The sections below provide more information on some of the topics covered in the Senses show. Click on the link above to switch between this page (on vision) and the page covering the hearing demonstrations.
Other visual illusions can be found on our Survival show page.Experiment #1: Synaesthesia
Click the image or link below to visit our page with more information about the peculiar jumbling of the senses that is synaesthesia, as well as to try your luck with a variety of number-colour synaesthetic pictures.
Recognising the face
As we discussed in our show, several parts of the brain are responsible for the recognition of aspects of the face. The fusiform gyrus in the temporal lobe does, however, appear to be particularly important in facial perception.
In particular, the brain is exceptionally sensitive to small changes in the shapes of the eyes and mouth. This makes evolutionary sense for humans, since so much of our understanding of the emotional state of another person comes from detecting subtle changes in these parts of the face. Primates in general, and humans in particular, recognise not only individual faces, but also pick up important communication and emotional cues from the eyes and mouth (in particular the corners: see below).
We can show that the shapes of the eyes and mouth are overwhelmingly important with the upside-down face images below, a couple of which you'll have seen during the show.
Subtle clues, and da Vinci's genius?
As we've described above, the corners of the eyes and mouth are particularly important in working out the emotions of the person we're looking at. These are high-spatial-frequency parts of the face, and the visual system appears to respond to extremely tiny changes in their state.
If we take a picture of a face, and blur the corners of the eyes and mouth, people find it much more difficult to work out exactly what emotion the face is showing.
One possible example of this in art is the Mona Lisa, painted by Leonardo da Vinci, which has long been held to have an "ambiguous" expression, or 'mysterious smile'. If we examine the painting in detail, we can see that, after painting the face, da Vinci carefully smudged and blurred the corners of the woman's mouth and eyes! It would appear that he had great insight into what makes our visual centres tick...
Optical illusions are often fun to look at, but many of them have been designed (or discovered) to highlight the way in which the visual system works. A good example is the Tri-Zonal Space Warper (below), invented by magician Jerry Andrus in the mid-1970's, which illustrates a phenomenon known as the Waterfall Effect, an example of neural adaptation. You can click on the links below to download animated GIFs of the effect: for the larger versions you'll need to have a reasonably powerful graphics card, in order that the image rotates smoothly, without jerking. (The scalable image below is a mathematical set of curves based on a scan of my [Peter's] copy of the original space warper, which was published in OMNI magazine, way back...)
Once you look away at, say, the back of your hand, your visual field sees (for ten seconds or so) movement in the opposite direction: parts of your hand seem to bulge outwards, and others to go inwards, giving a strange, rippling effect. (You'll notice that if you stop the spirals hitting ESC will do that they'll appear to spin back the other way, for a second or two.)
Colour adaptation: two amazing examples
We couldn't spend much time during the show discussing colour-blindness, but (apart from the links below) we have some information on how you can create your own colour blindness test charts. You'll need access to a program such as Photoshop (or Illustrator), using which you can draw in specific colours, to create images such as the one below. Click on it (or the text) for more information.
Perception: the final film
Having looked briefly at the way in which the senses gather information from the outside world, and also at the ways in which regions of the brain process that information (and on ways in which both can be affected by damage or age), the final part of our show touches briefly on the ways in which we have to focus our attention on the information which has been gathered and processed.