The Borders of Perception
A Suitable Criterion Is Yet to Come
What can we perceive, in a metaphysical sense of the question – what legitimately is a target of a perceptual state? For a long while, in philosophy this venerable debate has concerned the issue of what the objects of perception are, sensory objects as they have been recently labeled (Nanay 2013). Yet there is no agreement at all among philosophers on which are such objects – for some intuitionists, even abstract objects can be perceived, while for some others, the so-called indirect realists, the only objects that are properly perceived are sense-data, mind-dependent entities.
This disagreement has prompted people to recently move the debate towards the issue of whether one can single out what are the perceivable properties (Siegel 2010). Even there, however, pretheoretically speaking a cloud of vagueness spreads over such matters. For on the one hand, there are paradigmatic examples of properties that are perceivable, low-level properties such as colours, sounds, and shapes. On the other hand, there are paradigmatic examples of properties that cannot seemingly be perceived (for a different opinion, cf. Prinz 2006) – e.g., institutional properties like being a President or social properties like being an influencer.
Yet there is a huge dark area inbetween concerning so-called high-level properties – for example, are the (natural) kind property of being a pine tree or the semantic property of being a meaning that so-and-so perceivable properties? Some people following Siegel (2010) have opted more liberally for the rich view, according to which various high-order properties such as those just exemplified indeed are perceivable properties. Yet some other people have opted more restrictedly for the thin view, according to which only low-level properties such as e.g. having a color or having a shape are perceivable – an old Berkeleyan idea that is reprised by many philosophers nowadays (e.g. Byrne 2009).
In the philosophical discussion about this second issue, two main approaches have recently been advanced. On the one hand, a 'from inside to outside' approach: perception is a limiting case of (multimodal) mental imagery. Or in other terms, whatever is imaginable in a sensuous way (e.g. by imagining seeing, or by imagining hearing etc.) is also perceivable. As a result, many high-order properties that are mentally imaginable as possessed by an object turn out in the end to be perceivable (e.g. action properties (Nanay 2013), or even synaestethic properties (Nanay 2017)).
On the other hand, a case-by-case approach: one must pick up one candidate high-order property at a time in order to see whether it is perceivable. This approach appeals to the so-called method of phenomenological contrast (Siegel 2010). According to this method, a property is perceivable iff the best way to account for a phenomenological difference between two similar yet non-identical perceptual experiences is to claim that unlike the first experience, the second experience grasps the property in question (whether or not the property constitutes the content of the experience) (Di Bona 2017). This method allows for a bunch of high-order properties like being an item of a certain natural kind (e.g., being a pine tree), being caused by something, or having a meaning, to be perceivable properties.
Both approaches sound objectionable. Although it may sound phenomenologically plausible – one may check by introspection whether one may may have a mental image of the relevant property's instantiation - the first approach lies on the assumption of a structural similarity between mental imagery and perception that many people find disputable. For example, there is a huge debate as to whether pictorial perception basically is a matter of mental imagery (Walton 1990) or is rather a matter of, albeit sui generis, perception (Wollheim 1980). This debate would lose its point if perception were a form of mental imagery. The second approach not only focuses merely on perceptual experiences, but in its being a case by case strategy it heavily and admittedly relies on an inference to the best explanation, whose outcome is obviously disputable. For example, various people find more convincing the idea that the phenomenological difference between an experience of a mere expression and an experience of that expression cum its meaning is cognitive and not perceptual (O’Callaghan 2011, Martina-Voltolini 2017, Voltolini 2020).
This philosophical impasse may lead one to think that the matter must be settled empirically, notably by appealing to neuroscience. Of course, neuroscience focuses on the empirical neural correlates of experiences, so the criterial procedure must follow two steps. First, the notion of a perceivable property involves the notion of a perceptual experience that allegedly grasps that property. Second, in order for an experience to be perceptual, it must be implemented in specific cerebral areas that neuroscience is in charge to discover (Mesulam 1998). Yet things have revealed to be more complex, for cerebral perceptual areas can hardly be individuated strictly anatomically. As Masrour (2011) stresses, the borders for anatomic implementation must be fixed functionally, i.e., by looking at the function that a certain experience must play. As far as high-order perceptual properties are concerned, this allows for more flexibility in looking for the neural implementation of their experiences.
For example, with respect to the so-called expressive properties, i.e., properties of an individual that allegedly express an emotion she is entertaining (e.g., traits of fear or of joy displayed in someone's behavior), neurologically speaking one may prima facie say that such properties are not perceivable. For the cerebral areas that are classically implicated in emotion disorders are different and distant from the areas that are classically implicated in perceptual disorder (see, respectively, Borod 2000 and Farah 2004). Yet this negative conclusion is no longer to be taken for granted. First of all, the experience of the others' expressions of emotions is linked with the perceptual experience of action properties (Ferretti 2015, 2017) and that experience resonates in a mirror neural mechanism that fires both when one acts or experiences an emotion in the first person and when one perceives others' actions and emotional expressions in the third-person (Gallese-Guerra 2019). Moreover, not only the experience of emotional expressions triggers amygdala, a neural structure that belongs to the lymbic system, but also the impairment of such a structure prompts a deficit in the recognition of emotional expressions in others' faces or others' voices (Schirmer-Adolphs 2017).
So up to now, no general criterion, whether theoretical or empirical, has successfully been proposed in order to establish whether a property is perceivable. But the search for that criterion is the right road to pursue, in particular from a philosophical point of view. Suppose that both an auditorily-oriented property like being a female voice and a visually-oriented property like being a cheerful smile were perceivable properties. Would this be just a sheer coincidence, or do such properties share some features that are both necessary and sufficient conditions for them to be perceivable? Finding a suitable criterion of perceivability would enable one to find a principled answer as to whether, for any conceivable candidate property, this property is perceivable or not.
In this respect, different steps must be followed. First, there are many proposals as to what makes high-order properties perceivable – e.g. immediacy and velocity in their grasping, being subject to adaptation phenomena such as the one involved in the famous waterfall illusion (Block 2010, 2014, Fish 2013), or even being irresistibly grasped (Toribio 2018). Yet these proposals only provide allegedly necessary conditions of perceivability, but not sufficient conditions. In other words, no shared recipe as regards what makes a high-order property perceivable qua high-order property has already been given. In this direction, the role of attention in non-conceptual recognition of object-Gestalten (Byrne 2009, Jagnow 2015, Masrour 2011) is still to be properly explored. For it is quite likely that, in its working not locally but holistically, attention here plays a proper perceptual role (Jagnow 2011, Burnston 2017, Stokes 2018, Voltolini 2015, forthcoming). This exploration will allow one to also check whether its function in the adaptation phenomena fits with that role.
All this is particularly relevant as far as aesthetic properties are concerned. Clearly enough, aesthetic properties are high-order properties, certainly dependent but not always supervening on low-order properties, as Danto’s (1981) thought experiment about an original artwork and its trivial indistinguishable copy is famously intended to show. When are they perceivable? If the same sort of attention that is involved in Gestalt-recognition is also involved in their grasping (Nanay 2015), then they may count as perceivable. This is a form of attention that is focused on an object and distributed across its properties (Nanay 2016, 2020). Pace Nanay, only when it is also disinterested, it may be regarded as a properly aesthetic attention. Incidentally, this may help one to distinguish between expressive properties and aesthetic properties: all such properties are addressed via that form of attention, but only the latter ones are invested with a disinterested kind of such an attention.
Alberto Voltolini is a philosopher of language and mind whose works have focused mainly on fiction, intentionality, depiction, and Wittgenstein. He is currently Full Professor in Philosophy of Mind at the University of Turin (Italy)