Evidence is presented that in the early stages of design or composition the
mental processes used by artists for visual invention require a different type of
support from those used for visualising a nearly complete object. Most research
into machine visualisation has as its goal the production of realistic images which
simulate the light pattern presented to the retina by real objects. In contrast sketch
attributes preserve the results of cognitive processing which can be used
interactively to amplify visual thought. The traditional attributes of sketches
include many types of indeterminacy which may reflect the artist's need to be
Drawing on contemporary theories of visual cognition and neuroscience this
study discusses in detail the evidence for the following functions which are better
served by rough sketches than by the very realistic imagery favoured in machine
1. Sketches are intermediate representational types which facilitate the
mental translation between descriptive and depictive modes of representing visual
2. Sketch attributes exploit automatic processes of perceptual retrieval and
object recognition to improve the availability of tacit knowledge for visual
3. Sketches are percept-image hybrids. The incomplete physical attributes
of sketches elicit and stabilise a stream of super-imposed mental images which
amplify inventive thought.
4. By segregating and isolating meaningful components of visual
experience, sketches may assist the user to attend selectively to a limited part of a
visual task, freeing otherwise over-loaded cognitive resources for visual thought.
5. Sequences of sketches and sketching acts support the short term episodic
memory for cognitive actions. This assists creativity, providing voluntary control
over highly practised mental processes which can otherwise become stereotyped.
An attempt is made to unite the five hypothetical functions. Drawing on the
Baddeley and Hitch model of working memory, it is speculated that the five
functions may be related to a limited capacity monitoring mechanism which makes
tacit visual knowledge explicitly available for conscious control and manipulation.
It is suggested that the resources available to the human brain for imagining nonexistent
objects are a cultural adaptation of visual mechanisms which evolved in
early hominids for responding to confusing or incomplete stimuli from immediately
present objects and events. Sketches are cultural inventions which artificially
mimic aspects of such stimuli in order to capture these shared resources for the
different purpose of imagining objects which do not yet exist.
Finally the implications of the theory for the design of improved machine
systems is discussed. The untidy attributes of traditional sketches are revealed to
include cultural inventions which serve subtle cognitive functions. However
traditional media have many short-comings which it should be possible to correct
with new technology. Existing machine systems for sketching tend to imitate nonselectively
the media bound properties of sketches without regard to the functions
they serve. This may prove to be a mistake. It is concluded that new system
designs are needed in which meaningfully structured data and specialised imagery
amplify without interference or replacement the impressive but limited creative
resources of the visual brain.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University. NOTE: Images removed for copyright purposes.