It is an unsettling fact that the majority of noises that rats emit are beyond human hearing. Rats produce sounds in the ultrasonic range (20 kHz to 50 kHz), which is well above the human hearing ceiling of around 20 kHz. The squeaks we hear are at the lower end of their range and the very upper end of ours.

We hear clichéd statements like we are never a metre away from a rat. In the UK, they outnumber humans by about 2 to 1. If we shared their ultrasonic range, their chatter would be almost as ubiquitous as the chirping of birds. Birdsong. Ratsong. Imagine it in your walls. Underneath your parquet. In your ceiling. Between the floors of your house. It would be relentless. We wouldn’t sleep.

Think about how this would change our perception of the world. What else would we hear on this range? For a start, we would hear all other noises from all kinds of rodents, like the ultrasonic love songs that mice sing. We would hear bats and moths in their eternal fight with one another. We would hear plants and trees in distress or injured: hear the screams of our hedgerows as we trim them back or the agony of potatoes as they boil. We would not see a tractor harvesting crops: we’d hear a massacre instead. We would hear fungi everywhere.

Cityscapes would be full of noises of the creaking and moaning of tired steel. We would hear the distress of bridges and elevated roads as vehicles and trains routinely pass over them. We would hear the manic rattling of metal sheets welded together of an airplane during take-off, landing and in-flight. Imagine if this superpower suddenly came to us at 33 000 feet, how would we convince ourselves that these noises were perfectly… normal? It would be terrifying. Thankfully, these are all sounds that occur beyond our sensory window.

The limits on what we can hear are just one example of how our biology shapes what we perceive. We are programmed to hear frequencies that are most relevant to our evolutionary biology. It helps us to identify danger from predators, sounds from other humans (i.e. also predators) and cues from the immediate environment. We do not hear the ultrasonic realm because we focus on frequencies that are tied to survival and social interaction.

How we read

Our biology also shapes how we process information: whether through sight, smell, hearing, taste. When we read, our visual system does not perceive an entire page at once. Instead, we process text sequentially. We typically process one word or phrase at a time, scanning line by line. This is because our foveal vision, which is the sharp focus in the centre of our gaze, can only absorb a few words at once.

Our reading feels linear because it is. Our eyes make quick saccades, or jumps, from left to right (or the opposite in right to left writing systems). Our eyes then process small clusters of words in bursts, which are then decoded by our brains. We can only build meaning one chunk at a time, just as we ‘hear’ in limited frequency bands. This contrasts with how an AI reads, which bounds through text in split seconds, leaving our capabilities looking puny in comparison. I often wonder if AI could enhance our perception of the world, but that is a whole other topic.

The Dimension of Culture

Our writing systems throughout history have been engineered to fit around our biological limitations. However, how we process information does differ across cultures.

In Western cultures, writing is left-to-right. You start at the top left-hand corner and gradually proceed down to the bottom right-hand corner. We follow linear patterns that are reinforced by how the information is presented, such as alphabetic text and bullet points, headings and sub-headings. When materials like Clinical Outcome Assessments are designed in a Western culture, which most of them are, the assumption is that everybody around the world visually processes information in the same way.

This is a terrible assumption to make. Cultures shape not just what we read, but how we read. In many East Asian cultures, for example, traditional writing systems follow vertical columns, read from top to bottom, right to left. This changes the rhythm and eye movements that readers use. Right to left scripts reverse the directional scanning that is second nature to Western readers

Beyond directionality (the direction in which people read), certain cultures prioritise information in ways that can seem alien to Western expectations. The Western way of presenting information value hierarchy and bullet points, while other cultures look more for context and relationships when they process information.

Our brains are trained within specific cultural ecosystems and they are wired for these patterns when reading. What feels intuitive to one group may feel fragmented and confusing to another. A Clinical Outcome Assessment developed with a Western eye that prioritises clarity through linear argument might clash with other traditions that weave meaning through other ways.

Yet, we keep exporting and imposing Western-shaped documents, with the expectation that all human readers will “see” the information in the same way. But we do not: many readers interpret information using cognitive and cultural filters that may be invisible to the developers of the information.

The challenge, then, is to become aware of these blind spots. To realise that our limits define what we think is “normal”. Just as we live in blissful ignorance of the ultrasonic noise that fills our auditory environments, so too are we often oblivious to the silent signals in the way others read and process information. We do not hear the ratsong around us, but it is there: constant and insistent, shaping an unseen narrative. In the same way, the cultural frequencies embedded in how we design and read information persist silently in the background – often unheard by the developers, but deafening to those using the information. When are we going to start attuning ourselves to these silent signals?

The next batch of articles will focus on how COA items are processed differently across cultures.

Thank you for reading,

Mark Gibson

Leeds, United Kingdom, March 2025