'And this was done in collaboration with my wife and with Sid Koudier, and it came out as a Science paper a few years ago ('A Neural Marker of Perceptual Consciousness in Infants', Science, April 19, 2013, Vol. Once he was able to establish this marker, Dehaene and his team decided to do the same tests in infants. 'So there is a second wave which is completely non-linear,' Dehaene said, 'where we either get a lot of activation, stable in time, and the subjects say, 'I saw the picture', or we get very little activation, the brain waves go back to zero basically, and the subjects say, 'I saw nothing.' But the subject does not indicate awareness.īut at longer duration, between 500ms and 700ms, for example, something dramatic occurs-multiple parts of the brain 'light up' and the test subject indicates his or her awareness of the image, either by pressing a button or vocally reporting so. Very short exposure, under 300 milliseconds, reveals a base level of activity on EEG, indicating the brain is processing the information. In other words, the brain crosses a threshold, he said, when the test subject's exposure to the image is long enough. And then there is a stage where the brain decides, whether there is enough evidence to call it ‘seeing’, in a certain sense.' 'What we found,' said Dehaene, when we spoke via Skype, 'is there are two stages: there is a stage where the brain unconsciously processes the information, it accumulates evidence about the nature of the initial image. The advantage of the former, is more refined 3-D detail of the location of activity in the brain, while the advantage of EEG is better recording of the brain's electrical activity in real time. During the tests the adults are monitored either by fMRI or EEG. One technique is called masking: you flash an image in front of the subject, follow it quickly with another image, and if the conditions are right, they don’t see the first image, they only see the second. To do this, Dehaene utilizes a combination of Functional Magnetic Resonance Imaging (fMRI) and electro-encephalography (EEG) to measure what he calls the signatures of consciousness. And for Dehaene this means engaging the test subject in a way that unambiguously reveals conscious action-for example, by reporting or indicating that they can visually make out an image flashed on a screen. To pin down consciousness in the lab, you need to catch it in the act of access to an event or process.

When does a fetus have brain activity