Mental rotation of unfamiliar stimuli by teenagers with mental retardation: role of feature salience.

Teenagers with mental retardation and two groups of children without mental retardation matched on MA or CA carried out mental rotation tasks of unfamiliar stimuli. Three shapes composed of four arms were used. For each shape, there was a version with a salient feature (F+), and a version with no salient feature (F-). Results showed that teenagers with mental retardation could perform mental rotation tasks with unfamiliar stimuli. However, they had a steeper increase in error rate for F- stimuli than did the MA and CA groups. Individuals with mental retardation may have difficulties in performing mental rotation tasks when stimuli have no feature with a salient axis of elongation.

The impact of acuity on performance of four clinical measures of contrast sensitivity in Alzheimer's disease.

Investigations of contrast sensitivity losses in Alzheimer's disease (AD) have yielded mixed findings, with some investigators reporting deficits and others not. Potential reasons for these discrepancies include differences between samples and assessments utilized and the failure of some investigators to account for acuity differences between groups. To investigate these issues, we administered four clinical contrast sensitivity assessments to the same group of AD patients and elderly control participants and examined the impact of acuity on performance for each assessment. Results revealed group differences across the spatial frequency range. Further, group acuity differences significantly affected performance on two of the four measures (the Regan and the Vistech but not on the Pelli-Robson or Freiburg assessments). Information regarding the availability of established age norms, test-retest reliability data, and other factors including the time, cost, and training needed to administer each measure is provided to aid clinicians and researchers in their search for an effective measure of contrast sensitivity.