I have been reading up on drawing - the complex interplay between visual observation and hand coordination required to make a pencil record of what an artist or scientist sees either with the naked eye or with optical aids (lenses, mirrors, camera obscura, camera lucida).
This is clearly of direct interest in art (e.g. the Hockney-Falco thesis) but it is also of real interest in the history of scientific illustration (from the work of Galileo, through that of Audubon to the camera lucida work of Harry Whittington in the Burgess Shale) - as ET put it in Beautiful Evidence "Science and art have in common intense seeing, the wide-eyed observing that generates empirical information".
As mentioned previously with respect to Ruskin drawing forces us to really see. This is true for science as well - Prof Harry Whittington, one of the lead academics on the re-analysis of the Burgess Shale fauna, reflecting on his methods said the following on the occasion of the award of the Geological Society's Wollaston Medal to him in 2001;
"I soon realised, in my work on Burgess Shale fossils, that explanatory drawings would be needed as well as photographs, to describe these fossils. This is where Dr Wollaston enters the scene - a late 18th to early 19th Century physician, who practised in London for many years, and made valuable contributions to chemistry and optics. He had a cracked shaving mirror, but instead of throwing it away he puzzled over the refractions and reflections of light caused by the cracks.
This led to his realising that by inserting a prism into a microscope tube, the image could be directed laterally, then down on to paper beside the microscope, and provide a way to draw an accurate picture. In much refined form this is his invention, the camera lucida, which I used to make my drawings."
Our ability to make detailed records of what we observe is dictated by our artistic ability and the capacity of the human eye-brain-hand system. Drawing is an extremely complex and interesting process requiring high levels of motor co-ordination and only achieved by long practice.
To illustrate this complexity the figure below will repay careful study. It shows a montage of data that was extracted from a study by John Tchalenko and colleagues at Camberwell College of Arts. http://www.arts.ac.uk/research/drawing_cognition/.
In this study they used an eyetracker, movement sensor and close-up video to study how the painter, Humphrey Ocean, drew portraits. Their analysis concentrated on the painter's eye-hand coordination. They observed that in general his eye closely followed the drawing hand, with fixations on, or very near, the line being drawn. They also found frequent exceptions to this behaviour when the artist's eye moved from the drawing hand to look at other parts of the drawing or he turned to look at the model. The study concludes that they show evidence, `illustrating the process of visual memory fading and refreshing, and the possible action of a motor memory component in the drawing method of this painter'.
The figure to the right shows data about the fixation of the eye above the horizontal line and data about the position of the hand below it as the artist composed the portrait of Nick to the left. In both cases vertical distance away from the horizontal line corresponds to physical distance away from the paper; which is the physical fulcrum of the exercise (eye, pencil and paper come together). There is an initial period of practice during which no contact is made between paper and pencil but the eye flicks back and forward from the model to tracking the pencil. Then the eye focuses on the paper and immediately fater the pencil hits the paper to begin the first four strokes H1-H4. These take 2.68 seconds and a total of 10 cm of pencil stroke is created. The eye evaluates what the pencil has done then back onto the model and so on.
The graphic is quite special - the physical paper is represented by a horizontal line and the two times series (eye data and hand data) are running in synchrony.