Maruff P, Currie J
Neurophysiology and Neurovisual Research Unit, Mental Health Research Institute of Victoria, Parkville, Australia.
Neuropsychologia. 1995 Jun;33(6):689-701. doi: 10.1016/0028-3932(95)00016-v.
Motor and visual grasp reflexes often occur as part of the symptomatology of Alzheimer's disease (AD). Similar grasp reflexes may also be associated with the impaired performance of AD patients on tasks which require direction of visual attention without eye movements. The covert orienting of visual attention task (COVAT) requires subjects to keep their eyes fixed on a central point and manually respond to the appearance of a peripheral target in one of two locations in the left or right visual field. Before the target appears, a cue is presented at either the target location or the contralateral location to the target, although the nature of the cue is not known until the target appears. We hypothesised that the attentional grasp reflex would become evident in patients with AD when attentional shifts away from the cue were required but there was no target for the shift present. Twelve patients who met the clinical criteria for AD and 12 age and education matched controls were administered three COVAT conditions in which the target appeared at the cued location with either an 80, 50 or 20% probability. For the 80 and 50% probability conditions. RTs for targets at the cued location were significantly faster than RTs for targets contralateral to the cue in both AD subjects and controls indicating that AD subjects were able to disengage attention when there was a target for the attentional shift. For the 20% probability condition, control subjects showed significantly faster RTs for targets appearing contralateral to the cue than for targets at the cued location indicating that when they expected the target to appear in the opposite visual field to the cue, they could initiate the shift of attention before the target appeared. However, AD subjects continued to show significantly faster RTs for targets at the cued location than for targets appearing contralateral to the cue, despite the high probability that targets would not occur at the cued location. This suggests that the covert redirection of attention away from a peripheral visual cue could not be initiated until the contralateral target appeared. Taken together these results suggest an attentional grap reflex in patients with AD.
运动和视觉抓握反射常常作为阿尔茨海默病（AD）症状学的一部分出现。类似的抓握反射也可能与AD患者在需要在不进行眼球运动的情况下定向视觉注意力的任务中表现受损有关。视觉注意力隐蔽定向任务（COVAT）要求受试者将眼睛固定在中心点上，并手动对左或右视野中两个位置之一的外周目标的出现做出反应。在目标出现之前，会在目标位置或与目标相对的位置呈现一个线索，不过直到目标出现，线索的性质才会明确。我们假设，当需要将注意力从线索上转移但没有转移目标出现时，AD患者的注意力抓握反射会变得明显。对12名符合AD临床标准的患者以及12名年龄和教育程度匹配的对照组进行了三种COVAT条件测试，目标以80%、50%或20%的概率出现在线索位置。对于80%和50%概率的条件，无论是AD受试者还是对照组，线索位置的目标反应时间都显著快于线索对侧的目标反应时间，这表明当存在注意力转移目标时，AD受试者能够转移注意力。对于20%概率的条件，对照组中线索对侧出现的目标的反应时间显著快于线索位置的目标，这表明当他们预期目标会出现在与线索相反的视野中时，他们可以在目标出现之前启动注意力转移。然而，尽管目标出现在线索位置的概率很低，但AD受试者中线索位置的目标反应时间仍显著快于线索对侧出现的目标。这表明，直到对侧目标出现，才能够启动从外周视觉线索上隐蔽地重新定向注意力。综合这些结果表明AD患者存在注意力抓握反射。
