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Abstract:
Changes in magnetoencephalographic (MEG) gamma activity during biological motion percep-tion have been assessed. Subjects saw a set of 200 displays of two types: a canonical point-lightfigure and a `scrambled walker' that consisted of spatially scrambled points on the joints of acanonical one. In separate runs, both configurations (9.3 deg by 6.4 deg) were presented eitherwith an upright or with an inverted display orientation. MEG responses were recorded with awhole-head system. After a blank screen (baseline), a display appeared for 650 ms. Subjectswere asked to respond to the second of two consecutive identical stimuli of each type. Onlycorrect trials without motor responses were processed. For both upright and inverted canonical figures, gamma activity (25 ^ 30 Hz) increased over the occipital areas already 100 ms fromstimulus onset. It was greater to the upright figure, which also evoked gamma responses over thetemporal and parietal areas. Yet, neither upright nor inverted `scrambled walker' evoked anyenhancements in gamma activity. The findings indicate that processing of meaningful coherentstructure from motion leads to greater gamma oscillations than the same display presentedupside ^ down. Moreover, non-coherent configurations consisting of the same amount of absolutemotion do not yield any enhancement in MEG gamma activity.
