CATEGORIES:

Biology Chemistry Construction Culture Ecology Economy Electronics Finance Geography History Informatics Law Mathematics Mechanics Medicine Other Pedagogy Philosophy Physics Policy Psychology Sociology Sport Tourism

Three Kinds of Motor Control

There are three classes of control system used to moderate movements while they occur, and these are used in situations from needing to move your arm more to catch a ball in a high wind to your legs changing their walking pattern onboard a ship.

Feedback

All neural systems include some noise [Hack #33], so even if your movements are planned correctly (you calculated the right amount of force to apply, etc.), your brain needs to check they are not going off course and reset them if they are. You are trying to catch a ball and realize your hand is out of place, so, while you're moving it toward the ball, you speed up your movement so it gets to the right place in time. An additional complication is learning movements across trials, when you know what you want to do (juggle three balls, for example) but you have to train your movements to successively improve each time you try.

Feedforward

A feedback system can work in isolation, detecting error and compensating for its effect. In comparison, feedforward systems use information from a component that may introduce error to anticipate the error itself. This component sends information ahead to whatever has to deal with the potential difficulty so it can be accommodated for. For example, the vestibular-ocular reflex [Hack #30] translates head velocity into compensatory eye velocities. Head movements introduce distortions into vision, so the feedforward mechanism notices the head motion and triggers eye movements to cancel out any motion blur before it even occurs.

Forward modeling

Some movements need correcting during their execution at a rate quicker than is possible with simple feedback. One way of doing this is to make a prediction of what the effect of a signal from your brain to your muscles will do (as described in [Hack #65] ). The prediction can then be used as pseudofeedback to control movements at a speed faster than would be possible with actual sensory feedback. Forward modeling allows batters to hit baseballs (or batsmen to hit cricket balls, depending on your preferred game) thrown at them at speeds faster than their simple sensory systems should allow them to deal with. This system also has advantages over feedback because of the difficulties that occur when a feedback signal is delayed. A late feedback signal means it's actually responding to a situation now past in which the error was larger, so the correction applied can cause an overshoot and lead to oscillations around the correct position rather than an iteration toward it (although introducing a damping factoran automatic reduction of the delayed feedback signalcan compensate for this).

So movement control is more complex than it might at first seem. Making a muscle movement isn't as simple as sending it a simple "go" or "don't go" signal and letting ballistics (launch it, let it go) take care of the rest. Movements have to be controlled while they're in action, and the best control mechanism of the three in the list depends on the characteristics of the system: that is, how long it takes for information to influence action.

In Real Life

It isn't just strength that can be trained, but coordination as well. I once practiced with a very senior judo instructor who told me that an hour's worth of going through judo techniques in the imagination was as good as an hour's worth of actual training. I was skeptical at the time, but research seems to confirm his suggestion. For example, mental rehearsal of a piano sequence results in similar levels of improvement (and similar strengthening of cortical signals) as actual practice.⁵

So if you can't get to the gym, put aside some time for mental rehearsal of your exercises. You won't lose any weight, but you'll be better coordinated.

End Notes

1. Jordan, M. I. (1996). Computational aspects of motor control and motor learning. In H. Heuer & S. W. Keele (eds.), Handbook of Perception and Action. New York: Academic Press.

2. Ranganathan, V. K., Siemionow, V., Liu, J. Z., Sahgal, V., & Yue, G. H. (2004). From mental power to muscle powergaining strength by using the mind. Neuropsychologia, 42, 944-956.

3. Yue, G. H., & Cole, K. J. (1992). Strength increases from the motor program: Comparison of training with maximal voluntary and imagined muscle contractions. Journal of Neurophysiology, 67, 1114-1123.

4. Gabriele, T. E., Hall, C. R., & Lee, T. O. (1989). Cognition in motor learning: Imagery effects on contextual interference. Human Movement Science, 8, 227-245.

5. Pascual-Leone, A. et al. (1995). Modulation of muscle responses evoked by transcranial magnetic stimulation during the acquisition of new fine motor skills. Journal of Neurophysiology, 74(3), 1037-1045.

Hack 89. Navigate Your Way Through Memory

A 2,500-year-old memory trick shows how our memory for events may be based on our ability to remember routes to get to places. Remembering where you are and what is currently happening are (as you might expect) both rather important. It turns out that orienting yourself in space may rely on some of the same brain areas as are used for remembering what has happened to youareas that originally evolved to help animals find their way around, but now allow us to retain the episodes that make up our personal narratives. The demonstration we'll use is a famous memory trick used to remember a list of arbitrary things, with the added bonus that the things are remembered in order. It's called the method of loci and involves remembering things according to where they are positioned along a route. Simply take your list of things to remember and place them along a familiar route, imagining each item (or something that will remind you of it) at key points on the route. 9.10.1. In Action How many words do you think you could remember if given an arbitrary list and around 10 seconds per word in which to learn them? Knowing that my memory isn't all that good, I thought perhaps I could remember around 10. So I decided to use the method of loci to remember 20 words, twice that number. I didn't want to come up with my own list, because it would be easier for me to remember, so I used the 20 most common words appearing in the lyrics of the songwriter Tom Waits, as kindly provided by the excellent Tom Waits Supplement (http://www.keeslau.com/TomWaitsSupplement/Lyrics/common.htm) and shown in Table 9-5.

Table 9-5. Imagine an item for each word at points along a route that is familiar to you. Rehearse for 4 minutes and then test yourself
1. NIGHT	8. HOME	15. DRINK
2. TIME	9. RAIN	16. STREET
3. LOVE	10. HEART	17. BLOOD
4. DAY	11. DEATH	18. RED
5. EYE	12. DOG	19. HAIR
6. DREAM	13. BLUE	20. GIRL
7. MOON	14. ROAD

Perhaps you think 20 is too easy; feel free to use a longer list or give yourself less time, if you're so inclined. But 20 in 4 minutes seemed daunting enough for me. Starting with "night" (131 mentions across Tom Waits' entire discography) and finishing with "girl" (40 mentions), I imagined something to do with each item at each point of the journey from the front room of my house, where I was sitting, to my nearest subway station.

After mentally doing the journey and noting the items strewn along the way (a "love" letter at the foot of the stairs, a "drink" of coffee at the café on the corner, and so forth) and checking that I thought I'd remembered them all, my 4 minutes were up and I pulled out my notebook and got my pen ready to write down the list of items.

Normally with things like this my mind goes blank as soon as the thing I'm supposed to be remembering leaves my sight. But, using the method of loci, I was impressed with how quick and easy it was to remember all the words. (Yeah, yeah, I know I'm supposed to know that it works, but I still managed to impress myself.) I got every item right, and only two out of order.

Try it yourself. It doesn't have to be these words. It can be things, people, numbersanything. This is one of the tricks professional memory artists use to remember lists of hundred, or even thousands, of things.

How It Works

The are several reasons this method works to help aid your memory, but the main one is the attaching of things to locations in space.

The memory technique also benefits from something inherent in the dual structure of navigating: the landmarks and route mutually define each other, but each exists in its own right. The route allows you to chain from one memory item (or landmark) to the next. Because the landmarks exist apart from the route, even if you can't remember what is at a particular location, it doesn't have to stop your journey onto the next location or item.

T.S.

We know that the human brain has specialized mechanisms dedicated to remembering landmarks,¹ and that (interestingly) this region and those nearby seem to be responsible for giving humans and other animals a sense of where they are in space.² Brain imaging of people navigating through virtual environments has shown that even if we don't consciously recognize something as a landmark it still triggers a response in this specialized part of the brain.

This part of the brain, the hippocampus and nearby nuclei, is also known to be absolutely crucial for storing our memory for events. Psychologists call this kind of memory episodic memory, to distinguish it from memory for facts or memories of how to do things. People with hippocampal damage (like the hero of the film Memento (http://www.imdb.com/title/tt0209144), for example) aren't able to store new episodic memories, although they can retain memories for episodes that they stored before their injury and they can learn new facts (with lots of effort) and skills.

So we know that this same part of the brain, the hippocampus, seems to be crucial both for recording events and for helping us understand where we are in space. Evidence that this first function may have evolved from the second has recently been published.³ It was found that the expectations and intentions an animal has affect how the hippocampus encodes memory for locations in the hippocampus. This encoding of context for locations at different times may have laid the foundations for the encoding of context in time for other memories. From this may have developed the memory for events, that ability to mentally time travel, which makes up what most of us think of as our memories.

In Real Life

You can see this landmark-specialized processing at work when we give and follow directions. If you are following directions and go past something that's an obvious landmark and your directions don't specify it, you know something's wrong. Interestingly there is also evidence from brain imaging that supports the well-known fact that men and women tend to navigate in a different manner; women tend to rely more on landmarks alone, whereas men rely more on absolute spatial position (the geometry of the situation) in combination with landmarks.⁴ The information architect Christina Wodtke has observed that "On the Web, everyone's a woman," because there is no consistent spatial geometry; we are all forced to rely on landmarks.5

End Notes

1. Janzen, G., & van Turennout, M. (2004). Selective neural representation of objects relevant for navigation. Nature Neuroscience, 7, 673-677.

2. Burgess N., Maguire, E. A., & O'Keefe, J. (2002). The human hippocampus and spatial and episodic memory. Neuron, 35, 625-641.

3. Ferbinteanu, J., & Shapiro, M. L. (2003). Prospective and retrospective memory coding in the hippocampus. Neuron, 40, 1227-1239. Discussed in Jeffery, K. J. (2004). Remembrance of futures past. Trends in Cognitive Sciences, 8, 197-199.

4. Gron, G., Wunderlich, A. P., Spitzer, M., Tomczak, R., & Riepe, M. W. (2000). Brain activation during human navigation: Gender-different neural networks as substrate of performance. Nature Neuroscience, 3, 404-408.

5. Wodke, C. (2002). Information Architecture: Blueprints for the Web. Pearson. (See the sample chapter at http://eleganthack.com/blueprint/sample.php for the particular observation.)

Hack 90. Have an Out-of-Body Experience

Our regular experience of the world is first person, but in some situations, we see ourselves from an external perspective. These out-of-body experiences may even have a neurological basis. We are used to experiencing the world from a first-person perspective, looking out through our eyes with our bodies at the center of our consciousness. This is sometimes known as the Cartesian theater. Some people, however, claim to have out-of-body experiences, in which their consciousness seems separated from their body, sometimes to the extent that people feel as if they are looking down on themselves from a third-person perspective, rather than looking out from the inside. These claims are not common, but most people can experience similar out-of-body phenomena, in the form of memories of past events. Furthermore, research has identified certain specific brain areas that may be involved in producing the egocentric, "looking out of our eyes" perspective and found that out-of-body experiences can be induced by unusual activity there. 9.11.1. In Action Remember back to when you were last lying down reading something: perhaps it was on holiday at the beach, in a local park, or just on the couch at home. Try and fix that image in your mind. Now, notice where your "mind's eye" is. Are you looking at yourself from an external point of viewmuch like someone wandering by might have seen youor are you remembering yourself looking out through your own eyes as you are while reading this book right now? The majority of people remember a scene like this from a seemingly disembodied third-person perspective, despite originally having experienced it from a first-person point of view. 9.11.2. How It Works The first study to explore this effect in detail was published in 1983 by Nigro and Neisser.¹ They made the link between the likelihood of recalling a memory as either a first-person or third-person image and emotions and discovered that asking someone to focus on their feelings at the time of the event was more likely to result in a first-person memory. The example in the preceding "In Action" section focused on a situation and was probably a fairly neutral emotional experience, so is likely to produce a third-person memory in most people. Although this is a common experience when remembering the past, the majority of people do not have out-of-body experiences in the present. People who have recounted out-of-body experiences have sometimes been suspected of being overimaginative or worse, but such experiences are a well-known phenomenon in certain types of epilepsy and with specific forms of brain injury. This does not mean that people who experience out-of-body states necessarily have epilepsy or brain injury, but these sorts of conditions suggest that normal, but usually hidden, aspects of brain function may be involved in producing such experiences. A study by Blanke and colleagues² examined five neurological patients who had frequent out-of-body experiences. On one occasion, a surgeon managed to reliably induce such an experience by electrically stimulating the cortex of a patient during brain surgery. When the surgeon stimulated the tempero-parietal junction (the area of the brain where the temporal and parietal lobes meet [Hack #8]), the patient reported that she felt an instantaneous sensation of floating near the ceiling and experienced the operating theater as if she were looking down on it, "seeing" the top of the doctors' heads and herself on the operating table. Ceasing the stimulation "returned" the patient to her body, and resuming it caused her to feel disembodied once more. Brain imaging studies have shown that the tempero-parietal junction is activated in situations that involve calculating point of view from an egocentric perspective and mentally switching between views to understand a scene (for example, mentally working out a good place to stand to get the best view of a football game). With this in mind, it is perhaps not so surprising that unusual activity in this area might cause feelings of being detached from the body. Although it is too early to say for sure, it seems likely that when we recall images that appear in the third-person perspective, the tempero-parietal junction is being recruited to help create this image. The previous exercise demonstrates that, in the context of memory, we all have the ability to experience the out-of-body state. It also suggests that there may be a sound neurological basis for such experiences and that healthy people who report out-of-body experiences are being less fanciful than some skeptics presume. 9.11.3. End Notes 1. Nigro, G., & Neisser, U. (1983). Point of view in personal memories. Cognitive Psychology, 15, 467-482. 2. Blanke, O., Landis, T., Spinelli, L., & Seeck, M. (2004). Out-of-body experience and autoscopy of neurological origin. Brain, 127 (Pt. 2), 243-258. Vaughan Bell

Hack 91. Enter the Twilight Zone: The Hypnagogic State

On the edge of sleep, you may enter hypnagogia, a state of freewheeling thoughts and sometimes hallucinations.

Hypnagogia, or the hypnagogic state, is a brief period of altered consciousness that occurs between wakefulness and sleep, typically as people "doze off" on their way to normal sleep. During this period, thoughts can become loosely associated, whimsical, and even bizarre. Hallucinations are very common and may take the form of flashes of lights or colors, sounds, voices (hearing your own name being called is quite common), faces, or fully formed pictures. Mental imagery may become particularly vivid and fantastical, and some people may experience synaesthesia, in which experiences in one sense are experienced in anothersounds, for example, may be experienced as visual phenomena.

It is a normal stage of sleep and most people experience it to some degree, although it may go unnoticed or be very brief or quite subdued in some people. It is possible, however, to be more aware of the hypnagogic state as it occurs and to experience the effects of the brain's transition into sleep more fully.

In Action

Although there is no guaranteed technique to extend or intensify the hypnagogic state, sometimes it can be enough to simply make a conscious effort to be aware of any changes in consciousness as you relax and drop off, if practiced regularly. Trying to visualize or imagine moving objects and scenes, or passively noting any visual phenomena during this period might allow you to notice any changes that take place. Extended periods of light sleep seem more likely to produce noticeable hypnagogia, so being very tired may mean you enter deep sleep too quickly. For this reason, afternoon dozing works well for some.

Some experimenters have tried to extend or induce hypnagogia by using light arousal techniques to prevent a quick transition into deep sleep. A microphone and speaker were used in one study to feed the sound of breathing back to the sleeper. Another method is the use of "repeat alarm clocks" (like the snooze function on many modern alarm clocks)on entering sleep, subjects are required to try and maintain enough awareness to press a key every 5 minutes; otherwise, a soft alarm sounds and rouses them.

Try this yourself on public transport. Because of the low background noise and occasional external prompting, if you manage to fall asleep, dozing on buses and trains can often lead to striking hypnagogic states. In spite of this, this is not always the most practical technique, as you can sometimes end up having to explore more than your own consciousness if you miss your stop.

How It Works

Very little research has been done on brain function during the hypnagogic state, partly because conducting psychology experiments with semiconscious people is difficult at the best of times and partly because many of the neuroimaging technologies are not very soporific. fMRI [Hack #4] scanning tends to be noisy and PET scanning [Hack #3] often involves having a drip inserted into a vein to inject radioactive tracer into the bloodstreamhardly the most relaxing of experiences. As a result, most of the research has been done with EEG (electroencephalogram) readings [Hack #2] that involve using small scalp electrodes to read electrical activity from the brain.

Hideki Tanaka and colleagues¹ used EEG during sleep onset and discovered that the brain does not decrease its activity evenly across all areas when entering sleep. A form of alpha wave activity (electrical signals in the frequency range of 8-12 Hz that are linked to relaxed states) spreads from the front of the brain to the other areas before fading away. The frontal cortex is associated with attention (among other things), and it may be that the hypnagogic state results from the progressive defocusing of attention. This could cause a reduction in normal perception filtering, resulting in loosely connected thoughts and unusual experiences.

Electroencephalography (EEG) measures electrical activity from the brain, through small electrodes attached to the skull. The electrical signals are generated by neurons and the amount of synchronous neural activity results in characteristic EEG waveforms. Beta activity (above 14 Hz) is usually linked to high levels of mental effort and cortical activation, characteristic of the waking EEG. As mental activation decreases and sleepiness appears, both alpha (8-13 Hz) and theta (4-7 Hz) activity become more prominent. Delta activity (activity below 4 Hz) is associated with deep, "slow-wave" sleep.

Some scientists have argued that the hypnagogic state is not necessarily sleep-related and may be the result of a reduction in meaningful perceptual information, perhaps leading to defocused attention or other similar effects. A study published in 20022 aimed to test this by comparing hypnagogic states with a condition in which awake participants were fed unstructured sensory information in the form of white noise and diffuse white light. The researchers used EEG recordings and found that, although participants in both conditions reported unusual visual experiences, the pattern of brain activation were quite different, suggesting that hypnagogia is more than just the result of relaxation and lack of structured sensory input.

One problem with recording electrical activity from the scalp is that activity from structures that lie deep in the brain may not be detected. This means we could be missing important information when it comes to understanding what happens as we slip from consciousness into sleep, and even back again into wakefulness (known as the hypnopompic state)particularly as deep structures (such as the brain stem, pons, thalamus, and hypothalamus) are known to be crucial in initiating and regulating sleep.

An ingenious study published in Science did manage to investigate the role of some of the deeper brain structures in hypnagogia,³ specifically the medial temporal lobes, which are particularly linked to memory function. The researchers asked five patients who had suffered medial temporal lobe damage to play several hours of Tetris. Damage to this area of the brain often causes amnesia, and the patients in this study had little conscious memory for more than a few minutes at a time. On one evening, some hours after their last game, the players were woken up just as they started to doze and were asked for their experiences. Although they had no conscious memory of playing the game, all of the patients mentioned images of falling, rotating Tetris blocks. This has given us some strong evidence that the hypnagogic state may be due (at least in part) to unconscious memories appearing as unusual hypnagogic experiences.

In Real Life

Many authors and artists have been fascinated by this state and have tried to extend or use it to explore ideas or gain inspiration. To name a couple, Robert Louis Stevenson's The Strange Case of Dr. Jekyll and Mr. Hyde and many of Paul Klee's paintings were reportedly inspired by hypnagogic experiences.

End Notes

1. Tanaka, H., Hayashi, M., & Hori, T. (1997). Topographical characteristics and principal component structure of the hypnagogic EEG. Sleep, 20(7), 523-534.

2. Wackermann, J., Putz, P., Buchi, S., Strauch, I., & Lehmann, D. (2002). Brain electrical activity and subjective experience during altered states of consciousness: ganzfeld and hypnagogic states. International Journal of Psychophysiology, 46(2), 123-146.

3. Stickgold, R., Malia, A., Maguire, D., Roddenberry, D., & O'Connor, M. (2000). Replaying the game: Hypnagogic images in normals and amnesics. Science, 290(5490), 350-353.

See Also

· Although this is quite an old paper now, it is still one of the best reviews of the history, phenomena, and techniques associated with the hypnagogic state. Schacter, D. L. (1976). The hypnagogic state: A critical review of the literature. Psychological Bulletin, 83(3), 452-481.

Vaughan Bell

Date: 2015-12-11; view: 961

<== previous page	\|	next page ==>
Hack 88. Think Yourself Strong	\|	Hack 92. Make the Caffeine Habit Taste Good

doclecture.net - lectures - 2014-2025 year. Copyright infringement or personal data (0.981 sec.)