Spatial perception

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Space perception - referred to in scientific literature as depth perception - is the kinesthetic, acoustic and visual experience or construction of space . Fundamental to this is the perception of the distance from the observer, i. H. the spatial depth.

Binocular space perception

Similar to a camera, the eye lens creates a two-dimensional image of the environment on the retina. However, spatial perception , i.e. seeing from spatial depth, is possible. It is based on two principles: on the one hand, the distance between an object and the eyes is perceived; on the other hand, knowledge of the world and the objects within it provide an interpretation of the spatial depth.

parallax

Humans and many animals have two eyes lying next to each other, with which the same point in space can be viewed at the same time and stereoscopic vision is possible. Due to the small lateral distance, the image of the two eyes is seen from a slightly different perspective, which results in lateral shifts (so-called transverse disparity ) between different points in space. Up to a distance of approx. 10 m, this parallax can be interpreted by the brain as spatial depth information.

convergence

To look at objects in the vicinity, the eyes are turned inwards by the nasal eye muscles, while the eyes are parallel when looking at objects that are far away. Up to a distance of about 3 meters, the brain can derive information about the distance from the convergence of the viewing axes.

Monocular space perception

Spatial depth in a two-dimensional image.
A space shuttle taking off. The sun is behind the camera to the left, and the shadow of the column of smoke is cast in the earth's atmosphere towards the moon.

If stereoscopic viewing is not possible or if an image, such as a photograph or a painting, is viewed, the spatial assignment must be reconstructed from the depicted objects. Conversely, the monocular cues are used by painters, etc. to achieve a spatial effect.

Accommodation

In order to be able to see a point in space clearly, the curvature of the eye lenses is varied ( accommodation ). Over time, one learns which distance is related to which strength of the curvature, so that conversely, from the change in the curvature of the lens, a conclusion about the spatial depth is possible. Here the estimate of the distance is limited to approx. 1–2 m.

Linear perspective

Everyone knows the example of railroad tracks or a road that seem to unite to form a point on the horizon. This effect of converging lines can be seen in all straight edges and boundaries of bodies that are spatially parallel to each other. We know that they run parallel and are not tempted to actually assume that they unite on the horizon - instead we also read their image as that of a spatial situation.

In the Renaissance , the geometric methods of linear perspective flourished and produced an abundance of painted trompe-l'œils . In the Baroque era, this law was also used to create impressive architectural effects in the smallest of spaces, as Bernini masterfully accomplished in the forecourt of St. Peter's Basilica in Rome and almost virtuoso in the small staircase that leads into the more private apartments of the Pope, the famous Scala Regia to the right of the main facade of St. Peter's Basilica.

Example: In both images, the actually parallel edges of the road and shadow converge on the photo and are interpreted as an impression of depth. A lack of experience also leads to misinterpretations, for example sun rays .

Relative size

If we know the size of an object, we can estimate its distance from its relative size (i.e. how big it is on the retinal image). If we see several identical objects in different relative sizes, we “read” them as different distances away and not as differently sized specimens that are at the same distance.

Concealment - backdrop effect

Due to the peculiarity of our perceptual apparatus to involuntarily fill in missing parts of known shapes in our minds, we suspect a sequence in the case where one shape hides another and would not get the idea that the only partially visible shape is missing a piece. We owe this principle, among other things, the majestic effect of mountain chains lying one behind the other or the enormous spatial effect of multi-aisled Gothic cathedrals , the column and arch forests of the Alhambra in Granada or the cathedral-like effect of large beech forests.

In the theater, this effect is used together with the principle of constant size in order to simulate spacious hall arrangements in the limited space of the stage. The more overlaps of forms we see and the more layers we can read, the stronger our spatial impression becomes.

Example: The above photo shows an example of mountains arranged one behind the other.

shadow

We take further information about the three-dimensionality of bodies and spaces from their shadows. From the incidence of light, we read off their volume and surface properties, but also the predominant direction and quality of light. In case of doubt, our brain assumes that the light comes from above (so-called light-from- above heuristic ), preferably from the top left (at least in cultures that write and read from left to right). In this way we can see whether the shapes are convex or concave, what the boundaries and transitions between them are, etc. Accordingly, the shaded representation of the bodies increases their degree of recognition. A body's own shadow (the darker side, because it faces away from the light) gives it volume and expansion, while the cast shadow (i.e. the shadow that the body casts on its surroundings) defines its spatial relationship to other surfaces and bodies - this is where the principle comes in the concealment (see above) as an effect.

Example: Examples and possible misinterpretations can be found in the article Kippfigur .

Aerial perspective

Objects far away appear blurred, brighter and more bluish. We owe this distance information to the fact that we live in a clouding medium - the air that surrounds us. In the atmosphere, the actual air molecules as well as water vapor and suspended particles such as soot, smoke or sand cloud the sunlight and the light that is reflected from the bodies.

This clouding causes the contrasts to decrease in the distance. Black surfaces no longer appear black, white no longer white, the colors lose their saturation and, on sunny days, show an increasing proportion of blue the further away their position is from the viewer (see Rayleigh scattering ). This effect can be seen very well on days when there is heavy haze .

In contrast, one should pay attention to the lighting effect of the photos of the astronauts on the moon or the images that were transmitted by the space shuttles: no clouding of the sky black; the lunar horizon and just above it the small blue ball of our home planet seem close enough to touch.

Example: In the foreground in the photo above, the color of the trees is dark green. With increasing distance, it brightens and shifts to bluish. The distant mountain ranges are only a little darker than the sky.

Relative height

Objects that are close to the horizon line in the two-dimensional image are interpreted as being further away than objects that are seen further above or below. On this heuristic is based u. a. the moon illusion .

Motion parallax

When we move through a scene (e.g. in a car), objects close to us pass the eye faster than objects further away. This is also known as motion parallax .

Acoustic space perception

Interiors can also be experienced acoustically; each one has its specific acoustic room signature . Experienced listeners know e.g. As well as with closed eyes, whether they are in the Musikverein in Vienna , in a storage hall ( reverb !), Or in the Abbey of Le Thoronet are. Due to the 360 ​​° reception of the ears, the acoustic impression of the room is, unlike the visual, holistic.

Despite the physical and acoustic sciences (e.g. for the construction of concert halls), the neurobiological investigation of acoustic space perception is still in its infancy.

In bats, the perception of space is almost exclusively acoustic, and blind people can also learn to use the sound of self-generated clicking noises reflected by objects and walls for space perception.

swell

  • E. Bruce Goldstein: Sensation and Perception. Wadsworth, Pacific Grove (USA), 2002.
  • Michael W. Eysenck , Mark T. Keane: Cognitive Psychology. Psychology Press, Hove, 2000.
  • Jourdain, Robert (1997, German 1998): Music, the Brain, and Ecstasy. How Music Captures Our Imagination. NY

Individual evidence

  1. ^ E. Bruce Goldstein: Perceptual Psychology . Springer, Berlin, Heidelberg 2008, ISBN 978-3-8274-1766-4 . , Chap. 8th
  2. Robert F. Jourdain wrote (1997): “Reverberations ... are relatively rare in nature, and our brains have not evolved a special mechanism for overlooking them. Like musical sound itself, reverberation is a minor aspect of our natural experience that we have magnified into art. Much music becomes lifeless without reverberation. Early recordings lacked reverberation and they sound off kilter, as if the music were played in the wrong style. Indeed, some Late Romantic music simply doesn't work outside halls with long reverberation times, where hundreds of reflections add up to the 'big sound' such music requires ”(JOURDAIN 1997: 49). And: “In the late 1980s, French archaeologists explored prehistoric caves in southwestern France in a unique way - by singing. They discovered that the chambers with the most paintings were those that were the most resonant. This starting insight suggests that caves were the sites of religious ceremonies involving music ”(JOURDAIN 1997: 305).