Langley, K., Fleet, D.J., and Hibbard, P.
Linear filtering precedes nonlinear processing in early vision.
Current Biology, 6(7) 891-896, July 1996
Nonlinearities play a significant role in early visual
processing. They are central to the perception of spatial contrast
variations, multiplicative transparencies and texture boundaries.
This article concerns the
stage of processing at which nonlinearities first become significant.
Subjects were adapted to a high contrast sinusoidal grating followed by
a brief presentation of a contrast modulated test (plaid) pattern.
Thresholds for the detection of the contrast modulation (the beat) were
measured. Results show that threshold elevation is greatest when the
orientation and spatial frequency of the adapting grating are close to the
principal Fourier frequency (the carrier) of the test pattern. Adaptation
to sinewave-gratings near the frequency of the contrast modulation has
relatively little effect. The data also show that the processing of contrast
is frequency selective, with a peak tuning frequency near 0.4 cpd.
The data are consistent with a model in which the contrast beats are
processed in a frequency-specific manner, after an initial stage of
frequency-specific and orientation-specific linear filtering.
Return to David Fleet's home page.