The process of vision and the interpretation of visual information is an intricate phenomenon, with many aspects still eluding the grasp of scientists. However, one thing is certain: we see with our eyes, but it is our brain that makes sense of what we see. The eye, in essence, is an extension of the brain, protruding forward to gather visual data.
Vision is only possible with the presence of a rapid-acting analyzer capable of sifting through the vast and often chaotic input received by the eye. This analyzer must recognize familiar shapes, forms, and arrangements, extracting essential features from its memory and comparing them to each newly encountered object. This complex task, among others, is the responsibility of the eye’s master: the human brain.
Human Eye is Extension of Brain
The eye, like any converging lens, projects an inverted image of its surroundings onto the retina. This discovery once baffled scientists. Why then do we not perceive the world upside down? To investigate this, an experiment was conducted. Individuals were fitted with glasses containing reversing prisms, causing their world to appear inverted. Surprisingly, within a few days, their perception reverted back to normal. However, upon removing the glasses, the inversion returned, albeit taking a few hours to readjust.
Early researchers speculated that a tiny homunculus, a miniature human, resided within the eye, relaying information about the unfolding scene before it. Later, theories suggested that the brain itself somehow compensated for the inverted image, restoring it to its upright orientation. In reality, neither of these notions is accurate. The human brain does not possess a screen upon which nerve impulses from individual receptors form a precise representation of real-world objects.
Instead, the brain analyzes the image projected onto the retina, employing processes that are far from optical in nature. It receives nerve impulses as electrical signals, operating much like a computer, albeit an unimaginably complex and still largely unknown structure. Furthermore, it is possible that the brain acquires information precisely at the moment the image changes.
Human Eye is Ultimate Photographic Camera
Among all the devices created by humans inspired by parts of the human body, none bear greater resemblance than the eye and the photo-camera. While the inventors of the camera did not literally copy the structure of the eye, there are striking parallels between the two.
English scientist J. Wald wrote that over the years, much has been learned about vision thanks to the camera, but little in photography thanks to the eye.
Today, every schoolchild knows that the eye is similar to a camera. In both cases, a lens projects an inverted image onto a light-sensitive surface – film in the camera and the retina in the eye. The eye, like the photographic camera, regulates the amount of incoming light using a diaphragm (the pupil diameter).
Both have an internal surface that absorbs scattered light. The eye focuses the image by changing the curvature of the lens, unlike the displacement of the lens when focusing in a camera.
In low-light conditions, the photographer switches to more sensitive film, which significantly increases graininess and deteriorates image quality. The eye switches from cone vision to rod vision. Visual acuity also decreases. Cones are smaller in size, each of them connected to the brain by a separate fiber of the optic nerve, while the coarser rods are “connected” to the brain in large groups. The excitation of rods gives a sensation of only neutral gray color. We poorly distinguish colors in the dark. In addition, the yellow lens cuts off the ultraviolet part of the spectrum, that is, it works like a filter.
The central fovea of the retina is smaller than the head of a pin, about 0.5 mm, and it accounts for an angle of less than 3 degrees with a total field of view of 160 degrees. But the central fovea consists only of cones, which allows you to distinguish the smallest details. In fact, looking at an object means turning the eye so that the image falls on the central fovea. Sometimes a cone of clear vision (2-3 degrees) and a visual cone of relatively clear vision are distinguished.
Our eyes are constantly in motion, and what was blurry a second ago can become clear in the next. With a stationary eye from a distance of 4 meters, it would be possible to instantly consider only part of the face of a person passing by, and a person in full – from a distance of 48 meters, so small is the central fovea of sharp vision.
It is also known that at any given moment our attention can be focused only on one small part of the entire field of view. Everything else, the so-called peripheral vision, has a completely different status in consciousness. So, we often hear the noise of many voices, but we perceive only one conversation that interests us.
In what the eye significantly surpasses light-sensitive photographic materials is in its ability to detect the smallest sources of light. Here it has no equal. If you stay in complete darkness for half an hour, your eyes adapt to it and even a barely visible light source will be detected instantly. For the most sensitive film, this will require at least a two-hour exposure, that is, the light from a weak source will be summed up by the photoemulsion for two hours. The threshold of irritation of the rods, which we see at night, allows us to see an ordinary candle from a distance of several tens of kilometers.
Just as irreplaceable is the eye when it comes to comparing two colors, finding differences in their saturation and shades. No wonder scientists call the eye the most perfect optician. Nothing, no existing device can compare with it in sensitivity and reliability.
Deceptive Delights: The Human Eye’s Susceptibility to Illusions
Despite its remarkable capabilities, the human eye can be easily deceived, giving rise to fascinating visual illusions. These phenomena have long intrigued scientists, yet the precise mechanisms behind them remain elusive. It is believed that conflicting stimuli overwhelm the eye’s ability to make a definitive interpretation.
Consider the well-known Necker cube, which presents an ambiguous spatial perception. As you observe the figure, it appears to “flip” between two distinct three-dimensional projections. The brain attempts to reconcile both interpretations, never settling on a definitive one.
Similarly, Rubin’s vase illusion challenges our perception of foreground and background. The eye struggles to simultaneously perceive both profiles within the single plane, alternating between viewing one as the figure and the other as the background.
These visual illusions, along with countless others, underscore the inherent imperfections of our vision and demonstrate the brain’s struggle to interpret ambiguous visual information. These illusions occur when conflicting stimuli overwhelm the eye’s ability to make a definitive interpretation, revealing the inherent imperfections in our visual processing system.
Paradoxically, this very susceptibility to deception is what enables us to perceive depth not only in the real world but also in two-dimensional representations such as paintings and photographic prints. Our ability to interpret flat images as three-dimensional spaces stands as one of the most remarkable illusions inherent to human sight.
The Paradoxical Nature of Paintings: A Psychological Perspective
Any painting represents a perceptual paradox. After all, every object is itself, and only paintings have a dual nature, and therefore they are a unique class of paradoxical objects. No one but a person is capable of creating (and perhaps perceiving) paintings and any other symbols. … but the object visible in the picture is not where the plane of the picture is perceived, and at the same time it has completely different sizes and a completely different volume.
Psychologist Richard Gregory
“Paintings lead a double existence. First of all, they are objects as objects, patterns on flat sheets of paper, but at the same time the eye sees in them completely different objects. The pattern consists of spots, lines, dots, strokes or photographic grain. But these same elements add up to a face, a house, a ship in a stormy sea.
Paintings are a unique class of objects, because they are simultaneously visible both in themselves and as something completely different from just a sheet of paper on which they are drawn. Paintings are paradoxical. No object can be in two places at the same time, no object can be both two-dimensional and three-dimensional at the same time. And we see pictures exactly like that. The painting has a completely definite size, and at the same time it shows the true size of a human face, building or ship. Paintings are an impossible object,” asserts R. Gregory.
Paintings possess a unique dual nature in visual perception. They exist simultaneously as flat, two-dimensional objects (canvas or paper with patterns) and as representations of three-dimensional scenes or objects. This paradoxical quality allows us to perceive both the physical artwork and the imaginary space it depicts, creating a rich visual experience.
In order to use apparent depth in photographs, to learn to control it, it is necessary to understand the reasons for the illusion of space, to understand what makes the eye see a flat image as voluminous.
It is very important to note the fundamental difference between the perception of spatially ambiguous optical illusions, in which we see either one or the other image alternately, and the perception of a picture. In the case of a picture, we simultaneously (which is very important) perceive both the plane of the carrier (canvas, photo paper) and objects in the imaginary space.
The Duality of Perception: Yin and Yang of Visual Experience
Within us reside two distinct modes of perceiving reality: one visual, sensory, and subconscious, and the other conscious, logical, and analytical.
When confronted with a flat image (such as a painting or photograph), it is the visual perception that can be considered objective. It reveals what is literally depicted in the image: flat geometric shapes, tonal and color patches. Logical perception, on the other hand, interprets these shapes and patches not only as two-dimensional but also as three-dimensional spaces, populated with real-world objects, people, trees, houses, and clouds.
If an image is perceived ambiguously, the culprit is not visual perception but rather consciousness, which struggles to resolve the conflicting information. As a result, consciousness may either accept both interpretations or, more often, favor one, potentially leading to an erroneous conclusion.
These two modes of perception, visual and logical, embody the principles of Yin and Yang. They are interdependent yet often contradictory, engaged in a constant interplay, offering fundamentally different interpretations of the same visual stimuli. Sometimes Yin perception prevails, while at other times Yang takes over. In some instances, they reach a compromise, while in others, their contradictions run too deep, resulting in an irresolvable duality of perception, manifested as visual illusions.
Together, these two modes of perception provide us with the rich tapestry of sensations we experience when interpreting visual representations on a flat surface, particularly in the context of paintings. The conflict between these two modes often becomes the very essence of the image’s content.
The eye merely gathers visual information and delivers it to the brain, which then processes and interprets it, making inferences about the nature, properties, and spatial arrangement of the perceived objects. In many cases, the brain adjusts the incoming information, particularly regarding the size, shape, and distance of very far or very near objects. Thus, the eye may perceive one thing, while the brain “sees” something entirely different.
In the real world, we also encounter instances of ambiguous perception, visual illusions that arise from the inherent complexity of the visual world. However, when it comes to flat images, ambiguity is inherent in their very nature: they are simultaneously both flat and spatial.
Demonstrating Illusory Depth in Flat Images
To effectively illustrate the illusion of depth in flat images, consider a simple example: two circles of different sizes, one larger and one smaller. The smaller circle is perceived as being farther away, hence its reduced size. Can we determine its “true” position in space in this scenario?
Assume that the larger circle lies on plane I. Draw a circle of the same size on plane II. Now, the person conducting the experiment moves backward with plane II, while the observers compare the sizes of the smaller circle on plane I and the circle on plane II in the distance until they appear equal.
With the dimensions shown in the diagram, the perceived and illusory distance of the smaller circle receding from the plane of the drawing is approximately equal to the distance between the drawing and the observer.
This simple experiment demonstrates the powerful illusion of a third dimension when perceiving flat images. This illusion arises naturally as a result of our experience of viewing distant objects in real space.
What is the Difference Between Vision and Perception?
Vision and perception are closely related concepts, but they represent different stages of how we process visual information. While vision provides the raw data by capturing light and converting it into signals, perception gives meaning to this data, allowing us to understand and navigate the world around us. This distinction highlights the remarkable complexity of the human brain and its ability to construct our visual reality from simple light patterns.
Vision is the initial, physiological process of capturing light and converting it into electrical signals that the brain can interpret. It involves several key steps, beginning with light detection. Light enters the eye through the cornea and passes through the pupil, which is controlled by the iris to regulate the amount of light. Next, the lens focuses the light onto the retina at the back of the eye. The retina is lined with photoreceptor cells called rods and cones that detect light and color. These photoreceptor cells then convert the light into electrical signals. Rods are responsible for low-light vision, while cones handle color and detailed vision. Finally, the electrical signals are transmitted via the optic nerve to the brain, particularly to the primary visual cortex located in the occipital lobe.
Perception, on the other hand, is a higher-order cognitive process that involves interpreting and making sense of the visual information received from the eyes. This process is more complex and subjective, involving several brain regions and cognitive functions. Initially, the primary visual cortex processes basic visual information such as edges, orientation, and motion. This data is then sent to other parts of the brain for further processing. Higher visual areas, including the temporal and parietal lobes, integrate this information to recognize shapes, patterns, objects, and their spatial relationships. The brain uses memory, prior knowledge, and contextual information to interpret what is being seen. This includes recognizing familiar objects, understanding scenes, and making sense of new visual stimuli. Finally, perception influences how we interact with our environment, guiding actions and decisions based on the interpreted visual information.
The key differences between vision and perception lie in their processes, nature, and outcomes. Vision is a mechanical and physiological process of capturing and transmitting visual data, while perception is a psychological and cognitive process of interpreting and understanding that data. Vision is objective and consistent across individuals, as it relies on the physical properties of light and the eye’s anatomy. In contrast, perception is subjective and can vary widely, influenced by individual experiences, memories, and cognitive biases. The outcome of vision is raw visual input in the form of electrical signals, whereas the outcome of perception is a meaningful interpretation of that input, allowing us to recognize and interact with our surroundings.
