Tuesday 3 March 2015

The Virtual Bodily Self

This is the fifth in our series of posts on the papers published in a special issue of Consciousness and Cognition on the Costs and Benefits of Imperfect Cognitions. Here Aikaterini Fotopoulou summarises her paper 'The Virtual Bodily Self: Mentalisation of the Body as Revealed in Anosognosia for Hemiplegia'. 

How do humans know what is real? As though the philosophical issues raised by this question were not complex enough, my paper tries to tackle an even more convoluted question; how do humans know what is real about their own body? A simple answer would be that they have an evolutionary prescribed perceptual system that allows their brain to combine and ‘read out’ various signals about the body deriving from (a) within the body (e.g. heart beats), (b) outside the body (e.g. light), and (c) the body’s boundary, the skin (e.g. pressure).

This answer however turns out to be simplistic both philosophically and scientifically. Thankfully for the reader, the paper does not aim to reveal all the sources of trouble in this answer. Instead, I focus on one neuropsychiatric syndrome, unawareness of the body following right hemisphere stroke (anosognosia) and one computational theory of brain functions, the free energy principle to discuss only certain facets of a potential answer to the aforementioned grand question. First, this syndrome and theory are useful for reminding us that we may not be so good at knowing what is real about our own body.

Our brain seems to be biased in how it perceives current signals from the body and the world. These biases seem to rely first and foremost on its own phylogenetic and ontogenetic history, including spatial biases (e.g. the position of the eyes on the head and the body’s midline), emotional biases (e.g. basic motivational needs and learned emotional associations), and cognitive biases (e.g. paying attention to what it has learned is useful and inferring the rest). Second, this syndrome and theory are useful for reminding us that what we perceive as real is actually co-constituted as such with other individuals.

Most counterintuitively, this applies to our own body. In order to come to cognitively and emotionally know our own body as an object among other objects in the world, we need to be able to first both perceive it from within and experience it in relation to other individuals. Following many of such first- and second-person experiences we come to schematize our perception of the body as an animated object in the world that can be perceived by any third-person perspective (I have called this the ‘impersonalised body’).

Such abstract schemata then guide our inferences about current perceptions. The counterintuitive syndrome of anosognosia for hemiplegia, the striking, apparent unawareness of paralysis following right hemisphere stroke further teaches us that these facets of body perception may be served by different, interacting systems in the brain, in the sense that damage to one of these systems may lead these patients to have contrasting perceptions of their own body from different visuospatial and mental perspectives. Thus, despite the coherence and seeming directness of our bodily experience, our perception of the body may constitute an inference based on ambiguous sensory data and prior, competing models of the body from different perspectives.

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