A number of neuroimaging findings have been interpreted as evidence that the left inferior frontal gyrus (IFG) subserves retrieval of semantic knowledge. We provide a fundamentally different interpretation, that it is not retrieval of semantic knowledge per se that is associated with left IFG activity but rather selection of information among competing alternatives from semantic memory. Selection demands were varied across three semantic tasks in a single group of subjects. Functional magnetic resonance imaging signal in overlapping regions of left IFG was dependent on selection demands in all three tasks. In addition, the degree of semantic processing was varied independently of selection demands in one of the tasks. The absence of left IFG activity for this comparison counters the argument that the effects of selection can be attributed solely to variations in degree of semantic retrieval. Our findings suggest that it is selection, not retrieval, of semantic knowledge that drives activity in the left IFG.What parts of the brain subserve the retrieval of semantic knowledge? A number of recent neuroimaging studies, using a range of different tasks, implicate the left inferior frontal gyrus (IFG) (1-8). Despite the impressive convergence of localizations across tasks as disparate as verb generation, stem completion, and abstract͞concrete judgments, the conclusion that semantic retrieval critically involves left IFG remains uncertain for two reasons. First, a smaller but still significant number of neuroimaging studies have failed to find left IFG activation during semantic retrieval tasks. For example, neither naming pictures nor verifying word associations consistently leads to left IFG activation, despite the prima facie involvement of semantic knowledge in both tasks (9, 10). Additionally, practice of a semantic retrieval task, even after just a single repetition, causes a marked decrease in left IFG activation (2,8). Second, neuropsychological studies of patient populations have so far failed to demonstrate the necessity of left IFG for semantic retrieval. Instead, impairments of semantic knowledge are most associated with temporal lobe pathology (11-13).The goal of this article is to propose and test an alternative interpretation of the activation of left IFG during semantic retrieval tasks, based on recent theorizing about the role of prefrontal cortex in nonsemantic domains. Cohen and ServanSchreiber (14) argued that prefrontal cortex enables flexible and context-sensitive responses, particularly in tasks where a response other than the prepotent one must be selected. Kimberg and Farah (15) characterized the role of prefrontal cortex in cognition as mediating the selection of action by the weighting of information active in working memory. When the contents of working memory are not critical for action selection, because the action is prepotent, or when the contents of working memory overwhelming support one action, then demands on prefrontal cortex are low. Their model implies that demands on pre...

Are faces recognized using more holistic representations than other types of stimuli? Taking holistic representation to mean representation without an internal part structure, we interpret the available evidence on this issue and then design new empirical tests. Based on previous research, we reasoned that if a portion of an object corresponds to an explicitly represented part in a hierarchical visual representation, then when that portion is presented in isolation it will be identified relatively more easily than if it did not have the status of an explicitly represented part. The hypothesis that face recognition is holistic therefore predicts that a part of a face will be disproportionately more easily recognized in the whole face than as an isolated part, relative to recognition of the parts and wholes of other kinds of stimuli. This prediction was borne out in three experiments: subjects were more accurate at identifying the parts of faces, presented in the whole object, than they were at identifying the same part presented in isolation, even though both parts and wholes were tested in a forced-choice format and the whole faces differed only by one part. In contrast, three other types of stimuli--scrambled faces, inverted faces, and houses--did not show this advantage for part identification in whole object recognition.

There is growing evidence that face recognition is "special" but less certainty concerning the way in which it is special. The authors review and compare previous proposals and their own more recent hypothesis, that faces are recognized "holistically" (i.e., using relatively less part decomposition than other types of objects). This hypothesis, which can account for a variety of data from experiments on face memory, was tested with 4 new experiments on face perception. A selective attention paradigm and a masking paradigm were used to compare the perception of faces with the perception of inverted faces, words, and houses. Evidence was found of relatively less part-based shape representation for faces. The literatures on machine vision and single unit recording in monkey temporal cortex are also reviewed for converging evidence on face representation. The neuropsychological literature is reviewed for-evidence on the question of whether face representation differs in degree or kind from the representation of other types of objects.

Human brain development occurs within a socioeconomic context and childhood socioeconomic status (SES) influences neural development — particularly of the systems that subserve language and executive function. Research in humans and in animal models has implicated prenatal factors, parent–child interactions and cognitive stimulation in the home environment in the effects of SES on neural development. These findings provide a unique opportunity for understanding how environmental factors can lead to individual differences in brain development, and for improving the programmes and policies that are designed to alleviate SES-related disparities in mental health and academic achievement.

Childhood socioeconomic status (SES) is associated with cognitive achievement throughout life. How does SES relate to brain development, and what are the mechanisms by which SES might exert its influence? We review studies in which behavioral, electrophysio-logical and neuroimaging methods have been used to characterize SES disparities in neurocognitive function. These studies indicate that SES is an important predictor of neurocognitive performance, particularly of language and executive function, and that SES differences are found in neural processing even when performance levels are equal. Implications for basic cognitive neuroscience and for understanding and ameliorating the problems related to childhood poverty are discussed.