A Ticklish Problem

You can easily make your niece giggle and squirm by tickling her. But no matter how ticklish you are, you can’t tickle yourself. Why not?

What is a tickle?

It’s a sensation between an itch and a brush, yet it can often provoke laughter and a pleasant response. It can play a social role. Your niece may merely giggle because of the sensation, but it could also be due to conditioning – tickling might be a learned way for adults and children to bond, for example. Tickling can also be a form of couples-bonding or sexual foreplay – perhaps the laughter and retreat may be a way of showing some level of submission to your partner.

So why can’t you tickle yourself?

Part of this may be psychological. If social conventions play a role, you may not react because tickling yourself involves no interaction with another person. This is not the whole story, however as studies have shown that tickling by a perceived machine is as effective as tickling by another person.

So it probably comes down to prior knowledge. When you move your hand, your brain accurately predicts the movement and then attenuates or dampens responses at the expected tickle location.

Experiments using a progressively less controllable robotic arm showed that as the ability to predict the touching sensation is reduced, the tickliness increases. When another person (or machine) tickles you, you cannot predict the motion exactly and thus it feels more tickley.

References

Blakemore SJ, Wolpert D, Frith C (2000) Why can’t you tickle yourself? Neuroreport 11(11):R11-6.

Blakemore SJ, Wolpert DM, Frith CD (1998) Central cancellation of self-produced tickle sensation. Nat Neurosci. 1(7):635-40.

Harris CR, Christenfeld N (1999) Can a machine tickle? Psychon Bull Rev. 6(3):504-10

Selden ST (2004) Tickle J Am Acad Dermatol. 50(1) 93-7

Mind over mortality

Can the will to live triumph death and disease?

This is a difficult theory to test. Since it is impossible to predict exactly when someone will die, it is not possible to see if a will to survive will keep them alive longer.

A number of studies have looked at personality variables such as positivity and calmness on longevity. These have shown that contentedness, both early and late in life is linked to slightly longer life spans. Indeed mortality rates for the neurotic, unhappy and angry elderly people were often more than twice that of their contented peers.

It is possible that happier people have a stronger will to live. Or, conversely, that healthier people (who are more likely to live longer) are happier.

But happiness should not necessarily translate into a stronger will to live. Hasn’t everyone heard of the grumpy old grandfather hanging on just to spite the relatives? It could be that reduced mortality in the chirpy set is due to the health benefits of stress reduction.

So how could you test the will to live? Scientists have looked for occasions people may wish to live for. Religious, cultural or family-oriented days may provide a focal point – perhaps grandpa can will himself to live until his birthday so that he can see his family once again.

Thus a number of studies have looked at death rates before and after major events. These have included birthdays, Christmas, Passover and Chinese lunar celebrations. By testing specific events which are only important for a selection of the population at any one time, mortality rates can be compared between those for whom it may be important, and those for whom the date is irrelevant.

Many studies have demonstrated reduced death rates prior to such occasions, with a significant surge directly after the event. The importance of these events has apparently delayed deaths from diseases including cancer and heart disease.

No clear mechanism is obvious. Possible explanations have included reduced stress levels, better adherence to medication schedules, benefits of companionship or some psycho-biological process as a results of religious or emotional feelings.

There are confounding factors. Many of these events involve over-indulgence and high fat meals are known to cause heart attacks. Also, the holidays can be very stressful. This could lead to slightly higher death levels after the holiday. Only a few studies take into account the cause of death. Road deaths from drink driving or celebratory shootings (this is an American term relating to people accidentally killed when people shoot guns to celebrate holidays) and other such seasonally affected events may skew calculations.

Indeed reanalysis of the data presented in many of these accounts often alters the conclusions. Secondary research re-examining the spread of diseases covered, the specific time periods before and after an event and the calculation of the mortality percentages seems to deny any effects of willpower.

So, while tantalising, the evidence is not conclusive. Though, if I were a betting person, I would put money on willpower overcoming death in the short term. From personal experience I have seen the terminally ill hang on months beyond the best estimates of doctors, only to fade fast when they suddenly lose the will to survive.

References

Skala JA, Freedland KE (2004) Death takes a raincheck Psychosom Med. 66(3):382-6.

Danner DD, Snowdon DA, Friesen WV (2001) Positive emotions in early life and longevity findings from the nun study. J Pers Soc Psychol 80: 804–13

Lee P, Smith G. (2000) Are Jewish deathdates affected by the timing of important religious events? Soc Biol. 47(1-2):127-34.

Phillips DP, King EW (1988) Death takes a holiday: mortality surrounding major social occasions Lancet 2(8613):728-32.

Phillips DP, Smith DG (1990) Postponement of death until symbolically meaningful occasions JAMA 263(14):1947-51.

Smith G. (2004) Asian-American deaths near the Harvest Moon Festival.
Psychosom Med 66(3):378-81.

Wilson RS, Bienias JL, Mendes de Leon CF, Evans DA, Bennett DA (2003) Negative affect and mortality in older persons Am J Epidemiol. 158(9):827-35.

Wilson RS, Mendes de Leon CF, Bienias JL, Evans DA, Bennett DA (2004) Personality and mortality in old age J Gerontol B Psychol Sci Soc Sci 59(3):P110-6.

Young DC, Hade EM. (2004) Holidays, birthdays, and postponement of cancer death.
JAMA 292(24):3012-6.

Cocktails and hearing aids

It’s a Saturday night and you are going out. You can hear the bass beat a block before you get to the party. As you walk into the house, you are surrounded by people talking, the clinking of glasses and the ever-present music. Waving at you, the host appears and asks “What would you like to drink?”

It’s a common enough opening, and the interesting part is not the drink of choice, but how you could understand the question.

Every day, in buses, trains, crowded restaurants and open plan offices, most people easily understand other people talking. It hardly seems exciting and yet it has fascinated scientists for over half a century – ever since Cherry first described “the cocktail party problem”. The mechanisms underlying this talent are still not fully understood.

Why is it such a mystery?

The ear hears by collecting soundwaves and passing them along the ear canal, though a series of small bones, to the inner ear, where the soundwaves vibrate the basilar membrane (a tiny organ curled inside the spiral cochlear). The basilar membrane tapers along its length and different parts vibrate depending on the frequency of the sound waves. The narrow end vibrates in response to high frequencies (high pitch sounds), and the wide end to low frequencies (low pitch sounds). Hair cells pick up the vibrations and pass them along into the brain.

Since sounds are comprised of a number of frequencies (the average human voice ranges from the buzz of a mosquito to the highest note on a piccolo), all sounds sum to create the vibrations. Thus your brain knows only which frequencies are present in a room of noise, not which frequencies belong to the person you are trying to hear.

So how can we isolate just one person?

The tempo of their speech is different from that of the music, the conversation flows unlike the sporadic clink of glasses; they may have a lovely accent or a deep voice. Similarly hand gestures, facial expressions and lip movements also add to the experience. All of these speech cues can help you work out which sounds belong to the person you are listening to and which to unwanted intrusions.

Expectation is a factor. When someone is speaking about the latest football results, you can safely ignore any words and phrases relating to politics.

Having two ears also helps. Speech coming from a person on your left side will hit your left ear first and be louder in that ear than in the right ear. The brain can then use that time and volume difference to separate frequencies belonging to that person from those belonging to someone standing on your right.

But all this is done without thought. Can you consciously help?

How often have you missed a sentence because you “weren’t paying attention”? Concentrating on a person makes it easier to follow them. But when you concentrate on understanding a person, are you attending to their accent? their location? the cadence of their speech? or a mix of everything? Experiments are currently trying to work out which factors you can attend to and how this attention can make understanding easier. For example, do you increase your brain responses to speech when you are paying attention or do you just put more resources into interpreting the responses you subconsciously receive?

Who cares HOW you understand since it’s so easy?

If you don’t already, you will. As you age you will slowly lose the ability to listen to a friend in a noisy environment. This is the greatest hearing-related complaint from the aged and from hearing aid users.

Until we understand how a person with normal hearing can solve the cocktail party problem, we cannot work out what is going wrong as people age, nor can we design better hearing aids or assist those with impairments.

So next time you are offered a drink at a noisy party, spare a thought for your auditory system. Chances are its miracles are being wasted on acquiring luke-warm chardonnay.

References

This is the topic of my thesis, so to date I have well over 200 references. They would not all fit here, so I shall limit the list to the original paper that started the scientific debate:

Cherry EC (1953) Some experiments on the recognition of speech, with one and with two ears. J. Acoust. Soc. Am. 25: 975-979