A total of 23 figure positions were presented (the distance of the RF center relative to the figure center ranged from −5.5° to 5.5° with 0.5° steps, see Figure 2B). For 9 of the 46 V4 recording sites, we did not present figures at all

these CX-5461 molecular weight positions, but we used a subset of five positions (one center, two edge, and two background positions), and the data from these recording sites were not included in the space-time plots (Figures 6C and 6D). The stimulus also contained two curves (width 0.27°, luminance 82 cd·m-2) and two red circles (size 1.5°) in the hemifield opposite to the figure (upper hemifield for monkeys B and J and right hemifield for monkey C). One of the curves was connected to the fixation point (target curve) and the other curve was not (distracter Cilengitide concentration curve). A small change close to the fixation point switched the target and distracter curve (in the example of Figures 2A and 2C the left curve is the target curve but in other trials the right curve was connected to the fixation point). All 23 figure positions × 2 curve configurations were presented in a randomly interleaved

sequence in both tasks. The animals underwent two surgeries under general anesthesia that was induced with ketamine (15 mg kg-1 injected intramuscularly) and maintained after intubation by ventilation with a mixture of 70% N2O and 30% O2, supplemented with 0.8% isoflurane, fentanyl (0.005 mg kg-1 intravenously), unless and midazolam (0.5 mg kg-1 h-1 intravenously). In the first operation a head

holder was implanted and a gold ring was inserted under the conjunctiva of one eye for the measurement of eye position. In the second operation, arrays of 4 × 5 electrodes (Cyberkinetics Neurotechnology Systems Inc.) were chronically implanted in areas V1 and V4 (see Figure S1). All procedures complied with the NIH Guide for Care and Use of Laboratory Animals (National Institutes of Health, Bethesda, Maryland), and were approved by the institutional animal care and use committee of the Royal Netherlands Academy of Arts and Sciences. Details about the recording methods and information about the measurement of RFs in V1 and V4 can be found in Supplemental Experimental Procedures. We quantified visual responsiveness by first calculating the spontaneous mean activity, Sp, and the standard deviation, s, across trials in a 200 ms time window preceding stimulus onset. We then computed the peak response, Pe, by smoothing the average response over conditions with a moving window of 25 ms and taking the maximum during the stimulus period (0–600 ms after stimulus onset). The visual responsiveness index was then given by VR = (Pe-Sp)/s.