There is increasing experimental and neuropsychological evidence that action selection is directly constrained by perceptual information from objects as well as by more abstract semantic knowledge. To capture this evidence, we develop a new connectionist model of action and name selection from objects—NAM (Naming and Action Model), based on the idea that action selection is determined semantic knowledge. We show that NAM is able to simulate evidence for a direct route to action selection from both normal subjects (Experiments 1 and 2) and neuropsychological patients (Experiments 3–6). The model provides a useful framework for understanding how perceptual knowledge influences action selection. SEMANTICALLY MEDIATED ACTION SELECTION What are the mental operations involved when we select an action to an object, when we make a cutting action with a knife? Traditional cognitive models have emphasized that this process involves the retrieval of semantic knowledge about the object, with the semantic knowledge then being used to guide retrieval of the action (e.g., Roy & Square, 1985, for one example). For instance, for the knife, this may involve accessing knowledge that it is a utensil frequently found in the kitchen, that it is used in the preparation and eating of food, that it is employed along with a fork, and so forth. This semantic information, based on contextual and associative knowledge, is then used to “look up ” a

■ Research on the spatio-temporal dynamics of visual object recognition suggests a recurrent, interactive model whereby an initial feedforward sweep through the ventral stream to prefrontal cortex is followed by recurrent interactions. However, critical questions remain regarding the factors that mediate the degree of recurrent interactions necessary for meaningful object recognition. The novel prediction we test here is that recurrent interactivity is driven by increasing semantic integration demands as defined by the complexity of semantic information required by the task and driven by the stimuli. To test this prediction, we recorded magnetoencephalography data while participants named living and nonliving objects during two naming tasks. We found that the spatio-temporal dynamics of neural activity were modulated by the level of semantic integration required. Specifically, source reconstructed time courses and phase synchronization measures showed increased recurrent interactions as a function of semantic integration demands. These findings demonstrate that the cortical dynamics of object processing are modulated by the complexity of semantic information required from the visual input. ■

c, because the visual form of a digit is only arbitrarily related to its corresponding phonological form. This raises the possibility that processing of numbers in the two notations engages fundamentally different pathways and mechanisms. Two simple tasks that are used to compare digit and number word processing are naming aloud and numerical judgements. With number words, it is likely that the same processing routes support naming and access to conceptual knowledge that are involved in the processing of words in general. Models of visual word recognition and naming generally assume that written input can be converted to phonological codes based on non-semantic processing pathways, with some debate about whether one or more routes are required for this conversion (e.g., Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001; Plaut, McClelland, Seidenberg, & Patterson, 1996; Seidenberg & McClelland, 1989). Hence, if a number Markus F. Damian, Department of Experimental Psychology, Universi

Neuropsychological studies have demonstrated that the production of nouns and verbs can be dissociated in aphasia. These reports have been taken as evidence for separate representations of nouns and verbs in the human brain. We used whole-head magnetoencephalography to record cortical dynamics of action and object naming in 10 healthy adults and in 1 anomic patient with superior naming of verbs compared with nouns due to a left posterior parietal lesion. A single set of 100 line drawings was used for both action and object naming. In normal subjects, the activation sequences in action and object naming were essentially identical, advancing from the occipital to posterior temporoparietal and further to the left frontal cortex, without consistent involvement of the classical left inferior frontal (Broca) and temporal (Wernicke) language areas. In the anomic patient, pronounced differences between action and object naming emerged in the left hemisphere. The activation sequence was disrupted at the level of the damaged parietal cortex and did not reach the left frontal cortex even in the relatively easier action naming. The more severely impaired object naming was associated with exceptionally strong and early activation of the left inferior frontal cortex (Broca) and subsequent pronounced activation of the left middle temporal cortex, silent in action naming. Verb and noun retrieval thus utilized a spatiotemporally similar neuronal network in healthy individuals. A clear dissociation in cortical correlates of verb and noun retrieval only became evident in our anomic patient, in whom damage to the language network has resulted in disproportionately worse performance in object than action naming.