The representation of orientation in primary visual cortex (V1) has been examined extensively at a fine spatial scale corresponding to the columnar architecture. In humans, orientation can be decoded from functional magnetic resonance imaging (fMRI) signals using multivariate classification methods, but it is unknown whether orientation decoding depends on the fine-scale, columnar architecture in cortex. We have shown that orientation is also represented in human cortex at a coarse spatial scale, and we have argued that this organization provides the basis for orientation decoding (Freeman et al., 2011). This topic remains highly controversial, and several labs have provided new evidence suggesting that a columnar-scale signal is present in fMRI measurements at conventional resolution. In this talk, I will review the evidence for and against a columnar contribution to orientation decoding. I will present recent evidence from our lab in which we measure fMRI responses in V1 to a variety of spatially structured stimuli — including oriented gratings with different spatial configurations and logarithmic spirals — and apply decoding and spatial filtering analyses to the data. Together, the results of our analyses strongly suggest that orientation decoding does not reflect the irregular spatial arrangements of orientation columns. Rather, it is likely that the coarse-scale topographic map of orientation in V1 is the major, if not the only, source of information that is exploited by multivariate decoding methods.
Meeting abstract presented at VSS 2013