Psychophysics Content from the guide to life, the universe and everything


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Psychophysics, believe it or not, is a genuine academic subject. You can get books about it and everything. The reason this has to be made clear from the outset is that its name simply sounds too good to be true. Psycho... physics. Wow.

Well, we all know what physics is: it's all about Grand Unified Theories and big bangs and time dilation and black holes and sub-atomic particles moving at mind-boggling speeds and seriously cool stuff. As for the 'psycho' bit, it's equally well-known that a psycho-subject has to be more intense and meaningful than an ordinary subject: that a psychodrama is deeper and more gripping than a regular drama, and that your psychosexual problems reveal more sensitive and intriguing facets of your character than your run-of-the-mill sexual problems. The mere mention of psychology conjures up ideas of the dynamic tension between ego and id1, the nature of consciousness; our subconscious urges.

Psychophysics is the study of how our brains use the information from our senses. The brain is very good at doing very complex processing: for instance, we can make sense of the odd jumble of shapes and shadows we are looking at and recognise it as a face. We can recognise the shapes that make up a coffee mug, despite having never seen it before from that precise angle, and we can work out how far away it is and how to pick it up. We can track a person walking across a crowded room, and we can disentangle what they are saying from the hubbub around them. We can work out where a sound is coming from, despite the fact that echoes of the same sound are coming from all directions off the surrounding walls.

All these processes are complex. The tasks mentioned may seem easy to you, but that is only because you are using a frighteningly sophisticated bit of processing technology to help you do them - your brain. It would, for instance, be very difficult to programme a computer to do the same things: computer scientists have made a start on this, but at the turn of the millennium, artificial seeing and hearing systems are no match for the brain of even a simple animal. This is because we don't know much about how the brain is doing it. Psychophysicists aim to find out how exactly the brain works.

Psychophysics is related to psychology because it concerns human behaviour and human mental abilities. It involves experiments that try to 'look inside' the brain, without all that ethically dubious mucking around with monkeys and electrodes. Such an experiment might involve, for example, testing people to see whether they can tell the difference between two subtly different visual images, or two sounds. If a person can tell the difference between two images, that tells you about the sort of information the brain can use. If they cannot, that tells you about the sort of information the brain cannot or does not use. The results can be used, for example, to make images and movies on the Internet take up less disk space, by removing a lot of information that the human brain wouldn't be able to use anyway. This is the basis of the JPEG and MPEG compression methods, among others.

Psychophysics is related to physics because it involves subjects like light and sound, which are areas that scientists understand fairly well on a physics basis. Understanding how light gets refracted through a lens helps us understand how much information can get in through our eyes onto the retina, so we can work out what input the brain is receiving. Any pattern of light or sound (any images or noise) can be described mathematically, using equations. That doesn't mean that the thoughts and feelings you get while looking at a picture can be reduced to equations, but the picture itself can be. If that weren't the case, then television wouldn't work. A psychophysicist would start with these equations, and then use experiments to work out what aspects of those equations are important when the brain analyzes a visual scene. The end goal is to have an accurate idea2 of how the brain is extracting the relevant information from what it sees and hears.

The history of psychophysics is short as sciences go. It's only about 100 - 150 years young, having begun in the 19th Century with people like Hermann von Helmholtz (remember Helmholtz coils from physics at school?) and Ernst Mach, the same guy who gave his name to things that go faster than sound, as in Mach 1. Up until now, psychophysicists have concentrated on using very simple abstract images and sounds in their experiments; images and sounds that are easy to describe mathematically. As a result, the fruits of their research, while making for good copy in the Scientific American, can sometimes seem a bit simplistic in terms of actual benefit to the world. But hang on a minute - understanding the human brain is a tall order; it is more complex than any other object yet discovered or manufactured. Things are improving: more complex (and hence more realistic) stimuli are beginning to be used, and techniques for analysis are getting better. In the year 2000, a computer that can recognise people and objects as well as a human can is still some years in the future, and the idea of, for example, a camera that can plug into a blind person's brain and allow them to see, sounds like science fiction. However, these things already exist in crude form, and psychophysical research will help to refine them and make them a more useful part of everyday reality.

Vision Science Links

1The id is the part of the mind where impulses and primary processes appear.2An idea that can be written down, again, as a bunch of equations.

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