Building The Knowledge


London Taxi Photo: David Iliff, License: CC-BY-SA 3.0


The classic source of information for a newcomer in any major city was the taxi driver. Usually they knew their city in detail and would drive you around the important features, (for a fee of course,) while educating you in the politics and the comings and goings of the important and beautiful people of the place. Now the GPS has replaced that detailed mental map and you get more politics and gossip than education.

London, though, is hanging on to tradition. GPS units are not for the London cabbie who needs to find short cuts to dodge the usual traffic jams. The cabbie’s job needs more brain than can be found in a little box of electronics. Flexibility and instant decisions are required in addition to the map.

To get a Hackney Cab License in the City of London, a potential cab driver has to study hard to acquire “The Knowledge”. It can take about four years to pack the details of 320 routes around Charing Cross into one's brain. Details, details and more details have to be instantly recalled. How many of us could instantly recall any one of 25,000 different streets let alone not fail to mention one of 20,000 landmarks when asked.

That’s a lot of “Knowledge” to stuff into anyone’s head and Woollett and Maguire of U College have followed the stuffing process with 79 prospective London cabbies. Of course, the big magnet was rolled out and fMRI scans were done over the four-year training period (along with controls of course).

Some of the candidates showed increasing gray matter building up in the front part of their brains, their posterior hippocampi to be exact.  These guys passed the test and got their licenses. The ones whose brains didn’t change failed and are now going by bus.

It is interesting to note that their heads didn’t get bigger to accommodate the fresh gray matter. It appears that the failing potential cabbies were able to do better on complex visual memory tasks than the passing ones. So it seems that the spatial memory required for  “The Knowledge” takes up a lot of space and crowds out other functions. All part of the price for getting a license to drive the rich and famous as well as you or I, I suppose. 
  1. http://www.bbc.co.uk/news/health-16086233
  2. K. Woollett & E.A.Maguire, J. Curr. Biol, (2011), doi: 10.1016/j.cub.2011.11.018

Eyeing Up The Opposition, or Is Compounding The Solution?


In yesterday’s post, the topic was our visual perception. Clearly, our eyes are very sophisticated sensors and one of our great assets is our ability to focus on objects at both long and short distances. Color is also of critical importance in the resolution of shapes. Some birds and mammals have sharper visual acuity than us, but we do pretty well.

The majority of creatures out there now, and in the past, don’t have our type of eye, though. Most have compound eyes made up of hexagonally packed units or ommatidia. Each unit has a lens and an arrangement of pigment cells to ensure that only light that comes full on gets focused onto the nerve cells, so there is no peripheral information coming into that unit.

That would be pretty limiting if there were only one unit, though. But with a large number of units packed together on a curved surface a nice pixelated picture is formed. The resolution depends on the number of pixels.  At the bottom of the pecking order is the grasshopper with only 5 compared to a dragonfly with 30,000.

The downside of the compound eye is the distance problem where far off objects are not resolved. For good resolution, they have to be pretty close. However, motion is well resolved as movement across the field of vision produces a flicker effect. Really nice for close up and personal hunting, which is one reason dragonflies have been successful for such a long time.

Eyeing today’s pixelated version of the Guardian, my attention was drawn to a report of fossilized eyes from the early Cambrian period, that is over 500M years ago (1, 2). The large sea-going insect was an Anomalocaris that had large compound eyes on stalks. The 16,000 ommatidia in each eye would have made it easy to spot lunch as it swam around close to the bottom looking for large trilobites to bite.

Having great sensors must have been of critical importance, even rivaling sex as the number one priority way back in the Cambrian and even the pre-Cambrian era – as it is today, of course.

  1. http://www.guardian.co.uk/science/2011/dec/07/predator-compound-eyes-stalks-cambrian
  2.  J.R. Paterson et al, Nature, 480, 237, (2011).

Emotive Colors


We have a sophisticated set of sensors that we use everyday and usually take for granted. But in interpreting the electrical signals from the sensors our brain has to do a great deal of processing whilst multitasking. Cross-talk occurs, of course, and this is often put to good use. As we build up our databank through experience, we can cut the processing time and jump to the final result, which may not always be correct. There are many examples of optical illusions with which we’ve been entertained.

Our everyday world seems to be three-dimensional and change with time, so our brains are geared to turn the signals from our retinas into an understanding of the three-dimensional forms in front of us. Light, shade and perspective is what we think of immediately as supplying those clues, and artists have been working their magic with these since the renaissance.

Apparently surface texture is also a major clue to shape. Fleming et al in the Proceedings of the National Academy of Science, (1), have shown 2-D shapes patterned from random (“white”) noise and their subjects saw 3-D shapes. The more intense the pattern, the more 3-D the shape appeared to be.

Sometimes the cross-talk can be interesting, though. An extreme example is seen with people who are synesthetic and see sounds as distinct colors. Some recent work by Ludwig et al has shown that this interaction between sound and color is widespread (2). Of course, you and I expected that already.

The sound/color experiment used thirty-three humans and six chimpanzees. (Note; that there were no political implications in the choice of participants.) The candidates had to classify black or white squares while listening to background noise. The noise was irrelevant to the task in hand and was either high pitch or low pitch.

Both humans and chimps found it easier to pick out the white squares when the sounds were high pitched, and the black when it was low pitched. So high noises are brighter (higher luminance) and low pitched are darker. One has to think about film background music when the low notes dominate and our spines shiver, and then it’s all over and the music gets lighter and higher as we move into the sunshine, and all is well after all.

  1. http://www.pnas.org/content/early/2011/12/05/1114619109.full.pdf+html 
  2. http://www.pnas.org/content/early/2011/11/29/1112605108.abstract 

Happy Hour Could Last All Day


Much of the world is feeling the economic pressure with lack of jobs, home equity shrinking, and no sign of politicians getting on with their job effectively. The speculators seem to be having it all their own way. Ireland was riding high just a few short years ago and now their austerity measures are resulting in a lot of glum faces.

The Irish Times reported a few days ago that the suicide rate in Ireland last year was 8 to 10 times higher than in the ‘60s (1). These were figures discussed at a metal health forum held in County Clare. Dr. Bhamjee urged the members of the forum to recommend that the politicians should act to reduce the rate by running an experiment to add Lithium salts to the water supply of a town to determine the best level to control the depression of the population and thereby reduce the suicide rate (1,2).

After all, the government was already adding fluoride, so this would not be much of a philosophical change. It could help the 200,000 depressed Irish and there would be no chance of getting addicted to the drinking water, as the Lithium levels would be very low. It is well that he didn’t suggest it be added to the Guinness.

To those of us already spending far too much money on bottled water, the proposal will be making us nervous, but it is backed up by two studies both indicating good results that more Lithium meant fewer suicides.

One study was done in Texas a long time ago by Schrauzer and Shresha in Biol. Trace Elements Res. 105, 25 1990 using data from 1978 – 1987 (3). They found levels between 70 and 170 µg/L reduced not only the suicide rate, but also the rates of rape and homicide. They followed this up with analysis of the 1981 – 1986 data to show that arrests for possession of “hard” drugs were lower in those areas, although drink-driving and marijuana possession rates were unaffected.

The other study was more recent and was carried out by Prof. Terao and his team of the Oita prefecture in Japan. This study is published in the Brit. J. of Psychiatry, 464, 194, 2009 (4). They confirmed the trend for a reduced suicide rate and indicated that 50µg/L would do the job. They did not, however, check crime statistics. 

They did note that the lithium, which was naturally occurring in the water (as it was in Texas), had been drunk for a long time and that was why such low levels were sufficient.If our politicians decide to dose us before the results of the next election are known, it may well be at a higher rate.

  1. http://www.irishtimes.com/newspaper/ireland/2011/1202/1224308474582.html
  2. http://www.improbable.com/page/2/
  3. http://www.ncbi.nlm.nih.gov/pubmed/1699579
  4. http://bjp.rcpsych.org/content/194/5/464.full