Prominent models of attentional control assert a dichotomy between top-down and bottom-up control, with the former determined by current selection goals and the latter determined by physical salience. This theoretical dichotomy, however, fails to explain a growing number of cases in which neither current goals nor physical salience can account for strong selection biases. For example, equally salient stimuli associated with reward can capture attention, even when this contradicts current selection goals. Thus, although ‘top-down’ sources of bias are sometimes defined as those that are not due to physical salience, this conception conflates distinct – and sometimes contradictory – sources of selection bias. We describe an alternative framework, in which past selection history is integrated with current goals and physical salience to shape an integrated priority map.

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Working memory (WM) involves maintaining information in an on-line state. One emerging view is that information in WM is maintained via sensory recruitment, such that information is stored via sustained activity in the sensory areas that encode the to-be-remembered information. Using functional magnetic resonance imaging, we observed that key sensory regions such as primary visual cortex (V1) showed little evidence of sustained increases in mean activation during a WM delay period, though such amplitude increases have typically been used to determine whether a region is involved in on-line maintenance. However, a multivoxel pattern analysis of delay-period activity revealed a sustained pattern of activation in V1 that represented only the intentionally stored feature of a multifeature object. Moreover, the pattern of delay activity was qualitatively similar to that observed during the discrimination of sensory stimuli, suggesting that WM representations in V1 are reasonable "copies" of those evoked during pure sensory processing.Working memory (WM) allows the on-line storage of behaviorally relevant information. One emerging view is that WM is supported by the same neural mechanisms that encode the sensory information being remembered (we term this the sensory-recruitment model of WM; see Awh & Jonides, 2001;D'Esposito, 2007;Jonides, Lacey, & Nee, 2005;Postle, 2006). For example, neurons in face-selective regions of inferotemporal cortex show sustained amplitude increases while an observer is holding a face in WM (Chelazzi, Miller, Duncan, & Desimone, 1993;Courtney, Ungerleider, Keil, & Haxby, 1997;Druzgal & D'Esposito, 2001;Lepsien & Nobre, 2007;Miller, Li, & Desimone, 1993;Ranganath, Cohen, Dam, & D'Esposito, 2004). The sensory-recruitment hypothesis assumes that this activity represents the specific stimulus values of the stored items. Here we report a study in which functional magnetic resonance imaging (fMRI) and multivoxel pattern analysis (MVPA) provided direct support for this claim, showing that activation patterns in relevant sensory regions represent the specific stimulus value that is held in WM.MVPA provides a useful tool for identifying the neural regions that mediate WM by focusing on changes in activation patterns as opposed to simply changes in the mean amplitude of the blood-oxygenation-level-dependent (BOLD) response. For example, Offen, Schluppeck, and Heeger (in press) used fMRI to index activation changes in primary visual cortex (V1), a region known to represent orientation and spatial frequency. Although mean response amplitudes in V1 increased during sustained deployments of spatial attention, activation levels were indistinguishable from a low-level baseline when information about orientation (or spatial frequency) was stored in WM. This finding appears to contradict the sensory-recruitment model. preferentially to the remembered orientation should become more active, whereas neurons tuned away from the remembered orientation should be suppressed (relatively speaking; see, e.g.,...

The concept of working memory is central to theories of human cognition because working memory is essential to such human skills as language comprehension and deductive reasoning. Working memory is thought to be composed of two parts, a set of buffers that temporarily store information in either a phonological or visuospatial form, and a central executive responsible for various computations such as mental arithmetic. Although most data on working memory come from behavioural studies of normal and brain-injured humans, there is evidence about its physiological basis from invasive studies of monkeys. Here we report positron emission tomography (PET) studies of regional cerebral blood flow in normal humans that reveal activation in right-hemisphere prefrontal, occipital, parietal and premotor cortices accompanying spatial working memory processes. These results begin to uncover the circuitry of a working memory system in humans.

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Current cognitive models of verbal working memory include two components a phonological store and a rehearsal mechanism that refreshes the contents of this store We present research using positron emission tomography (PET) to provide further evidence for this functional division In Experiment 1, subjects performed a variant of Sternberg's (1966) item recognition task Experiment 2 used a continuous memory task with control conditions designed to separate the brain regions underlying storage and rehearsal The results show that independent brain regions mediate storage and rehearsal In Experiment 3, a dual-task procedure supported the assumption that these memory tasks elicited a rehearsal strategy

We report an experiment that assesses the effect of variations in memory load on brain activations that mediate verbal working memory. The paradigm that forms the basis of this experiment is the "n-back" task in which subjects must decide for each letter in a series whether it matches the one presented n items back in the series. This task is of interest because it recruits processes involved in both the storage and manipulation of information in working memory. Variations in task difficulty were accomplished by varying the value of n. As n increased, subjects showed poorer behavioral performance as well as monotonically increasing magnitudes of brain activation in a large number of sites that together have been identified with verbal working-memory processes. By contrast, there was no reliable increase in activation in sites that are unrelated to working memory. These results validate the use of parametric manipulation of task variables in neuroimaging research, and they converge with the subtraction paradigm used most often in neuroimaging. In addition, the data support a model of working memory that includes both storage and executive processes that recruit a network of brain areas, all of which are involved in task performance.