ed smith - Academia.edu (original) (raw)
Papers by ed smith
Neuroimaging studies of normal subjects and studies of patients with focal lesions implicate regi... more Neuroimaging studies of normal subjects and studies of patients with focal lesions implicate regions of parietal cortex in verbal working memory (VWM), yet the precise role of parietal cortex in VWM remains unclear. Some evidence suggests that the parietal cortex mediates the storage of verbal information, but these studies and most previous ones included encoding and retrieval processes as well as storage and rehearsal of verbal information. A recent positron emission tomography (PET) study by isolated storage and rehearsal from other VWM processes and did not find reliable activation in parietal cortex. This result suggests that parietal cortex may not be involved in VWM storage, contrary to previous proposals. However, we report two behavioral studies indicating that some of the verbal material used by may not have required phonological representations in VWM. In addition, we report a PET study that isolated VWM encoding, retrieval, and storage and rehearsal processes in different PET scans and used material likely to require phonological codes in VWM. After subtraction of appropriate controls, the encoding condition revealed no reliable activations; the retrieval condition revealed reliable activations in dorsolateral prefrontal, anterior cingulate, posterior parietal, and extrastriate cortices, and the storage condition revealed reliable activations in dorsolateral prefrontal, inferior frontal, premotor, and posterior parietal cortices, as well as cerebellum. These results suggest that parietal regions are part of a network of brain areas that mediate the short-term storage and retrieval of phonologically coded verbal material.
Journal of Abnormal Psychology, 1980
APA PsycNET Our Apologies! - The following features are not available with your current Browser c... more APA PsycNET Our Apologies! - The following features are not available with your current Browser configuration. - alerts user that their session is about to expire - display, print, save, export, and email selected records - get My ...
Cognitive Psychology, 1997
We have used neuroimaging techniques, mainly positron emission tomography (PET), to study cogniti... more We have used neuroimaging techniques, mainly positron emission tomography (PET), to study cognitively driven issues about working memory. Two kinds of experiments are described. In the first kind, we employ standard subtraction logic to uncover the basic components of working memory. These studies indicate that: (a) there are different working-memory systems for spatial, object, and verbal information (with the spatial system localized more in the right hemisphere, and the verbal system more in the left hemisphere); (b) within at least the spatial and verbal systems, separable components seem to be responsible for the passive storage of information and the active maintenance of information (with the storage component being localized more in the back of the brain, and the maintenance component in the front); and (c) there may be separate components responsible for processing the contents of working memory (localized in prefrontal cortex). In our second kind of experiment we have focused on verbal working memory and incrementally varied one task parameter-memory load-in an effort to obtain a more fine-grained analysis of the system's operations.
Proceedings of The National Academy of Sciences, 1998
We review a program of research that uses neuroimaging techniques to determine the functional and... more We review a program of research that uses neuroimaging techniques to determine the functional and neural architecture of human working memory. A first set of studies indicates that verbal working memory includes a storage component, which is implemented neurally by areas in the left-hemisphere posterior parietal cortex, and a subvocal rehearsal component, which is implemented by lefthemisphere speech areas, including Broca's area as well as the premotor and supplementary motor areas. We provide a number of neuroimaging dissociations between the storage and rehearsal areas. A second set of studies focuses on spatial working memory and indicates that it is mediated by a network of predominantly right-hemisphere regions that include areas in posterior parietal, occipital, and frontal cortex. We provide some suggestive evidence that these areas, too, divide into storage and rehearsal regions, with right-hemisphere posterior parietal and premotor regions subserving spatial rehearsal. In a final set of studies, we turn to ''executive processes,'' metaprocesses that regulate the processing of working-memory contents. We focus on the executive process of inhibition as it is used in verbal working memory. We provide evidence that such inhibition is mediated by the left-hemisphere prefrontal region and that it can be dissociated from verbal storage and rehearsal processes.
Journal of Cognitive Neuroscience, 1995
We used positron emission tomography (PET) to answer the following question: Is working memory a ... more We used positron emission tomography (PET) to answer the following question: Is working memory a unitary storage system, or does it instead include different storage buffers for different kinds of information? In Experiment 1, PET measures were taken while subjects engaged in either a spatial-memory task (retain the position of three dots for 3 sec) or an object-memory task (retain the identity of two objects for 3 sec). The results manifested a striking double dissociation, as the spatial task activated only right-hemisphere regions, whereas the object task activated primarily left-hemisphere regions. The spatial (right-hemisphere) regions included occipital, parietal, and prefrontal areas, while the object (left-hemisphere) regions included inferotemporal and parietal areas. Experiment 2 was similar to Experiment 1 except that the stimuli and trial events were identical for the spatial and object tasks; whether spatial or object memory was required was manipulated by instructions. The PET results once more showed a double dissociation, as the spatial task activated primarily right-hemisphere regions (again including occipital, parietal and prefrontal areas), whereas the object task activated only left-hemisphere regions (again including inferotemporal and parietal areas). Experiment 3 was a strictly behavioral study, which produced another double dissociation. It used the same tasks as Experiment 2, and showed that a variation in spatial similarity affected performance in the spatial but not the object task, whereas a variation in shape similarity affected performance in the object but not the spatial task. Taken together, the results of the three experiments clearly imply that different working-memory buffers are used for storing spatial and object information.
Proceedings of The National Academy of Sciences, 1999
Research on the prefrontal cortex (PFC) of monkeys and humans indicates that this region supports... more Research on the prefrontal cortex (PFC) of monkeys and humans indicates that this region supports a heterogeneous repertoire of mental processes that contribute to many complex behaviors, such as working memory. Anatomical evidence for some of these processes derives from functional neuroimaging experiments using blocked experimental designs, which average signal across all components of many trials and therefore cannot dissociate distinct processes with different time courses. Using event-related functional MRI, we were able to isolate temporally the neural correlates of processes contributing to the target presentation, delay, and probe portions of an item-recognition task. Two types of trials were of greatest interest: those with Recent Negative probes that matched an item from the target set of the previous, but not the present, two trials, and those with Nonrecent Negative probes that did not match a target item from either the present or the two previous trials. There was no difference between the two trial types in target presentation (i.e., encoding) or delay-period (i.e., active maintenance) PFC activation, but there was significantly greater activation for Recent Negatives than Nonrecent Negative activation associated with the probe period within left ventrolateral PFC. These findings characterize spatially and temporally a proactive interference effect that may ref lect the operation of a PFC-mediated response-inhibition mechanism that contributes to working memory performance.
Science, 1999
The human frontal cortex helps mediate working memory, a system that is used for temporary storag... more The human frontal cortex helps mediate working memory, a system that is used for temporary storage and manipulation of information and that is involved in many higher cognitive functions. Working memory includes two components: short-term storage (on the order of seconds) and executive processes that operate on the contents of storage. Recently, these two components have been investigated in functional neuroimaging studies. Studies of storage indicate that different frontal regions are activated for different kinds of information: storage for verbal materials activates Broca's area and left-hemisphere supplementary and premotor areas; storage of spatial information activates the right-hemisphere premotor cortex; and storage of object information activates other areas of the prefrontal cortex. Two of the fundamental executive processes are selective attention and task management. Both processes activate the anterior cingulate and dorsolateral prefrontal cortex.
Proceedings of The National Academy of Sciences, 1998
There are many occasions in which humans and other animals must inhibit the production of some be... more There are many occasions in which humans and other animals must inhibit the production of some behavior or inhibit the processing of some internal representation. Success in inhibitory processing under normal circumstances can be revealed by the fact that certain brain pathologies render inhibitory processing ineffective. These pathologies often have been associated with damage to frontal cortex, including lateral and inferior aspects. We provide behavioral evidence of a verbal working memory task that, by hypothesis, engaged inhibitory processing, and we show (by using positron emission tomograpny) that the inhibitory processing is associated with a lateral portion of the left prefrontal cortex. The task in which subjects engaged was item-recognition: Four target letters were presented for storage followed, after a brief interval, by a probe letter that could match a target letter or not. On some trials, when the probe did not match a target letter and therefore required a ''no'' response, the probe had matched a target letter of the previous trial, so on these trials a ''yes'' response was prepotent and had to be inhibited, by hypothesis. Compared with a condition in which no prepotent response was created, this condition yielded brain activation in left inferior frontal gyrus, in the region of Brodmann's area 45.
Neuroimage, 1996
Current models of verbal working memory assume that modality-specific representations are transla... more Current models of verbal working memory assume that modality-specific representations are translated into phonological representations before entering the working memory system. We report an experiment that tests this assumption. Positron emission tomography measures were taken while subjects performed a verbal working memory task. Stimuli were presented either visually or aurally, and a visual or auditory search task, respectively, was used as a control. Results revealed an almost complete overlap between the active memory areas regardless of input modality. These areas included dorsolateral frontal, Broca's area, SMA, and premotor cortex in the left hemisphere; bilateral superior and posterior parietal cortices and anterior cingulate; and right cerebellum. These results correspond well with previous research and suggest that verbal working memory is modality independent and is mediated by a circuit involving frontal, parietal, and cerebellar mechanisms. r
Journal of Cognitive Neuroscience, 1997
Journal of Cognitive Neuroscience, 2000
& Age-related decline in working memory figures prominently in theories of cognitive aging. Howev... more & Age-related decline in working memory figures prominently in theories of cognitive aging. However, the effects of aging on the neural substrate of working memory are largely unknown. Positron emission tomography (PET) was used to investigate verbal and spatial short-term storage (3 sec) in older and younger adults. Previous investigations with younger subjects performing these same tasks have revealed asymmetries in the lateral organization of verbal and spatial working memory. Using volume of interest (VOI) analyses that specifically compared activation at sites identified with working memory to their homologous twin in the opposite hemisphere, we show pronounced age differences in this organization, particularly in the frontal lobes: In younger adults, activation is predominantly left lateralized for verbal working memory, and right lateralized for spatial working memory, whereas older adults show a global pattern of anterior bilateral activation for both types of memory. Analyses of frontal subregions indicate that several underlying patterns contribute to global bilaterality in older adults: most notably, bilateral activation in areas associated with rehearsal, and paradoxical laterality in dorsolateral prefrontal sites (DLPFC; greater left activation for spatial and greater right activation for verbal). We consider several mechanisms that could account for these age differences including the possibility that bilateral activation reflects recruitment to compensate for neural decline. &
Proceedings of The National Academy of Sciences, 1998
We review research on the neural bases of verbal working memory, focusing on human neuroimaging s... more We review research on the neural bases of verbal working memory, focusing on human neuroimaging studies. We first consider experiments that indicate that verbal working memory is composed of multiple components. One component involves the subvocal rehearsal of phonological information and is neurally implemented by left-hemisphere speech areas, including Broca's area, the premotor area, and the supplementary motor area. Other components of verbal working memory may be devoted to pure storage and to executive processing of the contents of memory. These studies rest on a subtraction logic, in which two tasks are imaged, differing only in that one task presumably has an extra process, and the difference image is taken to ref lect that process. We then review studies that show that the previous results can be obtained with experimental methods other than subtraction. We focus on the method of parametric variation, in which a parameter that presumably ref lects a single process is varied. In the last section, we consider the distinction between working memory tasks that require only storage of information vs. those that require that the stored items be processed in some way. These experiments provide some support for the hypothesis that, when a task requires processing the contents of working memory, the dorsolateral prefrontal cortex is disproportionately activated.
Page 1. PSYCHOLOGICAL SCIENCE Research Article DISSOCIATION OF STORAGE AND REHEARSAL IN VERBAL WO... more Page 1. PSYCHOLOGICAL SCIENCE Research Article DISSOCIATION OF STORAGE AND REHEARSAL IN VERBAL WORKING MEMORY: Evidence From Positron Emission Tomography Edward Awh, John Jonides, Edward ...
Nature, 1997
by distinct cortical structures, with the prefrontal cortex housing the executive control process... more by distinct cortical structures, with the prefrontal cortex housing the executive control processes, and more posterior regions housing the content-specific buffers (for example verbal versus visuospatial) responsible for active maintenance334. However, studies in non-human primates suggest that dorsolateral regions of the prefrontal cortex may also be involved in active mainte-nance5-'. We have used functional magnetic resonance imaging to examine brain activation in human subjects during performance of a working memory task. We used the temporal resolution of this technique to examine the dynamics of regional activation, and to show that prefrontal cortex along with parietal cortex appears to play a role in active maintenance.
Cognition, 1998
Psychological studies of categorization often assume that all concepts are of the same general ki... more Psychological studies of categorization often assume that all concepts are of the same general kind, and are operated on by the same kind of categorization process. In this paper, we argue against this unitary view, and for the existence of qualitatively different categorization processes. In particular, we focus on the distinction between categorizing an item by: (a) applying a category-defining rule to the item vs. (b) determining the similarity of that item to remembered exemplars of a category. We begin by characterizing rule application and similarity computations as strategies of categorization. Next, we review experimental studies that have used artificial categories and shown that differences in instructions or time pressure can lead to either rule-based categorization or similarity-based categorization. Then we consider studies that have used natural concepts and again demonstrated that categorization can be done by either rule application or similarity calculations. Lastly, we take up evidence from cognitive neuroscience relevant to the rule vs. similarity issue. There is some indirect evidence from brain-damaged patients for neurological differences between categorization based on rules vs. that based on similarity (with the former involving frontal regions, and the latter relying more on posterior areas). For more direct evidence, we present the results of a recent neuroimaging experiment, which indicates that different neural circuits are involved when people categorize items on the basis of a rule as compared with when they categorize the same items on the basis of similarity.
Cerebral Cortex, 1996
Three experiments used position emission tomography (PET) to study the neural basis of human work... more Three experiments used position emission tomography (PET) to study the neural basis of human working memory. These studies ask whether different neural circuits underly verbal and spatial memory. In Experiment 1, subjects had to retain for 3 sec. either the names of four letters (verbal memory) or the positions of three dots (spatial memory). The PET results manifested a clear cut double dissociation, as the verbal task activated primarily left-hemisphere regions whereas the spatial task activated only right-hemisphere regions. In Experiment 2, the identical sequence of letters was presented in all conditions, and what varied was whether subjects had to remember the names of the letters (verbal memory) or their positions in the display (spatial memory). In the verbal task, activation was concentrated more in the left than the right hemisphere; in the spatial task, there was substantial activation in both hemispheres, though in key regions, there was more activation in the right than the left hemisphere. Experiment 3 studied only verbal memory, and showed that a continuous memory task activated the same regions as the discrete verbal task used in Experiment 1. Taken together, these results indicate that verbal and spatial working memory are implemented by different neural structures.
Neuroimaging studies of normal subjects and studies of patients with focal lesions implicate regi... more Neuroimaging studies of normal subjects and studies of patients with focal lesions implicate regions of parietal cortex in verbal working memory (VWM), yet the precise role of parietal cortex in VWM remains unclear. Some evidence suggests that the parietal cortex mediates the storage of verbal information, but these studies and most previous ones included encoding and retrieval processes as well as storage and rehearsal of verbal information. A recent positron emission tomography (PET) study by isolated storage and rehearsal from other VWM processes and did not find reliable activation in parietal cortex. This result suggests that parietal cortex may not be involved in VWM storage, contrary to previous proposals. However, we report two behavioral studies indicating that some of the verbal material used by may not have required phonological representations in VWM. In addition, we report a PET study that isolated VWM encoding, retrieval, and storage and rehearsal processes in different PET scans and used material likely to require phonological codes in VWM. After subtraction of appropriate controls, the encoding condition revealed no reliable activations; the retrieval condition revealed reliable activations in dorsolateral prefrontal, anterior cingulate, posterior parietal, and extrastriate cortices, and the storage condition revealed reliable activations in dorsolateral prefrontal, inferior frontal, premotor, and posterior parietal cortices, as well as cerebellum. These results suggest that parietal regions are part of a network of brain areas that mediate the short-term storage and retrieval of phonologically coded verbal material.
Journal of Abnormal Psychology, 1980
APA PsycNET Our Apologies! - The following features are not available with your current Browser c... more APA PsycNET Our Apologies! - The following features are not available with your current Browser configuration. - alerts user that their session is about to expire - display, print, save, export, and email selected records - get My ...
Cognitive Psychology, 1997
We have used neuroimaging techniques, mainly positron emission tomography (PET), to study cogniti... more We have used neuroimaging techniques, mainly positron emission tomography (PET), to study cognitively driven issues about working memory. Two kinds of experiments are described. In the first kind, we employ standard subtraction logic to uncover the basic components of working memory. These studies indicate that: (a) there are different working-memory systems for spatial, object, and verbal information (with the spatial system localized more in the right hemisphere, and the verbal system more in the left hemisphere); (b) within at least the spatial and verbal systems, separable components seem to be responsible for the passive storage of information and the active maintenance of information (with the storage component being localized more in the back of the brain, and the maintenance component in the front); and (c) there may be separate components responsible for processing the contents of working memory (localized in prefrontal cortex). In our second kind of experiment we have focused on verbal working memory and incrementally varied one task parameter-memory load-in an effort to obtain a more fine-grained analysis of the system's operations.
Proceedings of The National Academy of Sciences, 1998
We review a program of research that uses neuroimaging techniques to determine the functional and... more We review a program of research that uses neuroimaging techniques to determine the functional and neural architecture of human working memory. A first set of studies indicates that verbal working memory includes a storage component, which is implemented neurally by areas in the left-hemisphere posterior parietal cortex, and a subvocal rehearsal component, which is implemented by lefthemisphere speech areas, including Broca's area as well as the premotor and supplementary motor areas. We provide a number of neuroimaging dissociations between the storage and rehearsal areas. A second set of studies focuses on spatial working memory and indicates that it is mediated by a network of predominantly right-hemisphere regions that include areas in posterior parietal, occipital, and frontal cortex. We provide some suggestive evidence that these areas, too, divide into storage and rehearsal regions, with right-hemisphere posterior parietal and premotor regions subserving spatial rehearsal. In a final set of studies, we turn to ''executive processes,'' metaprocesses that regulate the processing of working-memory contents. We focus on the executive process of inhibition as it is used in verbal working memory. We provide evidence that such inhibition is mediated by the left-hemisphere prefrontal region and that it can be dissociated from verbal storage and rehearsal processes.
Journal of Cognitive Neuroscience, 1995
We used positron emission tomography (PET) to answer the following question: Is working memory a ... more We used positron emission tomography (PET) to answer the following question: Is working memory a unitary storage system, or does it instead include different storage buffers for different kinds of information? In Experiment 1, PET measures were taken while subjects engaged in either a spatial-memory task (retain the position of three dots for 3 sec) or an object-memory task (retain the identity of two objects for 3 sec). The results manifested a striking double dissociation, as the spatial task activated only right-hemisphere regions, whereas the object task activated primarily left-hemisphere regions. The spatial (right-hemisphere) regions included occipital, parietal, and prefrontal areas, while the object (left-hemisphere) regions included inferotemporal and parietal areas. Experiment 2 was similar to Experiment 1 except that the stimuli and trial events were identical for the spatial and object tasks; whether spatial or object memory was required was manipulated by instructions. The PET results once more showed a double dissociation, as the spatial task activated primarily right-hemisphere regions (again including occipital, parietal and prefrontal areas), whereas the object task activated only left-hemisphere regions (again including inferotemporal and parietal areas). Experiment 3 was a strictly behavioral study, which produced another double dissociation. It used the same tasks as Experiment 2, and showed that a variation in spatial similarity affected performance in the spatial but not the object task, whereas a variation in shape similarity affected performance in the object but not the spatial task. Taken together, the results of the three experiments clearly imply that different working-memory buffers are used for storing spatial and object information.
Proceedings of The National Academy of Sciences, 1999
Research on the prefrontal cortex (PFC) of monkeys and humans indicates that this region supports... more Research on the prefrontal cortex (PFC) of monkeys and humans indicates that this region supports a heterogeneous repertoire of mental processes that contribute to many complex behaviors, such as working memory. Anatomical evidence for some of these processes derives from functional neuroimaging experiments using blocked experimental designs, which average signal across all components of many trials and therefore cannot dissociate distinct processes with different time courses. Using event-related functional MRI, we were able to isolate temporally the neural correlates of processes contributing to the target presentation, delay, and probe portions of an item-recognition task. Two types of trials were of greatest interest: those with Recent Negative probes that matched an item from the target set of the previous, but not the present, two trials, and those with Nonrecent Negative probes that did not match a target item from either the present or the two previous trials. There was no difference between the two trial types in target presentation (i.e., encoding) or delay-period (i.e., active maintenance) PFC activation, but there was significantly greater activation for Recent Negatives than Nonrecent Negative activation associated with the probe period within left ventrolateral PFC. These findings characterize spatially and temporally a proactive interference effect that may ref lect the operation of a PFC-mediated response-inhibition mechanism that contributes to working memory performance.
Science, 1999
The human frontal cortex helps mediate working memory, a system that is used for temporary storag... more The human frontal cortex helps mediate working memory, a system that is used for temporary storage and manipulation of information and that is involved in many higher cognitive functions. Working memory includes two components: short-term storage (on the order of seconds) and executive processes that operate on the contents of storage. Recently, these two components have been investigated in functional neuroimaging studies. Studies of storage indicate that different frontal regions are activated for different kinds of information: storage for verbal materials activates Broca's area and left-hemisphere supplementary and premotor areas; storage of spatial information activates the right-hemisphere premotor cortex; and storage of object information activates other areas of the prefrontal cortex. Two of the fundamental executive processes are selective attention and task management. Both processes activate the anterior cingulate and dorsolateral prefrontal cortex.
Proceedings of The National Academy of Sciences, 1998
There are many occasions in which humans and other animals must inhibit the production of some be... more There are many occasions in which humans and other animals must inhibit the production of some behavior or inhibit the processing of some internal representation. Success in inhibitory processing under normal circumstances can be revealed by the fact that certain brain pathologies render inhibitory processing ineffective. These pathologies often have been associated with damage to frontal cortex, including lateral and inferior aspects. We provide behavioral evidence of a verbal working memory task that, by hypothesis, engaged inhibitory processing, and we show (by using positron emission tomograpny) that the inhibitory processing is associated with a lateral portion of the left prefrontal cortex. The task in which subjects engaged was item-recognition: Four target letters were presented for storage followed, after a brief interval, by a probe letter that could match a target letter or not. On some trials, when the probe did not match a target letter and therefore required a ''no'' response, the probe had matched a target letter of the previous trial, so on these trials a ''yes'' response was prepotent and had to be inhibited, by hypothesis. Compared with a condition in which no prepotent response was created, this condition yielded brain activation in left inferior frontal gyrus, in the region of Brodmann's area 45.
Neuroimage, 1996
Current models of verbal working memory assume that modality-specific representations are transla... more Current models of verbal working memory assume that modality-specific representations are translated into phonological representations before entering the working memory system. We report an experiment that tests this assumption. Positron emission tomography measures were taken while subjects performed a verbal working memory task. Stimuli were presented either visually or aurally, and a visual or auditory search task, respectively, was used as a control. Results revealed an almost complete overlap between the active memory areas regardless of input modality. These areas included dorsolateral frontal, Broca's area, SMA, and premotor cortex in the left hemisphere; bilateral superior and posterior parietal cortices and anterior cingulate; and right cerebellum. These results correspond well with previous research and suggest that verbal working memory is modality independent and is mediated by a circuit involving frontal, parietal, and cerebellar mechanisms. r
Journal of Cognitive Neuroscience, 1997
Journal of Cognitive Neuroscience, 2000
& Age-related decline in working memory figures prominently in theories of cognitive aging. Howev... more & Age-related decline in working memory figures prominently in theories of cognitive aging. However, the effects of aging on the neural substrate of working memory are largely unknown. Positron emission tomography (PET) was used to investigate verbal and spatial short-term storage (3 sec) in older and younger adults. Previous investigations with younger subjects performing these same tasks have revealed asymmetries in the lateral organization of verbal and spatial working memory. Using volume of interest (VOI) analyses that specifically compared activation at sites identified with working memory to their homologous twin in the opposite hemisphere, we show pronounced age differences in this organization, particularly in the frontal lobes: In younger adults, activation is predominantly left lateralized for verbal working memory, and right lateralized for spatial working memory, whereas older adults show a global pattern of anterior bilateral activation for both types of memory. Analyses of frontal subregions indicate that several underlying patterns contribute to global bilaterality in older adults: most notably, bilateral activation in areas associated with rehearsal, and paradoxical laterality in dorsolateral prefrontal sites (DLPFC; greater left activation for spatial and greater right activation for verbal). We consider several mechanisms that could account for these age differences including the possibility that bilateral activation reflects recruitment to compensate for neural decline. &
Proceedings of The National Academy of Sciences, 1998
We review research on the neural bases of verbal working memory, focusing on human neuroimaging s... more We review research on the neural bases of verbal working memory, focusing on human neuroimaging studies. We first consider experiments that indicate that verbal working memory is composed of multiple components. One component involves the subvocal rehearsal of phonological information and is neurally implemented by left-hemisphere speech areas, including Broca's area, the premotor area, and the supplementary motor area. Other components of verbal working memory may be devoted to pure storage and to executive processing of the contents of memory. These studies rest on a subtraction logic, in which two tasks are imaged, differing only in that one task presumably has an extra process, and the difference image is taken to ref lect that process. We then review studies that show that the previous results can be obtained with experimental methods other than subtraction. We focus on the method of parametric variation, in which a parameter that presumably ref lects a single process is varied. In the last section, we consider the distinction between working memory tasks that require only storage of information vs. those that require that the stored items be processed in some way. These experiments provide some support for the hypothesis that, when a task requires processing the contents of working memory, the dorsolateral prefrontal cortex is disproportionately activated.
Page 1. PSYCHOLOGICAL SCIENCE Research Article DISSOCIATION OF STORAGE AND REHEARSAL IN VERBAL WO... more Page 1. PSYCHOLOGICAL SCIENCE Research Article DISSOCIATION OF STORAGE AND REHEARSAL IN VERBAL WORKING MEMORY: Evidence From Positron Emission Tomography Edward Awh, John Jonides, Edward ...
Nature, 1997
by distinct cortical structures, with the prefrontal cortex housing the executive control process... more by distinct cortical structures, with the prefrontal cortex housing the executive control processes, and more posterior regions housing the content-specific buffers (for example verbal versus visuospatial) responsible for active maintenance334. However, studies in non-human primates suggest that dorsolateral regions of the prefrontal cortex may also be involved in active mainte-nance5-'. We have used functional magnetic resonance imaging to examine brain activation in human subjects during performance of a working memory task. We used the temporal resolution of this technique to examine the dynamics of regional activation, and to show that prefrontal cortex along with parietal cortex appears to play a role in active maintenance.
Cognition, 1998
Psychological studies of categorization often assume that all concepts are of the same general ki... more Psychological studies of categorization often assume that all concepts are of the same general kind, and are operated on by the same kind of categorization process. In this paper, we argue against this unitary view, and for the existence of qualitatively different categorization processes. In particular, we focus on the distinction between categorizing an item by: (a) applying a category-defining rule to the item vs. (b) determining the similarity of that item to remembered exemplars of a category. We begin by characterizing rule application and similarity computations as strategies of categorization. Next, we review experimental studies that have used artificial categories and shown that differences in instructions or time pressure can lead to either rule-based categorization or similarity-based categorization. Then we consider studies that have used natural concepts and again demonstrated that categorization can be done by either rule application or similarity calculations. Lastly, we take up evidence from cognitive neuroscience relevant to the rule vs. similarity issue. There is some indirect evidence from brain-damaged patients for neurological differences between categorization based on rules vs. that based on similarity (with the former involving frontal regions, and the latter relying more on posterior areas). For more direct evidence, we present the results of a recent neuroimaging experiment, which indicates that different neural circuits are involved when people categorize items on the basis of a rule as compared with when they categorize the same items on the basis of similarity.
Cerebral Cortex, 1996
Three experiments used position emission tomography (PET) to study the neural basis of human work... more Three experiments used position emission tomography (PET) to study the neural basis of human working memory. These studies ask whether different neural circuits underly verbal and spatial memory. In Experiment 1, subjects had to retain for 3 sec. either the names of four letters (verbal memory) or the positions of three dots (spatial memory). The PET results manifested a clear cut double dissociation, as the verbal task activated primarily left-hemisphere regions whereas the spatial task activated only right-hemisphere regions. In Experiment 2, the identical sequence of letters was presented in all conditions, and what varied was whether subjects had to remember the names of the letters (verbal memory) or their positions in the display (spatial memory). In the verbal task, activation was concentrated more in the left than the right hemisphere; in the spatial task, there was substantial activation in both hemispheres, though in key regions, there was more activation in the right than the left hemisphere. Experiment 3 studied only verbal memory, and showed that a continuous memory task activated the same regions as the discrete verbal task used in Experiment 1. Taken together, these results indicate that verbal and spatial working memory are implemented by different neural structures.