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McCollough and Watercolor Effects: Visual Illusions that Fade in Early Alzheimer's Disease

Vaiva Sutnikiene1, Gyte Pakulaite-Kazliene1, Egle Audronyte1

  • 1Clinic of Neurology and Neurosurgery, Vilnius University, Vilnius, Lithuania.

Medical Science Monitor : International Medical Journal of Experimental and Clinical Research
|November 22, 2025
PubMed

Insights

Visual illusions like the McCollough effect (ME) and watercolor effect (WE) reveal differences in visual perception between healthy adults and those with early Alzheimer disease (AD). These findings offer insights into neurodegeneration and visual system changes in AD.

Area of Science:

  • Neuroscience
  • Ophthalmology
  • Cognitive Science

Background:

  • Visual illusions, such as the McCollough effect (ME) and watercolor effect (WE), offer valuable insights into the mechanisms of visual perception.
  • Investigating these effects in individuals with early Alzheimer disease (AD) can illuminate functional alterations in the visual system associated with neurodegeneration.

Purpose of the Study:

  • To examine McCollough effects (ME) and watercolor effects (WE) in patients with mild dementia (MD) due to AD, amnestic mild cognitive impairment (MCI), and cognitively healthy controls.
  • To evaluate the influence of acetylcholinesterase inhibitors on ME and WE perception in patients with mild dementia (MD).

Main Methods:

  • The study included 28 patients with MD, 27 with MCI, and 26 healthy controls, who underwent cognitive assessments (CDR, MMSE, ADAS-Cog 13) and visual tests, including the Ishihara test, ME, and WE evaluations.
  • ME was assessed by identifying chromatic changes in line patterns, while WE involved identifying white or colored sections.

Main Results:

  • No significant differences were found between groups for ME in vertical lines (P=0.659). However, significant differences emerged in the perception of white horizontal lines appearing green (P=0.006).
  • Watercolor effects (WE) were reported by all controls, 25/27 in the MCI group, and 22/28 in the MD group (P=0.024). Cognitive tests and Ishihara results predicted WE perception.
  • No significant differences in ME or WE perception were observed between patients with MD taking or not taking acetylcholinesterase inhibitors.

Conclusions:

  • Perceptions of ME and WE significantly differ between cognitively normal individuals and those with early AD, indicating functional visual system alterations and neurodegeneration.
  • The altered perception of ME, specifically the after-effect of red horizontal lines, may serve as an early indicator of AD.
  • These findings contribute to understanding visual perception changes in AD and may aid in early detection and diagnosis.

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