Rectification nonlinearity in cortical end-stopped perceptive fields.

End-stopped perceptive fields associated with line targets were demonstrated previously with length and width Westheimer functions. In this study we investigated rectifying non-linearity in these perceptive fields to examine whether they directly reflect the organization of cortical receptive fields. Specifically, we reversed the polarity of parts of the background field associated with a specific perceptive field sub-region and examined threshold changes in corresponding length or width Westheimer functions. Results showed full-wave rectification in end-stopping and half-wave rectification in center summation and flank-inhibition preceding linear summation in end-stopped perceptive fields. Half-wave rectification in center summation and surround-inhibition preceding linear summation was also found in circular perceptive fields associated with spot targets. These results are inconsistent with direct links between perceptive fields and cortical receptive fields. Rather they suggest that these perceptive fields are likely the second-order fields formed by pooled non-linearly rectified outputs from cortical receptive fields.