Forms of Visual Space in Phenomenology

Brentano argued that visual space is three-dimensional through analysis of the properties of the primary continuum that account for perceptual expe­rience. His conclusion puts the long-established claim that visual space is two-dimensional into question. Berkeley had reasoned that distance is a line directed to the eye projecting one and the same point on the retina regardless of its becoming longer or shorter; hence, depth cannot be a perceptual datum. Koffka (1930: 162) remarked that this reasoning assumes that the dimension of visual space is determined according to that of the retinal surface and implies that the study of visual space regards the adjacent points on its surface. How­ever, he claimed that the assumption is contrary to perceptual experience and the implication does not live up to the experimental research. Katz (1911) and Fuchs (1923) studied the phenomenal transparency in which points or regions appear to lie on surfaces one behind the other. Moreover, Wertheimer (1912a: 224) discovered that two lines presented in the optimal stroboscopic interval are unified into a single line that moves behind a third line at rest. Finally, the modes of appearances of colors show that spatial properties can assume many forms, for example a plane or a volume, that are connected with particular qualitative features.

Metzger’s (1929) experiments in the Ganzfeld provide a proof against the theoretical tenet that visual space is originally a two-dimensional surface from which subjects extract points or regions, by means of monocular or bin­ocular cues, which are then imagined or inferred to hold relations in a three­dimensional space. In addition, he shows that the forms that visual space may assume, like the hemisphere of the sky vault or the empty space that fills the visual field, emerge from its three-dimensional structure. The Ganzfeld is the visual field that is filled completely by as homogeneous a brightness as possi­ble. Metzger has the subjects sit and look obliquely, from bottom up, at a point 1.50 metres above the floor on a whitewashed panel. The panel has a width of 4 x 4 m and, with further panels placed at its sides, it completely covers the visual field so that a light projected on it from the rear spreads brightness over the whole visual field filling it. Metzger reports that at low illuminations, sub­jects see a volume of uniform neutral color that resembles a fog mass, with the panel surface as its rear boundary. At high illumination, an illuminated surface appears as a white wall immersed in a bright space. The colors of the wall and of the illumination are not as clearly distinct as in the ordinary space that is replete with visual things. For different intensities of illumination, the white color of the surface is not always preserved, yet a proper change of this color is not perceived either. Both the color of the wall and the illumination are seen to vary, although not in parallel, so that it is sometimes difficult to discern them. The material character of the wall’s appearance becomes clear if a small figure is alternatively made to appear and vanish over it in the Ganzfeld. The small figure appears more homogeneous, thick and rigid than the wall, which ap­pears loose and less resistant to sight. Nonetheless, the wall does not have the film-color mode of appearance. Its color is a surface-color. Moreover, the wall is not oriented in the frontal-parallel plane, as is the norm for film-colors, rath­er it appears perpendicular to the subject. Furthermore, if a square is projected on this surface, it also appears to be perpendicular. It does not appear distort­ed at all, rather of constant form, in spite of the actually oblique line of sight of the subjects. The color mode of appearance, the orientation and the form constancy show that the Ganzfeld appears really as a thing surface. Between the homogeneous color mass and the surface, there are other appearances of intermediate nature that occur at varying intensities of illumination. Starting from high illumination intensities, as the intensity is gradually decreased the vertically straight surface wall changes into a curved cavity (Hohlraum) that surrounds subjects. The cavity appears as a hollow cupped space that, like the sky vault, is slightly flattened in the middle. Metzger reports that when the surface wall is changed into a cavity, its rigid material becomes an elastic sub­stance that is distinctly extended, like a ball that has been suddenly inflated. Consequently, the color of the surface looks like it is being stretched until it is condensed in a film surface with the form of a cup. With prolonged obser­vation or a further decrease of intensity, the elastic boundaries of the curved cavity become a fog that is nevertheless still perceived to be at a distance from the perceiver. It is not something the subject is immersed in, rather a mass that does not reach her but is located in front of and separated from her by an empty space (Leerraum) through which it is seen.

This evidence proves that the two-dimensional surface and the frontal- parallel orientation are one of the possible perceptual appearances. The visual space appears from the outset to be endowed with a third dimension. In the most fundamental condition of very low illumination, the visual space is a vol­ume that is filled by the fog mass. While it is true that this fog does not appear at a determinate distance from the subject, it is also true that it appears to be thick, hence with differences in depth between some of its parts, and located at a distance, albeit not at a definite one. In this sense, the homogeneity of the color filling the visual field is not complete. In the fog that appears through the empty space, the thickness of its layers increases at increasing distances from the observer. Some spatial relations may occur even in this space. When a small (8 cm) circular figure is introduced in the field at a distance of 1 m from the subjects and its intensity with respect to the Ganzfeld is increased gradu­ally, for some values of this intensity difference the figure moves forward while the fog recedes. The opposite case occurs by lessening this difference. The fig­ure is covered by the empty space, but remains visible through it, as when the moon shines through the clouds that pass in front of it (see Cohen, 1957, 1958). If the transition to the hollow curved cup, which is concave toward subjects, is obtained by means of a rapid increase of the illumination intensity, the color moves away from it and appears at a distance that approximates that of the panel. Instead, when the perpendicular wall appears, for increasing intensi­ties of illumination it appears to recede from subjects at increasing distances, so that the wall can reach the apparent distance of 2 m or 2.5 m away from subjects. If the light is alternately turned off and on at higher illumination, the darkness appears as a screen that is located near the subject’s eyes and at a distance of 1 m from the bright wall.

Therefore, the appearance of a surface is embedded in the phenomenal space, which can take the form of a filled volume, an empty space or a concave surface curved toward the observer. Far from being two-dimensional, the space is originally endowed with the third dimension. The depth appears as different degrees of thickness, and while the distance is not always clearly determined, its values range within a defined interval from the wall surface to the fog mass. Consequently, Metzger (1966) points out that the question of space percep­tion is not how to recover depth from a surface, but how a surface may appear in a three-dimensional space. Metzger (1929) shows that the crucial factor is the perception of discontinuities in the Ganzfeld. At higher intensities of il­lumination, the heterogeneities of surface grain may be noticed. Even when single heterogeneities in the surface remain under the threshold if presented in isolation, their interaction over a sufficient extent of the surface allows them to exceed the “surface formation threshold” and appear as surface structure (1929: 10). Metzger projects a little square on the Ganzfeld illuminated at such low intensity as to appear as a frontal-parallel film surface. If the intensity of the square is the same as that of the wall appearance, then it appears as the surface of an object with constant form. If the square is illuminated at a lower intensity than that of the Ganzfeld, as when the square is left unlit in the low- illuminated Ganzfeld, it does not appear detached from the surrounding field, rather it has a film-color appearance that spreads over an area that looks more wide than tall.

Metzger concludes that the appearance of surfaces requires qualitative dis­continuity and boundaries within which it is extended. A surface always ap­pears embedded in space or, at least, it requires further spatial properties as phenomenal conditions. Therefore the perception of a completely homoge­neous surface with a spatial extent that would amount to the whole visual field is impossible. If no heterogeneity appears, the nature of the source of light stimulation is indifferent. Whether the subject is presented with a surface, which may be near or far, straight or bent, or real fog, she is bound to have the same experience: being immersed in a foggy light mass that becomes thicker as the distance of its layers increases.

Source: Calì Carmelo (2017), Phenomenology of Perception: Theories and Experimental Evidence, Brill.