The Platypus and the Sensory Deprivation Tank

The darkness is absolute, a deep black that seems to erase sight. The silence is absolute too: every sound from the outside world disappears. The water, meanwhile, is warm and rich in salts, creating the illusion of floating in a void.

Closing yourself inside a sensory deprivation tank means confronting your senses, and your own ability to produce meaning, in a completely new and unusual way. The real surprise, however, is that the device does not work.

The tank was developed in the 1970s by neuroscientist John Lilly, with the aim of eliminating all the stimuli that activate our brain.

“The original idea behind the sensory deprivation tank was to gain access to the brain in its pure state, in a void, so that the human mind could be studied in the absence of stimuli,” says Luigi Lobaccaro, a researcher at the Department of Philosophy whose work focuses on cognitive semiotics and cognitive science. “In this respect, however, the device does not work, because the space inside the tank is not truly empty. On the contrary, it contains what Umberto Eco might have called ‘ersatz’ versions of emptiness: substitute stimuli for darkness, silence and the absence of signals.”

This contradiction at the heart of the sensory deprivation tank experience, which Lobaccaro has explored in a volume devoted to the Forme del silenzio” , raises a number of questions about how we assign meaning and significance to the world around us. It opens up a vast field of enquiry connecting Umberto Eco’s thought with neuroscientific research into the mechanisms of the brain.

“Our brain is a prediction machine: based on the stimuli it receives, it constantly generates hypotheses to interpret the world around us,” explains Giuseppe Di Pellegrino, a professor at the Department of Psychology “Renzo Canestrari” and an expert in neuropsychology and cognitive neuroscience. “To do this, we rely on mental representations and models built from what we already know. These help us interpret new information from the outside world as efficiently as possible.”

But what happens when we encounter something completely unfamiliar? A new experience, for instance, such as floating in a sensory deprivation tank. Or, as Umberto Eco might put it , when we see a platypus for the first time without having the knowledge needed to recognise it.

“Eco explored this problem extensively and asked precisely this question,” says Lobaccaro. “When late eighteenth-century explorers encountered a platypus, they could not find a label that would allow them to recognise what kind of animal it was. They were therefore forced to construct a new label for the platypus or, as Eco would say, a new ‘cognitive type’.”

When we observe a platypus for the first time, in other words, our mind has to draw on a range of prior knowledge in an attempt to give form to this stimulus and categorise it in some way, linking it to a specific concept. 

“When we look at a platypus, we search our minds for something similar to what we are seeing. But when we fail to find anything, we experience a prediction error,” explains Di Pellegrino. “This is a particular moment in which our neural activity intensifies and our synaptic connections change. Put simply, we are learning something new.”

But constructing a “cognitive type” also involves engaging with others: everyone may have their own idea of what a platypus is. And we need to reach an agreement in order to define a shared “cognitive type”.

“Once a cognitive type has formed in our mind, it can be described or represented and thus become a ‘nuclear content’. This can then be shared within a community, allowing us to arrive at a common recognition of reality,” confirms Lobaccaro.

“The mental models that allow us to recognise the world around us are strongly shaped by culture and interpersonal relationships,” adds Di Pellegrino. “We are a social species, and this gives us an enormous adaptive advantage.”

“We are a social species, and this gives us an enormous adaptive advantage.” In the darkness and silence of a sensory deprivation tank, then, the emptiness is only apparent. However hard we try to isolate ourselves from the world, our minds continue to generate signals, thoughts, ideas and emotions. In a word, meaning.