touch. Potentially, a link between the object-tracking and guided-touch functions allowed multitasking interference to be partially spared when both functions used the same items. This interpretation is consistent with the claim that there is a common mechanism involved with both functions.

Of course, if a common mechanism underlies the functions, then this interference interaction should work in the other direction. Thus, the object tracking task should interfere less with the visually-guided touch task if both tasks use the same items. Terry and Trick tested this by measuring the time it took subjects to touch the spheres after they changed color. Again, they found the predicted result: The reaction time to touch the spheres slowed overall when subjects also performed the target-tracking task. However, this slowing occurred less when the tracked and tapped spheres were the same. Again, this finding is consistent with a common mechanism involved with tracking and touching.

Besides providing important support for the object-tracking and visuo-motor link, this research has implications for driving safety. In previous work, Trick and her lab used a driving simulator (shown in the image below) to show how the multiple object tracking skill is essential for driving, and how this skill often wanes in the elderly.

Potentially, this diminished skill might underlie the increased number of accidents that occur for elderly drivers at intersections. By gaining a better understanding of how object tracking interacts with visuo-motor coordination, Terry and Trick’s research should have implications for training, rehabilitation, and licensing programs for elderly drivers.

Featured Psychonomic Society Article

Terry, M.E., & Trick, L.M. (2021). Multiple-object tracking and visually guided touch. Attention Perception & Psychophysics, 83, 1907–1927. https://doi.org/10.3758/s13414-021-02291-4