Stimulus Contrast and Word Reading Speed in Alzheimer's Disease

Abstract

The oral word reading speed of patients with Alzheimer's disease (AD) and healthy young and older control participants was evaluated across a broad range of stimulus contrast levels in two experiments. The impact of stimulus repetition on reading speed also was examined. It was found that the older adult participants, and particularly the AD patients, were more sensitive to contrast reductions. Each subject group was able to read repeated words more rapidly than novel words but this repetition effect emerged only at lower stimulus contrast levels. It was concluded that AD patients have feature extraction speeds comparable to nondemented older adults but only when the stimuli are presented at a relatively high contrast. These findings suggest that the automatic encoding processes involved in word recognition remain intact in mildly demented AD patients given stimuli of sufficient strength.

Notes

The research was supported by NIH grants AG04391, AG11549, AG15361, and the Alzheimer's Association. The Alzheimer Center of University Hospitals and Case Western Reserve University identified and screened participants for this study with the support of NIH grant AG08012, NIMH grant MH43444, and an Ohio Department of Aging Center grant. Lisa Townsend and Heidi Wenk assisted in data collection and analysis. The authors wish to thank the research participants and their family members for their interest and dedication to the project and Robert Greene for his comments on an earlier version.

¹To evaluate the contribution of pupil dilation in the filter condition of Experiment 2, the pupil size of three young adults was measured with and without the imposition of a filter under the same lightning conditions as used for the original testing procedures and at the original test distance. No measurable pupil size change was associated with the presence of the filter. We thank an anonymous reviewer for this suggestion.