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Ari Rosenberg, T. Robert Husson, Naoum P. Issa; The representation of transparent motion in the non-Fourier responses of LGN Y-cells. Journal of Vision 2009;9(8):755. doi: 10.1167/9.8.755.
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Recently, we showed that non-Fourier (second-order) image features are represented subcortically in the responses of LGN Y-cells. To further investigate this representation, we characterized tuning for the envelope and carrier parameters of interference patterns. We found that Y-cell responses depended strongly on carrier temporal frequency (TF), and had lowpass, bandpass, or highpass tuning. Envelope TF tuning, on the other hand, was bandpass and peaked at relatively low temporal frequencies. In addition, many neurons were moderately selective for the orientation of the carrier but were not selective for drift direction. Responses oscillated at the envelope TF, regardless of the carrier TF, indicating that Y-cells encode the position of the envelope relative to the receptive field, but only when that envelope modulates a carrier within a defined range of spatiotemporal frequencies.
Perceptually, the envelope of an interference pattern is perceived as drifting across the carrier. Since Y-cell responses modulate at the TF of the envelope but not the carrier, they may signal this occlusion of a background object (the high spatial frequency carrier) by an object in the foreground (the low spatial frequency envelope). Thus, Y-cells carry a monocular cue for the dynamic occlusions that signal depth ordering and that underlie the perception of multiple object velocities within a local retinotopic space (motion transparency). While representations of depth structure and motion transparency are traditionally thought to arise from intra-cortical processing, our results suggest that they may first be represented subcortically by the nonlinear responses of Y-cells.
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