Title
A STUDY OF ILLUSORY CONTOURS IN HUMAN CEREBRAL CORTEX WITH FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI)

Authors
(J. Hirsch^1,3, R. DeLaPaz^2,3, N. Relkin³, J. Victor³, K. Kim^1,3, T. Li¹, N. Rubin⁴, and R. Shapley⁵) Dept of Neurology¹ and Radiology ², Memorial Sloan-Kettering Cancer Center; Dept of Neurology and Neuroscience, Cornell University Medical College ³, NY, NY; Dept of Psychology, Harvard University ⁴, Cambridge, MA; Center for Neural Science, NYU ⁵, NY, NY.

Purpose:
Illusory contours are an example of the perceptual grouping of local features into a global percept. The cortical localization for illusory contour perception in human was studied in 3 subjects using fMRI.

Methods:
Images were acquired on a GE Signa 1.5T scanner equipped for echoplanar imaging with resolution of 1.5 x 1.5mm². Sixteen contiguous 5 mm thick axial slices aligned parallel to the AC/PC line were acquired during baseline, visual stimulation, and post-stimulation periods. Four stimulation conditions included: 1) fixation mark alone; 2) four non-aligned pacmen; 3) four pacmen at the corners of Kanizsa square (illusory contours); and 4) a real square formed by contiguous contours. Stimuli were flickered at 4 Hz. Signal intensities for each pixel were compared using a multistage statistical process to identify active regions.

Results:
Specific regions of activity were observed in extra-striate cortex for the illusory contour condition and tended to be lateralized in the right hemisphere.

Conclusion:
We found areas in extra-striate cortex in which fMRI activity was correlated with the perception of illusory contours and, hence, perceptual grouping.

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Supported by MSKCC (JH, RD), C.V. Starr Foundation (NR), EY7977 (JV), Morris Foundation (KK), and EY1472 (RS). None.