Measuring position discrimination in the visual cortex.

<p>A. A representative subject's negative BOLD ROI (circled with dashed white line), composed of 2084 voxels. B. The response of each of the 2084 voxels in the negative BOLD ROI is plotted for two of the conditions (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000410#pone-0000410-g001" target="_blank">Fig. 1A and 1B</a>). The abscissa shows the response to the stimulus in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000410#pone-0000410-g001" target="_blank">Fig. 1A</a> (t score generated by a general linear model contrast relative to fixation baseline, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000410#s4" target="_blank">Materials and Methods</a>). The ordinate shows the response to the stimulus in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000410#pone-0000410-g001" target="_blank">Fig. 1B</a>. Across the population of voxels, there was a strong correlation in the responses to the two stimuli (r = 0.94, P<0.001). This is not surprising, given how similar the two conditions were. C. Within the same ROI, the response to the stimulus in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000410#pone-0000410-g001" target="_blank">Fig. 1A</a> was compared to the response to the stimulus in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000410#pone-0000410-g001" target="_blank">Fig. 1E</a> (a condition in which the Gabors were positionally skewed by 0.77 deg). Across the population of 2084 voxels, the correlation was r = 0.47. There was a significantly stronger correlation in (B) than in (C) (Fisher z difference = 1.75−0.51 = 1.24, Z = 44.2, P<0.001). That is, the Gabors that were close to each other produced a higher correlation than the Gabors that were separated by a greater distance.