5. The Participants In The Categorisation Process

The categorisation process is a systematic interaction between: 

(1) the perceivable: what can be detected and categorised; 

(2) a means of detecting the categorisable, specifically: light in the case of visual perception[1]; and 

(3) a recognition system that can categorise what it can detect through sensory modalities like vision, hearing, smell, taste, touch. 

The distinction between (1) and (2) does not hold for all sensory modalities. For example, in the case of touch, there is no intermediary between the perceivable surface and the tactile sensory detectors. The same is true for taste, where there is no intermediary between the perceivable chemicals and the olfactory sensory detectors. In the case of smell, there is no intermediary between the perceivable chemicals and the olfactory sensory detectors, but the perceivable chemicals may emanate from a source that is not otherwise directly perceivable. This is also the case for hearing: there is no intermediary between the perceivable air compression waves and the auditory sensory detectors, but the perceivable air compression waves may emanate from a source that is not otherwise directly perceivable. 

Crucially, the distinction does hold for the primary modality of humans: vision. Visual perception does involve an intermediary between the perceivable and the visual sensory detectors. What makes contact with the sensory modalities, photons, is distinct from the perceivable being categorised visually, but is the means by which the perceivable is detected. The one exception here is the visual perception of light sources, which patterns like smell and hearing, where the perceivable light emanates from a source that may not be otherwise directly perceivable. Visual perception is both atypical and the primary modality through which humans categorise the perceivable, which gives unique status to the rôle of photons in human experience.[2]

Failure to make this distinction between the visible and the visual means of perceiving the visible has resulted in confusions like “colour (unlike other properties) exists only in the head of the observer”. Colour perception involves the detection and categorisation of difference (categorised by other means as light frequencies) reflecting off and refracting through the visible, and depends, inter alia, on the light frequencies emitted by the source and the molecular arrangement of the visible. 

Footnotes:

[1] A similar example in some species is the use of echo location, where the perceiver emits the radiation that reflects off surfaces in its vicinity.

[2] More of which later.

ChatGPT said:

Categorisation and the Modalities of Perception

Categorisation is a systematic interaction between:

1. The perceivable — that which can be detected and categorised;

2. The medium of detection — the physical means through which the perceivable becomes available to the senses (e.g. light for vision); and

3. The recognition system — the organism’s sensory and neural apparatus capable of detecting and categorising inputs through modalities such as vision, hearing, touch, smell, and taste.

This tripartite model holds clearly for some modalities and less distinctly for others. In the case of touch and taste, there is no mediating substance or signal between the perceivable and the receptor: the skin makes contact with the surface, the tongue with the chemical. Similarly, for smell and hearing, while there is no intermediary medium between stimulus and receptor — airborne molecules and compression waves respectively interact directly with the olfactory or auditory systems — these stimuli often emanate from sources that are not themselves directly perceivable. The same logic applies to echolocation in certain species, where emitted signals reflect off surfaces and return as perceptual data.

Vision, however, is structurally distinct. It introduces a mediating layer between the perceivable and the perceiver: photons. These photons are not the visible themselves, but the means by which the visible is detected. What is received by the visual system (light) is ontologically distinct from the object that emits or reflects it. This mediation is absent in other sensory modalities, making vision both atypical and, in humans, primary. One exception within vision is the perception of light sources themselves, which — like sound or smell — involves perceiving an emission rather than light reflected off another surface.

This layered structure has philosophical consequences. The failure to distinguish between the visible and the means of perceiving the visible has led to confusions, such as the claim that “colour (unlike other properties) exists only in the head of the observer.” Colour is not a free-floating quale but a categorisation of difference — specifically, differences in the frequencies of light reflected from and refracted through material surfaces, modulated by the properties of the light source and the molecular composition of what is seen.

---

Footnotes:

[1] Echolocation in species such as bats and dolphins offers an analogous structure: the perceiver emits the signal that reflects off nearby surfaces and returns as a perceptual input.

[2] The mediating role of photons in human experience — their ontological and epistemological status — will be addressed in more detail later.