Attentional orienting in two-dimensional space

This paper examines how the covert orienting of spatial attention affects m otor responses to visual stimuli. Premotor theories, as well as hemi-field inhibition accounts of visual attention predict an increase in response tim es when a target stimulus appears in the opposite direction to a spatial cu e. Some models also suggest that this meridional effect should be increased across oblique meridians. Two types of cue (central and peripheral) were u sed to orient attention towards locations prior to the onset of visual targ ets. Simple manual (press button) and saccadic responses were measured. No meridional effects were found with peripheral cues, whereas central cueing produced meridional effects across all meridians. Cueing effects did not va ry significantly with two-dimensional axis for either manual or saccadic re sponses. Increases in response time with cue-target distance were found for both response and cue types. For saccades, distance gradients were shallow er moving distally rather than proximally from the cued position. However, simple manual responses did not show this asymmetry. Orienting to central c ues also modulated the amplitude of saccades. The results are consistent wi th an effect of attentional cues in oculomotor centres as well as the exist ence of action-dependent attentional representations. However, it is propos ed that, rather than reflecting oculomotor programming, meridional effects arise from a directional organization within spatio-cognitive representatio ns.