Kohler’s arguments on the epistemology of perception and the scientific method show that the philosophical tenets of phenomenology have experimental implications. Kohler (1944) claims that phenomenology provides the foundation of philosophy and science because it demands that a construct is admitted if justified by a valid description of phenomena. Of course, the explanation of phenomena employs constructs that may have no “direct contact” with them. Still, phenomenology is required to give a complete description of the facts with respect to which the meaningfulness of constructs and the reasonableness of measures is tested. In particular, the terms and sentences of the psychology of perception must not refer to physiological posits and physical causes. Rather, their meaning has to be set from what the direct experience attests to be the features and real referents of perception.
In his lectures on epistemology, Kohler emphasizes the importance of Husserl’s phenomenology for philosophical and scientific theories (Jaeger, 1994). He claims that Husserl shows that the theories of Descartes and Hume, which have looked for an evidential basis of immediate data, are inadequate because they do not define the concept of immediate data and the criteria used to select them. Consequently, much of what is proposed as immediate data amounts to unreliable contingent observations that are neither generalized nor representative, like Hume’s data for the model of causality. The evidence is bestowed on the alleged immediate data by theoretical assumptions so that the distinction between facts and theories is blurred. Therefore, these theories give such different descriptions of the same phenomena that the truth of the propositions that are derivable from them is really undecidable.
Kohler (1944) claims that Husserl’s phenomenology has succeeded in correctly reducing philosophical and scientific knowledge to experience without introducing controversial posits, for instance the function of synthetic judgements or a priori intuitions, which do not agree with either the ordinary cognitive behaviour of naive subjects or the real practice of science. Besides, in his lectures Kohler acknowledges that Husserl rejects a misconceived naturalism that reduces knowledge and cognition to a mechanical adaptation to external conditions, so that both natural and human sciences would be forced to choose only between naturalistic positivism and historic relativism.
Kohler (1938) points out that phenomenology provides an analysis of what perceptual things really consist of. The phenomenological analysis demonstrates that the world subjects have direct access to is neither a collection of disparate sensory elements nor a continuum of undistinguished sensations.
Rather, it is a ruled collection of whole perceptual unities that are both segregated from one another and segmented into parts that are connected at varying degrees of extension, definiteness and complexity. This world is not coincident with the world of physics, which is constructed by inferences on the grounds of theoretical constructs and data that are detected indirectly from a selected class of observations through measurement devices in experimental conditions.
Therefore theories of perception must not include from the outset hypothetical constructs on the physical and physiological causes, because they do not denote anything that appears bona fide in the world. This does not mean denying that perception has a physiological basis, but if perception and science are two different sources of knowledge on the world, the theory of perception still has to satisfy the principle of “the preservation of the immanent form of phenomena.” According to this principle the formal structure, the empirical constructs and the observable variables of the theory should form the same “manifold” as that of the appearances at the scale of direct experience, provided a well-specified rule of correspondence between the units of analysis and the set of the relevant features. For instance, the phenomenological description identifies as perceptual referent what is invariant, that is, the phenomenal feature that is repeatable across appearances in varying conditions. Kohler maintains that things appearing in the world independent of subjects can be considered the bona fide referents of perception once the invariance of their relevant properties is recognized as a perceptual characteristic and the condition at which it obtains is studied as such. The phenomenological analysis aims at explaining how certain features of perceivable things emerge as invariant by specifying the laws of perception according to which they are observable pieces of the phenomenal structures of the world. Accordingly this analysis is not concerned with the actual causal dependence of perception upon unobservable factors, be they constructed as physical measures of stimuli or as neurophysiologic evidence. This dependence is not a fact that appears, hence it cannot play the same role as the phenomenal structures in specifying the conditions of invariance, which enables subjects to have access to the outer world. If it is reasonably true that appearances are caused by the neurophysiology of the organism, it is also unconditionally true that the organism and its neurophysiologic processes are not part of the phenomenal world (1929a).
Kohler carries out an epistemological clarification of this argument. On the one hand, he claims that the fact that things and qualities appear before and outside of perceivers seems paradoxical only if they are reduced to a physical and physiological reconstruction. If one reconstructs the perceivable things and qualities as terms of the physical and physiological causal chain of perception, they can no longer be identified with perceptual appearances but at most with the cortical locus that is the last stage of the underlying neurophysiologic process, namely with their neurophysiologic correlate. The hardly debated question whether phenomenal properties are actually commensurable with physical properties stems from this kind of reconstruction. It implies a subjectivist characterization of perception in opposition to the objectivist interpretation of the results of the indirect methods of natural sciences. On the other hand, Kohler draws a distinction between the self with her phenomenal body, to whom the things and qualities appear in the outside world, and the physical body upon which the appearances of both the self and the environment are functionally dependent. It does not make sense to state that the things really appear inside or within the self, because we know by conceptual and empirical means that perceived things and self depend on brain functions. Conversely, it would not make sense to state that what happens in the brain appears in the perceptual field.
Kohler agrees with Stumpf that phenomenology contributes substantially to a valid, complete theory of perception. The description of the structures of the phenomenal world and the discovery of the laws of perception justifies the concepts and constructs of the theory. If the constructs refer to entities that are not directly observable, the phenomenological description retraces their meaning to the structures of phenomena corresponding to particular contexts of perceptual experience. The rule of correspondence between constructs and phenomena is founded on the fact that the phenomenal world shows forms of order and inherent connections. Like Stumpf, Kohler contends that appearances have qualitative and quantitative dimensions. The subjects exploit them intuitively to make meaningful judgements on the properties of perceived things and qualities. This may happen directly, as for the distances of distinct places of things in the visual field or the instances of color similarity. It may happen indirectly, as in the perception of length by the comparison of the disparity between the ends of two things. If the subjects could not ascertain the phenomenal quantitative properties of things and qualities, it would be impossible to construct sophisticated and reliable methods to define the principles of measurement that play a fundamental role in the knowledge of the non-perceptual properties of things (1938: 115-118). Phenomenology plays a fundamental epistemological role in assessing the forms and validity of the two main modes of access to the world: perception and science. It describes the structure of phenomena, makes clear the meaning of concepts in terms of perceptual facts and evaluates the logical form of theories by judging the reasonableness and reliability of constructs and measures.
Source: Calì Carmelo (2017), Phenomenology of Perception: Theories and Experimental Evidence, Brill.