Poster E121, Monday, March 27, 2:30 – 4:30 pm, Pacific Concourse
Perceptual uncertainty of long-range apparent motion and the neural correlates underlying the resolution of this uncertainty in favor of the motion interpretation.
Yasuhiro Sakamoto1, Yoshihito Shigihara2, Michael Wibral3, Hideyuki Hoshi1, David Poeppel1,4, Winfried Menninghaus1; 1Max Planck Institute for Empirical Aesthetics, 2University College London, 3Goethe University Frankfurt, 4New York University
As early as 1912, Max Wertheimer described apparent motion: two shapes presented consecutively with an ISI under 30 ms are perceived as simultaneous; apparent motion is perceived if the ISI is 60—200 ms. In the 30—60 ms time-window, though, there is perceptual uncertainty: identical stimuli are varyingly perceived as moving or simultaneous. To investigate why this ambiguity arises, we measured neural activity using a 275 channel MEG system. 27 participants (mean age 30.6) judged 600 critical stimuli within the ISI-range 30—60 ms and reported their percept (simultaneous vs. left-to-right motion). Visually evoked M50, M100, M150 and M180 post-onset peaks were evident in the event-related fields from occipital sensors. Waveforms and sources (dipole modeling) over the visual cortex for both response-types were very similar until 200 ms. Between 250 and 300 ms, ERFs were significantly higher for the motion response-type than the simultaneous response-type in the right occipital region. Time frequency analysis was done using Morlet wavelet. Spectral estimation including 7 cycles on a fixed time-window of 50 ms from -100 to 400 ms was performed. We found a significant beta-band activation between 250 and 300 ms when participants perceived the stimuli as simultaneous. The results suggest that the perception of apparent motion is constructed subsequent to the initial cascade of visual responses, after ~250 ms. The first of the two stimulus components (i.e., the object on the left) appears to play an important role in the apparent motion decision, as evidenced by the significant effect in the right occipital cortex.
Topic Area: PERCEPTION & ACTION: Vision