Normal tactile threshold in monkeys with neglect.

To learn whether animals with parietotemporal lesions have sensory inattention or defective intention, we trained monkeys to respond with the contralateral limb to a threshold tactile stimulus. After parietotemporal lesions that induced neglect, the monkeys continued to respond normally to threshold stimuli on the side opposite the lesion (the neglected side), but made errors when stimulated on the normal side (ipsilateral to the lesion), often failing to use the contralateral extremity. On this learned task, there was no abnormality of sensory input or sensory attention. The problem was attributed to an impaired preparation to respond (intention).