Department of Neurobiology, Harvard Medical School, Division of Neurosurgery, Duke University Medical Center
Optical images of visible and invisible percepts in the primary visual cortex of primates
Using optical imaging techniques, we asked whether activity in the primary visual cortex (area V-1) of rhesus monkeys more closely resembles the physical stimulus or the generated percept. Visual illusions are a powerful way to address this question because they have the benefit of dissociating the stimulus from the perception. The stimulus we used was the "Standing Wave of Invisibility", an illusion in which a flickering target (a bar oriented in visual space) is rendered invisible by two counter-phase flickering bars, called masks, which flank and abut the target. To see a dynamic version of this illusion, please go to the website at: http://cortex.med.harvard.edu/macknik. The target and masks, when shown separately, each generated correlated activity on the surface of the cortex. During the illusory condition, however, we found that the cortex's representation of the target was suppressed although the image of the masks remained visible: the optical image was correlated with the perception but not with the physical stimulus. The functional anatomy of area V-1 can thus be functional not only in terms of how information is organized and processed in the early visual system, but also in terms of how we perceive that information.
Supported by grants from NIH to SLM and MMH, as well as from direct support from SLM's postdoctoral advisor, Dr. David H. Hubel.