What lies beneath?

Gaze into the 'eyes' of the leather bag above. Perhaps you see a complex and uncertain soul, both startled and a little angry. The cheese grater is desperately eager to please, but nervous that its rigid posture and forced grin will not win our approval. The fencing is friendly, wondering, but surely slightly inebriated. The anxiety and anticipation written so eloquently on the features of the sink unit invoke our sympathy and concern.

We often see 'found' faces incongruously and accidentally embedded in our everyday surroundings. To see such a spectacular diversity of patterns as faces is remarkable enough. More remarkable is that these faces are not merely recognised, but are imbued with 'hidden depths' of personality and emotion. Yet all of this emotional 'inner life' is, of course, complete fabrication, a product of the wild inventiveness with which we interpret the world. For all their human-like appearance, these images are no more than unremarkable snapshots of inert objects.

Rembrandt's wonderful series of self-portraits are, in many ways, quite the opposite of these accidental faces. Indeed, they are constructed with care and astonishing subtlety to conjure, in the viewer, a sense of almost limitless inner depth and possibility; the person we see is not merely an embodiment of stylised 'cartoon' emotion. The gaze that looks back at us is penetrating, inquisitive, perhaps slightly careworn. Each 'reading' of the painting seems slightly different from the last; the artist both reveals himself plainly and yet remains shrouded in ambiguity.

It is of course tempting to imagine that faces, whether natural, accidental, or artfully created by a great painter, allow glimpses into an inner mental world: the world of the soul, spirit, or thought itself. But, on reflection, this is surely an illusion. Accidental faces and painted canvases have no inner life, lurking under the surface of the image. The imagined and ambiguous depths are are an act of creative interpretation by the viewer. And our interpretation of real faces (whether our own, or Rembrandt's) are no different.

Suppose, for a moment, that we could observe, or even interrupt, Rembrandt in his workshop in 17th century Leiden. How could we gain additional insight into the inner depths of thought and feeling? Quizzing him on his state of mind would surely not uncover the artist's secret thoughts, but instead trigger some mix of surprise, bafflement or downright irritation. And gazing into his own eyes, whether in the mirror or canvas, Rembrandt surely sees just the same sense of uncharted, ambiguous hidden depths that we do ourselves. Rembrandt is not setting a crossword for which he alone knows all the answers; he is, rather, creating a mysterious image whose very wonder, from both viewer and artist, is its endless ambiguities and reinterpretations.

The same story applies to language. Consider how we interpret each other through words – whether through poems, prose, or the banter of everything conversation. A fragment of poetry (perhaps Andrew Marvell's 'But at my back I always hear/Time's wingèd chariot hurrying near'), a kindly tone of voice, or an uncharitable remark, may sometimes strike the hearer as a revelation. Yet, as with our readings of faces, what precisely has been unearthed remains a matter of creative interpretation, filled with ambiguity and uncertainty. We can, of course, be challenged to explain ourselves. But, as with Rembrandt viewing his own self-portrait, we have no special insights into precisely what we meant by that line of verse, verbal inflection, or tactless comment. Our words are no more a window into a hidden inner world than our facial expressions.

From the point of view of literary or artistic criticism, this line of argument is familiar enough. But, I suggest, it is less familiar when turned on the interpretation of human behaviour. We are happy to admit that works of art and literature are rich and fascinating precisely because of their openness and ambiguity – we accept that there is no 'true' interpretation, lurking beneath the images and words. Yet most of us balk at the idea that the complexity and subtlety of the people around us – ourselves included – has the very same source.

Indeed, interpreting ourselves, and the people around us, is no different, in principle, from the interpretation of characters in fiction: we are, quite literally, imaginary characters of our own creation. Our sense of our depth and richness depends on the open, ambiguous nature of our literary creations. There is no crisply defined 'real me', hidden behind by my words and actions, any more than there is a precisely delineated 'real Rembrandt' below the surface of his painting; or a 'real meaning' encrypted in lines of poetry. For artworks as for human beings, what matters are the multiple patterns conjured by the glittering surface; there is no single 'real essence' submerged in some shadowy inner realm. If we're trying to make sense of the flow of words, images, and actions that compose our lives, we can generate stories, and explanations, clarifications. If challenged further, we can back up, elaborate, or revise these initial explanations; and reinterpret these later explanations, and so on, forever. But we are merely laying interpretation upon interpretation, not uncovering some bedrock truths about contents of our minds.

Decades of perceptual, cognitive and social psychology show that we can't simply introspect the feelings, thoughts, memories and motives that lie under our mental surface. To pick a few well-known examples, from a very long list of possibilities:

• Self-report in perception falls at the first hurdle: I report that I see a world in full colour and detail. But outside the few degrees of the fovea, the image is blurry; and colour-sensitive cone-cells almost entirely absent. Perceptual richness is Daniel Dennett's 'Grand Illusion'; introspection about even our immediate perceptual experience is a mirage.
• We interpret, rather introspect, our own emotions: recall Schachter and Singer's celebrated studies, in which people unknowingly given adrenalin interpreted their 'jittery' feelings as indicating heightened irritation or amusement in later social interactions, just as we interpret found faces or lines of poetry.
• False memories can be implanted all too easily by the devious experimenter. The brain has to interpret what we recall, rather than merely look up records in an inner library.

We can't uncover the depths of our own minds, not because those depths are murky or difficult to fathom: but because, just as with an accidental face, or a Rembrandt self-portrait, there are no depths to uncover. The stream of our conscious experience is a flow of improvised interpretation and re-interpretation: of our environment, art-works, poems, other people, and even ourselves.

Our mental depths, then, like the depths of Rembrandt's steady gaze, are compelling products of our imagination. But trying to plumb those mental depths, whether by word associations, conversation, interpretation of dreams, or brain imaging, is no more likely to succeed than searching for the inner life in Rembrandt's self-portrait by peeling away successive layers of paint.

Nick Chater is Professor of Behavioural Science at Warwick Business School and author of The Mind is Flat (Penguin Allen Lane, 2018), winner of the Association of American Publishers PROSE Award for the best book in the category Clinical Psychology
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This article is part of the 'Under…' special issue.