We aimed to determine whether there is a significant effect of age on the relative change in suppression strength between parallel and orthogonal center-surround combinations.
Figure 4 shows individual and group mean values for parallel (blue) and orthogonal (orange) suppression ratios for horizontal (
Figure. 4A) and vertical (
Figure 4B) center orientations at 6° (as horizontal orientation bias was evident at 6°) and for radial (
Figure 4C) and tangential (
Figure 4D) center orientations at 15° eccentricities (as radial orientation bias was evident at 15°). A three-way ANOVA at 6° (3 retinotopic locations × 2 center orientations × 2 surround orientations) showed a main effect of the center, F (1, 35) = 4.8,
p = 0.036, η
p2 = 0.12, and surround, F (1, 35) = 45,
p < 0.001, η
p2 = 0.56, orientations. Further, there were interactions between center orientation × surround orientation, F (1, 35) = 5.5,
p = 0.025, η
p2 = 0.14, surround orientation × age group, F (1, 35) = 4.5,
p = 0.041, η
p2 = 0.11, and a significant main effect of age, F (1, 35) = 4.9,
p = 0.032, η
p2 = 0.13. There was no significant interaction between center orientation × age group, F (1, 35) = 0.48,
p = 0.49. As expected from the literature, parallel surrounds generated greater perceptual suppression than orthogonal. As observed in
Malavita et al. (2018), the horizontal center configuration was more susceptible to suppression than the vertical case. As indicated by the significant interaction between the surround orientation and age, the older age group showed a relatively greater elevation of suppression for parallel (open vs. filled blue bars in
Figures 4A and B) than orthogonal conditions (open vs. filled orange bars in
Figures 4A and B) when compared with the younger age group.