APHASIA A language impairment that is acquired as a result of stroke or other brain injury.

DORSAL AND VENTRAL VISUAL STREAMS Visual information from V1 is processed in two interconnected but partly dissociable visual pathways: a 'ventral' pathway that extends into the temporal lobe and is thought to be primarily involved in visual object recognition, and a 'dorsal' pathway that extends into the parietal lobes and is thought to be more involved in extracting information about 'where' an object is or 'how' to execute a visually guided action towards it.

EXECUTIVE FUNCTIONING A cluster of high-order capacities, which include selective attention, behavioural planning and response inhibition, and the manipulation of information in problem-solving tasks.

MIRROR NEURONS A particular class of neurons, originally discovered in the ventral premotor cortex, that code goal-related motor acts such as grasping. Specifically, mirror neurons require action observation for their activation; they become active both when the subject makes a particular action and when it observes another subject making a similar action.

PRECUNEUS An area of the inner surface of the cerebral hemisphere, above and in front of the corpus callosum.

SPECIFIC LANGUAGE IMPAIRMENT A term that is often assigned to a developmental language disorder that cannot be explained by any other apparent environmental, perceptual, cognitive or motor cause.

WISCONSIN CARD SORTING TEST A test that is used to measure behavioural flexibility in which subjects receive cards with different symbols and are asked to sort them by a certain feature (such as their colour). After the rule is learned, the subjects, without warning, are required to 'shift set' and sort them by a different feature (such as the shape of the symbols). People with prefrontal cortex lesions show impaired performance on this task and 'perseverate' — they carry on sorting the cards by a particular feature despite being told that it is incorrect.