Recent research suggests 2 principal processes are assessed in many neuropsychological tests of prefrontal functioning: the ability to keep transient information on-line (working memory) and the ability to inhibit prepotent, but incorrect, responses. The current studies examined the hypothesis that taxing working memory beyond some threshold can result in decreased inhibition, resembling the errors committed by patients with prefrontal dysfunctions. Across 3 studies, 70 nonpatient subjects were tested on the antisaccade (AS) task (D. Guitton, H. A. Buchtel, & R. M. Douglas, 1985)-a task sensitive to inhibitory deficits. Subjects were required to look in the opposite direction of a flashed cue, inhibiting the reflexive tendency to saccade to the cue. Subjects performed concurrent tasks that varied working-memory load. The results indicated that conditions with the highest working-memory load produced inhibitory errors comparable to patients with prefrontal dysfunctions. The findings are discussed in terms of the interaction between working memory and the inhibition of prepotent responses.

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This study explored whether functional properties of the hand and tools influence the allocation of spatial attention. In four experiments that used a visual-orienting paradigm with predictable lateral cues, hands or tools were placed near potential target locations. Results showed that targets appearing in the hand's grasping space (i.e., near the palm) and the rake's raking space (i.e., near the prongs) produced faster responses than did targets appearing to the back of the hand, to the back of the rake, or near the forearm. Validity effects were found regardless of condition in all experiments, but they did not interact with the target-in-grasping/raking-space bias. Thus, the topology of the facilitated space around the hand is, in part, defined by the hand's grasping function and can be flexibly extended by functional experience using a tool. These findings are consistent with the operation of bimodal neurons, and this embodied component is incorporated into a neurally based model of spatial attention.

PLATE 1. Stratigraphic sections of preLate Mississippian rocks in north-central Nevada. 2. Correlation chart of Paleozoic formations, north-central Nevada. 3. Map showing distribution of Paleozoic assemblages, north-central Nevada. 4. Geologic map of the Antler Peak quadrangle. 5. Aeromagnetic map of the Antler Peak quadrangle. 6. Structural map of the Antler Peak quadrangle. 7. Isometric diagram showing structural geology of the Antler Peak quadrangle.

A neuropsychological approach was used to examine the frontal lobe and right parietal lobe theories of attention deficit hyperactivity disorder (ADHD). Considerable attempts were made to select as pure a group of ADHD boys as possible. The performance of 10-14-year-old ADHD boys (n = 22), both on and off stimulant medication, was compared with the performance of non-ADHD control boys (n = 22) on tasks purported to assess frontal lobe functioning (Stopping Task, Antisaccade Task, Tower of Hanoi) and right parietal lobe functioning (Visual-Spatial Cuing Task, Turning Task, Spatial Relations). Three important findings emerged: (a) unmedicated ADHD boys exhibited performance deficits on tasks in both frontal and parietal domains compared with control boys, (b) unmedicated ADHD boys appeared to be more severely impaired on the frontal tasks than on the parietal tasks, and (c) medicated ADHD boys performed better in both task domains compared with unmedicated ADHD boys. Several alternative interpretations of the results are discussed.