ABSTRACT
Since the pioneering work of Paul Broca (1861), it has been known that damage to the left frontal lobe can have serious consequences for language function. Most typically, patients with damage to this brain region develop a form of nonfluent aphasia characterized by halting speech and poor name retrieval, often affecting most the retrieval of grammatical articles and verbs (e.g., Kertesz, 1979). There are also problems in language processing associated with damage to the right frontal lobe (e.g., Code, 1987). For example, patients with right frontal lesions have been reported to have difficulties in both expressing and comprehending prosody (e.g., Ross, 1981), but, as we shall report here, more subtle deficits in aspects of word selection can also be observed. Damage to the frontal lobes is also known to generate problems in the “executive functions”, which operate to control other aspects of information processing. Patients can exhibit poor generation and maintenance of goal-driven behaviour, impulsive responding to stimuli, and abnormal responses to affective stimuli associated with prior rewards or punishments (Humphreys & Samson, 2004; Stuss & Knight, 2002). These deficits may cooccur with intact performance on “basic” tasks requiring (for example) object recognition, spatial coding, and motor programming. Rather than holding that the frontal lobes perform basic cognitive functions, such as object recognition or access to semantic knowledge, many current theories suppose that the frontal lobes play a role in controlling low-level modulessetting the goals and contexts that constrain activation during stimulus and response selection (e.g., Braver & Cohen, 2000; Cooper, 2002; Cooper & Shallice, 2000; Miller, 2000), or, in language tasks, modulating the response set of words and the response criteria set for output (Roelofs, 2003). Alternatively, the frontal lobes may serve as a “global workspace” (cf. Dehaene, Sergent, & Changeux, 2003), supporting the basic operations when tasks become more difficult (e.g., when working-memory requirements are increased) (Duncan & Owen, 2000).
