PEARL sensations

This week we have been testing the ability of PEARL to achieve a full blackout. This capability is important, as it gives us a baseline for our lighting work - we need to be sure that all the light in the Space comes from 'our' lighting installation, so that we know precisely what light is present, with no other light, natural or artificial, changing this. We started testing for this a few weeks ago, and discovered a small number of leaks, that meant that, although the light level was very low, it was not absolute zero. We set about fixing the leaks, so we needed to test again for the absolute minimum light level.

This week when we ran the tests again, there was no visible light at all in the Space - and so, because we can only see objects as a result of light reflecting from them, nothing in the Space was visible. It was quite disconcerting - one had no sensation of space at all, or even a sense of which way one was facing. However, when standing on the balcony in the Space there was another sensation of interest.

The Space has a balcony (called the View) along one side of the Groove, which is set about 5m above the floor. This is useful for seeing the Space from above and provides a convenient viewing platform. When all the visible light is removed from the Space, of course nothing is visible anywhere - including from the View. However, when standing on the View under such conditions, another aspect of our sensory system became apparent. To explain this, we need to understand about how we use multisensory information in our daily lives.

image of the PEARL Space from the View showing the floor level of the main space several metres below
The view from the View, showing the main floor level below

Our only source of information about the environment comes through our senses. This information arrives through a variety of sensorial pathways in the form photons (vision), pressure waves (hearing, touch, balance). We process the sensory information in dedicated parts of the brain before passing the resulting information on to create our perception of the world around us and thus to inform the conscious and preconscious decisions that we make all the time. All the senses are considered in parallel (although some take longer to process than others), so that our perception of the world is driven by all of our senses all of the time.

Let's take a simple example. When we stand on the ground we can (usually) see the ground beneath us. We know where it is, not only because we see it, but also because we feel it through our feet, and we can hear sound reflected from the surface. Our balance system tells us that we are upright, confirmed by our vision system that the sky is "above" and the ground is "below" and this is also confirmed by our hearing because sound is being reflected from the ground and vertical surfaces around us, but not from the sky. These sensory information flows confirm that the world makes sense - we see the ground at the same place as we hear and feel it. When one or more of these confirmatory senses is absent, we feel odd - in a ship at sea, the sense of solidity of the 'ground' beneath our feet conflicts with our sense of balance (that tells us we are in motion) and (if we can see it) with the motion of the horizon, and the combination of these perceptions does not make sense; on a narrow mountain pass, the visual evidence of solid ground goes and we feel unsafe, even though our feet are telling us that the world beneath our feet is solid. The conflict here can lead to a sense of vertigo. Normally we are not aware of these confirmatory sensory information flows, because we believe our eyes and rely a lot on our vision to tell us about the world.

PEARL has another sensory characteristic: the background sound is very low - inside the building the sound level is similar to that observed in a quiet bedroom. In addition, the walls are designed to absorb sound produced within the building. Although the building is not "anechoic" ('anechoic' means that there is no echo at all in the space, and all sound is absorbed into the walls, and no sound at all is reflected by any surface in the space), the average reverberation time in the Space is about 1 second (this means that if you were to clap your hands in PEARL, the sound you make would reduce to 60% of its loudness in less than one second) - maybe similar to a lounge in a small house. We use our hearing system to tell us about the size of a space, and normally this agrees with the visual sense of the same space. Sometimes it differs - for example in an empty theatre, the space might seem to be quite large to the eye, but because it has been designed to allow the transmission of human speech, the space seems quite small to our hearing system. It can take a few seconds to resolve the difference in spatial perception between vision and hearing, until we can explain it - "it's a theatre, so it is what I expect - everything is fine!".

However, what happens if we remove vision from the sensory information flow? I asked a visitor to PEARL who has no vision capability at all - not even a sensation of the difference between light and dark - how big they thought PEARL was. After listening for a short time, they decided that it was not such a big space. It was only as we walked along the Space, and after about 60m, that they realised that the building was much larger than they had thought.

At the very low light levels mentioned earlier - zero light - even people with a functioning vision system can no longer use their eyes. As mentioned before they could see nothing at all. However, in PEARL under such conditions, the sense of hearing is also lost - the sounds reflecting from the floor and walls are very small (which is why the blind person thought the room was small). When standing on the View, even the very small sound reflection from the floor is lost - because the floor in front of a person standing on the View is over 6m below their ears - and, once the light is removed, the only sense of position comes through the feet. Our feet tell us that the ground is where we expect it to be - around 1.5m below our ears, but our ears are telling us that the ground is much lower than this. We have to work hard to figure out this conundrum, and we struggle to find an answer to the question "where am I?" - our understanding of the information we are receiving from the environment is severely challenged. How can we be standing (upright), apparently on solid ground, yet our ears are telling us that there is no ground for us to stand on? From our lived experience we might be able to associate this with being at sea - but not quite. In this case we can neither see nor hear anything of a ship, and our sense of balance is telling us that we are not moving. So what might be our situation? Floating in space? Instinctively we grab the handrail to stabilise ourselves, and by so doing, the handrail provides us with an additional physical sensory information flow. Now the hands and arms tell us that we are indeed stationary, and this confirms the message from our feet that we are standing still on a solid surface, so therefore the world is there and all is fine (if a bit odd). I wonder what it would feel like if there were no handrail to hold on to?

What this shows us is the importance of multisensory information to our existence. How important it is that we understand how all our senses inform the perceptual system about the environment, even though for much of the time we are not aware that we are being informed in such a multisensorial way. The design of the environment needs to be considered in terms of these preconscious information processes, not just in terms of those stimuli of which we are conscious.

We designed PEARL, not just to be able to reproduce physical and sensory environments, but also to be able to 'remove' sensory information from real environments, so that we can begin to understand just how we really do perceive the world. From this understanding we can learn how to design the environment to communicate better with us through the information pathways that our senses use. Thus PEARL can help us to make built environments work better for people.

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