Visually guided reaching: bilateral posterior parietal lesions cause a switch from fast visuomotor to slow cognitive control.

The visually guided reaching of two patients with bilateral optic ataxia was explored in two experiments. In Experiment 1 simple delayed pointing was compared with immediate pointing. In the immediate pointing task both variable and constant errors increased with target eccentricity. In contrast to the performance of control subjects and contrary to their own beliefs, the patients both showed improved accuracy in the delay condition. This improvement was manifest as a reduction in both pointing variability and in the constant angular error towards the point of fixation. Both angular errors and their improvement with the delay were proportional to target eccentricity. Experiment 2 used a task in which the target was pre-viewed 5s prior to its re-exposure for pointing ('delayed real pointing'). On some trials a conflict was introduced between the present and previous visual information by changing the target's location during the delay. In contrast to control subjects, who ignored the pre-viewed location and aimed directly at the current target, both patients with optic ataxia initiated their movements towards the previously viewed target location. Evidently they relied on off-line information in preference to on-line visual information. In addition, the patients often failed to detect the changes in target location. One of the patients sometimes even guessed incorrectly that the target had changed its location, and her movement trajectory was then more affected by her false belief than by the target's actual location. These findings confirm that posterior parietal lesions severely disrupt direct visuomotor transformations, and suggest that the residual performance is mediated indirectly by expectations or beliefs about target position.

Copying without perceiving: motor imagery in visual form agnosia.

Patient DF has severely impaired visual contour perception, despite being able to use that same visual information to guide her motor actions. We report that DF has developed a strategy to overcome some of her perceptual deficits. DF was first asked to copy single lines set at different orientations. She performed surprisingly accurately, although her responses were slow. When questioned, DF reported imagining tracing the line with her finger before copying the line on paper, although she was still unable to discriminate perceptually between different line orientations. We found that time restraints, or the requirement to perform secondary concurrent tasks, severely disrupted DF's orientation copying ability. We conclude that DF can use pure motor imagery to compensate for some of her perceptual difficulties.

CNV abnormalities following closed head injury.

Event-related potentials (ERPs) were recorded in a GO/NO-GO reaction time task from 20 closed head injury patients, at least 6 months postinjury, and from 20 controls. In this task the pitch of an initial tone (Sl) indicated whether or not a response was required to a second tone (S2) occurring 1.5 s later. In the control group both the early, frontal-maximum, and the later vertex-maximum, components of the contingent negative variation (CNV) were larger on GO than NO-GO trials. In the patients, the early frontal CNV wave did not differentiate GO and NO-GO trials, and the late CNV showed a smaller separation between these trial types than did the late CNV of the control group. These CNV abnormalities may reflect impairments in selectively orienting to salient stimuli, and in differential response preparation. Such impairments might in turn reflect the damage to the frontal lobes and/or their connections that commonly occurs as a result of closed head injury.

Nebulised therapy in acute severe bronchiolitis in infancy.

We have measured total work of breathing before and after the inhalation of water, salbutamol, and ipratropium bromide, given as nebulised solutions, in 39 studies on 25 infants with acute, severe bronchiolitis. Twenty minutes after nebulised water, mean work of breathing per minute was increased by 4% and work per litre by 10% with 2 infants having significant improvement and 2 others showing deterioration. After salbutamol, mean work of breathing per minute showed a 22% increase and work per litre a 0.5% rise. The condition of only one child improved by greater than 25% after this drug. Ipratropium bromide led to significant improvement in 6 out of 15 studies and no corresponding deterioration. The group results showed a fall in work of breathing, 18% in work per minute and 16% in work per litre.

Treatment of acute viral croup.

Total respiratory resistance (RT) was measured before and after nebulised alpha-adrenergic stimulant therapy in 8 children aged 4 to 18 months who had the clinical symptoms of acute viral croup. In 7 children there was a mean fall in RT of 30% after treatment, associated with an improvement in their clinical condition. This improvement was shortlived, the resistance returning to pretreatment levels within 30 minutes. The remaining child showed no improvement after phenylephrine but was subsequently found to have acute epiglottitis. Nebulised water did not produce any change, indicating that the response was not due to moisture alone.