General Neuroscience

Descriptive Approach of Human Visual Perception of Physical World reality

ANJANA ELAPOLU, Ganesh Elumalai, Tajnin Hashim, HARSHITA CATHERINE, Nicolas Ceresoli, MOJESS NANDURI


The interpretation of what we view and how we see the physical world is referred to as visual perception. Our brain processes what our eyes congregate, creating a perception that sometimes is not parallel with reality. The brain has a peculiarity of acting in a bizarre way of perceiving the subjective physical reality of the objective state, even when there’s no creation of illusion by the object. Even after multiple attempts of solving the theories behind such perceptions, our knowledge on them is still insubstantial. The mystery behind some perplexing aspects of human visual perceptions like color, luminance, motion, distance, and depth are attempted to be simplified. An amalgamation of various parameters of judgment leads to the perception of an object. This study focuses on parameters, such as psychological, physiological, interpretational, empirical, and neurological aspects. This analysis will evaluate the factors that help to convey outputs in a subjective manner under different conditions, will explain why our judgment is challenged by the moderate disparity in the framework of our field of vision, and demonstrates how much we rely on comparative analysis.
Keywords: visual perception, physical world perception, brain process, bizarre human visual perception



The prediction of the physical reality through our sense of vision is termed visual perception. The human eye can view the world in a wider range of focus levels than any high-quality camera, yet in terms of visual perception, it often tends to get tricked into seeing things apart from reality. Sometimes our perception doesn’t quite match up with physical reality, but rather perceives an illusion that was never created by the object. Here, we attempt to illustrate some of these illusions in terms of color, luminance, motion, depth, and distance.


1. Color

Bezold Effect

The Bezold Effect was first described by Von Bezold in 1853. It occurs when the chromaticity (hue and saturation) of colors is altered due to the change in the intensity of light [1]. This effect shows the same red lines on a solid black background and a solid white background, yet the red hue appears to be lighter on the latter background. Though being the same color,  both lines appear to be different to the human eye due to the corresponding backgrounds [2].


2. Luminance

Simultaneous Contrast Effect

The Simultaneous Contrast Effect was demonstrated by the German physiologist Ewald Hering. It is the visual perception of two colors as intensified or diminished when viewed simultaneously with greater or lesser exposure of light in the same direction [3].

Figure 1(a) - An illustration of simultaneous color contrast [4].

Explanatory Strategies For Color & Luminance Perception

a. Psychological: “The color of an object or light is specified in terms of the additive mixture of three primary lights (red, blue and green).” Even though the stimulus has drastically different wavelengths of light, they are perceived as identical by the visual system [2].

b. Physiological: Mach bands are the consequence of a visual process that describes the image in terms of “edges” and “bars.” It was first demonstrated by Ernst Mach and was named after him [5].

Figure: 1(b) - Mach band. [6].

When looking at the band along the dark edge, the color appears darker than the surrounding colors, and at the lighter edge, the color appears to be lighter than the adjacent colours, which is a direct consequence of a phenomenon known as lateral inhibition. This is important for visual perception and inhibition and enhances the representation of contrast, improving perception of edges by interneurons that pool signals over a neighborhood of presynaptic feed and send inhibitory signals back to them [6].

c. Empirical: The visual system evolved and formed the ability to transform small, biologically determined image patterns to useful perpetual responses that have the same frequency of occurrence [7].

Figure 1(c) - Accumulated human experience with luminance patterns [7].

Figure 1(c) has unique patterns that occur only once, and it is highly unlikely to have the same luminance patterns on the retina. A large catalog of such images are less effective, so a confined size of a sample can give the maximal frequency of occurrence, which corresponds to the way retinal images, roughly the size of the template shown in figure 1(c), are processed [7].

d. Interpretational: It can be explained by a phenomenon known as simultaneous contrast [8].

Figure: 1(d) - shows a glare effect or luminous-mist effect [8].

Though having the same luminance, the center white square surrounded by four dark rectangles gives an effect that light is emitted from the center [8].

e. Neurological: V1 transforms information received from the lateral geniculate nucleus (LGN) and distributes it to separate domains in V2 for transmission to higher visual areas. According to Hubel and Wiesel, retinal activation induced by bars of light led to the selective response of V1 neurons. In the second visual area of the primate (area V2), the segregation and compartmentalization of cells processing form, color, and depth information is evident [9].


3. Motion

The Barber Pole effect would best explain this attribute as its effect is “the orientation of the grating presented behind the rectangular aperture and the aspect ratio of the aperture, which in combination determine the relative contributions of local motion signals perpendicular to the gratings and parallel to the aperture borders, respectively.” [10]

Explanatory Strategies for Motion Perception

a. Psychological: Diagonally moving grating is perceived as moving vertically because of the narrow, vertical, rectangular shape of the aperture through which it is viewed. This shape–motion interaction endured through a wide range of parametric disparities in the shape of a window, the spatial and temporal frequencies of the moving grating, the contrast of the moving grating, complex variations in the composition of the grating and window shape, and the duration of viewing [11].  

b. Interpretational: The perception of an image includes the brain’s interpretation of the image on the retina. Many 2D visual image features transpire where edges from two contrasting, yet overlapping, surfaces meet. Such compound features are “intrinsic” to neither surface and have been termed “extrinsic.” Human observers rationalize intrinsic and extrinsic aspects on the basis of depth-ordering cues that exist at occlusion periphery [12].

c. Empirical: Perceived motion can be determined by “linking retinal stimuli with moving objects according to the relative success of behaviour over evolutionary and individual time; however, by accurately modelling the relationships between moving objects and the perspective projection of their corresponding images, the simulated environment serves as a proxy for the relative success of visual behaviour instantiated in visual circuitry” [13].

d. Neurological: “In identifying an action, the perception of biological motions plays an enormous adaptive role. It may, therefore, be hypothesized that the perception of biological motions is subserved by a specific neural network” [14]. According to a functional MRI study on ‘motion areas’ involved in visual motion, processing occurred in the bilateral middle-temporal complex (V5+), the left SOG (lSOG; V3/V3A), the bilateral lingual and middle occipital gyri (V1/V2), and the ventral part of the occipito-temporal junction [15].


4. Depth

The perception of depth is substantially enhanced by the fact that we have binocular vision. This provides us with more precise and accurate estimates of depth and an improved qualitative appreciation of the three-dimensional (3D) shapes and positions of objects [16]. We took an example of inserting a pencil into a nut hole. With one eye, it was difficult to insert the pencil into the hole, whereas it was easy with two eyes. This is because with one eye, the human eye sees everything in 2D orientation, whereas with two eyes, the human eye can perceive everything in 3D orientation.


5. Distance

Ponzo Effect

This illusion is demonstrated by two lines. The line that is above appears to be longer than the line below, despite the fact that both lines are of the same length [17].

Explanatory Strategies For Depth And Distance Perceptions

a. Psychophysiological: Depth and distance are ascertained through both monocular (one eye) and binocular (two eyes) cues. The brain uses these cues to perceive depth and distance.

Monocular cue: We chose linear perspective to understand the monocular cue and how it influences the perception depth and distance. Linear perspective occurs when two parallel lines converge as they travel away from the viewer into the distance. As we look at train tracks, for instance, the tracks appear to join together in the distance, even though they stay parallel.

Binocular cue: We chose retinal disparity to understand the binocular cue and how it influences the perception of depth and distance. One can see the difference in the images of the same object on the retina of two eyes. To demonstrate the example of retinal disparity, hold any object (pencil) close to your face, view it with just your left eye, then just your right eye, and you will see the image ‘jump’ back and forth.

b. Interpretational: Interpretation can be perceived by changing the distance of an object (pencil) in different angles from the observer. The retinal image appears to be different from different angles.

c. Empirical:We chose texture gradient as an example to explain the perception of depth and distance. One can see the clear texture of grass when it is right in front of one’s eyes, but as one goes further into the distance, grass appears to be blurred or isn’t clear in regard to texture.

d. Neurological: In humans, experiments using random dot stereograms have shown a stream of areas that respond to these three-dimensional cues: V1, V2, V3, VP, and V3A. V5 (hMT+). Nevertheless, all the regions activated by random dot stereograms show a correlation between the amplitude of the fMRI signal and disparity [18, 19].



This review on descriptive analysis is an attempt to simplify the complexities of the human visual perception of the physical world. It is a summary of how important our judgment is in situations where our comparative ability is challenged (what we perceive versus what exists in physical reality).


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Ganesh Elumalai

Ganesh Elumalai

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Tajnin Hashim

Tajnin Hashim

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Nicolas Ceresoli

Nicolas Ceresoli

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