Mental rotation of faces in healthy aging and Alzheimer's disease

Abstract

Background: Previous research has shown that individuals with Alzheimer's disease (AD) develop visuospatial difficulties that affect their ability to mentally rotate objects. Surprisingly, the existing literature has generally ignored the impact of this mental rotation deficit on the ability of AD patients to recognize faces from different angles. Instead, the devastating loss of the ability to recognize friends and family members in AD has primarily been attributed to memory loss and agnosia in later stages of the disorder. The impact of AD on areas of the brain important for mental rotation should not be overlooked by face processing investigations -- even in early stages of the disorder.

Methodology/principal findings: This study investigated the sensitivity of face processing in AD, young controls and older non-neurological controls to two changes of the stimuli -- a rotation in depth and an inversion. The control groups showed a systematic effect of depth rotation, with errors increasing with the angle of rotation, and with inversion. The majority of the AD group was not impaired when faces were presented upright and no transformation in depth was required, and were most accurate when all faces were presented in frontal views, but accuracy was severely impaired with any rotation or inversion.

Conclusions/significance: These results suggest that with the onset of AD, mental rotation difficulties arise that affect the ability to recognize faces presented at different angles. The finding that a frontal view is "preferred" by these patients provides a valuable communication strategy for health care workers.

Figure 1. Sample of stimuli used (from Max-Planck Face Database) inverted and rotated in depth around the vertical axis.

Figure 2. Accuracy under both upright and inverted conditions for both the younger and older viewers (errors bars: SEM's).

Figure 3. The effects of target face views for both upright and inverted orientation conditions in frontal, three-quarter, and profile views, on older and young adults' ability to match faces (error bars: SEM's).

Figure 4. Comparing the impact of increasing the angular disparity between target and choice face angle (0°, 45°, and 90°) for each AD participant (number) in both (a) upright and (b) inverted orientation conditions.

Hatched regions represent 95% CIs for the oldest-old control participants (n = 6).

Figure 5. The effects of planar orientation and angular disparity between target and choice face in accuracy for the (A) oldest-old control participants, and (B) for the six AD participants (error bars: SEM's).

Figure 6. The impact of choice face orientation on matching accuracy for both the oldest-old control participants, and the six AD participants (error bars: SEM's).