Interactions between luminance and contrast signals in global form detection.
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.
Badcock
David R
DR
School of Psychology, The University of Western Australia, 35 Stirling Highway, Nedlands, WA 6009, Australia. david@psy.uwa.edu.au
Clifford
Colin W G
CW
Khuu
Sieu K
SK
D015350:Contrast Sensitivity / Q000502:physiology*; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology