The effects of collinearity and orientation on texture visual evoked potentials

Objective: The aim of the research was to study the effects of stimulus orientation at both the local (textons) and the global (segregated elements) level on texture visual evoked potentials (tVEPs). Methods: Two tVEP paradigms were presented to 10 volunteers. The paradigms were characterized by alternating uniform textures (random mixture of square dots and lines) and textures in which stripes of randomly disposed lines segregated from a square dotsʹ background. In one paradigm, the stripes were horizontal and in the other, vertical. The lines could be either horizontal or vertical in single stimuli of both paradigms. Thus, two stimuli with local/global collinearity and two stimuli without local/global collinearity were available. tVEPs were derived from Oz referenced to the left earlobe and averaged separately for each condition. Segregation-related components were obtained subtracting the traces without segregation from the traces with segregation. Results: A negative segregation component starting at the latency of P1 and extending until the end of N2 characterized the tVEPs, without significant differences among the 4 stimulus conditions. In the presence of local/global collinearity, we found an early modulation of N1 amplitude. This modulation was orientation-dependent, as vertical collinearity increased N1 negativity and horizontal collinearity reduced N1 negativity. Conclusions: Our experiment confirms previous findings about the segregation negativity, which may depend on contextual modulation of V1 neurons by long-range horizontal and feed-back connections. The early effect of collinearity may depend on more local modulatory connections.