University of Edinburgh

Tactile Graphics

CHAPTER SEVEN: The depiction of scenes

7.1 The information available in pictures

Gibson observed two conflicting theories of what a picture is. The first theory assumes that it consists of a sheaf of light rays coming to a station point or perceiver, each corresponding to a spot of colour on the picture surface. (Reed and Jones, 1982, p 272).

The second theory assumes that it consists of a set of symbols, more or less like words and that a painting is comparable to a written text. (Reed and Jones, 1982, p 274). On the first theory a picture could represent a real object or scene, insofar as the light rays from the picture are the same as the light rays from the original. On the second theory, a picture can stand for a real object or scene, insofar as the language of pictures is understood. It also implies that one has to learn to 'read' a picture, much as the child learns to read written speech, but the first theory suggests that as soon as a child can perceive an object directly, he can perceive it in a picture. (Ibid, p 267). Gibson points out that the point projection theory can only strictly apply to a painting or a photograph and not to a line drawing and in fact does not apply if the viewer's vantage point is changed. There is no point-to-point correspondence of brightness or colour between the optic array from a line drawing and the optic array from the objects represented.

This theory also cannot explain the situation which pertains in cartoons. The cartoonist's drawing of a man is not even a faithful projection of the shape of his features and his body and yet it may be faithful to those features of the man that distinguish him from all other men find thus may truly represent him in the higher sense of the term. It may be uniquely specific to him - more so than a projective drawing or a photographic portrait would be. Even where a political cartoonist deliberately distorts and plays with a representation of a face for humorous reasons, recognisable characteristics of the face are preserved. That is part of the skill of caricature.

This is, as Gibson asserts (loc cit) a compelling objection to the whole theory that pictorial information can be reduced to light rays. A caricature is not a mixture of optical projection and symbolic distortion but something different from either one. Gibson suggests that it is an effort at displaying relevant information.

In considering the symbol theory, Gibson points out that a picture is not simply a matter of symbolic language (Ibid, p 276). Gibson goes on to construct his own theory of pictorial information by whose formal definition, "a picture is a surface so treated that a delimited optic array to a point of observation is made available that contains the same kind of information that is found in the ambient optic arrays of an ordinary environment". (Ibid , p 277).

This definition is broad enough to admit the case of a caricature. An artist can capture the information about something without replicating its sensations. Indeed, for Gibson having sensations is at most only an accompaniment of perceiving, not a prerequisite of perceiving. (Ibid, p 361). Gibson then goes on to describe the emergence of invariants from the optic array and the way in which these invariants carry information which describes features of the environment. In looking at the world, one begins to see the elements of non-change underlying the changes. Primitive artists, eg; ice-age hunters, did not fully appreciate the changes in appearance of an animal from the from, the side, the rear and above, but they learned these things when they attempted to represent them and they learned from their mistakes.

Through experience it is possible to perceive the real size and distance of one of the objects represented in a picture, as well as the size of the representation; for example, in looking at a picture of a tree the distance and size of the tree and of its picture are not the same, for they are not in the same space, but it is nevertheless possible to perceive and estimate both. In the same fashion a picture of a room contains information for both the perception of the room space and the perception of the picture space.

It is also possible to have pictures of objects which do not exist in fact. There are pictures of mermaids, of buildings not yet constructed and of events that will never happen. (Ibid, p 281) The information provided by a picture is information for perceiving, in the widest sense of the term, not only for remembering something in the past but also for conceiving something in the future.

Displays which are ambiguous or reversible with respect to what is seen, have been interpreted as proving that perceiving depends more on the perceiver than it does on the external stimulus. The fact of two alternative percepts from the same drawing is very puzzling. The light to the eye has not changed when a pair of faces is seen instead of a goblet, but the percept has. If such drawings are analysed as sources of information instead of mere stimulation, the puzzle becomes intelligible. The information in the array is equivocal. There are two incompatible kinds of pictorial information in the light to the eye and the percept changes when the beholder shifts from one kind to the other. (Ibid) Kennedy (1974) has also studied and reported this question of equivocal representation in drawings of the edges and corners of surfaces in the world.

To speak of the information in an optic array does not imply that it consists of conventional symbols or that pictures constitute a language, for they are still subject to some of the basic principals of what Gibson calls ecological optics. The informative structure of ambient light is richer and more inexhaustible than the informative structure of language. Indeed, animals and people could see things long before people began to describe them and we can still see many things that we cannot, as yet, describe.

Picturing becomes a means of communication and a way of storing, accumulating and transmitting knowledge to successive generations of people in much the same way that speaking and hearing and reading and writing are ways of accumulating and transmitting knowledge. The difference is that picturing exploits some of the information in the structure of light. (Reed & Jones, 1982, p 283).

Not only do we perceive in terms of visual information, we can also think in those terms. The present writer would agree with Gibson that visual thinking is freer and less stereotyped than verbal thinking, but it would appear that to state as he does that 'there is no vocabulary of picturing as there is of saying' (Ibid) denies the effect of cultural experience on the viewer of a work of art, and also denies the stylistic conventions of modern advertising.

Gibson used his theory of visual perception as the basis of a theory of picture perception. It was then possible for him to distinguish between the pictorially mediated perception of the features of a world, and the direct perception of the features of the surroundings, and yet to understand there is common information for the features they have in common.

7.2 The perception of works of art

Some artists have expended a great deal of effort in attempting to create pictures which deceive the eye into believing that they really are the objects that they portray. Such paintings are commonly known as 'trompe l'oeil' and there are examples to be found in architecture and cartography as well. Unfortunately one of the characteristics of solid objects is that they look different from differing viewpoints, and a truly effective trompe l'oeil painting works best if it is mounted in a peepshow box so that one particular viewing point is imposed upon the observer. Thus trompe l'oeil paintings are a very special case.

All other paintings attempt to portray the world as seen by the artist, and using various approaches to the task of portrayal which vary through the eras of an history, and also vary according to the individual artist's style and intentions.

In certain works, eg; impressionist painting and caricatures, certain features which the artist takes to be the essence of the subject are emphasised in an uncommon way to portray the subject. Very often the artist's means are difficult to describe in words, and yet the message is understood, although it needs to be emphasised that this may require a measure of stylistic or cultural acclimatisation on the viewer's part.

Indeed, as Gombrich (1960) has pointed out, every artist is limited to the terms of his medium, and not one of the tones of a painting would correspond objectively to what we call the reality of the subject. (Ibid, p 30) The viewer can be conditioned into accepting and interpreting as reality representations which include negative images (Ibid, p 39) and other forms of illusion (Ibid, chapt VII) and can become attuned to transposed relationships between components of pictures, and gradients of colour and brightness and even to distorted viewpoints if necessary. (Ibid , pp 46 & 47)

7.3 Comparison with the tactile mode

The discussion of picture theory in this chapter so far has been confined to visual perception and visual pictures. These have been extensively discussed and written about for centuries and have been the subject of much research and philosophy in recent times. In comparison, tactual perception has been far less thoroughly investigated although JJ Gibson is one of the few writers with an interest in both senses, and his general theories are not incompatible with tactual phenomena. In particular his description of a recognisable invariant emerging from confusing background of sensations describes the touch sense equally well.

In the author's experience this is exactly what seems to happen in tactual exploration of an everyday object or a tactile picture. Recognisable features ('invariants') quickly emerge from an initial hand-scan and these can be identified and used.

In the present writer's experience caricature is of no direct use in tactile pictures for educational use. Present day teaching materials published in snappy cartoon style for 'user appeal' simply have to be depicted 'realistically' (though this term is itself problematic) when in tactile form. Otherwise the subject of the picture can be unidentifiable to the blind reader. The humorous distortions obstruct the message of the picture.

The same is true of any features of visual depiction which create ambiguities when they appear in a tactile picture. Laboratory experiments on figure/ground confusion may be very revealing to the experimental psychologist, but the educational diagram designer needs to take every precaution to avoid or minimise confusion and some of the techniques used have already been described in Chapter Six of this book.

This approach to interpreting visible information and picture information is of relevance to tactile pictures in that it directs attention towards the 'discontinuities' or boundaries of picture components and emphasises their importance to the emerging perception during a hand-scan, and the filtering process by which objects are located applies to touch as well as to vision. This is why questions of scale are important in tactile pictures. If the scale relationships are not clear, the blind user may completely misinterpret the picture. as in the dinner fork/human hand confusion mentioned in Section 6.1 in connection with one of Kennedy’s experiments (Kennedy 1974, p 152)

7.4 Depicting works of art for blind people

One extension of the research described in this book is the production of tactile versions of notable paintings from the National Gallery collection, under the auspices of a charity called the Living Paintings Trust. This trust had its formal development at the beginning of 1988 from a working party set up to explore the feasibility of interpretative materials on tape and in tactile form, designed to communicate the intentions and methods of the great painters to blind people who already had a practical interest in the arts.

It will be apparent that this kind of tactile picture has terms of reference markedly different from most educational diagrams, whose main intention is to describe a structure or process in such a way that the blind person can understand the principles involved. In such diagrams gross simplification or even distortion may be accepted in order that the educational principles may be conveyed to the user.

In rendering a work of art one has to be as faithful as possible to the intentions and methods of the original artist, while making the unusual transformation from a visual to a tactual medium. This is not to say that picture components will not have to be simplified; the smaller size on which one is working generally ensures that, if nothing else does. However, things cannot be modified simply at the will of the tactile artist or his user; there is a responsibility to the artist whose work is being portrayed.

In commencing this portrayal it would be possible simply to 'map' the canvas with stylised textured areas, or to attempt a flat strictly two-dimensional portrayal. Alternatively the task can be accomplished through a raised line drawing which merely marks out the limits of features in the painting, or what Kennedy (1974) calls 'visual discontinuities'. This has been done by other working parties, like the group in Finland known as 'Pictures for Listening' which is run by the Finnish Central Association for the Visually Handicapped and the Art Museum of the Ateneum. This group has confined its presentations to sparse line drawings or map-like presentations reproduced by the microcapsule process. (Personal communication)

It is the contention of the writer however that just as different painters have markedly different ways of using paint and colour to achieve their desired ends, so tactile representations would be doing blind people a great disservice if they did not attempt to convey these artistic differences if at all possible. If it is an impossible task then one might as well leave the project alone entirely; it becomes a sterile operation, and the task of description is better left entirely to the evocative power of words. 

7.5 Form and texture

In order to describe some of the problems and challenges involved in this task, this chapter will describe specific examples and discuss their effect on adult blind users of the tactile pictures.

The first such example concerns the depiction of water in oil-paintings. In discussing this, a congenitally blind person said, 'Well, water is just water isn't it? It's wet. Why should it be different from one painting to another?', (White, 1989).

The blind person knows water by its feel. It is uniformly wet. Its temperature may vary, and it may be still, rippled or wavy, but is otherwise very similar from place to place. The blind person thinks mainly of the mass or body of the water. He may have been told and remembered other characteristics such as its transparency, but never experienced them.

It was pointed out in conversation that the artist is generally depicting the surface of the water as it appears from a particular viewing-point. The appearance of this can change not only if it is wavy or still, but if the light falling upon it changes and is reflected differently to the viewer's eye. Reflections of surrounding objects are seen in it as in a mirror, although the mirror may be still and glassy or broken up into tiny independent pieces by ripples and waves. It is therefore the varying appearance of this water surface which the artist generally tries to convey.

This was described by a comparison between three situations in paintings:

(a) An even patch of water with no ripples and no noticeable reflections as in the canals of The Avenue, Middleharnis' by Hobbema. This was conveyed in the tactile picture by a smooth, glossy surface.

(b) A sea inlet with uniform wavelets painted as a regular pattern, as in Claude Ie Lorrain's 'Enchanted Castle'. This was depicted in the tactile version by a sheet of aluminium mesh on the master diagram.

(c) The surface of the river Thames on a misty morning as painted by the impressionist. Monet in his representation of ‘The Thames below Westminster'. Monet simply picks out the crests of the wavelets as they catch the light in small horizontal splashes of white paint. These were depicted in the tactile picture by horizontal blobs of cement of similar form to Monet's paint.

In a similar way Monet depicts a tree on the Thames embankment by using an array of blobs of paint of appropriate colour. It is interesting that just as the paint version is rather shapeless when seen at close quarters, but merges into a treelike form from a more distant viewpoint, so the tactile blobs coalesce into a treelike shape under the fingers.

One special problem in reproducing tactile versions of works of art is the need to illustrate features such as clouds, fog, reflections, and sunsets which are not solid but ethereal in nature. They are often essential to the understanding of particular pictures and so inescapable in the tactile portrayal.

Obviously any feature of a thermoformed tactile picture has a degree of solidity which is the property of the medium (a formed polymer sheet). It is, however, possible to minimise one feature in relation to the rest so that the perception appears less solid. This may still need some oral interpretation, but is nevertheless easier to understand than a picture where the inter-relationships are misleading. It was never the belief that these tactile representations of works of art would ever stand alone, however. They were designed to be used with a tape-recorded commentary.

One restriction on the tactile picture maker, particularly when his end-product is made of one material like a PVC thermoform or a capsule-paper print, is that he has at his disposal a relatively small palette of reproducible textures. This is the case even when the master pictures are predominantly modelled in cement as in the Living Paintings Trust pictures. Despite the variety of natural forms which appear on the picture, the surface textures are far less varied than the colour and shade palette of the visual artist . That this constitutes a restraint of the medium used is undeniable, but the effect on the final perception of the blind user is not as restricting as may at first appear. This is because the context in which each picture element finally appears influences the way that feature is perceived.

A simple example from the author's own work is the use of the aluminium mesh commonly sold for reinforcing fibreglass car body repairs in two entirely contrasting picture contexts. In the first the material was used to represent the ripple pattern of the water in Claude Ie Lorrain's 'Enchanted Castle' landscape already discussed. (Hinton, 1989b) In the second example, the same material was used to represent a cloth-of-gold shawl on which the infant Jesus was resting in the right-hand panel of the Wilton Diptych. (Ibid) Because of the completely new context there was no confusion for blind users of the picture. A blind person examining the two pictures in close succession, and questioned about the material used, would probably detect the similarity between the two picture elements, but in normal use the reader would tend to overlook this completely in searching for the wider meaning of the picture as a whole. (Hinton, 1990b)

For this reason all results of laboratory texture discrimination tests (eg; Nolan & Morris, 1971; Armstrong, JD, 1978) need to be considered with caution. Although they contribute useful information to our understanding of tactual perception and can guide the tactile picture designer's work, it is the picture as a whole which is most important in the end. Some elements which appear to work under laboratory conditions fail when incorporated into a diagram or picture; and conversely, some elements which appear to cause difficulty to blind users in laboratory trials are influenced by the context in which they appear in a diagram to the extent that the expected difficulty disappears.

In relation to texture and colour, the 'touch colour' suggestion of Elder and Tonelli (1982) in which colours and shades are indicated on a tactile picture by textured areas according to a code which they devised. The writer's entire experience of designing and making tactiles and of observing their use by people who are blind underlines the restricted 'palette' of textures which are available for effective use in tactiles, as compared with the vast array of tints and shading available to the visual artist.

In the wide range of tactile diagrams with which the writer is involved, the available diagram textures have important uses in describing the form and texture of the objects depicted, and occasionally as textural labels. One must also bear in mind the modifying effect of the medium in which the tactile diagram is made.

In this context, it appears to the writer that Elder and Tonelli's system conveys little of educational value to a blind person. Words would convey more, even in the absence of prior colour experience. At the same time their elaborate textural coding system appears to lock up textural effects which would be better used in ways which would be more informative to the blind person using the picture.

7.6 Perspective

For the person of normal vision perspective does not have to be understood to be used in the environment. A child learns to pick up visual clues which can allow it to make spatial judgements. To begin to do this it must move through the environment and learn by experience the relationship between the visual image and what will be experienced in reality. A baby learns this gradually, first by discovering its own body space, and then as crawling, and later, walking begin, discovers the relationships between 'other' things at first by relating them to itself. (Bower, 1974, pp 154ff) Phenomena such as the continued presence of an object which disappears from sight by being covered up by a cloth have to be experienced to be understood. (Ibid, p 187) With more experience the ability to interpret a scene in spatial terms becomes more widely developed.

If the visual field has a lot of depth so that occlusions occur, with one object partially covering another, then colouring and shading gradients must be interpreted in order to make depth judgements. In this connection small head movements can yield sufficient difference in the image from parallax and other effects to enrich the available information and thus assist interpretation of the image. (Gibson, 1950, p 29) This is particularly important in dealing with visual ambiguities or anomalies etc.

Perspective doesn't exist in the sensory experience of a totally and congenitally blind person (except by hearsay). It is solely a visual phenomenon. The blind person understands the environment by touch, hearing and smell, and so works mainly at close quarters. Size judgements, for example, are generally made in comparison with a person's own body measurements. Objects which are the same physical size always appear to be so, unlike the experience of vision where more distant objects appear to be smaller by perspective effects.

For this reason there is no need to trouble blind people with academic perspective knowledge during childhood, or even later in most cases. People with academic perspective knowledge during childhood, or even later in most cases. Such depictions as plans, side elevations, and sections of various sorts will supply all necessary information. Even adult blind people can spend their whole lives profitably with no practical or theoretical knowledge of perspective. Just as cavemen began to become aware of perspective only when they began to draw and paint, so blind people encounter perspective for the first time when they begin to meet tactile pictures of scenes (which are not in fact very common). Thus there is no particular reason for approaching perspective academically with blind people; it makes better pedagogic sense to allow them to experience it first through actual examples of visual art transcribed into tactile form. (Hinton, 1990b). It is then possible to discuss the picture in terms of the artist's visual experience.

In this connection it is also important to note the cultural differences in picture perception demonstrated by Hudson and others. Hudson found that many unsophisticated African subjects preferred illustrations of an elephant which depicted the animal from above, but with all of the legs which they knew it to possess shown at the same time (similar to an elephant skin spread out on the floor) rather than a normal orthogonal view preferred by Europeans. (Gregory and Gombrich, 1973, p 183)

This way of resolving the conflict between what is actually seen at one time, and what is known from other experience is understandable in people not schooled in draughtsmanship and artistic convention, and it is also interesting in the light of Kennedy's findings with congenitally blind adults and their modes of representation. (Kennedy, 1982, p 321) They, too, sometimes illustrated several aspects of an object which could not be seen simultaneously by normal vision. Such drawings are sometimes termed 'split representation' or 'chain-drawings' (Derogowski, 1970, p 21), although they also conform very closely to what mathematicians call a 'net' (or sometimes a partial net) of a solid object.

7.7 The work of C N Vincent

From the more practical standpoint of the teacher of technical drawing, C N Vincent developed a special drawing board by the use of which blind people could produce perspective drawings by measuring from the three axes of the specially shaped board and drawing along the T-squares provided. The T-squares clicked over the special graduations on the edges of the board so that measurements could be made. Vincent's trainees could make measurements of features in a room and from these produce a perspective drawing on the board. When they had once experienced perspective in this way they could interpret perspective drawings presented to them in tactile form, and from these assess and if necessary, measure and calculate real sizes of features of the environment depicted in the drawing (Vincent, 1970). Although in the literature the success of Vincent's subjects in drawing and interpreting perspective drawings was apparent, his idea appears not to have been taken up by the colleges where he did this work, and his drawing board has dropped out of use. (Vincent, 1984,p 17).

That Vincent achieved what he set out to do in the technical sense is undeniable, but as this book emphasises repeatedly (see Section 5.3 above), perspective is a purely visual phenomenon and quite outside the experience of a blind person. Tobin (personal communication) quotes the response of the late Reg Bonham, a blind mathematician who was present when Vincent's techniques were demonstrated and discussed. Bonham rephrased the well known saying thus 'to a blind person a cube is a cube is a cube'. In other words a blind person working by touch always encounters the edges of a cube as being of equal length and the sides as being parallel. The tapering effect of visual perspective is never experienced. So in seeking to do what he did, Vincent was imposing an alien viewpoint on touch experience, and as this chapter has discussed, perspective very rarely has any practical use for a totally blind person.

Ron Hinton
First published 1996
ISBN: 0901580775