Paper in Vision Research
- Badcock, D.R., Clifford, C.W.G.
& Khuu, S.K. (2005) "Interactions between luminance
and contrast signals in global form detection", Vision
Research, 45, 881-889.
The human visual system is adept at detecting global structure,
or form, within a scene. The initial stage of post-retinal
processing for all aspects of vision is fed by On- and Off-centre
cells sensitive to centred luminance increments and decrements
respectively. These cells provide input to two parallel pathways
that process variations in local luminance (first-order pathway)
and local contrast (second-order pathway). Here, we investigate
the contribution of luminance and contrast information to
global form detection, a stage between the extraction of local
orientation and the recognition of objects. The underlying
processes involve two stages. We find that signals in the
On-, Off- and second-order pathways are segregated at both
stages of processing. Surprisingly, the non-linear stage in
the second-order form pathway is different from that in motion
processing: the second-order form detectors show an asymmetry
in sensitivity to increments and decrements that is not apparent
in motion. A functional architecture for global form detection
is proposed along with its possible neural substrates.