Backward masking of words and faces: evidence for different processing speeds in the hemispheres?

Two tachistoscopic experiments with a lateralized presentation of function words and faces were carried out to investigate the influence of temporal factors and type of masking on visual field asymmetries. Accuracy, represented by signal detection measures (d' and beta), was calculated separately for the two visual fields, for various interstimulus intervals, and for noise and pattern masking. In both experiments, d' increased with prolonged temporal delay between target and mask. In the lexical decision task, visual field interacted with mask type confirming that only in the pattern mask condition did an advantage of the right visual field emerge. In the facial decision task, however, visual field interacted with interstimulus interval, confirming that, in the left visual field, the facial information escaped the masking effect earlier than in the right visual field. In the facial task, there was a higher response criterion (beta) in the left visual field. By applying different types of masks, visual processing of lexical stimuli can be disrupted at distinct stages where perceptual asymmetries are present to a varying extent. The results of both experiments suggest that words and faces are differentially affected by masking procedures.