Searching for neural and behavioural signatures of human consciousness in Belgium

Every day, a very high amount of visual information enters our brains through our eyes. Our retinas capture that information and then lots of different processes take place in the brain so we can make sense of such information. Then, consciousness happens. Some parts of what we perceived reach awareness, some others don’t.

In the past, scientists have been using different techniques to test whether the brain gives preference to certain kinds of visual information in the path to awareness. For instance, it has been claimed that human faces are particularly relevant – they reach awareness faster than other kinds of visual information, especially if they express strong emotions like fear. However, due to technical limitations, it had never been measured directly how much information is needed for the brain to push these pieces of information into awareness. Most studies on fast visual processing relied on masking techniques – presenting one very brief stimulus immediately after the brief target stimulus to prevent it from reaching awareness. This because normal screens simply can’t present images for durations briefer than around 15 milliseconds – a very long time for the brain to make sense of visual information.

Nevertheless, there is a newly developed machine in Belgium – an LCD tachistoscope that can present visual images for as low as 2 microseconds. This is just a very small fraction of a millisecond! Professor Axel Cleeremans (CRCN, CO3, ULB) invited me to run a series of experiments with this machine, which now has become a very important part of my PhD. I obtained very convincing evidence of how much exposure is needed for human faces to reach awareness. My experiments involved both behavioural and brain measures.

Student looking into the LCD tachistoscope's screen, which can present images for as brief as 2 microseconds.
LCD tachistoscope. A student helping me with one of the perceptual experiments.

I discovered that it takes about 2.5 milliseconds of visual exposure to discriminate a regular face image from its scrambled counterpart and that the brain can understand that such images are faces, with the holistic configuration they have, with about 4 milliseconds of visual exposure. Upright faces reach awareness faster than inverted faces, probably due to their holistic nature. There is a reason, after all, why we sometimes see faces where there are none! I also found that it takes about 6 milliseconds of visual exposure for the brain to extract emotional information from facial expressions. In summary, we can say the brain makes sense of faces and their emotional expressions with less than 6 milliseconds of visual exposure. That’s insanely quick!

Student wearing EEG cap to measure voltage changes in the brain.
A student wearing a 64-electrode EEG cap that measures voltage changes in the brain cortex. With EEG, we can measure neural markers of face and emotion processing.

I thank the University of Edinburgh and the British Psychological Society for funding my research stays in Belgium this year. Thanks to their awards I could address these and other very cool research questions empirically in a way that had never been done before. This project has yielded three conference presentations so far and will yield at least three journal papers. Thanks so much!

Categories: Belgium, Europe, Go Abroad FundTags: , , , , , , , , , ,

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