Some rambling thoughts, prompted by this passage:
In short, sensations differ from perceptions in that sensations are co-determined by the subjectivity of environmental source of stimulation together with the subjectivity of animal body stimulated, while perceptions by contrast are actively interpretative rather than passively revelatory of the surroundings; rather than co-determined as sensations are, perceptions are determined more by the nature of the animal perceiving than by whatever is in the subjective constitution of the stimulus, with the result that perception adds to the awareness of sensations relations that do not reduce to the subjectivity of organism and environment interacting to create an intersubjectivity, but add to that intersubjectivity already in play objectively (as apprehended) a further interpretation consisting in relations which relate the environment objectively to the organism not according to the constitution of the things in the environment but according to the need and desires of the organism itself. This is why the objective world, the Umwelt, is both superordinate to (while incorporative of something of) the physical surroundings, and superordinate to the physical environment in a species-specific way, that is, according to an objective organization based upon and provenating from what is proper to and characteristic of the biological species to which the animal belongs. The environment is, so to say, and by comparison, ‘meaning neutral’ , while the Umwelt, the objective world, is what it is precisely through and in consequence of the meanings that it provides for the animal that inhabits it.
– Deely, Purely Objective Reality, p.67
As a first note in glossing this passage, Deely typically speaks of the “subjective” not in the contemporary sense of psychological subjectivity, i.e., the domain of opinions and beliefs belonging to each individual in a (mythical) “private world”, but rather in the sense of how an individual is constituted in itself, independently of cognition. I am a subject, you are a subject, the trees I currently see in the Boston Common are each subjects, made up in relative independence from constitutive actions being sustained by other entities.
So when Deely speaks of the subjectivity of the “environmental source of stimulation” and the “subjectivity of animal body”, he is referring to the fact that the way things are determines how they announce themselves in sensible channels, and simultaneously that the particular manner in which sense organs are attuned determines how we, who possess such sense organs, are capable of receiving the “data” sent along in those channels (as the sun is issuing ultraviolent rays of light, but my eyes are not constituted so as to sense them). Sensation is a direct and immediate operation of efficient cause producing formal result in material recipient.
In contrast, perception always involves interpretation; that is, we do not merely take in, but take-as. Consequently, there is more of a contribution on the part of the perceiving subject than there is on the part of the environment, which provides mere data, whereas the perceiver brings a “world” of interpretation-shaping experience. There is a meaning in perception, even if the perceiver does not know the meaning as such. This meaning, however, as experienced by the animal, is species-specific in one sense (as the perception of a lone wolf means “threat” to a sheep but not to a healthy, full-grown moose), and idiosyncratic in another (as a healthy, full-grown moose which was attacked by a lone wolf while less healthy and full-grown may carry psychological scars and interpret it as a threat anyway).
There is, therefore, a continual process of development whereby the animal’s perception is shaped through interpretation of experience. Interpretation produces habits; a single act of interpretation may, if the sensory stimulus is strong enough, produce a strong habitual orientation. You need only burn yourself on the hot stove once to want never to do it again.
But an experience can possess a complex number of stimuli, arranged in various patterns. An individual sensory faculty may take in only a specific range of sensory data; but the perceptual animal takes in wholes, contexts, and therefore perceives these sensory data as parts of a whole. It is this perceived totality which allows perceptual objects to have meaning, to be seen as belonging to a referential totality, a totality of involvements–including but not reducing to the subjective self–and, moreover, which allows us to be affected by these perceived objects not through the simple impression of a form, but through the complex causality of objective specification (see here).