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Previous functional magnetic resonance imaging (fMRI) research on action observation has emphasized the role of putative mirror neuron areas such as Broca's area, ventral premotor cortex, and the inferior parietal lobule. However, recent evidence suggests action observation involves many distributed cortical regions, including dorsal premotor and superior parietal cortex. How these different regions relate to traditional mirror neuron areas, and whether traditional mirror neuron areas play a special role in action representation, is unclear. Here we use multi-voxel pattern analysis (MVPA) to show that action representations, including observation, imagery, and execution of reaching movements: (1) are distributed across both dorsal (superior) and ventral (inferior) premotor and parietal areas; (2) can be decoded from areas that are jointly activated by observation, execution, and imagery of reaching movements, even in cases of equal-amplitude blood oxygen level-dependent (BOLD) responses; and (3) can be equally accurately classified from either posterior parietal or frontal (premotor and inferior frontal) regions. These results challenge the presumed dominance of traditional mirror neuron areas such as Broca's area in action observation and action representation more generally. Unlike traditional univariate fMRI analyses, MVPA was able to discriminate between imagined and observed movements from previously indistinguishable BOLD activations in commonly activated regions, suggesting finer-grained distributed patterns of activation.

The processing of Navon figures (Navon, 1977), i.e.,hierarchical letter stimuli, has been studied in experimentalsettings for many years. In particular, they have been studiedin the context of visual hemifield studies and yielded aninteraction between hemifield and whether a target is at thelocal or global level, with a right hemisphere advantage forthe global level, and a left hemisphere advantage for thetargets at the local level (Sergent, 1982). This is a ventralstream process, however, and we were interested in whetherthere might be a similar interaction for hierarchical motionstimuli, presumably a dorsal stream process. Hence wedeveloped a series of dynamic geometric Navon figures inorder to study global/local rotation processing. These figuresconsist of a global figure (a triangle or a square) made up oflocal figures (also triangles or squares). Both global and localfigures can rotate in either clockwise or counterclockwisedirections independently. We found that there is no right orleft visual field perceptual advantage for either the global orlocal levels of these figures. However, curiously enough, wefound that there is a significant processing advantage forclockwise motion compared to counterclockwise motion. Wealso found a highly significant interaction between thedetection of a particular rotational motion and the presence orabsence of that motion in the figure being examined. Finally,our data strongly support the Global Precedence Hypothesiswhich says that people generally tend to focus on the globalproperties of an object before local properties and thatprocessing proceeds in a global-to-local direction.

The present study employed dynamic causal modeling to investigate the effective functional connectivity between regions of the neural network involved in top-down letter processing. We used an illusory letter detection paradigm in which participants detected letters while viewing pure noise images. When participants detected letters, the response of the right middle occipital gyrus (MOG) in the visual cortex was enhanced by increased feed-backward connectivity from the left inferior frontal gyrus (IFG). In addition, illusory letter detection increased feed-forward connectivity from the right MOG to the left inferior parietal lobules. Originating in the left IFG, this top-down letter processing network may facilitate the detection of letters by activating letter processing areas within the visual cortex. This activation in turns may highlight the visual features of letters and send letter information to activate the associated phonological representations in the identified parietal region.

Immediate repetition priming for faces was examined across a range of prime durations in a threshold identification task. Similar to word repetition priming results, short duration face primes produced positive priming whereas long duration face primes eliminated or reversed this effect. A habituation model of such priming effects predicted that the speed of identification should relate to the prime duration needed to achieve negative priming. We used face priming to test this prediction in two ways. First, we examined the relationship between priming effects and individual differences in the target duration needed for threshold performance. Second, we compared priming of upright and inverted faces. As predicted, the transition from positive to negative priming as a function of prime duration occurred more slowly for inverted faces and for individuals with longer threshold target durations. Additional experiments ruled out alternative explanations. (Contains 3 footnotes, 10 tables, and 11 figures.)