Hemispheric facilitation as a result of threatening and nonthreatening words: blocked vs mixed presentation effects and order effects.

Sixteen right-handed participants (eight male and eight female students) were administered a tachistoscopic unilateral letter-naming task. The design contained three valance conditions and two types of presentation. In baseline conditions no concurrent task was given. In threat and nonthreat conditions, each unilateral stimulus was preceded by a threatening or nonthreatening word in central vision. Participants were instructed to recall this word after reporting the unilateral letter string. With blocked presentations, a series of trials had the same emotional valence (threatening or nonthreatening), whereas with mixed presentations the valences were alternating within a series. Analysis of order effects for the blocked presentations revealed sustained effects of the initial block valence on visual field asymmetries. The sustained effect of the initial threatening block was a reduction of the right visual-field advantage. Mixed presentations resulted in a enhanced right visual-field advantage following the presentation of threatening information and an enhanced left visual-field advantage following the presentation of nonthreatening information. The research suggests that tonic and phasic reactions to emotional stimuli may affect visual field asymmetry in different ways.