After moving beyond VR as the only possible outcome, I needed to understand the physiological side of the system more carefully. If I am considering technology that can respond to changes in the body, I need to know what those signals can actually tell me and where their limitations are.
The term biosignal covers physiological information that can be measured from the body. Across the papers I have been reading, this includes heart rate, heart rate variability, electrodermal activity, respiration and EEG. These signals are interesting because they can change alongside stress, cognitive demand and emotional arousal, potentially providing information that is not dependent on somebody verbally explaining how they feel.
However, the more I read, the clearer it becomes that physiological arousal is not the same thing as sensory overload.
One signal that appears repeatedly in the research is Heart Rate Variability, or HRV. HRV describes variation in the timing between heartbeats and is commonly used as an indirect indicator of autonomic nervous system activity.
I read Bahameish et al. (2026), Comparative Analysis of Heart Rate Variability Across Cognitive Domains in Individuals with Autism and ADHD: A Systematic Review and Meta-Analysis. The review included 20 studies and 2,223 participants, comparing HRV during cognitive tasks across autistic, ADHD and neurotypical populations.
The overall effect across all included neurodevelopmental groups was not statistically significant compared with neurotypical participants, although the autism subgroup showed a significant difference. What is more important for my project is that the authors identify substantial heterogeneity and methodological inconsistency between studies.
This means I cannot treat HRV as a simple or universal marker of an autistic person's regulatory state.
The paper helped me understand why HRV is relevant in the first place. The autonomic nervous system includes the sympathetic and parasympathetic systems. The sympathetic system is associated with mobilisation and "fight or flight", while the parasympathetic system supports rest, recovery and energy conservation.
HRV is connected to this balance, which is why it is often explored in research around stress, cognition and emotional regulation.
For my project, this makes HRV interesting because an airport involves repeated changes in cognitive and sensory demand. Security, navigation, queues, crowds and unexpected changes could all influence the body's physiological state.
But this is also exactly why interpretation becomes difficult.
The same physiological signal can change for many reasons. A traveller's heart rate could rise because they are becoming overwhelmed, but it could also rise because they are walking quickly to a gate, carrying luggage, feeling excited, drinking caffeine or responding to another emotional or physical demand.
The anxiety-detection review reinforced this problem by warning against assuming that physiological markers can cleanly separate anxiety from other psychological states. Different measures also do not always agree with one another.
This is particularly important inside an airport because the environment is both physically active and cognitively demanding. A responsive system would need to understand physiological information in context rather than treating one number as a direct instruction to intervene.
This has made the idea of an individual baseline much more important to me. If people naturally have different heart-rate patterns and physiological responses, comparing everyone against the same threshold would make little sense.