The analysis of RT showed that there was a main effect of group, F (1,38) = 16.57, p < 0.001, η2 = 0.30, with SI:HP being slower than CI (SI:HP: M = 2712.11, SD = 93.93; CI: M = 2171.41, SD = 93.93). The analysis also showed main effects of search task saliency and distractors. For search task, F (1,38) = 347.34, p < 0.001, η2 = 0.90, RT was significantly slower in the low compared to high target-distractors saliency condition (Low: M = 3011.93, SD = 85.90; High: 1871.59, SD = 57.58). For distractors, F (2,76) = 74.38, p < 0.001, η2 = 0.66, RT was significantly slowed when the number of distractors increased, with significant differences between a target presented with 11 distractors, compared to 17 or 23 distractors, and between 17 and 23 distractors, (M = 2272.82, SD = 64.18; M = 2445.80, SD = 70.35; M = 2606.65, SD = 70.10, for 11, 17, and 23 distractors). As hypothesized, there was a significant interaction between search task saliency and distractors, F (2,76) = 71.97, p < 0.001, η2 = 0.65 (Fig. 2a). Separated ANOVAs were run for each search task. This showed that the effect of distractors was not significant for high target-distractors saliency stimuli (levels 1–3), F (2,76) = 2.06, p = 0.13, η2 = 0.05, but that there was a significant distractor effect for low target-distractors saliency stimuli, F (2,76) = 79.96, p < 0.001, η2 = 0.68. A Bonferroni post hoc analysis showed that mean RT significantly slowed as a function of increased number of distractors for low target-distractor saliency contrasts (with significant differences between each distractor set) (M = 2691.81, SD = 84.15; M = 3007.05, SD = 91.18; M = 3336.92, SD = 96.66, for 11, 17 & 23 distractors respectively).
There was also a significant interaction between search task saliency and group, F (1,38) = 7.50, p < 0.001, η2 = 0.16 (Fig. 3). Separate ANOVAs were run for each search task. This showed that the effect of group was significant for both sets of stimuli (high target-distractor salience contrasts: levels 1–3, F (1,38) = 10.50, p < 0.001, η2 = 0.22, and low target-distractor salience contrasts: levels 4–6, F (1,38) = 17.00, p < 0.001, η2 = 0.31). The alternative post-hoc analysis of the interaction was made by separating the ANOVA by group. This showed significant differences for search task saliency in both the SI:HP, F (1,19) = 219.97, p < 0.001, η2 = 0.92, and CI groups, F (1,19) = 131.45, p < 0.001, η2 = 0.87, with mean RT significantly slower for responses made to targets in the low compared to high target-distractor salience condition for both groups (SI: HP: Low: M = 3366.09, SD = 121.48; High: M = 2058.12, SD = 81.42 – CI: Low: 2657.77, SD = 121.48; High: M = 1685.05, SD = 81.43). To understand the interaction effect more clearly, we ran a third post hoc analysis that re-analysed the data by subtracting mean RT for target search to the high from low target-distractors saliency contrasts (i.e., low-high = inhibition cost; with the positive time illustrating the relative cost of inhibition and eliminating the speed differences observed between participant groups). This analysis showed a main effect of group, F (1, 38) = 7.50, p < 0.001, η2 = 0.16 (SI:HP: M = 1307.96, SD = 86.53; CI: M = 972.71, SD = 86.53), demonstrating that the SI:HP compared to CI groups showed a bigger difference between high and low target-distractor salience contrasts. The interaction between distractors and group was not significant, F (2,76) = 0.10, p = 0.91, η2 = 0.00, and the triple interaction between search task, distractors and groups was not significant, F (2, 76) = 0.73, p = 0.48, η2 = 0.02.
The analysis of MV showed that there was a main effect of group, F (1,38) = 7.43, p < 0.001, η2 = 0.16, with SI:HP making slower actions than CI (SI: HP: M = 0.36, SD = 0.02; CI: M = 0.43, SD = 0.02). The analysis also showed main effects of search task saliency and distractors. For search task, F (1,38) = 181.64, p < 0.001, η2 = 0.83, MV was significantly higher to targets presented in high target-distractors saliency (M = 0.45, SD = 0.01) than in low target-distractors saliency conditions (M = 0.33, SD = 0.01). For distractors, F (2,76) = 20.66, p < 0.001, η2 = 0.35, MV significantly decreased when the number of distractors increased (i.e., responses slowed), with significant differences between a target presented with 11 distractors, compared to 17 or 23 distractors, and between 17 and 23 distractors, (M = 0.41, SD = 0.01; M = 0.39, SD = 0.01; M = 0.38, SD = 0.01, for 11, 17, and 23 distractors). As hypothesized, there was a significant interaction between search task saliency and distractors, F (2,76) = 15.68, p < 0.001, η2 = 0.29 (Fig. 2b). Separated ANOVAs were run for each search task. This showed that the effect of distractors was not significant for high target-distractors saliency, F (2,76) = 1.69, p = 0.19, η2 = 0.04, but it was significant for low target-distractors saliency conditions, F (2,76) = 25.35, p < 0.001, η2 = 0.4. A Bonferroni post hoc analysis showed that mean MV significantly decreased when the number of distractors increased (i.e., responses slowed), (M = 0.36, SD = 0.01; M = 0.33, SD = 0.01; M = 0.31, SD = 0.01, for 11, 17, and 23 distractors). There were no interactions between search task saliency and group, F (1,38) = 0.02, p = 0.89, η2 = 0.00, distractors and group, F (2,76) = 0.66, p = 0.52, η2 = 0.02, and search task saliency, distractors and group, F (2,76) = 0.13, p = 0.87, η2 = 0.00.
The analysis of CV showed that there was also main effects of search task and distractors. For search task, F (1,38) = 49.26, p < 0.001, η2 = 0.56, CV was significantly higher in the low target-distractors saliency (M = 1.71, SD = 0.07) than high target-distractors saliency conditions (M = 1.43, SD = 0.05). For distractors, F (2,76) = 14.86, p < 0.001, η2 = 0.28, CV significantly increased with the number of distractors increasing (M = 1.51, SD = 0.06; M = 1.56, SD = 0.06; M = 1.62, SD = 0.06, for 11, 17, and 23 distractors). However, there was no main effect of group, F (1,38) = 3.9, p = 0.056, η2 = 0.09. As for RT and MV, the analysis showed a significant interaction between search task saliency and distractors, F (2,76) = 22.61, p < 0.001, η2 = 0.37 (Fig. 2c). Separated ANOVAs were run for each search task. This showed that the effect of distractors was not significant for high target-distractors saliency, F (2,76) = 0.25, p = 0.78, η2 = 0.00, but was significant for low target-distractors saliency conditions, F (2,76) = 25.84, p < 0.001, η2 = 0.40. A Bonferroni post hoc analysis showed that mean CV significantly increased when the number of distractors increased (M = 1.59, SD = 0.07; M = 1.70, SD = 0.08; M = 1.83, SD = 0.08, for 11, 17, and 23 distractors).
The analyses of CV also showed a significant three-way interaction between search task saliency, distractors and group, F (2,76) = 3.65, p < 0.001, η2 = 0.09. Separated ANOVA were run for each search task saliency. This showed that the interaction between search task and distractors was significant for SI: HP, F (2,38) = 18.49, p < 0.001, η2 = 0.49, and for CI, F (2,38) = 5.24, p < 0.001, η2 = 0.2. An alternative post hoc analysis, was performed for each group and search task. This showed that in high target distractors saliency, there was no effect of distractors for CI, F (2,38) = 0.007, p = 0.99, η2 = 0.00 and SI:HN, F (2,38) = 0.38, p = 0.69, η2 = 0.02. However, in low target distractors saliency, there was a significant effect of distractors in CI, F (2,38) = 6.09, p < 0.001, η2 = 0.24, and SI:HN, F (2,38) = 21.25, p < 0.001, η2 = 0.53. As in RT analysis, we run a third post hoc analysis that re-analysed the data by subtracting mean CV for target search to the high from low target-distractors saliency contrasts. This showed that there was no group effect, F (1,38) = 0.20, p = 0.66, η2 = 0.00.
------------------ Figure 2 & 3 here--------------------