Visual imagery is mediated via top-down activation of visual cortex. Similar to stimulus-driven perception, the neural configurations associated with visual imagery are differentiated according to content. For example, imagining faces or places differentially activates visual areas associated with perception of actual face or place stimuli. However, while top-down activation of topographically specific visual areas during visual imagery is well established, the extent to which internally generated visual activity resembles the fine-scale population coding responsible for stimulus-driven perception remains unknown. Here, we sought to determine whether top-down mechanisms can selectively activate perceptual representations coded across spatially overlapping neural populations. We explored the precision of top-down activation of perceptual representations using neural pattern classification to identify activation patterns associated with imagery of distinct letter stimuli. Pattern analysis of the neural population observed within high-level visual cortex, including lateral occipital complex, revealed that imagery activates the same neural representations that are activated by corresponding visual stimulation. We conclude that visual imagery is mediated via top-down activation of functionally distinct, yet spatially overlapping population codes for high-level visual representations.

Many tests of specific ‘executive functions’ show deficits after frontal lobe lesions. These deficits appear on a background of reduced fluid intelligence, best measured with tests of novel problem solving. For a range of specific executive tests, we ask how far frontal deficits can be explained by a general fluid intelligence loss. For some widely used tests, e.g. Wisconsin Card Sorting, we find that fluid intelligence entirely explains frontal deficits. When patients and controls are matched on fluid intelligence, no further frontal deficit remains. For these tasks too, deficits are unrelated to lesion location within the frontal lobe. A second group of tasks, including tests of both cognitive (e.g. Hotel, Proverbs) and social (Faux Pas) function, shows a different pattern. Deficits are not fully explained by fluid intelligence and the data suggest association with lesions in the right anterior frontal cortex. Understanding of frontal lobe deficits may be clarified by separating reduced fluid intelligence, important in most or all tasks, from other more specific impairments and their associated regions of damage.

Frontoparietal cortex is thought to be essential for flexible behavior, but the mechanism for control remains elusive. Here, we demonstrate a potentially critical property of this cortex: its dynamic configuration for coding of task-critical information. Using multivoxel pattern analysis of human functional imaging data, we demonstrate an adaptive change in the patterns of activation coding task-relevant stimulus distinctions. When task demands made perceptual information more difficult to discriminate, frontoparietal regions showed increased coding of this information. Visual cortices showed the opposite result: a weaker representation of perceptual information in line with the physical change in the stimulus. On a longer timescale, a rebalancing of coding was also seen after practice, with a diminished representation of task rules as they became familiar. The results suggest a flexible neural system, exerting cognitive control in a wide range of tasks by adaptively representing the task features most challenging for successful goal-directed behavior.

In goal neglect, a person ignores some task requirement though being able to describe it. Goal neglect is closely related to general intelligence or C. Spearman's (1904) g (J. Duncan, H. Emslie, P. Williams, R. Johnson, & C. Freer, 1996). The authors tested the role of task complexity in neglect and the hypothesis that different task components in some sense compete for attention. In contrast to many kinds of attentional limits, increasing the real-time demands of one task component does not promote neglect of another. Neither does neglect depend on preparation for different possible events in a block of trials. Instead, the key factor is complexity in the whole body of knowledge specified in task instructions. The authors suggest that as novel activity is constructed, relevant facts, rules, and requirements must be organized into a "task model." As this model increases in complexity, different task components compete for representation, and vulnerable components may be lost. Construction of effective task models is closely linked to g.