Painting and visual information processing

Paintings are creative ways of touching human vision and awaken certain feelings from the depths of the heart. In terms of science, these deep feelings result from our visual information processing. To achieve this effect, painters intentionally or unintentionally follow the principles of vision and psychology in which the brain network is extremely complicated [1, 2]. In fact, a masterpiece painting equals an excellent piece of visual art; that is to say, an outstanding painter is a visual expert.

The surrealist Salvador Dalí was a skilled draftsman, best known for the striking and bizarre images in his work. His best-known work, Persistence of Memory, shows his thoughts on indelible memory, with clocks deformed in a surrealistic manner, which presents a challenge to the visual science principle of visual invariance [3]. Visual invariance is described as follows: objects can be rotated, stretched, squeezed, or otherwise distorted and yet remain recognizable to human vision (Fig. 1a). In Persistence of Memory, Dali bends the clocks but we still recognize them as clocks, and not as something else (Fig. 1b). However, if he had gone beyond the limit of bending and instead folded the clocks, we would not be able to identify them as clocks. Thus, he is good at handling the deformation, conforming to the visual invariance principle, and allowing us to recognize the items for what they are, even when they appear visually to be different. His surrealistic expressions and deep thoughts are established with the appropriate application of visual invariance.

Fig. 1

(Color online) Paintings by talented artists always conform to visual psychological principles. a Visual invariance. The three objects may well be recognized as the same box with a hole in it, even though the visual shapes are different (from DCMs, http://changingminds.org). b In Persistence of Memory painted by Salvador Dali in 1931 (from Wikipedia, the free encyclopedia), the clocks were strikingly deformed. The bent clocks express the author’s surrealistic imagination on persistent memory. This painting skill challenges the visual invariance principle. c Peripheral vision. The human visual field is composed of the central and peripheral fields [4]. Please observe the fixation point and perceive the circle with the peripheral vision. d The peripheral vision perceives a circle as concave. e Dora Maar painted by Pablo Picasso in 1937 (from Allposter.com, order#: 1001201666985). The portrait shows a normal, beautiful, vivid, and 3-dimensional-like Dora when anyone fixes his/her eyes on the fixation point and perceives Dora face in the peripheral vision

Human vision comprises central and peripheral vision, organized in a rhombic-like visual field [4]. Peripheral vision is just as important as central vision although we clearly see every object with our central vision (Fig. 1c) [5]. As shown in Fig. 1d, peripheral vision can concave an object at the nasal side [6]. The Portrait of Dora Maar (Fig. 1e) painted by Pablo Picasso (1937) is one of the world’s aesthetic masterpieces [7]. Picasso painted the Portrait with thick lines, a clear-cut structure, and in bright color, which allows us to perceive a vivid Dora. He gives Dora an extended nose and cheek to compensate for the concaved effect of peripheral vision, although the spatial resolution is poor in the peripheral vision. With a master’s talent, Picasso has painted a portrait on a 2D plane that appears illusively full and has a 3D-like appearance in the peripheral vision. This is evidence that peripheral vision can result in the illusory perception of a normal object, depending upon the structure of that visual object.

Wheatfield with Crows was painted in July 1890 in the final weeks of van Gogh’s life. This masterpiece depicts a dramatic, cloudy sky filled with crows over a wheat field. The sense of isolation is heightened by a central path leading nowhere and by the uncertain direction of the crows’ flight. van Gogh painted the flying crows with thick black lines (Fig. 2a), which makes them appear as if they are really flying with their flap** wings.

Fig. 2

Different painting skills stimulate different visual information processing pathways. a Wheatfield with Crows (van Gogh, 1890, from Wikipedia, the free encyclopedia). He used thick black lines to paint the crows, which look like living crows flying over the wheat field. b Lateral inhibition. This makes the darker area falsely appear even darker and the lighter area falsely appear even lighter, along the boundary between adjacent shades of grey in the Mach band illusion. In Wheatfield with Crows, the thick black lines stimulate the magnocellular pathway, to create a perception of crows flying. This moving effect is at least related with lateral inhibition. c Irises in Monet’s Garden painted by Claude Monet in 1890 (from Wikipedia, the free encyclopedia) is in a different style from that of Wheatfield with Crows. There is a variegated patchwork, but no rims with dark lines between the flowers and trees. This painting style can stimulate the parvocellular visual pathway and awaken feelings of silence, relaxation, comfort, and thoughtfulness in its viewers. d Facing the variegated patchwork, a person could not perceive the imaging of the Mach band. This is why the flowers and trees in Irises in Monet’s Garden look silent and motionless. The three anatomically distinct parallel pathways projecting from the magnocellular, parvocellular, and koniocellular ganglion cells to the lateral geniculate nucleus, and through there to the primary visual cortex V1. These sub-systems have distinct structural and spatiotemporal characteristics

To understand why the crows appear to be really flying, we need to know the pathways that are projected from the retinae to the visual cortex. The human visual system is composed of three anatomically distinct parallel pathways projecting from the magnocellular, parvocellular, and koniocellular ganglion cells to the lateral geniculate nucleus, and via these to the primary visual cortex V1. The thick lines used by van Gogh to depict the crows at least conformed to the phenomenon of lateral inhibition in visual neurobiology [8]. Lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors, which makes the darker area falsely appear even darker and the lighter area falsely appear even lighter (Fig. 2b). This effect creates a contrast in stimulation that allows increased sensory perception. Magno cells with more myelin are activated by achromatic low spatial frequencies, and have high contrast sensitivity and temporal resolution with a high conduction velocity (Table S1). The magnocellular pathway is sensitive to movement and velocity. The thick lines used by van Gogh to depict the flying crows stimulate the magnocellular pathway and give the reader the perception that the crows are flying over the wheat field.

In contrast, the painting Irises in Monet’s Garden by Claude Monet shows the lush opulence of irises, shrubs, overhanging trees, and patchwork light (Fig. 2c). He did not use line drawing to depict the boundaries between the flowers, trees, and other objects, but instead used a variegated patchwork to obscure the boundaries. The magnocellular visual pathway is not sensitive to the irises without boundaries. The lush opulence of the irises should stimulate the parvocellular pathway in which the cells are small with less myelin, are color-opponent (so-called red/green) [9], have low contrast sensitivity, are high spatial, have low temporal resolution, and have low conduction velocity [10]. The painting of the Irises gives us the impression that Monet’s garden is silent, relaxed, comfortable, and more imaginative, at the moment when we observe the masterpiece. Furthermore, there is no horizon to our visual field and this perpetuates the abiding impressionist ambition of harmonizing the spatial depth and surface.

Different people may have different perceptions and feelings when they observe these global masterpieces because their understanding of these paintings is based on different backgrounds [11], such as language, culture, society, and history [12]. Each of the paintings has its own specific style and stimulates the magno-, carvo-, or konio-cellular pathway, or all three. Further perception to understand the deeper meaning of a painting is not only related with visual cortex but also the other cortexes. In addition, health conditions also influence visual perception. Ahmadi et al. found that dyslexic subjects capacity suffer from both magnocellular and parvocellular deficits as well as partial impairment of the koniocellular pathway. Neurodegenerations including Alzheimer’s [13] and Parkinson’s disease [14] may be associated with deficits in brain function [15]. In any case, it is imperative to understand and follow the visual and psychological principles in painting. Otherwise, it is difficult for the painting to elicit a response from the deep mind of the audience.