title: Effect of extending grating length and width on human visually evoked potentials.
abstract: Visually evoked potentials (VEPs) were elicited by Gabor gratings with different lengths and widths at three spatial frequencies (SFs): low, 1.45 c/deg, medium, 2.9 c/deg and high, 5.8 c/deg and at a contrast 3 times above the detection threshold at each SF. An increase of grating length enhanced N1 amplitude at occipital and parietal positions stronger than the increase of grating width at aspect ratios (length : width) above 4:1. The stronger effect of stimulus length than width was reflected also in the amplitude of the later P1 component at central and parietal positions. The larger effect of stimulus length than width on the VEP amplitude was SF specific: it was stronger at 5.8 c/deg, smaller at 2.9 c/deg and vanished at 1.45 c/deg. The results obtained suggest anisotropy in the physiological mechanisms that underlie grating perception and involve bottom- up processes initiated in the occipital cortex.
authors.affiliation: Department of Sensory Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria, milenski_vis@abv.bg.
authors.forename: Milena S
authors.initials: MS
authors.lastname: Mihaylova
authors.affiliation: Department of Sensory Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
authors.forename: Ivan
authors.initials: I
authors.lastname: Hristov
authors.affiliation: Department of Sensory Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
authors.forename: Kalina
authors.initials: K
authors.lastname: Racheva
authors.affiliation: Department of Sensory Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
authors.forename: Tsvetalin
authors.initials: T
authors.lastname: Totev
authors.affiliation: Department of Sensory Neurobiology, Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
authors.forename: Dimitar
authors.initials: D
authors.lastname: Mitov
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D015350:Contrast Sensitivity / Q000502:physiology; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009949:Orientation / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011601:Psychophysics; D011930:Reaction Time / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology