Monday, April 12, 2010

We separate identity and emotion of a stimulus in under 100 msec.

Liu and Ioannides record the small rapid magnetic signals caused by brain activity (using magnetoencephalography, or MEG) to study whether face affect recognition depends on where the face stimulus (happy, fearful, neutral) appears in the visual field. Emotional appraisal (amygdalar activity) occurs more rapidly than final cognitive appraisal in the pre-frontal cortex - (We jump away from a moving S-shaped figure in our peripheral vision before we have determined whether it is actually a snake). Here is their abstract:
It is now apparent that the visual system reacts to stimuli very fast, with many brain areas activated within 100 ms. It is, however, unclear how much detail is extracted about stimulus properties in the early stages of visual processing. Here, using magnetoencephalography we show that the visual system separates different facial expressions of emotion well within 100 ms after image onset, and that this separation is processed differently depending on where in the visual field the stimulus is presented. Seven right-handed males participated in a face affect recognition experiment in which they viewed happy, fearful and neutral faces. Blocks of images were shown either at the center or in one of the four quadrants of the visual field. For centrally presented faces, the emotions were separated fast, first in the right superior temporal sulcus (STS; 35–48 ms), followed by the right amygdala (57–64 ms) and medial pre-frontal cortex (83–96 ms). For faces presented in the periphery, the emotions were separated first in the ipsilateral amygdala and contralateral STS. We conclude that amygdala and STS likely play a different role in early visual processing, recruiting distinct neural networks for action: the amygdala alerts sub-cortical centers for appropriate autonomic system response for fight or flight decisions, while the STS facilitates more cognitive appraisal of situations and links appropriate cortical sites together. It is then likely that different problems may arise when either network fails to initiate or function properly.

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