Imagine visiting New York and stopping by the illustrious Museum of Modern Art. It is difficult to visit without pausing to admire the acclaimed painting Starry Night by Van Gogh [1]. Envision reaching a standstill, stopping in your tracks to take in the stunning beauty that is Van Gogh’s artwork. The spiraling colors, the latitude of blues from the dark Persian to lighter wild blue yonder, the bright luminous moon with circles of light rippling off the canvas. Though the painting itself is not moving, the viewer can tell that movement is being portrayed. How can our brains process movement in a non-moving, two-dimensional piece of art? How does the added element of movement affect one's enjoyment of the art? To address these questions, a field of neuroscience called neuroaesthetics has emerged.

Neuroaesthetics

The field of neuroaesthetics focuses on detangling whether aesthetic enjoyment is the result of the culture we grew up in, our individual preferences, or an evolutionary advantage [2]. Julie Mehretu, an artist who creates abstract art, describes her artistic interest as “the space in between, the moment of imagining what is possible and yet not knowing what it is” [3]. How Mehretu describes her artistic motivation is similar to what draws in neuroscientists: the idea of the brain as the great unknown. Neuroaesthetics researchers aim to test hypotheses that explain the connections between art and the brain, specifically investigating the brain processes that occur during the artistic experience [2]. The goal is to move past that middle state of imagining what could be true and knowing it to be so. Even if the research found doesn’t validate the original hypothesis, the research is still important to divulge new knowledge and inform new and better questions or hypotheses for future research.

A ubiquitous part of the human experience is enjoying art, which has led to many hypotheses and analyses made by scientists as to how the brain is involved. Although there are notable cross-cultural similarities in what many cultures find aesthetically pleasing and take enjoyment from, enjoyment and aesthetic tastes can still vary from person-to-person [2]. What makes one person or a culture’s aesthetic enjoyment similar or different from another’s? Take, for example, current beauty standards and how they can exemplify a culture's aesthetic tastes.

Symmetry is a trait that is often highly desired, sometimes to the point of using plastic surgery to obtain a symmetrical face. A study done on babies showed that even babies show a preference for women with faces that follow common beauty standards, meaning these aesthetic values is at least partially innate, and not learned [4]. Paintings of people, therefore, may depict more symmetrical faces because they are perceived as more aesthetically pleasing due to a preference common to many people. However, on the individual level, one might favor a painting of a woman without a symmetrical face due to the interactions between brain regions when one thinks introspectively about how the art relates to their own experiences. If someone viewing a piece of artwork has a fondness for their mother, who has a non-symmetrical face, a painting they make or look at that has non-symmetrical facial features could ultimately influence their enjoyment of the artwork [5][6]. As a field, neuroaesthetics aims to untangle what preferences vary from person to person, which have resulted from cultural standards, and those that persist cross-culturally due to evolutionary changes in how our brains process stimuli [2]. This paper, however, will focus on determining how the brain can process movement in two-dimensional paintings and whether participants' aesthetic enjoyment and preferences for a painting are dependent on whether motion is or is not being perceived.

The Brain Processing Visual Stimuli Begins with Light

“Beauty lies in the eye of the beholder” not only because different people judge works of art differently, but also because seeing beauty involves visual processing that occurs within the eye. Imagine once again that you are viewing the magnificent Starry Night. How does the painting on the canvas become an image in the brain?

Light reflects off from the painting and enters the cornea [5]. From there it goes through the pupil and farther back into the lens. The lens focuses light onto the retina, and this is where the neural image processing begins [5].

The retina has three layers of neural cells, the first being the photoreceptor cells, which include rods and cones [5]. Bipolar cells make up the following layer and the final layer is composed of ganglion cells which send signals to the visual cortex in the brain. When light hits the retina, it stimulates rod or cone cells, which then get excited and pass their signal on to the bipolar cells. These bipolar cells modify the signal before sending it onward to the ganglion cells, which are responsible for breaking down the information about the visual field into its component parts – intensity, contrast, texture, color, and movement. Now this processed information can be sent onward to the brain [5].

The Linear Concept of Time Contributes to the Illusion of Motion

After our brain receives and integrates the information gained from the light stimulus of paintings, one way that motion can be implied is with the linear concept of time [7]. Linear time has a distinct beginning and end, and all events occur sequentially to get there. For example, while flowing from one point to the next, a river must travel to all the points in between, from start to finish. In paintings, this concept creates an expectation for something in the artwork to continue moving [7]. Van Gogh’s swirling skies in Starry Night are expected to continue swirling down the page and across the image, even continuing off the canvas.

This idea of perceived motion contrasts the real motion which occurs when the position of something changes from one moment to the next [7], like when you watch a plane physically move across the sky or someone run across the street. Paintings, however, are stationary, and the position of subjects cannot change. Motion can only be portrayed through illusions that suggest the position of something will change, which is known as “perceived motion” and is common to many designs such as flow charts, graphics, and illustrations [8].

Despite this expectation, artists have the freedom to portray objects and time in their own way without the constraints of linear time. Paintings can be illogical because they do not have to show a real event or an event that would occur as it would in the real world. The expected chronological flow of linear time does not have to be followed.

Expectation of Motion in a Linear Time Scale Contributes to Perceived Motion

An artist's intention of painting could be to only capture one singular moment in time. For example, paintings can exist in imaginary and illogical realms, such as in David Hockney’s painting, "Picture emphasizing stillness," which is a comedic attempt at conveying that movement is simply a product of our perception [9]. In this painting, two people are talking with a leopard, dog-like animal fully stretched out, seemingly moments away from attack. The comedic aspect of this piece was his comment written on the painting, which reads “they are perfectly safe, this is a still” [9]. Real-life experience shows no evidence to support the idea that the dog-like creature’s movement will not continue, leading to pouncing on the people talking. However, like Hockney commented, it is in fact a painting and no movement is occurring. This expectation can enhance the viewer's perception of motion in paintings as one tries to consolidate what they expect to show motion and occur in a painting with a static, “still” painting in which no movement is occurring [9].

The mind's assumption about what will occur next when motion is suggested is called “implied motion” [10]. This is different from apparent motion in a series of photographs shown one after another, where something in the photo changes position, like in a video [10]. Research has shown that when presented with a still photo with this implied motion, the viewer will expect the motion to continue [11].

The V5 Area in the Brain Processes Intended Motion

When viewing a painting, whether passively enjoying or actively studying it, the visual cortex of your brain is activated [12]. This region of your brain is located in the occipital lobe, which is the backmost part of the brain and head. The visual cortex is broken up into five distinct areas, which each have distinct functions, named V1 through V5. Visual area five (V5), also called V5/MT or MT+, is the most significant area for sensing motion. To identify this area of the visual cortex as distinct from the other areas and to determine its function, researchers performed positron emission tomography (PET) scans [12].

Researchers showed participants moving stationary square patterns and observed what different regions of the brain were activated because of differing stimuli [12]. From this, it was found that when shown moving square patterns, V5 was sending more signals to the brain. This meant V5 was more active compared to participants who were shown stationary square patterns. This confirmed that V5 is a distinct fifth area in the visual cortex that was related to processing motion [12].

Bottom-up Categorization of Information is Another Artistic Technique of Portraying the Illusion of Motion

With the knowledge that the V5 is where motion is processed, how is this motion processed? One idea is that top-down and bottom-up processing is involved [13]. When interacting with a stimulus, such as viewing a painting or hearing an alarm, the way that a person pays attention to certain things is through top-down or bottom-up processing [13]. Top-down processing draws on knowledge from experience as information in the brain flows from higher centers of the brain at the top of the head to lower centers towards the back of the brain. This is in opposition to bottom-up processing that focuses on sensory input. When at the museum, if the guide points out more subtle, less obvious points in the painting, such as how Van Gogh used straight, controlled lines when painting the village at the bottom of the painting as opposed to the flowing curved brushstrokes used more commonly in this painting, the brain processes the painting with top-down processing because now the observer has knowledge on what to look for [13]. However, if instead of enjoying the original nighttime scene in Starry Night but instead a replica of the painting that included a big Space Needle centered in the painting, the brain would more readily recognize the unexpected, shocking images. This Space Needle becomes the more noticeable part of the painting. Bottom-up processing recognizes the more easily identifiable sensory information that is the Space Needle, but will use top-down processing to process the village once the museum guide discusses the brush strokes used to paint the village [13].

In paintings, top-down focuses on taking information outside of the senses (eyesight) to understand the image, while bottom-up relies on the sensory information of eyesight to understand a painting [13]. In the context of intended motion, ambiguous and unclear images are interpreted by the brain first by using low-level processing that doesn’t involve the use of knowledge. The brain receives sensory information that sends fewer signals throughout the brain to be more automatic. This is similar to how reflexes work. When at the doctor, if checking the knee-jerk reflex (patellar reflex), once striking the knee the signal is only sent to the spinal cord and not the brain, allowing for faster response. However, if the sensory information is not enough, to further understand the painting, top-down processing and knowledge are incorporated to understand an image. To fully understand a blurry, ambiguous image, top-down processing is needed, but without the initial bottom-up processing from sensory information, motion may not be perceived. Simply being told and having the knowledge that a painting has movement does not mean the viewer will perceive movement, and bottom-up processing may be more integral to perceiving movement [13].

A painting done by Giacomo Balla, Dynamism of a dog on a leash, demonstrates how bottom-down processing is needed [14]. If Balla were not trying to portray movement, everything might be crystal clear and still. However, to show movement, the dog’s tail is moving and is depicted in approximately eight places at once, as with the person’s feet. Initially, the painting can be confusing to the viewer if simply relying on the sensory visual information. Upon using the knowledge and experience of meeting many dogs or knowing the title, the painting becomes more comprehensible. The overlap of the dog’s feet and the person walking show the viewer that the tail and feet are not static but moving. Initially, the default is to rely on bottom-up processing when provided with clear, optimal objects in order to immediately recognize something. However, when participants are shown unclear, abstracted images, additional time and processing are required [6]. The overlap of legs creates the unclear, blurry sensory input that signals to the brain that the reliance on bottom-up processing is not enough and top-down processing is also required [14].

At this point, scientists know how the eye takes in visual information and integrates it into something the brain can further process and that this information is sent to the V5, further processing for real or intended motion. Perceived motion may result from unclear, abstracted images that cannot be fully processed with sensory input and so top-down processing then kicks in. What if scientists inhibited the V5’s ability to process the information through transcranial magnetic stimulation (TMS)? TMS can stimulate and disrupt normal brain activity by sending short electromagnetic pulses to specific portions of the brain such as the V5 [8]. Does disrupting normal brain activity, and therefore disrupting how the brain processes the visual stimuli, bottom-up processing, change the viewer's perception of whether or not motion is occurring in a painting?

How to Understand Data Retrieved from TMS

TMS is a technique used to noninvasively modulate brain activity and the activity of the central nervous system (CNS), which is the part of the body that includes the brain and spinal cord [8]. The CNS takes sensory information collected from sensory receptors around the whole body and processes it in the brain to build our experience of the world around us and allow us to interact with the world appropriately. TMS uses magnetic pulses to activate the outermost part of the brain, the cerebral cortex. The pulses are administered through a coil that painlessly transmits the stimulation through the skull. This allows the pulse to be sent to a very specific region and cause a change in the normal activity by causing more action potentials to occur [8].

In this study, TMS was applied to either a control area of the brain or to V5 in the left hemisphere [8]. The control area is known to be unrelated to V5 and visual processing and was used to ensure that the presence of TMS wasn’t in and of itself what was causing the response. Thus, if participants reacted the same way to stimulation of both V5 and the control, this would indicate that stimulation, and not specifically V5 activation, was responsible for the effects or that TMS had no effect. If participants derived the same amount of enjoyment or perceived the same amount of motion in the artwork during the control and the V5 stimulation, the authors could hypothesize that stimulation of V5 is not directly related to enjoyment or perceived motion [8].

In the experiment, before any TMS was applied, participants were asked if abstract paintings (art that is absent of scenes or objects, without physical form) or representational paintings (naturalistic objects or scenes) depicted movement and how much they liked each painting to determine baseline measurements [8]. One group of participants only looked at abstract paintings and the other only representational paintings. Participants were shown 80 paintings in random order with two trials. In one trial, stimulation was applied to the control area and then after a short break, the paintings were randomly shown again while TMS was applied to the cerebral cortex [8].

What was found was activation in the V5 decreased the amount of movement the participant saw with unstimulated brain activity in both the representational and abstract paintings [8]. This indicates that when stimulating the V5, normal neural activity was disturbed, so V5 must be involved in perceiving implied motion. In addition, enjoyment of the paintings decreased from the baseline enjoyment with no stimulation, but only in abstract paintings. Representational paintings saw no change in enjoyment of the paintings. This shows a correlation between V5 and enjoyment elicited from perceiving movement in paintings for some art forms. If when V5 cannot perform its normal activity, as when stimulated by TMS, there is a corresponding decrease in the movement a participant sees in the painting, this would affirm the idea that V5 is related to seeing movement [8].

The scientists explained that only seeing abstract art can lead to a decrease in enjoyment because abstract art’s defining feature is that it involves very indistinct features and unrecognizable objects [8]. Thus, the viewer relies on more sensory information such as motion perception. Opposite of perceived motion with top-down categorization, enjoyment of abstract art involves bottom-up categorization because of the reliance on sensory cues. According to this, because enjoyment relies on sensory input like motion, when TMS is applied and perceived motion is disrupted, the perception of less motion in the artwork decreases the viewer's enjoyment [8].

Conclusion

Research of the brain's involvement in processing art helps us understand how the brain is broken up into parts that each process art in distinct ways. By knowing that V5 is involved with understanding motion, real and perceived, this can go on to inform future research questions. We can now ask what molecules, hormones, and neurotransmitters work together to create this function. Are there specific forms of art or techniques that artists employ within abstract or representational paintings that increase perceived movement? The participants involved in the TMS study were all art-naive, meaning they had no formal training about art [8]. Would the results that were found be different in populations that were more knowledgeable in art? Additionally, all the participants were Italian. In order to make the results representative, more ethnicities and cultures would need to be represented, which could also cause the results to change. This research has the potential to not only impact artists and affect how they paint by informing them what types of art and techniques increase perceived motion and enjoyment, but also increase scientists' general understanding of the brain. With more knowledge comes more informed questions to ask to learn more about art and how it interacts with the brain.

References

1. Van Gogh, V. (1889). The starry night [Painting]. The Museum of Modern Art, New York, NY, United States. https://www.moma.org/learn/moma_learning/vincent-van-gogh-the-starry-night-1889/
2. Iigaya, K., O’Doherty, J. P., & Starr, G. G. (2020). Progress and promise in neuroaesthetics. Neuron, 108(4), 594-596.
3. Farago, J. (2013, June 20). Julie Mehretu paints chaos with Chaos – from Tahrir Square to zuccotti park. The Guardian. Retrieved April 1, 2022, from https://www.theguardian.com/artanddesign/2013/jun/20/painting-art
4. Bueller, H. (2018). Ideal facial relationships and goals. Facial Plastic Surgery, 34(05), 458–465. https://doi.org/10.1055/s-0038-1669401
5. Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S. A., Hudspeth, A. J., & Mack, S. (2013). Principles of neural science (Fifth edition.). New York, N.Y.: McGraw-Hill Education LLC.
6. Schendan, H. E., & Ganis, G. (2015). Top-down modulation of visual processing and knowledge after 250 ms supports object constancy of category decisions. Frontiers in psychology, 6, 1289.
7. Kanai, R., Sheth, B. R., & Shimojo, S. (2007). Dynamical evolution of motion perception. Vision Research, 47(7), 937–945. https://doi.org/10.1016/j.visres.2006.12.009
8. Cattaneo, Z., Schiavi, S., Silvanto, J., & Nadal, M. (2017). A TMS study on the contribution of visual area V5 to the perception of implied motion in art and its appreciation. Cognitive neuroscience, 8(1), 59–68.
9. Hockney, David (1962). Picture Emphasizing Stillness [painting]. https://www.thedavidhockneyfoundation.org/artwork/3588
10. David, A. S., & Senior, C. (2000). Implicit motion and the brain. Trends in Cognitive Sciences, 4(8), 293–295. https://doi.org/10.1016/s1364-6613(00)01511-4
11. Kourtzi, Z., & Kanwisher, N. (2000). Activation in human MT/MST by static images with implied motion. Journal of cognitive neuroscience, 12(1), 48–55. https://doi.org/10.1162/08989290051137594
12. Zeki, S., Watson, J. D., Lueck, C. J., Friston, K. J., Kennard, C., & Frackowiak, R. S. (1991). A direct demonstration of functional specialization in human visual cortex. The Journal of Neuroscience, 11(3), 641–649. https://doi.org/10.1523/jneurosci.11-03-00641.1991
13. Corbetta, M., Shulman, G. Control of goal-directed and stimulus-driven attention in the brain. Nat Rev Neurosci 3, 201–215 (2002). https://doi.org/10.1038/nrn755
14. Balla, Giacomo (1912) "Dynamism of a dog on a leash [oil on canvas]". Albright-Knox Art Gallery, Buffalo, NY, United States