Filling-in - FMRI Experiments in Human Subjects

FMRI Experiments in Human Subjects

The neuronal activity in different brain areas can be recorded in humans through non-invasive techniques, like fMRI (functional magnetic resonance imaging). Perna et al. (2005) used fMRI to investigate the neuronal mechanisms responsible for the Craik–O'Brien–Cornsweet illusion. These authors recorded the activity in different brain areas when observers were presented with a Cornsweet visual stimulus, and compared the activities with those elicited by a similar image, which however did not elicit any brightness filling-in.

Contrary to the predictions of isomorphic filling-in, these authors found an identical response to the stimulus that induced filling-in and to the control stimulus in early visual cortex.

Recently, Cornelissen et al. (2006) performed a similar experiment involving the simultaneous contrast illusion. These authors presented observers in an fMRI scan with simultaneous contrast stimuli composed of a central circle of uniform luminance and a peripheral region whose luminance was modulated in time (and also tested other conditions where the modulated and the constant regions were inverted). The brain activity was recorded in primary visual cortex in a retinotopic position corresponding to the perceptually filled-in region. Also in this condition, no activity was found at this level in response to the filled-in signal.