by Matthew Cobb
We all know about visual illusions, and the way that psychologists and neuroscientists use them to develop and test hypotheses about how the visual system works. Other kinds of sensory illusions are a bit trickier, however. ‘Phantom limb’ syndrome where amputees imagine they still have their limb (and, sadly, often feel pain in it) is an example of a touch illusion. And the ‘burning’ sensation you get from eating chili or curry is due to the fact that the pain receptors on your tongue (or your mucus membranes – ouch!) are activated by the capsaicins in the spice. It doesn’t ‘really’ hurt. Or rather, it hurts, but there is no damage being done.
This website contains 10 of the most fascinating auditory illusions. [NB – the sound files are linked to the small grey box *below* each text box describing the illusion.] Some of them are illusions that are like visual illusions. Such as number 7 (‘Falling Bells’): ‘This is a recording of a paradox where bells sound as if they are falling through space. As they fall their pitch seems to be getting lower, but in fact the pitch gets higher. If you loop this sample you will clearly see the pitch jump back down when the sample repeats. This reveals that the start pitch is obviously much lower than the finishing pitch.’
But perhaps the most striking examples are only an illusion in the way perspective is a visual illusion – you can perceive something in 3-D that’s only really in 2-D. Hear (!) you perceive something in space, when it’s just in your head. These are examples of ‘dummy head’ recording. Number 5 – ‘Virtual Barbershop’ features a session at the barber’s and is stupendous when listened to on headphones. The final seconds are great! Number 4 just features a box of matches.
If you want to know more about the science behind this, go to the web-page of Diana Deutsch, Professor of Psychology at San Diego, who developed many of these sound files.
h/t : Fellow fly-man Walton Jones.