5°, 15°, and 90° were included. Behavioral data again confirmed that the texture stimuli were invisible to subjects (7.5°: 50.2 ± 1.1%; 15°: 50.4 ± 1.1%; 90°: 50.5 ± 0.9%). Contralateral and ipsilateral regions of interest (ROIs) in V1–V4 and IPS were defined as being the cortical areas that responded to the retinal inputs in the foreground region and its contralateral counterpart (that would always contain

background bars). In V1–V4, texture stimuli with orientation contrasts of 15° and 90° generally evoked larger BOLD signals in the contralateral than the ipsilateral ROIs (Figure 4A). In other words, the foreground region evoked stronger neural activities than its contralateral counterpart. The differences between the peak BOLD signals at the contralateral ROIs and those at the ipsilateral ROIs are shown in Figure 4B and were submitted to a repeated-measures ANOVA with orientation contrast GSK1210151A research buy (7.5°, 15°, and 90°) and cortical area (V1–V4 and IPS) as within-subject factors. The main effect of orientation contrast was significant (F2, 18 = 20.352, p < 0.001), demonstrating that the peak amplitude difference increased with the orientation contrast. We also found a significant main effect of cortical area (F4, 36 = 3.425, p = 0.041) and a significant

interaction between orientation contrast and cortical area (F8, 72 = 3.221, p = 0.030). Hence, the effect of orientation contrast decreased gradually from lower to higher cortical areas. This was confirmed in further analysis selleck chemicals which showed that the main effect of orientation contrast was significant in V1–V4 (all F2, 18 > 13.722, p < 0.010), but not in IPS (F2, 18 = 0.120, p = .840). These findings revealed that neural activities in early visual areas were parallel to the attentional effect. To examine

several other areas of interest, including lateral geniculate nucleus (LGN) and FEF, we ran PAK6 a supplementary fMRI experiment. This employed a similar design, but with an increased repetition time (TR) of 2 s to enable whole brain scanning. ROI analyses showed that the main effect of orientation contrast was significant in V1–V4, but not in IPS, LGN, and FEF. Furthermore, we performed a group analysis and did a whole-brain search with a general linear model (GLM) procedure (Friston et al., 1995) for cortical areas whose activities increased with the orientation contrast. Only early visual cortical areas were found (Figure S3). To evaluate further the role of the early cortical activities in creating the bottom-up saliency map, we calculated the correlation coefficients between our psychophysical and ERP/fMRI measures across individual subjects. The attentional effect was significantly correlated with the C1 amplitude difference for orientation contrasts of 15° (r = 0.758, p = 0.001) and 90° (r = 0.798, p < 0.001), but not for the orientation contrast of 7.5° (r = 0.263, p = 0.