Yes, we’re finally getting to the end of the Daredevil Science series, though this post doesn’t actually mark the end. Yes, believe it or not, this text started running so long, I had to decide to leave the topics of balance and proprioception for a later post.
We’ve looked at some of the science of the Marvel Universe Handbook as well as how echolocation might be viewed as a plausible explanation for Daredevil’s radar sense. Now the time has come to cover everything we haven’t touched on yet, such as why Matt is such an accomplished acrobat (well, aside from the fact that he lives in a fictional universe where most superheroes routinely pull stunts that look like something out of Crouching Tiger, Hidden Dragon meets The Matrix) and whether or not it’s really possible to read print by touch. We’ll address the latter right now.
The sense of touch
The skin is our largest organ and responsible for a whole range of absolutely vital functions. It forms a barrier between the hostile environment around us and the tightly controlled one within us; it sweats to keep us cool, and its sensory functions tell us all kinds of information and keeps us safe from harm. Even the sensation we might sometimes wish we could live without – pain – is so crucial that people who are born without it sustain debilitating injuries and often die prematurely.
The sensations our sense of touch can perceive can be surprisingly complex when you think about it. The difference between a cool breeze on your face and the warm and wet feeling of stepping into a hot tub is huge, but the underlying mechanisms for relaying both experiences comes from a limited set of nerve endings and dedicated touch receptors distributed across the body. Some respond to hot and cold, and stages in between; some respond to pressure, and some detect light touch. Some respond quickly and some are a little sluggish. They adapt differently too, with some types of receptors craving novelty while being uninterested in a sustained stimulus. There’s a reason we pay little attention to the feel of our own clothes on our bodies after putting them on.
It is clear that the sense of touch is really a collection of different sensations. As far as Daredevil is concerned, most of the emphasis has been placed on his enhanced ability for fine touch and detection of hot and cold (though the latter is rarely showcased in the comic). The receptors which detect fine touch (these would be Merkel’s discs and Meissner’s corpuscles for those of you taking notes…) are unevenly distributed across the body, and the lips and fingertips are the most sensitive. One way to test the “resolution” of this sense is to test how far apart two pin pricks need to be in order to be registered as two rather than one.
Reading by touch
In a normal human being, the two point touch threshold of the fingertip is around 2 mm (0.08 inches). The spacing between the centers of two adjacent dots in a braille cell (each character in the braille system is one cell) is 2.34 mm (0.092 inches) which means that the ability to read braille requires an acuity close to the physical limit. In order to be able to discern the physical features of standard print, the resolution of the fingertip would have to be much better.
There is also a further complication in that the sense of touch wouldn’t be well adapted to feeling the continuous swirls we associate with standard letters. The fingertip prefers the “either present or absent” quality of dots, as evidenced by the fact that the raised, more or less standard, letters of the alphabets that predated the invention of braille were slow and difficult to read. Dot-based patterns go well with how the sense of touch works.
Aside from pondering the issue of spatial resolution, there is another parameter we need to take into account: How thick does the layer of ink need to be? That is, how high far above the page does a feature of text need to rise in order to be felt? Depending on the nature of the stimulus, it could be as little as just below 10 μm (one tenth the width of a human hair). Most standard newsprint can, in fact, be felt (try it) and this would have been even more true back in Stan Lee’s days. There is another problem, however, and we’re not going to let Matt off the hook this easily. The thinner the layer of ink is, even if we assume that it can theoretically be perceived, the more print reading by touch becomes a futile exercise in separating the signal from the noise. Because the paper the ink is deposited on has its own texture which may very well drown out the features of the print. By contrast, the height of a braille dot – 0.48 mm (or 0.019 inches) for standard American braille – provides plenty of signal.
As you may suspect by now, I actually find the idea that Matt would be able to easily read most forms of print by touch to be harder to swallow than his ability to hear heartbeats. Even more so if we are to accept that he can do this as if it were braille or with the same ease that a sighted person would. There is the noise problem, which has very little to do with his senses (and thus isn’t helped much by the presence of superpowers) as well as the resolution problem. The latter could be compensated for by adding more touch receptors with smaller so-called receptive fields, but there’s a limit to how densely you could pack these receptors.
Does this mean that I rule out this ability altogether? Not necessarily. Large print is easier to explain (though text the size of newspapers headlines becomes so large that it needs to be traced and can’t fit under the fingertip, making it rather slow and cumbersome), and for regular print, I’d go so far as to say that it might be possible to discern larger features, making it fairly easy to distinguish between an ‘l’ and an ‘o’ though more difficult to distinguish between an ‘a’ and an ‘o’ or an ‘l’ and an ‘i’.
In this sense, print reading for the “superpowered blind” might be seen as analogous to lip reading for the deaf (though speech reading is a more accurate, if less common, term). You’re taking a signal adapted for use by one sense (vision) and presenting it to another (touch) for which it’s not ideal. When you add in the knowledge of which combinations are common and rare and which words are likely to occur together, you can compensate to a degree for these imagined limitations and context would dictate whether a word should be read as ‘bad’, ‘bod’ or ‘bed’. In general, if this ability is to be able to operate at a decent speed, someone like Matt would likely be deciphering the shapes of whole words rather than the minuscule features of individual letters.
Yes, there’s another geek out for you. More will follow later in the week!