Explicit spatial compatibility is not critical to the object handle effect

In object perception studies, a response advantage arises when the handle of an object is congruent with the responding hand. This handle effect is thought to reflect increased motor activation of the hand most suited to grasp the object, consistent with affordance theories of object representation. An alternative explanation has been proposed, however, which suggests that the handle effect is related to a simple spatial compatibility effect (the Simon effect). In 3 experiments, we determined whether the handle effect would emerge in the absence of explicit spatial compatibility between handle and response. Stimulus and response location was varied vertically and participants made horizontally orthogonal, bimanual responses to objects’ kitchen/garage category, color (as in a traditional Simon effect) or upright/inverted orientation. Categorization and inversion tasks, which relied on object knowledge, elicited a handle effect and a vertical Simon effect regarding stimulus and response locations. When participants judged object color, as per standard Simon effect paradigms, the handle effect disappeared but the Simon effect strengthened. These data demonstrate a dissociation between affordance and spatial compatibility effects and prove that affordance plays an important role in the handle effect. Models that incorporate both affordance and spatial compatibility mechanisms are discussed.Elizabeth J. Saccone, Owen Churches, Michael E. R. Nicholl

Reinforcement history shapes primary visual cortical responses: an SSVEP study

Efficient learning requires allocating limited attentional resources to meaningful stimuli and away from irrelevant stimuli. This prioritization may occur via covert attention, evident in the activity of the visual cortex. We used steady-state visual evoked potentials (SSVEPs) to assess whether associability-driven changes in stimulus processing were evident in visuocortical responses. Participants were trained on a learned-predictiveness protocol, whereby one stimulus on each trial accurately predicted the correct response for that trial, and the other was irrelevant. In a second phase the task was arranged so that all cues were objectively predictive. Participants' overt attention (eye gaze) was affected by each cue's reinforcement history, as was their covert attention (SSVEP responses). These biases persisted into Phase 2 when all stimuli were objectively predictive, thereby demonstrating that learned attentional processes are evident in basic sensory processing, and exert an effect on covert attention above and beyond the effects of overt gaze bias.Oren Griffiths, O. Scott Gwinn, Salvatore Russo, Irina Baetu, Michael E.R. Nicholl

The effect of cognitive load on horizontal and vertical spatial asymmetries

Healthy individuals typically show a leftward attentional bias in the allocation of spatial attention along the horizontal plane, a phenomenon known as pseudoneglect, which relies on a right hemispheric dominance for visuospatial processing. Also, healthy individuals tend to overestimate the upper hemispace when orienting attention along the vertical plane, a phenomenon that may depend on asymmetric ventral and dorsal visual streams activation. Previous research has demonstrated that when attentional resources are reduced due to increased cognitive load, pseudoneglect is attenuated (or even reversed), due to decreased right-hemispheric activations. Critically, whether and how the reduction of attentional resources under load modulates vertical spatial asymmetries has not been addressed before. We asked participants to perform a line bisection task both with and without the addition of a concurrent auditory working memory task with lines oriented either horizontally or vertically. Results showed that increasing cognitive load reduced the typical leftward/upward bias with no difference between orientations. Our data suggest that the degree of cognitive load affects spatial attention not only in the horizontal but also in the vertical plane. Lastly, the similar effect of load on horizontal and vertical judgements suggests these biases may be related to only partially independent mechanisms.Andrea Ciricugno, Megan L. Bartlett, Owen S. Gwinn, Daniel J. Carragher and Michael E.R. Nicholl