The Fine Line Between What We Do and Don't See
Given that we see the world through two small, flat retinae at the back of our eyes, it truly is remarkable that what we perceive is a seamless, three dimensional world. Our retinae respond to wavelengths of light from the world around us, but that’s only Part One of a multi-step process. Our brains have a lot to do with the raw data that it receives, like stitching it together, choosing what to perceive into consciousness, and what to omit.
In the field of neuroscience, it’s that conscious perception and omission process that has been of great interest. Recently, a study was carried out that could help us to understand why similar visual stimuli are sometimes detected, and why they sometimes remain subliminal.
Much of what enters through our eyes, we never actually see. Many images stay subliminal, leading to a response in brain activity in the visual areas, but not entering our consciousness. What’s interesting is that very similar weak signals sometimes get through, but don’t make their way through conscious perception.
Research Into Conscious Perception & Omission
For a team of neuroscientists in the Netherlands, this phenomenon has prompted research into the influence of internal brain dynamics on conscious perception. Pieter Roelfsema from the Netherlands Institute of Neuroscience states, “With very weak stimuli close to the threshold of perception, we can learn a lot from comparing brain activity when everything about the stimulus environment is the same, except one time it is consciously experienced and the other time it isn’t.”
Roelfsema and his team investigated the route between the primary visual areas and dorsolateral Prefrontal Cortex (a higher processing area). During the study, conscious reactions would only occur when there was strong and sustained activity in the frontal cortex. Signals that went unnoticed had weaker activity and quickly decayed.
Theorists Create a Model To Replicate These Dynamics
To understand this further, the theorists on the study created a model to replicate these dynamics. The model combines elements from two tried and tested theories, namely the “Signal Detection Theory” and “Global Neuronal Workspace Theory”.
The “Signal Detection Theory” states that the ability or likelihood to detect some stimulus is affected by the intensity of the stimulus (e.g., how loud a noise is) and your physical and psychological state (e.g., how alert you are).
The “Global Neuronal Workspace Theory” states that “global ignition” has to occur in the brain for information to become consciously accessible. It suggests a fleeting memory capacity in which only one consistent content can be dominant at any given moment.
Connections Between The Parietal & Frontal Cortex
The model suggests that ignition is caused by strong connections between the parietal and frontal cortex. The analysis was very thorough, but the resulting model is actually quite simple. What the team found is truly remarkable because of how closely the model’s output resembles the real life measurements of their subjects.
To close, Roelfsema had the following to say, “While this study is certainly not yet the full picture about visual thresholds and conscious perception, the results are very exciting for our future work.”