This system can overrule the conscious, goal-orientated top-down system, which makes sense as it’s something of a survival instinct. The unfamiliar shape in your vision could turn out to be an oncoming attacker, or that boring office colleague who insists on talking about his athlete’s foot.
These visual details don’t have to appear in the fovea, the important middle bit of the retina, to attract our attention. Visually paying attention to something typically involves moving the eyes, but it doesn’t have to. You’ll have heard of “peripheral vision,” where you see something you’re not looking at directly. It won’t be greatly detailed, but if you’re at your desk working at your computer and see an unexpected movement in the corner of your vision that seems the right size and location to be a large spider, you maybe don’t want to look at it, in case that’s exactly what it is. While you carry on typing, you’re very alert to any movement in that particular spot, just waiting to see it again (while hoping not to). This shows that the focus of attention isn’t tied directly to where the eyes are pointing. As with the auditory cortex the brain can specify which part of the visual field to focus on, and the eyes don’t have to move to allow it. It may sound like the bottom-up processes are the most dominant, but there’s more to it. Stimulus orientation overrides the attention system when it detects a significant stimulus, but it’s often the conscious brain that determines what’s “significant” by deciding the context. A loud explosion in the sky would certainly be something that would count as significant, but, if you’re going for a walk on the evening of July Fourth, an absence of explosions in the sky would be more significant, as the brain is expecting fireworks.
Michael Posner, one of the dominant figures in the field of attention research, devised tests that involve getting subjects to spot a target on screen that is preceded by cues which may or may not predict the target location. If there are as few as two cues to look at, people tend to struggle. Attention can be divided between two different modalities (doing a visual test and a listening test at the same time) but if it’s anything more complex than a basic yes/no detection test, people typically fall apart trying it. Some people can do two simultaneous tasks if one is something they’re very adept at, such as an expert typist doing a math problem while typing. Or, to use an earlier example, an experienced driver holding a detailed conversation while operating a vehicle.
Attention can be very powerful. One well-known study concerned volunteers at Uppsala University in Sweden,14 where subjects reacted with sweaty palms to images of snakes and spiders that were shown on screen for less than 1/300th of a second. It usually takes about half a second for the brain to process a visual stimulus sufficiently for us to consciously recognize it, so subjects were experiencing responses to pictures of spiders and snakes in less than a tenth of the time it actually takes to “see” them. We’ve already established that the unconscious attention system responds to biologically relevant cues, and that the brain is primed to spot anything that might be dangerous and has seemingly evolved a tendency to fear natural threats like our eight-legged or no-legged friends. This experiment is a great demonstration of how attention spots something and rapidly alerts the parts of the brain that mediate responses before the conscious mind has even finished saying, “Huh? What?”
In other contexts, attention can miss important and very unsubtle things. As with the car example, too much occupying our attention means we miss very important things, such as pedestrians (or, more importantly, fail to miss them). A stark example of this was provided by Dan Simons and Daniel Levin in 1998.15 In their study, an experimenter approached random pedestrians with a map and asked them directions. While the pedestrians were looking at the map, a person carrying a door walked between them and the experimenter. In the brief moment when the door presented an obstruction, the experimenter changed places with someone who didn’t look or sound anything like the original person. At least 50 percent of the time, the map-consulting person didn’t notice any change, even though they were talking to a different person from the one they’d been speaking to seconds earlier. This invokes a process known as “change blindness,” where our brains are seemingly unable to track an important change in our visual scene if it’s interrupted even briefly.
This study is known as the “door study,” because the door is the most interesting element here, apparently. Scientists are a weird bunch.
The limits of human attention can and do have serious scientific and technological consequences too. For example, heads-up displays, where the instrument display in machines such as airplanes and space vehicles is projected onto the screen or canopy rather than read-outs in the cockpit area, seemed like a great idea for pilots. It saves them having to look down to see their instruments, thus taking their eyes off what’s going on outside. Safer all round, right?
No, not really. It turned out when a heads-up display is even slightly too cluttered with information, the pilot’s attention is maxed out.16 They can see right through the display, but they’re not looking through it. Pilots have been known to land their plane on top of another plane as a result of this (in simulations, thankfully). NASA itself has spent a lot of time working out the best ways to make heads-up displays workable, at the expense of hundreds of millions of dollars.
These are just some of the ways the human attention system can be seriously limited. You might like to argue otherwise, but if you do you clearly haven’t been paying attention. Luckily, we’ve now established you can’t really be blamed for that.
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* Some scientists have called this finding into question, arguing that this staggering number of smell sensations is more a quirk of questionable math used in the research than the result of our mighty nostrils.1
? It’s important to clarify the difference between illusions and hallucinations. Illusions are when the senses detect something but interpret it wrongly, so you end up perceiving something other than what the thing actually is. By contrast, if you smell something with no source, this is a hallucination; perceiving something that isn’t actually there, which suggests something isn’t working as it should deep in the sensory-processing areas of the brain. Illusions are a quirk of the brain’s workings; hallucinations are more serious.