The neural basis of the bilateral distribution advantage

Abstract

Letters can be matched by their physical identity (i.e., a-a: same/A-a: different) or by their name (both a-a and A-a: same). The latter, more demanding task has in previous experiments led to an advantage of bilateral over within-hemifield matches, which was not observed in the former. We have investigated the neural basis of this bilateral distribution advantage (BDA) in letter name matching with event-related fMRI. Unilateral, compared to bilateral, name matching led to increased activation in the contralateral fusiform and lateral occipital gyri. This increase went along with an ipsilateral increase of activation in homologous areas. Such a hemispheric resource sharing was not observed for letter shape matching. This pattern of activation shows that letter name matching induces hemispheric resource sharing in visual areas, which occurs when task demands in the hemisphere of input reach a critical level. Activation in anterior cingulate complex and posterior cingulate/retrosplenial cortex showed a task × visual field interaction with lower activation for bilateral than unilateral name matches but higher activation for bilateral than unilateral shape matches, which fits the interhemispheric transfer demands in these tasks.

How dynamic is interhemispheric interaction? Effects of task switching on the across-hemisphere advantage

“…A functional imaging study using a variation of the Banich paradigm demonstrated that a more complex letter name task led to more bilateral activation in the fusiform and lateral occipital gyri than a less complex letter shape task (Pollmann, Zaidel, & Cramon, 2003). These findings are consistent with the view that interhemispheric resource sharing increases with increasing task demands.…”

Hemispheric interaction, task complexity, and emotional valence: Evidence from naturalistic images

“…A and a) than physical matches (e.g. A and A) (Pollman et al, 2003), greater bilateral activation was found to negative than positive stimuli, whether the stimuli were faces with negative expressions (Killgore & Yurgelun-Todd, 2007) or were unpleasant images (Gerdes et al, 2010). Taken together, the evidence is compelling to suggest that the processing of negative stimuli is more demanding than positive stimuli.…”

“…Hemispheric interaction is predicted to benefit the processing of negative images, but not positive images, as follows from evidence suggesting that hemispheric interaction benefits the performance of complex tasks, but not simple ones (Banich & Belger, 1990;Belger & Banich, 1992Compton, 2002;Compton et al, 2004;Koivisto, 2000;Passarotti et al, 2002;Pollman et al, 2003;Tremblay et al, 2009). Laterality is predicted to favor the RH for negative images and the LH for positive images, as follows from assumptions of the valence hypothesis (Ehrlichman, 1987;Silberman & Weingartner, 1986).…”

“…Tests of hemispheric interaction typically use lateralized displays to present stimuli within the LVF or RVF to test within-hemisphere processing, or across the LVF and RVF to test hemispheric interaction (Banich & Belger, 1990;Belger & Banich, 1998;Compton, 2002;Compton, Wilson, & Wolf, 2004;Koivisto, 2000;Pollman et al, 2003;Tremblay et al, 2009). While lateralized displays provide valuable data on the relative competence of the hemispheres, as well as their interaction, the ecological validity of the procedure has been challenged (Christman, 2001;Luh & Levy, 1995).…”

“…''A'' and ''A'') and categorical identity (e.g. ''A'' and ''a'') (Pollman, Zaidel, & von Cramon, 2003). Each trial presented two letters to each of the LVF and RVF.…”