Send to

Choose Destination
See comment in PubMed Commons below
Curr Biol. 1996 Jul 1;6(7):891-6.

Linear filtering precedes nonlinear processing in early vision.

Author information

Department of Psychology, University College London, UK.



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 cycles per degree.


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.

[Indexed for MEDLINE]
Free full text
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for Elsevier Science
    Loading ...
    Support Center