title: Oblique effects beyond low-level visual processing.
abstract: A number of studies have demonstrated a reduction in neural activity for oblique gratings as compared to horizontal or vertical gratings. This has been associated with the psychophysical oblique effect. Using event-related potentials, we now assessed the neural activity associated with the processing of higher-order stimuli of different orientations. We applied a novel stimulus paradigm that is particularly suited to investigate mid- and high-level vision by obviating low-level responses. It consisted of a line grid that emerged perspicuously from a continuous movement of stimulus elements without any temporal discontinuances in stimulus presentation. This Gestalt could be oriented along the cardinal axes or rotated by 45 degrees . We obtained distinct event-related potentials with a moderate task-dependence. They showed a correlate of Gestalt processing that did not depend on the orientation, followed by a P300-like component that was 50% larger for the 45 degrees Gestalt. Surprisingly, this oblique effect is opposite to previous studies using gratings. We propose that it originated from a bias in neural processing, induced by the long-term environmental experience of the subjects.
authors.affiliation: Elektrophysiologisches Labor, Univ.-Augenklinik Freiburg, Killianstr. 5, 79106 Freiburg, Germany. sven.heinrich@uniklinik-freiburg.de
authors.forename: Sven P
authors.initials: SP
authors.lastname: Heinrich
authors.forename: Ad
authors.initials: A
authors.lastname: Aertsen
authors.forename: Michael
authors.initials: M
authors.lastname: Bach
mesh_terms: D000328:Adult; D018913:Event-Related Potentials, P300 / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009039:Motion Perception / Q000502:physiology*; D009949:Orientation; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010466:Perceptual Closure; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D014793:Visual Cortex / Q000502:physiology