Многозначные изображения и восприятие: иллюзии и механизмы зрения.

Image that exploits graphical similarities between two or more distinct images

Ambiguous images or reversible figures are visual forms that create ambiguity by exploiting graphical similarities and other properties of visual system interpretation between two or more distinct image forms. These are famous for inducing the phenomenon of multistable perception. Multistable perception is the occurrence of an image being able to provide multiple, although stable, perceptions. One of the earliest examples of this type is the rabbit–duck illusion, first published in Fliegende Blätter, a German humor magazine. Other classic examples are the Rubin vase, and the "My Wife and My Mother in Law" drawing, the latter dating from a German postcard of 1888. Ambiguous images are important to the field of psychology because they are often research tools used in experiments. There is varying evidence on whether ambiguous images can be represented mentally, but a majority of research has theorized that mental images cannot be ambiguous.

Middle vision is the stage in visual processing that combines all the basic features in the scene into distinct, recognizable object groups. This stage of vision comes before high level vision (understanding the scene) and after early vision (determining the basic features of an image). When perceiving and recognizing images, mid level vision comes into use when we need to classify the object we are seeing quickly. Whether perceived or actual, Negative space will play a role here. Higher level vision is used when the object classified must now be recognized as a specific member of its group. For example, through mid level vision we perceive a face, then through high level vision we recognize a face of a familiar person. Mid level vision and high level vision are crucial for understanding a reality that is filled with ambiguous perceptual inputs.

When we see an image, the first thing we do is attempt to organize all the parts of the scene into different groups. To do this, one of the most basic methods used is finding the edges. Edges can include obvious perceptions such as the edge of a house, and can include other perceptions that the brain needs to process deeper, such as the edges of a person's facial features. When finding edges, the brain's visual system detects a point on the image with a sharp contrast of lighting. Being able to detect the location of the edge of an object aids in recognizing the object. In ambiguous images, detecting edges still seems natural to the person perceiving the image. However, the brain undergoes deeper processing to resolve the ambiguity. For example, consider an image that involves an opposite change in magnitude of luminance between the object and the background (e. g. From the top, the background shifts from black to white, and the object shifts from white to black). The opposing gradients will eventually come to a point where there is an equal degree of luminance of the object and the background. At this point, there is no edge to be perceived. To counter this, the visual system connects the image as a whole rather than a set of edges, allowing one to see an object rather than edges and non edges. Although there is no complete image to be seen, the brain is able to accomplish this because of its understanding of the physical world and real incidents of ambiguous lighting. These illusory contours are processed by the brain in a similar way as real contours.

The rule of similarity states that images that are similar to each other can be grouped together as being the same type of object or part of the same object. Therefore, the more similar two images or objects are, the more likely it will be that they can be grouped together. For example, two squares among many circles will be grouped together. They can vary in similarity of colour, size, orientation and other properties, but will ultimately be grouped together with varying degrees of membership.

When a region of texture completely surrounds another region of texture, it is likely the background. Additionally, the smaller regions of texture in an image are likely the figure. Often, this image is perceived incorrectly and produces an illusion that differs from reality. For example, an image may be split in half, with the top half being enlarged and placed further away from the perceiver in space. This image will be perceived as one complete image from only a single viewpoint in space, rather than the reality of two separate halves of an object, creating an optical illusion. Street artists often use tricks of point of view to create two dimensional scenes on the ground that appear three dimensional.

Figures drawn in a way that avoids depth cues may become ambiguous. Classic examples of this phenomenon are the Necker cube, When making a mental representation of an ambiguous image, in the same way as normal images, each part is defined and then put onto the mental representation. The more complex the scene is, the longer it takes to process and add to the representation.

Our memory has a large impact on resolving an ambiguous image, as it helps the visual system to identify and recognize objects without having to analyze and categorize them repeatedly. Without memory and prior knowledge, an image with several groups of similar objects will be difficult to perceive. Any object can have an ambiguous representation and can be mistakenly categorized into the wrong groups without sufficient memory recognition of an object. This finding suggests that prior experience is necessary for proper perception. Studies have been done with the use of Greebles to show the role of memory in object recognition.