Free Mind Hacks™: Tips & Tools for Using Your Brain by Tom Stafford, Matt Webb

you that the light is
     either there or not, that’s only because your brain has done the work of removing the
     uncertainty for you. And on a neural level, everything is uncertain because neural signals
     always have noise in them.
    So as you wait for light to appear, your neuronal decision-making hardware is
     inspecting noisy inputs and trying to decide if there is enough evidence to say “Yes, it’s
     there!” Looking at it like this, your response time is the time to collect enough neural
     evidence that something has really appeared. This is why Pieron’s Law applies; more
     intense stimuli provide more evidence, and the way in which they provide more evidence
     results in the equation shown earlier.
    To see why, think of it like this: Pieron’s Law is a way of saying that the response
     time improves but at a decreasing rate, as the intensity (i.e., the rate at which evidence
     accumulates) increases. Try this analogy: stimulus intensity is your daily wage and making
     a response is buying a $900 holiday. If you get paid $10 a day, it’ll take 90 days to get
     the money for the holiday. If you get a raise of $5, you could afford the holiday in 60
     days — 30 days sooner. If you got two $5 raises, you’d be able to afford the holiday in 45
     days — only 15 days sooner than how long it would take with just one $5 raise. The time
     until you can afford a holiday gets shorter as your wage goesup, but it gets shorter more slowly, and if you do the math it turns out to be
     an example of Pieron’s Law.
    End Note
    Pins, D., & Bonnet, C. (1996). On the relation between
     stimulus intensity and processing time: Pieron’s law and choice reaction time. Perception & Psychophysics, 58 (3), 390–400.
    See Also
    Stafford, T., & Gurney, K. G. (in press). The role of response mechanisms
     in determining reaction time performance: Pieron’s law revisited. Psychonomic Bulletin & Review (in press).
Luce, R. D. (1986). Response Times: Their Role in Inferring Elementary
     Mental Organisation . New York: Clarendon Press. An essential one stop for
     all you need to know about modeling reaction times.
Pieron, H. (1952). The Sensations: Their Functions, Processes and
     Mechanisms . London: Frederick Muller Ltd. The book in which Pieron first
     proposed his law.
    Build Your Own Sensory Homunculus
    All abilities are skills; practice something and your brain will devote more resources
     to it.
    The sensory homunculus looks like a person, but swollen and out of all proportion. It
     has hands as big as its head; huge eyes, lips, ears, and nose; and skinny arms and legs.
     What kind of person is it? It’s you, the person in your head. Have a look at the sensory
     homunculus first, then make your own.
    In Action
    You can play around with Jaakko Hakulinen’s homunculus applet ( http://www.cs.uta.fi/~jh/homunculus.html ; Java) to see where different bits of the body are represented in the sensory
     and motor cortex. There’s a screenshot of it in Figure 1-3 .
    This is the person inside your head. Each part of the body has been scaled according
     to how much of your sensory cortex is devoted to it. The area of cortex responsible for
     processing touch sensations is the somatosensory cortex . It lives in
     the parietal lobe, further toward the back of the head than the motor cortex, running
     alongside it from the top of the head down each side of the brain. Areas for processing
     neighboring body parts are generallynext to each other in the cortex, although this isn’t always possible because
     of the constraints of mapping the 3D surface of your skin to a 2D map. The area
     representing your feet is next to the area representing your genitals, for example (the
     genital representation is at the very top of the somatosensory cortex, inside the groove
     between the two hemispheres).
    Figure 1-3. The figure shown is scaled according to the relative sizes of the body parts in the
     motor and sensory cortex areas; motor is shown on the