Hermann von Helmholtz has been widely acknowledged as one of the forerunners of contemporary theories of measurement. However, his conception of measurement differs from later, representational conceptions in two main respects. Firstly, Helmholtz advocated an empiricist philosophy of arithmetic as grounded in some psychological facts concerning quantification. Secondly, his theory implies that mathematical structures are common to both subjective experiences and objective ones. My suggestion is that both of these differences depend on a classical approach to measurement, according to which (...) the arithmetic laws of addition define what is measurable as a particular domain for their application, and, at the same time, the extensibility of these laws to all known physical processes works as a heuristic principle for empirical research. Such an approach is worth reconsidering, not only because it lends plausibility to some of the controversial aspects of Helmholtz’s theory, but also because it offers a philosophical perspective on quantification problems that originated in the nineteenth-century.This paper draws insights on Helmholtz’s philosophical views from his engagement with the measurability of sensations via Fechner’s psychophysical law. This seems to be in contrast with the fact that the reception of Helmholtz’s theory culminated with the formulation of the theory of extensive measurement. I will contend that Helmholtz reached a no less important standpoint in the nineteenth-century debate on whether sensations are different (i.e., intensive) kinds of magnitudes and on how, if at all, they can be measured. (shrink)

Flickering light induces visual hallucinations in human observers. Despite a long history of the phenomenon, little is known about the dependence of flicker-induced subjective impressions on the flicker frequency. We investigate this question using Ganzfeld stimulation and an experimental paradigm combining a continuous frequency scan with a focus on re-occurring, whole percepts. On the single-subject level, we find a high degree of frequency stability of percepts. To generalize across subjects, we apply two rating systems, a set of complex percept classes (...) derived from subjects’ reports and an enumeration of elementary percept features, and determine distributions of occurrences over flicker frequency. We observe a stronger frequency specificity for complex percept classes than elementary percept features. Comparing the similarity relations among percept categories to those among frequency profiles, we observe that though percepts are preferentially induced by particular frequencies, the frequency does not unambiguously determine the experienced percept. (shrink)

Our understanding of human visual perception generally rests on the assumption that conscious visual states represent the interaction of spatial structures in the environment and our nervous system. This assumption is questioned by circumstances where conscious visual states can be triggered by external stimulation which is not primarily spatially defined. This work discusses psychophysical experiments investigating flicker induced subjective experiences of colour and form. Using the presentation of spatially uniform flicker with a precise temporal resolution it is shown that subjective (...) experiences do not only depend on stimulation frequency, but also on stimulation phase. In addition, the occurrence of one subjective experience appears to be associated with the occurrence of others. The phenomenology of subjective colour and form is further explored and the physiological mechanisms underlying subjective colour are investigated using electroencephalography. While these data indicate that conscious visual experience may be evoked directly by particular variations in the flow of spatially unstructured light over time it may be assumed that the systems reponsible are essentially temporal in character and capable of representing a variety of visual forms and colours, coded in different frequencies or at different phases of the same processing rhythm. (shrink)

Summary In the visual arts, the constructions of the spatial and chromatic structures of pictures can hardly be separated from each other. The phenomenological approach from the perspective of the arts provides an independent and worthwhile approach to the topic of colour and space. We address some matters of composition in design and, to some extent, in naturalistic painting. The phenomenological approach from the perspective of the arts reveals various topics that invite further investigation by the means of generic vision (...) science. However, although such studies might lead to increased academic insight, a thorough inquiry by the means of experimental phenomenology might well lead to formal descriptions that come somewhat closer to possible applications in the visual arts. (shrink)

Our understanding of human visual perception generally rests on the assumption that conscious visual states represent the interaction of spatial structures in the environment and our nervous system. This assumption is questioned by circumstances where conscious visual states can be triggered by external stimulation which is not primarily spatially defined. Here, subjective colors and forms are evoked by flickering light while the precise nature of those experiences varies over flicker frequency and phase. What’s more, the occurrence of one subjective experience (...) appears to be associated with the occurrence of others. While these data indicate that conscious visual experience may be evoked directly by particular variations in the flow of spatially unstructured light over time, it must be assumed that the systems responsible are essentially temporal in character and capable of representing a variety of visual forms and colors, coded in different frequencies or at different phases of the same processing rhythm. (shrink)