Fast perceptual priming in the left and right hemispheres

Neural correlates of language and non-language visuospatial processing in adolescents with reading disability

Despite anecdotal evidence of relative visuospatial processing strengths in individuals with reading disability (RD), only a few studies have assessed the presence or the extent of these putative strengths. The current study examined the cognitive and neural bases of visuospatial processing abilities in adolescents with RD relative to typically developing (TD) peers. Using both cognitive tasks and functional magnetic resonance imaging (fMRI) we contrasted printed word recognition with non-language visuospatial processing tasks. Behaviorally, lower reading skill was related to a visuospatial processing advantage (shorter latencies and equivalent accuracy) on a geometric figure processing task, similar to findings shown in two published studies. FMRI analyses revealed key group by task interactions in patterns of cortical and subcortical activation, particularly in frontostriatal networks, and in the distributions of right and left hemisphere activation on the two tasks. The results are discussed in terms of a possible neural tradeoff in visuospatial processing in RD.

Automatic semantic priming in the left and right hemispheres

We investigated hemispheric differences and inter-hemispheric transfer of facilitation in automatic semantic priming, using prime-target pairs composed of words of the same category but not associated (e.g. skirt-glove), and a blank-target baseline condition. Reaction time and accuracy were measured at short (300 ms) intervals between prime and target onsets, using a go/no-go task to discriminate between word or non-word targets. Reaction times were facilitated more for target words presented in the right visual field (RVF) compared to the left visual field (LVF), and targets presented in RVF were primed in both visual fields, whereas targets presented in LVF were primed by primes in the LVF only. These results suggest that both hemispheres are capable of automatic priming at very short stimulus onset asymmetries (SOA), but cross-hemisphere priming occurs only in the left hemisphere.

Left frontal eye field remembers “where” but not “what”

Short-term memory of basic stimulus features seems to rely upon low-level functional components of the visual pathways. By using a repetition priming paradigm, we previously showed that visual area V5/MT is important for holding motion direction information, but not spatial position information. Here we extend our previous findings and investigate the possible locus of spatial position priming. We compare the effect of repetitive transcranial magnetic stimulation (rTMS) over right angular gyrus and left and right frontal eye fields on priming for spatial position and motion direction. TMS over left frontal eye field selectively and significantly reduced priming for spatial position but there was no significant effect of TMS over right parietal or right frontal eye field. These results suggest that FEF neurons are implicated in short-term memory storage of spatial position, and extend and support the idea that memory for basic stimulus features is retained within the sensory areas that respond to primary stimulus attributes. They add to a growing body of evidence that the frontal eye fields are involved in many visual functions independent of eye movements.