by Wolfgang Metzger (1974)

(published in: Hyroshima Forum for Psychology 1, 1974, 3-14; included in: R.B. MacLeod & H.L. Pick, eds., Perception. Essays in Honor of James J. Gibson. Ithaca and London: Cornell University Press, 1974, 57-71; page numbers of this latter publication are included in square brackets)
[W. Metzger Bibliography of Publications in English, French, Italian, Japanese and Spanish]

1st part

Perception in the System of Psychology

In talking to younger psychologists, one finds that many of them seem to believe that perception is something at the surface of the mind, a kind of borderline problem, and that preoccupation with it is obsolete. They look with disdain at every psychological problem that does not at least deal with personality, motivation, or social intercourse. But when discussing problems in which simple facts of stimulus and reaction play a role, as for example in behavior therapy, they prove that they would have done well to occupy themselves a little more with the fundamentals of perception. It is hard to get them clear on the differences between a stimulus in the physiological sense, such as impingement on receptor cells, and a valence or Aufforderungscharakter in the sense of Kurt LEWIN, or an IRM in the sense of ethology. Obviously they have never been confronted with facts that can only be understood by carefully distinguishing between an impact on a sense organ and a characteristic of a percept that has come into existence through such impacts, and which therefore cannot again act on a sense organ of the same organism but only on the perceiving subject. Subjects correspond somehow to organisms, but are percepts themselves existing within the same phenomenal world as the objects to whose valences or IRMs they react. Psychologists of the younger generation tend to forget that, taken strictly, all social interaction is primarily interaction between percepts, interaction which only by cybernetic mechanisms is transferred to the participating organisms and copied by them, so that the interaction of the organisms is but a mediating correlate of what happens in the phenomenal worlds of the interacting subjects. And if this is the case, the theory of perception plays a fundamental role for every other field of psychology (cf. METZGER, 1965, 1968, 1969; GRAEFE, 1961).

[p. 58:]

Objects and Percepts

Phenomenal worlds are not exact reflections of the physical world. What is lacking in them, if compared with it, can be seen in any physics textbook. But on the other hand they have quite a number of essential characteristics that cannot be found in the physical world: the secondary and tertiary qualities of percepts and situations and the valences and tensions existing between them have no counterpart in the corresponding physical facts. But still they represent the physical facts so reliably, and their deviations from them correspond so highly, that different subjects in spite of their different standpoints can consider their respective phenomenal worlds as identical, that is, as, for all practical purposes, one and the same objective reality.

How do these phenomenal worlds come about? The question has at least partially been answered by psychophysics, if this term is taken in a sonewhat loose sense. The decisive point is that there is no direct communication between physical objects and percepts corresponding to them, but that between them there is a more or less long and complicated chain of causation whose critical link is the stimulation of receptors, that is, the initial penetration of the organism. This point is decisive. For the only basis of a phenomenal world is the totality of stimulations of millions and millions of receptor cells in their ever-changing distribution, as called forth by the changes in the objects themselves and by changes in the relations between objects and organisms as caused by the subject itself, whether impulsively or intentionally.

Percepts are never structurally identical with the varying configurations on the receptor level. Percepts are units or wholes coherent in themselves and segregated from each other; stimuli are not. Percepts are tri-dimensional and move in a tri-dimensional space; underlying stimuli are distributed over two-dimensional surfaces of the body, such as retinae or the skin of the fingertips. Percepts have (approximately) constant attributes such as size, shape, surface color, and so on, just as their physical counterparts do, while the underlying stimulus configurations vary continuously. For these reasons percepts are in decisive characteristics more like objects than like the stimuli intercalated between objects and percepts. Thus some thinkers (such as Max SCHELER) have been inclined to assume a direct, extrasensory connection between the two ends of the chain. Another attempt at accounting for the astonishing correspondence between the two ends of the causal chain between object and percept that must be
[p. 59:]
noted here is J.J. GIBSON's; if I do not misunderstand him he holds that this chain is circular in the sense that it finally returns to ist starting point (GIBSON, 1966). The formulations of these authors raise many new and unsolved problems. Therefore the conventional conception is preferable according to which there is neither direct connection nor identity between object and percept. This leaves the basic theoretical question of how and by what factors varying stimulus configurations are transformed into stable percepts.

A World Created by Mental Acts

The oldest source in which it is held that the ego creates its own world by an act of will is J. G. FICHTE's Introduction to Philosophy (Einleitungsvorlesungen in die Wissenschaftslehre, 1797), in which he tries to interpret KANTian epistemology. But his arguments are so highly speculative and so far from empirical evidence that in this connection he shall only be mentioned.

Twenty years later, in 1818, Arthur SCHOPENHAUER dealt with a concrete problem of perception. His problem is how it happens that objects are seen where they are, instead of at the place of the physiological processes in the retina or in the cortex. According to his hypothesis, the subject follows the light rays back to the point on the surface of an object from which they diverge to the foveae of the two eyes, and, recognizing the angle between them, is able to reconstruct its place. With this, he in a way anticipates the theory of judgement or inference brought forward by HELMHOLTZ in about 1860.

The starting point of HELMHOLTZ's theory is that invariably the nervous stimulations (we should say excitations) are directly perceived, but never the objects themselves. (Or in a more general and less hypothetical formulation: the immediate basis of object perception is invariably the sum of stimulations of receptor cells but never the objects themselves.) HELMHOLTZ continues his argument as follows: "But there are mental activities that enable us to form an idea as to the possible causes of the observed actions on the senses. In their result, these activities are equivalent to a conclusion or inference from analogy"; this is the well-known theory of unconscious inference. (From this follows his explanation of visual illusions as "erroneous interpretations" [Urteilstäuschungen].) HELMHOLTZ does not deny that there are certain differences between the hypothesized analogical inference made by the subject and his observable free acts of conscious
[p. 60]
inference: the former are instantaneous; they are unconscious, and - as Wolfgang KÖHLER (1913) adds - concerned with unconscious material; they are irresistible, that is, cannot be corrected by better knowledge. There is one more fundamental difference that was not yet known to HELMHOLTZ and KÖHLER: conscious inferential thinking becomes the more difficult the higher the complexity of the problem situation grows. However, with the phenomena that HELMHOLTZ intended to explain by unconscious inference, this relation is exactly reversed: the more complex the situation, the more irresistible and unambiguous the effect (METZGER, 1934).

Actually there are many more problems left open. Everybody knows what "an idea to a possible cause" is, and that an idea such as a pure thought or a mental image is quite different from a true percept, that is from a thing of our environment that can be seen and manipulated. And the question arises how this special kind of idea is related to the palpable things in our surroundings through processes originating in the retina and skin receptors. Another problem is the unavoidable inference that the subject must sit in the middle of the organism and from there observe all the stimulations around him, forming ideas as to their possible causes, ideas which by a rather miraculous additional act are "projected" or "externalized" beyond the surface of the organism into its nearer or farther surroundings.

KÖHLER (1913) points to the fact that no unconscious inferences are assumed by HELMHOLTZ if a plausible objective explanation for a phenomenon exists, as in the case of color mixture. Actually, HELMHOLTZ´s theory applies to all those phenomena which cannot be understood without the assumption of lateral interaction of simultaneous nervous processes (Querfunktionen, as WERTHEIMER called it in 1912). Lateral interaction was not yet believed to be possible in the nervous system at HELMHOLTZ`s time. Unconscious reasoning as well as unconscious sensations were constructs that could be dispensed with as soon as this possibility had been acknowledged.

Nevertheless, HELMHOLTZ´s theory is still alive. More than forty years after KÖHLER`s criticism it has been revived by TAUSCH (1954), KRISTOF (1961), and GREGORY (1962), but was refuted again by ZANFORLIN (1967), FISHER (1968), and METZGER (1970). One more instance of a relapse into HELMHOLTZian speculations can be found in an article on decision
[p. 61:]
theory by SWETS et al. (1964). We owe to these authors not only the wellknown concept of sensitivity, but also the concept of choice of criterion in threshold observations, which means a valuable step forward in this field. But their decision theory makes sense only in the peculiar situation of threshold exposure, when the subject, presented with the task of detecting something hardly perceptible, is forced to make decisions observable by himself and by the experimenter. But the authors go further and try to apply their new-found principle to perception in general, with paradoxical consequences. Their generalization would imply that, for example, (1) while looking at a human face, a crowd in the street, a landscape, or a bunch of flowers, thousands of decisions would be necessary at one and the same moment, and that (2) all these decisions would never be noticed - in constrast to the observable deciding activity in threshold experiments.

But the whole waste of unconscious activities need not be assumed, because if the perceiver contents himself with clearly supraliminal differences, as is the case in all naive everyday vision in which no searching attidude is maintained, there is nothing to decide.

The most recent publication in which HELMHOLTZ´s theory expressly adopted is "Die Psychophysiologischen Grundlagen des Wahrnehmens" ("The psysiological foundations of perceiving") by Egon KÜPPERS, a German psychiatrist (1971). But the abundance of fictitious mental activities introduced by him goes far beyond HELMHOLTZ.

There are still other types of mental-act-theories of perception. In his Sinnespsychologische Untersuchungen (Sensory Psychological Investigations) of 1917 (which, by the way, are full of interesting and reliable observations), Julius PIKLER offers a theory of binocular depth perception according to which the subject is able to observe separately the two retinal images of the right and left eyes, to interpret them as geometrical projections of solid bodies, to compare them and from their deviations to draw conclusions as to the distance and shape of the object represented by them.

The "Komplextheorie", first brought forward by MÜLLER (1903, 1923) and later with slight alterations by PETERMANN (1929, 1931), deserves special mention, along with the "Produktionstheorie" of MEINONG and BENUSSI (1904). These are theories of unit formation and unit segregation in perception that agree in the assumption of a special mental activity on he part of the subject. He organizes the perceptive field out of the crowd of unconnected elementary sensations by "producing" real - as opposed
[p. 62:]
to merely imagined - relations between them or by directing collective or unifying attention to them.

These theories have the advantage of being based on activities of the subject that under certain conditions can actually be observed. Everybody knows what attention is, and can discriminate between an attentive and an inattentive state of mind. Beyond this, everybody knows the difference between seeing, for example, four points either as the corners of a square or as the ends of a cross, and can experience how by a change of attitude one of these apprehensions of the configuration can be changed into the other. (By the way, these two are not the only alternatives!) In the theories of production or collectice attention this observable unifying mental activity is generalized to all cases of unit formation, and where it - as in the vast majority of cases - cannot be observed, it is thought to work unconsciously. BÜHLER (1913) and KÖHLER (1926) have pointed to the numerous facts that contradict such assumptions. The range of deliberate unification proved to be surprisingly narrow; unit formation in innumerable cases does not follow intentional, and to that extent observable, unifying or segregating efforts, and so many objective "cues" controlling attention behavior must be introduced by these authors right from the outset (MÜLLER, 1903), that finally the concept of attention is reduced to an x that occasions the subject to build very definite units, an x that can be omitted without any loss if the "cues" of these theories are considered as factors acting immediately upon the perceptive field.

To sum up, none of the know theories of "creating" one´s own world by mental acts has proved to be adequate to facts.

continued in 2nd part

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