IMPAIRED CONTOUR INTEGRATION IN MILD COGNITIVE IMPAIRMENT: BEHAVIOURAL AND EEG EVIDENCE

Visuospatial deficits are a common early symptom of Alzheimer’s disease. Vision-based assessments may be sensitive to preclinical changes. The contour integration task (CIT) requires identification of a global contour composed of oriented elements embedded in clutter, engaging both feedforward and top-down recurrent processing within a distributed network including early visual, lateral occipital, and parietal cortices. Although contour integration declines with healthy aging, preliminary evidence suggests greater impairment in mild cognitive impairment (MCI), though this has not been well characterized.
Older adults with MCI (n=23, M age = 74.6) and controls (n=77, M age = 72.3) completed two sessions while electroencephalography (EEG) was recorded. During CIT, participants judged the global orientation of a briefly presented contour embedded in visual clutter, with clutter density varied to estimate perceptual thresholds. A simple reaction time (SRT) task involving responses to a high-contrast grating served as a control.
CIT density thresholds were significantly worse in the MCI group than controls at both sessions (Cohen’s d > 0.76), with a small practice effect across groups. Both groups exhibited a posterior negativity at ~200 ms post-stimulus, with no reliable group differences. In contrast, the MCI group showed reduced inter-trial phase coherence in the 6–13 Hz range over midline frontal electrodes. In the SRT task, response times were slower in the MCI group, but no robust group differences were observed in EEG measures.
These findings demonstrate impaired contour integration in MCI and suggest less reliable engagement of top-down or recurrent processes supporting global visual organization.