Stimulus Incongruency Effects on Visual Short-Term Memory Binding in Young and Older Adults with and Without Cognitive Impairment

Background: Literature suggests that both the Stroop task and visual short-term memory (VSTM) binding tasks can differentiate individuals with Mild Cognitive Impairment (MCI) from cognitively normal older adults. These cognitive processes have rarely been examined together. This study investigated how Stroop-like color-word incongruency and directional incongruency between arrow orientation and motion affect memory accuracy and reaction time (RT) measures during a VSTM binding task in cognitively normal adults and individuals screening positive for MCI. Methods: A total of 115 adults participated: 34 healthy young adults (mean age = 24.7 ± 3.0 years), 61 cognitively normal older adults (mean age = 70.5 ± 6.3 years), and 20 older adults screening positive for MCI (mean age = 73.9 ± 5.9 years), i.e., MCI-indicatives. Participants completed two non-speeded VSTM binding tasks under low (two items) and high (four items) memory load conditions. Experiment 1 used color words displayed in congruent or incongruent ink colors, while Experiment 2 used arrows whose orientation and motion directions were congruent or incongruent. Results: In Experiment 1, overall % memory accuracy was significantly lower in the MCI-indicative group than in the cognitively normal older group and the young healthy group (p < 0.001); the difference between the young and cognitively normal older group was, however, not significant. In Experiment 2, % memory accuracy in the cognitively normal older group was significantly lower than in the young group but better than in the MCI-indicative group (p < 0.01). Across both experiments, the MCI-indicative group showed slower RTs overall. Incongruency did not affect accuracy but significantly increased RTs in older adults and the MCI group in Experiment 1 (p < 0.001), with no significant effect in young adults. Conclusions: The MCI-indicative group showed significantly decreased overall accuracy and longer RTs during VSTM tasks involving Stroop-like colored word-location and directional binding. While Stroop-like incongruency and directional incongruency did not affect memory accuracy, they selectively increased RT in older and MCI-indicative groups, suggesting that executive processing demands may uncover subtle cognitive changes associated with normal aging and early MCI.