The Fronto-Parietal Network and Top-Down Modulation of Perceptual Grouping

Abstract

We examined the role of the fronto-parietal cortex in top-down modulation of perceptual grouping by proximity, collinearity, and similarity, by recording event related brain potentials from two patients with fronto-parietal lesions and eight controls. We found that grouping by proximity and collinearity in the controls was indexed by short-latency activities over the medial occipital cortex and long-latency activities over the occipito-parietal areas. For the patients, however, both the short- and long-latency activities were eliminated or weakened. The results suggest that the fronto-parietal network is involved in facilitation of both the early and late grouping processes in the human brain.

Keywords:

• ERP
• Perceptual grouping
• Proximity
• Collinearity
• Fronto-Parietal lesion

Acknowledgments

This work was supported by National Natural Science Foundation of China (Project 30630025, 30225026 and 30328016), the Ministry of Science and Technology of China (Project 2002CCA01000), the Medical Research Council (UK), and the Royal Society (UK). We thank Peter Praamstra and Paul Pope for help in EEG data collection.

Notes

¹One may notice that, besides grouping local items into columns or rows, the grouped stimuli were also different from the uniforms stimulus in other aspects such as the amount of overall spacing between the elements or clustering of the elements. The latter factors might contribute to the ERP grouping effects observed in the current study. Our previous ERP study (Han et al., 2001) examined the grouping ERP effects when removing other differences between uniform and grouping stimuli such as amount of overall spacing between the elements or clustering of the elements. In this study, local elements were defined by motion contrast. The background was composed of randomly moving dots. Local circles and squares were made up of stationary random dots. Such design made grouped and uniform stimuli were equal in amount of overall spacing between the elements or clustering of the elements. However, under these circumstances, we still observed similar grouping ERP effect, suggesting the factors such as amount of overall spacing between the elements contributed little to the ERP grouping effects.