In contextual modulation, bigger is not better for low luminance stimuli

Performance on a target can be modified by contextual elements. For example, thresholds strongly increase when a vernier is flanked by two lines. Increasing the number of flankers reduces contextual interference when the flankers are shorter or longer than the vernier: bigger is better. However, there is no improvement when flankers have the same length as the vernier (Malania et al, 2007 Journal of Vision 7(2):1 1–7). Stimuli were 80 cd/m² on a black background. Here, we used stimuli with the luminance of 1 cd/m². Performance deteriorated similarly as in the 80 cd/m² condition when the vernier was flanked by two lines that were longer than the vernier. However, increasing the number of flankers did not improve performance as in the 80 cd/m² condition: bigger is not better. Our results show that contextual modulation is highly dependent on the luminance of the stimuli.