Andrey R. Nikolaev, RIKEN BSI, Japan
Sergei Gepshtein, RIKEN BSI, Japan
Michael Kubovy, University of Virginia, USA
Cees van Leeuwen, RIKEN BSI, Japan

Perceptual grouping is a multi-stage process, irreducible to a single mechanism localized anatomically or chronometrically. To understand how various grouping mechanisms interact, we combined a phenomenological report paradigm with high-density event-related potentials (ERP) measurement, using a 256-channel electrode array. We varied the relative salience of competing organizations in multi-stable dot lattices and asked observers to report perceived groupings.

Observers’ ability to discriminate groupings (grouping sensitivity) was positively correlated with the amplitude of the earliest ERP peak C1 (about 60 ms after stimulus onset) over the primary visual cortex. This early activity is believed to reflect spontaneous feed-forward processes preceding perceptual awareness. Grouping sensitivity was negatively correlated with the amplitude of the next peak P1 (about 110 ms), which is believed to reflect lateral and feedback interactions associated with perceptual awareness and attention. This dissociation between C1 and P1 activity implies that the recruitment of fast, spontaneous mechanisms for grouping leads to high grouping sensitivity. Observers who fail to recruit these mechanisms try to compensate by using later, less efficient mechanisms.

References

Nikolaev AR, Gepshtein S, Kubovy M, van Leeuwen C.  Dissociation of early evoked cortical activity in perceptual grouping. Exp Brain Res. 2008 Mar; 186(1): 107-122.  

A.R. Nikolaev, S. Gepshtein, M. Kubovy, & C. van Leeuwen. Temporal structure of perceptual grouping: EEG analysis. Proceedings of the 23rd Annual Meeting of the International Society for Psychophysics (Fechner Day). S. Mori, T. Miyaoka, W. Wong (Eds.), 2007, p. 67-72. October 20-23, Tokyo, Japan.

Nikolaev AR, van Leeuwen, C. Flexibility in Spatial and Non-Spatial Feature Grouping: an Event-Related Potentials Study. Brain Res Cogn Brain Res. Dec. 2004, 22(1): 13-25.