Friday, August 14, 2015

Are lines always a means to more complex forms? Aleksander Rodchenko would not agree

Orientation selective cells of the visual cortex, which respond to lines of specific orientation, were discovered in 1959. They were first encountered in the primary visual cortex of the brain (area V1) – considered by many for much too long to be the only entering place of visual information into the rest of the visual brain.  Such cells have usually been thought of as the initial staging post for the elaboration of more complex forms. Some, indeed most, believe that they are the sole source for the elaboration of more complex forms such as faces, houses and objects. I am becoming increasingly skeptical of this view.

First of all, evidence which is largely ignored or at least marginalized, although it has been available since 1980, shows that V1 is not the only entering place of visual signals into other areas of the visual brain; there are alternative routes which reach them without passing through V1. Secondly, orientation selective cells are found in at least four other visual areas of the visual brain, and these cells survive functionally even when deprived of an input from V1 (i.e. they remain orientation selective cells); they are, very likely, fed by these alternative inputs. Thirdly, visual signals related to form (oriented lines) reach V1 and the other visual areas within the same time frame. And, finally, clinical evidence shows that humans can become agnosic (blind) for line drawings without at the same time becoming agnosic for real objects.

Hence, one must seek for sources besides V1 for elaborating orientation selective cells and complex forms, which is not to say that V1 cells do not contribute significantly to this process. But perhaps one should also consider, at the same time, that oriented lines stand on their own as forms in every sense, without their being mere “building blocks” for elaborating more complex forms.

Neurobiologists are not alone in considering oriented lines a means towards a more complex end. Mondrian, among others, sought for the constant elements in all forms and settled on the straight lines, provided they are vertical and horizontal. He abhorred diagonal lines, breaking off his working relationship with a colleague because “of the high handed way in which you have treated the diagonal line”. Ever the reductionist (though not accused of it, as we commonly are), he believed that “there are also constant truths concerning forms” and it was the function of the artist “to reduce natural forms to the constant elements”.

Many others, including Kazimir Malevich, Ellsworth Kelly and Barnet Newman, among others, have emphasized lines in some of their paintings, for different reasons. But it was perhaps Aleksander Rodchenko, the Russian Constructivist artist, who was most explicit in giving the straight line its autonomy. Influenced by Malevich and Suprematism, he wrote:  “ I introduced and proclaimed the line as an element of construction and as an independent form in painting”. In another context, he also wrote "I reduced painting to its logical conclusion” (although he, too, was not (as far as I know) accused of reductionism). There are, incidentally, very good perceptual reasons for why he should not have been accused of reductionism, but I will leave that to a future post.

The point of all this is simple: that lines are not only a means towards something more complex; they can also stand on their own as a form or forms; that, as the Gestalt psychologists emphasized, “the whole is other than the sum of the parts” and that a complex form, even when constituted from lines, is one that is other than a combination of lines – an important lesson in the physiology of forms; and that there is much more to the construction of forms in and by the brain than a single source which lies in the orientation selective cells of V1.

It seems to me that the physiology of form construction by the brain is still, in spite of all the excellent work that has been done in the field, a field that is rich for exploration but also requires some of the facts mentioned above to be taken into consideration. In that exploration perhaps the products of artists should also play some role, even if only a minor one.

© Semir Zeki


Christopher Gillespie said...

Hi, I was wondering if you could provide the references for the alternative routes you describe in the V1 and the responses to edge detection later in the visual system?

I think the question of what constitutes form perception and the role of line is one of the most fascinating and subtle I've come across (I do alot of line drawings that involve shifts in form and was doing research involving contextual shape level effects on perceptual organisation and detection).

I was wondering if you might agree that in some sense the very importance and autonomy of the line - that it can simultaneously give rise to 'flow' and weight, of stimulating softness or roughness, gentleness or violence, all kinds of seemingly disparate effects both perceptual and emotional - may in some sense disguise its autonomy?

So despite the fact that 'the line' cuts through and creates percepts associated with other perceptual dimensions those very things are treated as mere associations rather than evidence of the deeper and more complex neurophysiological connections that you have just described.

I also wonder what your assessment of the present state of the field of 'form perception' and whether you feel Kusne's assessment with respect to the difficulty of getting everyone to agree to rigorous and well formulated definitions still holds true? And, more pertinently, how it is that artistic exemplars may provide a better lead in overcoming this obstacle?


S.Z. said...

Thanks for your interesting comments.

there are many references to alternative routes to specialized visual areas that by-pass V1. Below, I give three from our own most recent work, but the anatomical pathways that by-pass V1 were charted as long ago as 1969 and 1980 by others. I must emphasize that the papers below are quite technical.


I find your other comments very interesting. I am of the view that there is no rigorous definition of form, either in art or in science; it falls into a category that everyone "knows" but no one has defined adequately, perhaps with the exception of the Gestalt psychologists. And your observation that lines may be associated with other perceptual dimensions has somewhat distracted from its "stand alone" status.


Semir Zeki

Christopher Gillespie said...

Those are much appeciated, I will take a look at them - I have some knowledge of the theory and I have a background in physics, so I'm confident I'll work through them.

At any rate, I'm the kind of person who gets decides to use the creases made by a pen to draw on image on jet black ink, so I'm always up for a Challenge!

Thanks again,