Abstracts

Traditional stereognosis tests are useful for demonstrating deficits associated with certain large lesions but not with detecting smaller, subtle ones. We devised a haptic search task similar to stereognosis tests but designed to be more sensitive. It requires tactile discrimination among objects that are identical except for size. As this skill should depend on the integrity of parietal cortex, our test is expected to help identify dysfunction in that brain region. 137 healthy volunteers (ages 18-92 years) and 18 patients with focal epilepsy completed sensory and motor control tasks (manual dexterity and two-point discrimination), followed by two experimental tasks using wooden balls that increased or decreased in increments of 1/32 inches from the diameter of a reference ball (1[frac14] inches). The first task determined size-discrimination thresholds. Subjects were then tested at their threshold on the second task, in which they located one target (odd ball) among other balls, all identical in size. Both tasks had unimanual and bimanual conditions. Reaction times and errors were measured. A hand-efficiency index for the bimanual search task produced a normal curve, with most healthy subjects showing no hand advantage, whereas the right hand of right-handed subjects showed a moderate advantage on the unimanual task. A significant increase in reaction times with age was observed on the discrimination tasks but not on the search tasks. Only patients without primary sensory deficits were tested. Patients with focal lesions in parietal cortex showed increased reaction times on the contralateral hand for both discrimination and search. By contrast, patients with frontal-lobe abnormalities were slower with both hands and normal performance was observed in patients with temporal-lobe abnormality. Results from a large group of healthy individuals provide normative data for this task, which is meant for use with patients. Age-related decline in healthy subjects warns that age must be taken into account when interpreting a patient[apos]s performance. Our initial results with patients suggest that the task is sensitive to lateralized damage in parietal regions, but performance is also affected by frontal-lobe lesions. (Supported by G.W. Stairs Memorial Fund.)