Both proposed models explain why multitasking is so difficult; with bottleneck models, you have one single stream of attention that keeps leaping between different tasks, making it very difficult to keep track. The capacity model would allow you to pay attention to more than one thing at a time, but only so far as you have the resources to process them effectively; as soon as you go beyond your capacity, you lose the ability to keep track of what’s going on. And the resources are limited enough to make it look like a “single” stream is all we’ve got in many scenarios.
But why this limited capacity? One explanation is that attention is strongly associated with working memory, what we use to store the information we’re consciously processing. Attention provides the information to be processed, so if working memory is already “full,” adding more information is going to be difficult, if not impossible. And we know working (short-term) memory has a limited capacity.
This is often sufficient for your typical human, but context is crucial. Many studies focus on how attention is used while driving, where a lack of attention can have serious consequences. In many states, driving while physically using a phone is not allowed; you have to use a hands-free set-up and keep both hands on the wheel. But a study from the University of Utah in 2013 revealed that, in terms of how it affects performance, using a hands-free set-up is just as bad as using the phone with your hands, because both require a similar amount of attention.12
The fact that you have two hands on the wheel as opposed to one may provide some advantage, but the study measured overall speed of responses, scanning of environment, noticing important cues; all these and more are reduced to a similar worrying extent whether using hands-free or not, because they require similar levels of attention. You may well be keeping your eyes on the road, but that’s irrelevant if you’re ignoring what your eyes are showing you.
Even more worrying, the data suggests it’s not just the phone: changing the radio or carrying on a conversation with a passenger can also be equally distracting. With increased technology found in cars and on phones (it’s technically not illegal at present to check your emails while driving) the options for distraction are bound to increase.
With all this, you may wonder how anyone can drive for more than ten minutes straight without ending up in a disastrous wreck. It’s because we’re talking about conscious attention, which is where the capacity is limited. As we’ve discussed, do something often enough and the brain adapts to it, allowing procedural memory, described in Chapter 2. People say they can do something “without thinking,” and that’s quite accurate here. Driving can be an anxious, overwhelming experience for beginners, but eventually it becomes so familiar the unconscious systems take over, so conscious attention can be applied elsewhere. However, driving is not something that can be done entirely without thinking; taking account of all other road users and hazards needs conscious awareness, as these are different each time.
Neurologically, attention is supported by many regions, one of which is that repeat offender the prefrontal cortex, which makes sense as that’s where working memory is processed. Also implicated is the anterior cingulate gyrus, a large and complex region deep in the temporal lobe that also extends into the parietal lobe, where a lot of sensory information is processed and linked to higher functions such as consciousness.
But the attention controlling systems are quite diffuse, and this has consequences. In Chapter 1, we saw how more advanced conscious parts of the brain and the more primitive “reptile” elements often end up getting in each other’s way. The attention-controlling systems are similar; better organized, but a familiar combination or conflict of conscious and subconscious processing.
For example, attention is directed by exogenous and endogenous cues. Or, in plain English, it has both bottom-up and top-down control systems. Or, even more simply, our attention responds to stuff that happens either outside our head, or inside it. Both of these are demonstrated by the cocktail-party effect, where we direct our attention to specific sounds, also known as “selective listening.” The sound of your name suddenly causes your attention to shift to it. You didn’t know it was coming; you weren’t consciously aware of it until it had happened. But, once aware of it, you direct your attention to the source, excluding anything else. An external sound diverted your attention, demonstrating a bottom-up attention process, and your conscious desire to hear more keeps your attention there, demonstrating an internal top-down attention process originating in the conscious brain.#
However, most attention research focuses on the visual system. We can and do physically point our eyes at the subject of attention, and the brain relies mostly on visual data. It’s an obvious target for research, and this research has produced a lot of information about how attention works.
The frontal eye fields, in the frontal lobe, receive information from the retinas and create a “map” of the visual field based on this, supported and reinforced by more spatial mapping and information via the parietal lobe. If something of interest occurs in the visual field, this system can very quickly point the eyes in that direction, to see what it is. This is called overt or “goal” orientation, as your brain has a goal that is “I want to look at that!” Say you see a sign that reads special offer: free bacon, then you direct your attention to it straight away, to see what the deal is, to complete the goal of getting bacon. The conscious brain drives the attention, so it’s a top-down system. Alongside all this there’s another system at work, called covert orientation, which is more of a “bottom-up” one. This system means something is detected that is of biological significance (for instance, the sound of a tiger growling nearby, or a crack from the tree branch you’re standing on) and attention is automatically directed towards it, before the conscious areas of the brain even know what’s going on, hence it’s a bottom-up system. This system uses the same visual input as the other one as well as sound cues, but is supported by a different set of neural processes in different regions.
According to current evidence, the most widely supported model is one where, on detection of a something potentially important, the posterior parietal cortex (already mentioned regarding vision processing) disengages the conscious attention system from whatever it’s currently doing, like a parent switching the television off when their child is supposed to take out the garbage. The superior colliculus in the midbrain then moves the attention system to the desired area, like a parent moving their child to the kitchen where the garbage is. The pulvinar nucleus, part of the thalamus, then reactivates the attention system, like a parent putting garbage bags in their child’s hand and pushing the child towards the door to put the damn things out!