Excerpt from
L.Kleine-Horst: Empiristic theory of visual gestalt perception. Hierarchy and interactions of visual functions. (ETVG), Part 7, I

 The lowest stages of visual perception

1. The complete system 

Parts 1 to 6 describe those factors (and their phenomenal effects) that constitute the perception of the static, two-dimensional "figure in its outfield", i.e. the percept type "moon in the sky". In addition, the quantity, orientation and form factors were dealt with. In this Part, the description of the visual system shall be completed by adding eleven further gestalt factors and two further physical factors that refer to the depth (d) and time (t) aspects of visual perception. They are responsible for the perception of depth and time as well as modal change and movement. The eleven gestalt factors belong to the hierarchy Levels 1 to 5 as well. With the complete hierarchy of gestalt factors, the individual motion of a three-dimensional object in three- dimensional space is perceptible. 

Figure 7-1. The three-level physical and the ten-level psychical factor hierarchies that govern visual perception

Fig. 7-1 shows the complete system of gestalt factors at Levels 1 to 10 as well as the physical visual factors (or classes of factors) upon which the hierarchy of psychic (gestalt) factors is built.  

2. Physical matters and physical functions 

The new physical factors involved are the depth factor "Zd", and the time factor "Zt". These physical factors, together with the physical matters (Yd,Yt), whose dependent correlates they are, constitute the physical basis for depth, time, and motion perception. Actualization of the Y-matters does not lead to any phenomenon, as the physical evolutionary level does not comprise the phenomenal sphere; actualization of the (physical) Y-matters only creates the (physical) Z-functions. 

As was shown in Fig. 3-13, the factor Zl is subdivided into four (or even six) functions for rotating the eyeball to the left (Zhl), to the right (Zhr), upwards (Zvu) and downwards (Zvd). There are two groups of eye muscles, one of which rotates the eye horizontally (Zh), the other vertically (Zv). Together they belong to the material conditions for the Zl-functions of a single eye.  

The factors Zl and Zd are assumed to be related to one and the same physical level. Despite this, there is also a certain hierarchical relationship: Zd is assumed to be a subfactor of Zl, as it represents the ability to perceive depth, due to the "binocular disparity" of the two slightly different projections of one and the same object onto the retinas of both the left and the right eye, when any point is focused on by both eyes.  

Factor Zm, too, seems to possess a hierarchical substructure; in the present developmental state of the ETVG, color perception is assumed to be a differentiation of brightness perception, just as one might understand Zd being a differentiation of Zl.  

The ability to perceive a difference in depth is ultimately based on the purely functional determination of depth by the physical factor Zd. One could try to determine the "depth matter" (Yd) that correlates to this "depth function" (Zd), but this is not necessary in order to postulate the depth function itself. We must, however, postulate the depth function: it is necessary as a physical function for the theory of depth experience.  

A particular distance, detected only with the aid of the physical factor Zd, is a purely functional parameter and can only lead to functional motor responses, for example, the reflex action of the human eyes to focus on an object, or of a frog catching flies. A (subjective, phenomenal) experience, however, does not result from such purely functional activities at any Z-level; an experience of "distance at all" occurs first at the P-level, with the subfactor Pd.    

The lowest physical function in the visual hierarchy is the "timer function" Zt, the ultimate reference system for all temporal aspects in vision. 

3. The gestalt factor Pmldt 

Pm + Pl = Pml
The lowest psychic factor of the visual system, "Pmldt", appears - as shown previously - in the form of Pml, and is responsible for the perception "here is something bright" or "here is something dark". In this perception, a distinction is to be made between the aspects "is something", "here", and "bright (dark)". The latter two aspects refer to the physical functions Zl and Zm, respectively. In this respect, it is meaningful to use the symbol "P" for "is something", to which we can append the indices "m" for "bright" and "l" for "here": "Pml". 

Pd
At the P-level, one experiences not only "here is something bright", but "here in front is something bright". "In front" signifies that the brightness is ahead of me, outside of me, at a distance from me. The object detected is experienced as something objective, not as a "picture in my head". At the P-level, depth cannot be experienced as a particular depth; this would require that a distinction be made between a particular depth and all other depths. An experience of this distinction, however, is not possible at the P-level; it only becomes possible at the D-level. Consequently, depth can only be experienced "absolutely" at the P-level: as "in front" or as "distance at all". The reference system of Pd is Zd. 

Pt
At the P-level the experience of time is confined to the general experience of "point in time", the experience of "now"; a particular point in time cannot yet be experienced. The "now"-aspect of P-experience is symbolized by the index "t" belonging to the symbol "P". In its full regalia we now have "Pmldt". If we deal only with the t-aspect of P, we can write "Pt" (also correspondingly true for Pm, Pl, and Pd, which can also be treated as separate factors, or subfactors). The reference system for the t-aspect of P is the "timer function" (or timer factor) Zt, which is located belothe localization factor Zl, as all perceptual processes are referred to, and determined by, the "timer function".   

4. The four difference factors

Dm and Dl
Differences between Pmldt-percepts are detected at the next-highest hierarchy level, with respect to the four aspects of P-percepts, each, of course, with a separate factor. As discussed previously, the differences between "heres" are detected with the factor Dl, and the differences between "brightnesses" with the factor Dm.  

Dd
It is "logical" that a separate factor is needed to be able to detect differences between Pmldt-percepts with respect to their depths; it shall be the gestalt factor "depth difference" with the symbol "Dd".  

Dd has been formed as a particular memory content for the detection of different depths in the Pmldt-percepts. For Dd, too, we must postulate that complementary functional depth relationships are memorized, whereby the antagonistic functions Dd+ and Dd- are formed, the actualization of which leads to the polar Dd+/Dd- experience. In this case, polarity means that a "small" depth difference cannot be perceived per se, but only along with a "large" depth difference, and vice versa.

Dt
As soon as the P-factor is formed in early infancy, it is actualized at different points in time, each of which is experienced at the P-level as "now". The various functional differences between the "nows" are implicitly memorized as "large" and "small" functional time differen- ces between P-percepts; these memory contents function as the positive and negative functions Dt+ and Dt- of the second-level gestalt factor Dt.

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