How to expect the unexpected: Fast motion overrides inattentional blindness

Imagine you are looking at a screen – much like you are doing now. On this screen are moving dots and you count how often they collide with each other. While you are doing that – unbeknownst to you – an unexpected moving square is entering the screen from the right and moves until it exits on the left side of the screen. Would you be surprised to learn that the *less* time the square is visible on the screen, the *more* likely you would be to notice it? Most people would – understandably – find that quite surprising. And yet, that is what is happening. As this might sound a bit counterintuitive, we have to go on a bit of a detour to fully understand it. So please bear with us, we promise it is all relevant.   

For the first two years of WW2, the US Navy did not possess a functional torpedo. This sounds like an incredible claim, given that the war in the Pacific made especially strong use of such weapons. The reason for this is that the Empire of Japan relied heavily on long supply lines throughout the Pacific rim (as the Japanese home islands are resource poor) rendering them particularly vulnerable to submarine attack. In theory, the US Navy possessed a very advanced weapons system – the Mark 14 torpedo – to get the job done. This torpedo featured several key innovations, one of them being that instead of detonating when colliding with the – often armored – side of the target ship, like conventional torpedoes (which usually requires multiple hits to sink a ship) it would run underneath it, when the steel of the ship would trigger the magnetic proximity fuse of the torpedo, setting off an explosion from directly underneath that would break the back of the ship and sink it with a single torpedo.  

So far the theory. And yet, between December 1941 and November 1943, over ⅔ of Mark 14 torpedoes fired in anger failed to detonate, most of them running harmlessly beneath the Japanese ships. How is this possible and what does this have to do with cognitive psychology?

The principal reason for the failure of Mark 14 torpedoes to detonate consists in the fact that they were running too deep, which did not trigger the magnetic proximity fuse as the torpedo was in fact much too far, and not proximate to the hull. The Mark 14 torpedo had a depth control mechanism that was designed to maintain a set depth below the surface which relied on a calibrated hydrostatic gyroscope system. This system was also state of the art for the time. So what was the problem and how could it persist for so long?

The crux of the problem is that when the torpedo is moving, cavitation creates turbulence, lowering the water pressure at the sensor locally, which will make the hydrostatic system that controls its depth believe that it is running too shallow, which will make the torpedo dive deeper in order to adjust. So far the key problem. The reason why it was not discovered for so long was that at first – incredibly – only static torpedos were tested, as this made retrieval easier, and the static torpedoes could maintain any desired depth that was set by the operators. Only when submariners frustrated by far too many duds insisted on realistic live firing exercises were they finally performed. Once the problem was identified and fixed, the US silent service had a very effective weapon in the form of the Mark 14, using it to devastating effect in 1944 and 1945.  

There were several other testing-related issues involving the Mark 14 as well, but the key take home message here is that it does matter a great deal under which conditions a system is tested, and whether these conditions are realistic or not. If they are not, even severe problems could remain undetected.   

This issue is not restricted to torpedoes or war. If an alien civilization found a piston-engine aircraft in a hangar and only tested it inside of it, aircraft would be very puzzling contraptions, and their true purpose would not be immediately obvious. Proper context matters.

Psychology often suffers from a similar problem. Many times, phenomena that appear to be devastating biases and deficits – for instance the “baserate fallacy” – disappear when investigated under more ecologically valid conditions. For instance, it can be shown that if doctors are presented with information about the accuracy of medical tests in terms of the probabilities that the test results will be false positives or false negatives, they are systematically unable to do so. Specifically, they overestimate the probability that a patient with a positive test result actually has the condition, if the medical condition is rare. This has been interpreted as “baserate neglect”, the inability of most doctors to take the low baserate into account when making their calculations. This is puzzling, as the doctors are certainly smart enough to do so, but they empirically don’t. 

However, it can also be shown that if the very same doctors are presented with the exact same information in terms of natural frequencies instead of probabilities, doctors can reason about this problem just fine and come up with the correct answer, without exhibiting baserate neglect. Apparently, these doctors are able to handle this information just fine, if they encounter it in the format that brains would have encountered it most of evolution: relative counts. In contrast, as the concept of probability is a relatively recent cultural invention that is only a few hundred years old, one would not expect brains to be particularly comfortable with probabilistic information.   

To summarize – what can appear as a cognitive deficit or an impairment of reasoning – baserate neglect – disappears, when tested under conditions humans would have encountered for most of their evolutionary history. 

This state of affairs seems to also be true for other cognitive domains, such as attention.

Inattentional blindness is the failure of an observer to notice unexpected but readily perceivable stimuli when they are focusing on some task. This phenomenon has been documented in many contexts, even including unexpected stimuli that are moving. It is commonly explained in terms of the overriding strength of top-down goals and expectations over bottom-up signals and often seen as an inescapable flip side of focusing attention. In other words, the benefit an observer gets from deploying attentional resources to task-relevant stimuli is paid in form of an increased likelihood of missing less relevant stimuli.

Importantly, this phenomenon is often interpreted as a deficit, as it manifests as a pervasive failure of observers to notice unexpected objects and events in more and less serious real world settings, from the failure of experts to notice a gorilla embedded in radiographs to the failure to notice Barack Obama to the failure to notice brawls while on a run, the latter which could have implications for the veracity of eyewitness accounts and on and on. 

Some even went so far as to suggest that inattentional blindness might be an inescapable cognitive universal, insofar as it has been documented in every culture it has been tested.

Given how prevalent and – indeed inescapable and deleterious – the phenomenon of inattentional blindness seems to be, it struck us that it would leave organisms in an extremely vulnerable state. 

As we are all the offspring of an unbroken chain of organisms who all successfully managed to meet the key evolutionary challenge of reproduction before disintegration, this seems implausible.            

It could be argued that the real cognitive task all organisms are engaged in is the management of uncertainty. Specifically, an organism does not a priori know which stimulus type in the environment is most relevant. Of course, there are some potential stimuli that are either expected or consistent with goals, but that does not mean that unexpectedly appearing threats might not suddenly be more relevant. Thus, it would be unwise if an organism overcommitted to focusing attention solely on those it deemed relevant at the time it decided to focus. In other words, there should be a path for evolutionarily relevant stimuli to override top-down attention.

Fast motion is an ideal such stimulus, for several reasons. First, most organisms devote a tremendous amount of cortical real estate to the processing of visual motion. Second, motion is generally a fairly good life-form detector. Third, fast objects are particularly likely to be associated with threats like (close) predators. Fourth, fast moving stimuli are relatively rare in the environment, which makes false positives less likely.

We could not fail to notice that in spite of the many variations of inattentional blindness experiments performed in the past 3 decades, no one had tried to measure the impact of fast motion on inattentional blindness, not even those who had created experimental setups that made the parametric variation of speed straightforward. In fact, the only studies that – to our knowledge – varied speed systematically at all tried slow and slower speed conditions (relative to background motion), concluding that duration on screen – not speed – matters for the detectability of unexpected objects. Thus, to our knowledge, the attention system had never been explored under conditions of fast motion, a very plausible and – in evolutionary terms – important stimulus.   

So we did. Briefly, we used a high powered sample of research participants in 3 studies that included conditions where the unexpected moving object (UMO) was fast, relative to background motion. The first experiment was a replication of the original “Gorilla” study. The second experiment involved detecting an unexpected moving triangle when counting dots passing a vertical line and the third experiment replicated this, while also including conditions that featured triangles that were moving slower than the dots.  

The results from these experiments are clear and consistent. Faster moving unexpected objects are significantly more likely to be noticed, implying diminished inattentional blindness. Importantly, this effect is asymmetric. Even though the UMOs are on the screen much longer when moving slower than the dots, remarkably the faster moving UMOs are much more noticeable. This rules out that mere physical salience (the contrast between stimulus features) is driving this effect – if it was, slower moving UMOs should be as noticeable as fast ones. But this is not the case.

In other words, far from being a deficit that somehow diminishes cognition – in the same way cognitive biases have been suggested to do – “inattentional blindness” might be ironically named, as it highlights the elegance and sophistication of attentional deployment.

As we mentioned, an organism does not know ahead of time what will be the most relevant stimulus at any given time, under conditions of uncertainty. In the real world, uncertainty is unavoidable, so it has to be managed. Put differently, it would behoove an organism to hedge their attentional bets before going all in on one goal. Fast motion is a reasonable evolutionary bet to signify highly relevant stimuli – be they predator or prey – that an organism should be apprised of, whether they expected them or not. And it is precisely with fast motion that we get – to our knowledge for the first time – demonstrably strong attenuation of inattentional blindness. 

Thus, rebalancing top-down goal-focused attention with relevant bottom up signals such as fast motion allows an organism to eat its proverbial cognitive cheesecake (by focusing attentional resources on what matters as defined by an important task) and “have it” too, by allowing for fast motion to override this focus, thus hedging for potential unexpected real life threats.

On a deeper level, big data management principles suggest that it is critical to filter large amounts of information up front. As perceptual systems are in this situation – having to handle high volumes of information, it is plausible that a key task is to reduce the information, ideally by filtering by relevance for the organism. In this view, “inattentional blindness” is simply one way in which this filtering by relevance manifests. So this view is incomplete, as it only captures the part of filtering by relevance that is due to top-down, goal-dependent relevance. Other ways in which stimuli might be relevant is due to expectations or inherently relevance, like fast motion.

So, when tested under the right conditions, people behave smarter than commonly believed.