Right-hemisphere specialization for contour grouping

Previous studies often revealed a right-hemisphere specialization for processing the global level of compound visual stimuli. Here we explore whether a similar specialization exists for the detection of intersected contours defined by a chain of local elements. Subjects were presented with arrays of randomly oriented Gabor patches that could contain a global path of collinearly arranged elements in the left or in the right visual hemifield. As expected, the detection accuracy was higher for contours presented to the left visual field/right hemisphere. This difference was absent in two control conditions where the smoothness of the contour was decreased. The results demonstrate that the contour detection, often considered to be driven by lateral coactivation in primary visual cortex, relies on higher-level visual representations that differ between the hemispheres. Furthermore, because contour and non-contour stimuli had the same spatial frequency spectra, the results challenge the view that the right-hemisphere advantage in global processing depends on a specialization for processing low spatial frequencies.

The cerebral hemispheres differ in their capacity for content-to-level binding but not for identification: evidence from conjunction errors obtained with bilateral hierarchical stimuli

It is widely assumed that the right and left cerebral hemispheres are specialised for processing the global and local information of hierarchical stimuli, respectively. This idea has further been specified in the content-to-level binding theory (Hübner & Volberg, 2005) by stating that the hemispheres differ in their efficiency for binding the contents of a stimulus to their respective level. In contrast, it is assumed that the hemispheres do not differ in their capacity for the identification of the information at the two levels. This latter hypothesis was tested in the present experiment by presenting a hierarchical letter to each visual field. As expected, there were visual field effects only for errors involving the erroneous binding between a letter and a level. For errors that result from the mislocalisation of a letter, there were no visual field effects. Together, the data support the hypothesis that the hemispheres do not differ in their identification capacity.