Psychology. In the article “Spatial attention affects brain activity in human primary visual cortex” by Sunil P. Gandhi, David J. Heeger, and Geoffrey M. Boynton, which appeared in number 6, March 16, 1999, of Proc. Natl. Acad. Sci. USA (96, 3314–3319), due to an error in the PNAS office, a sentence was omitted. The sentence is shown in bold type in context in the complete paragraph below.

On the other hand, it is certainly possible that the V1 modulation we observed might have nothing to do with the improved behavioral performance. For example, the memory load differs between the tasks in the main experiment and the spatial uncertainty experiment. In the spatial uncertainty experiment, subjects must remember two speeds instead of one during the 250 msec inter-stimulus interval. This difference in memory load might be causing the improved behavioral performance. Or the improved performance may result from subjects simply ignoring information from the uncued side, and thus may not be causally related to V1 modulation. It is difficult, however, to imagine that such a significant modulation of activity in visual cortex would fail to have consequences on perceptual thresholds.