e. [sR(fC) > cR(fC)], [sL(fC) > cL(fC)], [sL(fR) > cL(fR)] and [sR(fL) > cR(fL)]) showed

that the areas in this network were activated differently depending on the particular search condition. Figure 2E–H presents t-maps that are clipped at the threshold of P < 0.001, with a minimum of 40 neighbouring voxels. Enhanced activity was observed in early and later visual cortical regions contralateral to the VF, in which covert search was carried out, independent of eye orientation (Fig. 2E–H). Thus, left early and later visual cortical regions exhibited a larger BOLD response when the covert search was directed to the right VF, both when the subject looked straight ahead or to the selleck inhibitor left. The reverse pattern was observed Selleckchem Olaparib in the right early and later visual cortical regions, when eyes were kept straight ahead or right relative to the head. These results are in accordance with the known retinotopy in early and later visual areas, and demonstrate that attention enhanced visual responses in our paradigm. The quantitative assessement of the percentage signal change in early and later visual cortical regions mirrored the above-mentioned results.

In both hemispheres our statistical assessment (anovas with subsequent post hoc comparisons by t-tests) revealed significantly higher attentional modulation for covert search directed to the contralateral VF (Fig. 3A and B; Table 2). Next we focused on areas in higher stages of the visual hierarchy for which we wanted to identify the FOR in which BOLD responses are modulated by covert search. The group-based random-effect contrast analysis of the specific search conditions with its respective control for the conditions, in which the eyes are oriented straight ahead (i.e. [sR(fC) > cR(fC)], [sL(fC) > cL(fC)]), revealed that the left IPS region was most strongly activated, when covert search was carried out in the right VF (Fig. 2E and F). However, this strong bias for the contralateral VF was not observed Dipeptidyl peptidase in the right IPS. This pattern is in accordance with Heilman’s ‘Hemispatial’ theory (Heilman & Van Den Abell, 1980), which

proposes that the RH directs attention to both VFs, whereas the LH directs attention to the right VF only (Fig. 2A and B; only the IPS response according to this model is depicted for simplicity). Next we asked to which FOR the contralaterality bias of the left IPS is anchored to. The remaining two conditions in which eye gaze was directed to the right and to the left, respectively, with respect to the head could disentangle eye-centred from non-eye-centred coding. The above-mentioned Heilman ‘Hemispatial’ theory makes different predictions for the left IPS in the two remaining search conditions, depending on whether the contralaterality bias is anchored in eye- or non-eye-centred FOR. These predictions are shown in Fig. 2C and D. The actual group results for these two conditions (Fig.