I think the discussion on serial vs parallel processing is incomplete in the linked paper, and is one reason I think the 10 bits/s bottleneck is an incomplete or misinterpreted result. Here’s a review with sources on serial processing,
https://journalofcognition.org/articles/10.5334/joc.185> Cognitive psychology has mainly focused on structural and functional limitations of cognitive processes when facing multitasking requirements. Structural limitations assume strict serial processing for at least one processing stage, while functional limitations assume flexible, parallel processing only limited by the number of available resources. Human movement science, on the other hand, emphasizes the plasticity of cognition and training possibilities. As both approaches have provided ample empirical evidence for their views but have predominantly worked in isolation, this example clearly illustrates the need for a more integrative approach to multitasking. A challenge for the contemporary research on multitasking is to bring together the issues of structure, flexibility, and plasticity in human multitasking, offering a new integrative theoretical framework that accounts for this fundamental aspect of human behaviour.
From one of the papers cited by the above reference (Hommel 2020),
> A closer look reveals that the questions being asked in dual-task research are not particularly interesting or realistic, and the answers being given lack mechanistic detail. In fact, present theorizing can be considered mere empirical generalization, which has led to merely labeling processing bottlenecks rather than describing how they operate and how they actually produce the bottleneck.
So, while I applaud the authors on generating buzz and discussion, I think their promising work will benefit from more serious consideration of the underlying neurophysiology.