Different theoretical interpretations have been offered in order to account for a specific langua... more Different theoretical interpretations have been offered in order to account for a specific language impairment termed dynamic aphasia. We report a patient (CH) who presented with a dynamic aphasia in the context of nonfluent progressive aphasia. CH had the hallmark of reduced spontaneous speech in the context of preserved naming, reading, and single word repetition and comprehension. Articulatory and grammatical difficulties were also present. CH had a very severe verbal generation impairment despite being able to describe pictorial scenes and action sequences well. In the experimental investigations CH was severely impaired in word, phrase, and sentence generation tasks when many competing responses were activated by a stimulus. By contrast, he could generate verbal responses satisfactorily when a dominant response was activated by a stimulus. For the first time, we demonstrated that the verbal generation impairment was specific to the production of language. Strikingly, our patient was unimpaired on a number of nonverbal generation tasks (e.g., design fluency, gesture fluency, and motor movement generation). MRI revealed focal left frontal atrophy that predominantly affected Brodmann's Areas 44 and 45. Our findings are discussed with reference to alternative accounts of dynamic aphasia and models of speech production. We interpret our patient's impairment as being underpinned by an inability to select between competing verbal response options. This interpretation converges with evidence from the neuroimaging literature, which implicates the left inferior frontal gyrus in the selection of a response among competing information. We conclude that the left posterior inferior frontal gyrus is involved in the generation of verbal output, and specifically in the selection between competing verbal responses.
... Neuropsychology: A Case Study David C. Plaut Department of Psychology, Carnegie Mellon Univer... more ... Neuropsychology: A Case Study David C. Plaut Department of Psychology, Carnegie Mellon University, Pittsburgh, USA Tim Shallice Department ... Empirical support for modularity comes from the existence of highly specialised cortical areas (Van Essen, 1985), and the relative ...
Summary Functional neuroimaging studies of episodic memory consistently report an association bet... more Summary Functional neuroimaging studies of episodic memory consistently report an association between memory encoding operations and left prefrontal cortex (PFC) activation. Encoding-related activation has been described in dorsolateral, ventrolateral and anterior prefrontal regions. We tested the hypothesis that a specific component of this left PFC activation reflects organizational processes necessary for optimal memory encoding. Subjects underwent PET scans while learning
Age is known to affect prefrontal brain structure and executive functioning in healthy older adul... more Age is known to affect prefrontal brain structure and executive functioning in healthy older adults, patients with neurodegenerative conditions and TBI. Yet, no studies appear to have systematically investigated the effect of age on cognitive performance in patients with focal lesions. We investigated the effect of age on the cognitive performance of a large sample of tumour and stroke patients with focal unilateral, frontal (n=68), or non-frontal lesions (n=45) and healthy controls (n=52). We retrospectively reviewed their cross sectional cognitive and imaging data. In our frontal patients, age significantly predicted the magnitude of their impairment on two executive tests (Raven's Advanced Progressive Matrices, RAPM and the Stroop test) but not on nominal (Graded Naming Test, GNT) or perceptual (Incomplete letters) task. In our non-frontal patients, age did not predict the magnitude of their impairment on the RAPM and GNT. Furthermore, the exacerbated executive impairment obs...
Cognitive effects of brain surgery for the removal of intracranial tumors are still under investi... more Cognitive effects of brain surgery for the removal of intracranial tumors are still under investigation. For many basic sensory/motor or language-based functions, focal, albeit transient, cognitive deficits have been reported low-grade gliomas (LGGs); however, the effects of surgery on higher-level cognitive functions are still largely unknown. It has recently been shown that, following brain tumors, damage to different brain regions causes a variety of deficits at different levels in the perception and interpretation of emotions and intentions. However, the effects of different tumor histologies and, more importantly, the effects of surgery on these functions have not been examined. The performance of 66 patients affected by high-grade glioma (HGG), LGG, and meningioma on 4 tasks tapping different levels of perception and interpretations of emotion and intentions was assessed before, immediately after, and (for LGG patients) 4 months following surgery. Results showed that HGG patie...
Episodic memory provides information about the ''when'' of events as well as ''what'' and ''where... more Episodic memory provides information about the ''when'' of events as well as ''what'' and ''where'' they happened. Using functional imaging, we investigated the domain specificity of retrieval-related processes following encoding of complex, naturalistic events. Subjects watched a 42-min TV episode, and 24 h later, made discriminative choices of scenes from the clip during fMRI. Subjects were presented with two scenes and required to either choose the scene that happened earlier in the film (Temporal), or the scene with a correct spatial arrangement (Spatial), or the scene that had been shown (Object). We identified a retrieval network comprising the precuneus, lateral and dorsal parietal cortex, middle frontal and medial temporal areas. The precuneus and angular gyrus are associated with temporal retrieval, with precuneal activity correlating negatively with temporal distance between two happenings at encoding. A dorsal fronto-parietal network engages during spatial retrieval, while antero-medial temporal regions activate during object-related retrieval. We propose that access to episodic memory traces involves different processes depending on task requirements. These include memory-searching within an organised knowledge structure in the precuneus (Temporal task), online maintenance of spatial information in dorsal fronto-parietal cortices (Spatial task) and combining scene-related spatial and non-spatial information in the hippocampus (Object task). Our findings support the proposal of process-specific dissociations of retrieval.
Patients affected by brain tumours may show behavioural and emotional regulation deficits, someti... more Patients affected by brain tumours may show behavioural and emotional regulation deficits, sometimes showing flattened affect and sometimes experiencing a true 'change' in personality. However, little evidence is available to the surgeon as to what changes are likely to occur with damage at specific sites, as previous studies have either relied on single cases or provided only limited anatomical specificity, mostly reporting associations rather than dissociations of symptoms. We investigated these aspects in patients undergoing surgery for the removal of cerebral tumours. We argued that many of the problems described can be ascribed to the onset of difficulties in one or more of the different levels of the process of mentalizing (i.e. abstracting and reflecting upon) emotion and intentions, which impacts on everyday behaviour. These were investigated in terms of (i) emotion recognition; (ii) Theory of Mind; (iii) alexithymia; and (iv) self-maturity (personality disorder). We...
The Quarterly journal of experimental psychology, 1975
The systems underlying word recognition were investigated in a single case study of a patient (K.... more The systems underlying word recognition were investigated in a single case study of a patient (K.F.) with an acquired dyslexia. His reading performance was related to parts of speech, word frequency and word concreteness, and his reading errors were analysed. There was a very striking difference between his ability to read concrete and abstract words. Furthermore visual errors, which could
Verbal initiation, suppression and strategy generation/use are cognitive processes widely held to... more Verbal initiation, suppression and strategy generation/use are cognitive processes widely held to be supported by the frontal cortex. The Hayling Test was designed to tap these cognitive processes within the same sentence completion task. There are few studies specifically investigating the neural correlates of the Hayling Test but it has been primarily used to detect frontal lobe damage. This study investigates the components of the Hayling Test in a large sample of patients with unselected focal frontal (n = 60) and posterior (n = 30) lesions. Patients and controls (n = 40) matched for education, age and sex were administered the Hayling Test as well as background cognitive tests. The standard Hayling Test clinical measures (initiation response time, suppression response time, suppression errors and overall score), composite errors scores and strategy-based responses were calculated. Lesions were analysed by classical frontal/posterior subdivisions as well as a finer-grained front...
Ninety-one patients with cerebral lesions were tested on a task involving two conditions. In the ... more Ninety-one patients with cerebral lesions were tested on a task involving two conditions. In the first condition (response initiation) subjects were read a sentence from which the last word was omitted and were required to give a word which completed the sentence reasonably. In the second condition (response suppression) subjects were asked to produce a word unrelated to the sentence. Patients with frontal lobe involvement showed longer response latencies in the first condition and produced more words which were related to the sentence in the second, in comparison to patients with lesions elsewhere. Moreover, in the second condition patients with frontal lobe lesions produced fewer words which showed the use of a strategy during response preparation. Performance on the initiation and suppression conditions was unrelated at the group or single case level. The relationships between response initiation, suppression and strategy use are discussed.
Journal of the International Neuropsychological Society, 2015
Part B of the Trail Making Test (TMT-B) is one of the most widely used neuropsychological tests o... more Part B of the Trail Making Test (TMT-B) is one of the most widely used neuropsychological tests of "executive" function. A commonly held assumption is that the TMT-B can be used to detect frontal executive dysfunction. However, so far, research evidence has been limited and somewhat inconclusive. In this retrospective study, performance on the TMT-B of 55 patients with known focal frontal lesions, 27 patients with focal non-frontal lesions and 70 healthy controls was compared. Completion time and the number of errors made were examined. Patients with frontal and non-frontal lesions performed significantly worse than healthy controls for both completion time and the number of errors. However, there was no significant difference for both completion time and the number of errors when patients with frontal and non-frontal lesions were compared. Performance was also not significantly different between patients with focal lesions within different regions of the frontal lobe (orbital, left lateral, right lateral, medial). Our findings suggest that the TMT-B is a robust test for detection of brain dysfunction. However, its capacity for detecting frontal executive dysfunction appears rather limited. Clinicians should be cautious when drawing conclusions from performance on the TMT-B alone. (JINS, 2015, 21, 1-6)
Neuropsychological group study methodology is considered one of the primary methods to further un... more Neuropsychological group study methodology is considered one of the primary methods to further understanding of the organisation of frontal 'executive' functions. Typically, patients with frontal lesions caused by stroke or tumours have been grouped together to obtain sufficient power. However, it has been debated whether it is methodologically appropriate to group together patients with neurological lesions of different aetiologies. Despite this debate, very few studies have directly compared the performance of patients with different neurological aetiologies on neuropsychological measures. The few that did included patients with both anterior and posterior lesions.
Two views on the semantics of concrete words are that their core mental representations are featu... more Two views on the semantics of concrete words are that their core mental representations are feature-based or are reconstructions of sensory experience. We argue that neither of these approaches is capable of representing the semantics of abstract words, which involve the representation of possibly hypothetical physical and mental states, the binding of entities within a structure, and the possible use of embedding (or recursion) in such structures. Brain based evidence in the form of dissociations between deficits related to concrete and abstract semantics corroborates the hypothesis. Neuroimaging evidence suggests that left lateral inferior frontal cortex supports those processes responsible for the representation of abstract words.
This study examined the performance of 41 patients with focal prefrontal cortical lesions and 38 ... more This study examined the performance of 41 patients with focal prefrontal cortical lesions and 38 healthy controls on a task-switching procedure. Three different conditions were evaluated: single tasks without switches and two switching tasks with the currently relevant task signalled either 1500 ms (Long Cue) or 200 ms (Short Cue) before the stimulus. Patients with Superior Medial lesions showed both a general slowing of reaction time (RT) and a significantly increased switch cost as measured by RT. No other prefrontal group showed this increased reaction time switch cost. Increased error rates in the switching conditions, on the other hand, were observed in patients with Inferior Medial lesions and, to a lesser extent, ones with Superior Medial lesions. Patients with left dorsolateral lesions (9/46v) showed slower learning of the task as indicated by a high error rate early on. Several different processes are involved in task-switching and these are selectively disrupted by lesions...
This paper considers evidence provided by large neuropsychological group studies and meta-analyse... more This paper considers evidence provided by large neuropsychological group studies and meta-analyses of functional imaging experiments on the location in frontal cortex of the subprocesses involved in the carrying out of task-switching paradigms. The function of the individual subprocesses is also considered in the light of analyses of the performance of normal subjects.
The British Journal for the Philosophy of Science, 1995
BJPS owes a great debt of gratitude to all of its referees. Though most of the refereeing is done... more BJPS owes a great debt of gratitude to all of its referees. Though most of the refereeing is done by members of the editorial advisory panel and the editorial team, a number of other individuals are asked to read submissions. We would like to thank the following referees of papers during the period April 1995 to July 1996.
Traditional accounts of sequential behavior assume that schemas and goals play a causal role in t... more Traditional accounts of sequential behavior assume that schemas and goals play a causal role in the control of behavior. In contrast, M. argued that, at least in routine behavior, schemas and goals are epiphenomenal. The authors evaluate the Botvinick and Plaut account by contrasting the simple recurrent network model of Botvinick and Plaut with their own more traditional hierarchically structured interactive activation model (R. P. . The authors present a range of arguments and additional simulations that demonstrate theoretical and empirical difficulties for both Botvinick and Plaut's model and their theoretical position. The authors conclude that explicit hierarchically organized and causally efficacious schema and goal representations are required to provide an adequate account of the flexibility of sequential behavior. We are grateful to Nicolas Ruh for many helpful discussions of the simple recurrent network (SRN) model, particularly in relation to the role of the training set in shaping the model's attractors and the role of the resulting context representations in the SRN model's implementation of choice. We are also grateful to Gordon Brown for his comments on the effect of rate of production on error profiles, to Matthew Botvinick for providing additional details of his implementation of the SRN model and for insightful comments on an earlier draft of this article, and to Padraic Monaghan for insightful comments on an earlier draft of this article.
A recurrent connectionist network was trained to output semantic feature vectors when presented w... more A recurrent connectionist network was trained to output semantic feature vectors when presented with letter strings. When damaged, the network exhibited characteristics that resembled several of the phenomena found in deep dyslexia and semantic-access dyslexia. Damaged networks sometimes settled to the semantic vectors for semantically similar but visually dissimilar words. With severe damage, a forced-choice decision between categories was possible even when the choice of the particular semantic vector within the category was not possible. The damaged networks typically exhibited many mixed visual and semantic errors in which the output corresponded to a word that was both visually and semantically similar. Surprisingly, damage near the output sometimes caused pure visual errors. Indeed, the characteristic error pattern of deep dyslexia occurred with damage to virtually any part of the network.
SYNOPSIS Neuropsychological studies of schizophrenia typically apply a small number of tests to a... more SYNOPSIS Neuropsychological studies of schizophrenia typically apply a small number of tests to a large group of patients. This approach has at least two drawbacks. First, the heterogeneity of the condition will lead to group means which may not reflect the behaviour of any individual. Secondly, it is difficult to infer the nature of the underlying cognitive impairments from a small number of tests, since good performance on a particular test depends on many different cognitive processes. In these circumstances it is more appropriate to apply the methods of cognitive neuropsychology where a large number of tests are used on a single case. This approach has proved fruitful in the study of neurological patients. We have intensively studied 5 chronic schizophrenic patients. These patients varied greatly in terms of overall ability. However, all patients, whatever their overall ability, performed badly on tests sensitive to frontal lobe lesions. This result suggests impairment of the supervisory attentional system in these patients. In addition, one patient suffered from a visual agnosia.
Different theoretical interpretations have been offered in order to account for a specific langua... more Different theoretical interpretations have been offered in order to account for a specific language impairment termed dynamic aphasia. We report a patient (CH) who presented with a dynamic aphasia in the context of nonfluent progressive aphasia. CH had the hallmark of reduced spontaneous speech in the context of preserved naming, reading, and single word repetition and comprehension. Articulatory and grammatical difficulties were also present. CH had a very severe verbal generation impairment despite being able to describe pictorial scenes and action sequences well. In the experimental investigations CH was severely impaired in word, phrase, and sentence generation tasks when many competing responses were activated by a stimulus. By contrast, he could generate verbal responses satisfactorily when a dominant response was activated by a stimulus. For the first time, we demonstrated that the verbal generation impairment was specific to the production of language. Strikingly, our patient was unimpaired on a number of nonverbal generation tasks (e.g., design fluency, gesture fluency, and motor movement generation). MRI revealed focal left frontal atrophy that predominantly affected Brodmann's Areas 44 and 45. Our findings are discussed with reference to alternative accounts of dynamic aphasia and models of speech production. We interpret our patient's impairment as being underpinned by an inability to select between competing verbal response options. This interpretation converges with evidence from the neuroimaging literature, which implicates the left inferior frontal gyrus in the selection of a response among competing information. We conclude that the left posterior inferior frontal gyrus is involved in the generation of verbal output, and specifically in the selection between competing verbal responses.
... Neuropsychology: A Case Study David C. Plaut Department of Psychology, Carnegie Mellon Univer... more ... Neuropsychology: A Case Study David C. Plaut Department of Psychology, Carnegie Mellon University, Pittsburgh, USA Tim Shallice Department ... Empirical support for modularity comes from the existence of highly specialised cortical areas (Van Essen, 1985), and the relative ...
Summary Functional neuroimaging studies of episodic memory consistently report an association bet... more Summary Functional neuroimaging studies of episodic memory consistently report an association between memory encoding operations and left prefrontal cortex (PFC) activation. Encoding-related activation has been described in dorsolateral, ventrolateral and anterior prefrontal regions. We tested the hypothesis that a specific component of this left PFC activation reflects organizational processes necessary for optimal memory encoding. Subjects underwent PET scans while learning
Age is known to affect prefrontal brain structure and executive functioning in healthy older adul... more Age is known to affect prefrontal brain structure and executive functioning in healthy older adults, patients with neurodegenerative conditions and TBI. Yet, no studies appear to have systematically investigated the effect of age on cognitive performance in patients with focal lesions. We investigated the effect of age on the cognitive performance of a large sample of tumour and stroke patients with focal unilateral, frontal (n=68), or non-frontal lesions (n=45) and healthy controls (n=52). We retrospectively reviewed their cross sectional cognitive and imaging data. In our frontal patients, age significantly predicted the magnitude of their impairment on two executive tests (Raven's Advanced Progressive Matrices, RAPM and the Stroop test) but not on nominal (Graded Naming Test, GNT) or perceptual (Incomplete letters) task. In our non-frontal patients, age did not predict the magnitude of their impairment on the RAPM and GNT. Furthermore, the exacerbated executive impairment obs...
Cognitive effects of brain surgery for the removal of intracranial tumors are still under investi... more Cognitive effects of brain surgery for the removal of intracranial tumors are still under investigation. For many basic sensory/motor or language-based functions, focal, albeit transient, cognitive deficits have been reported low-grade gliomas (LGGs); however, the effects of surgery on higher-level cognitive functions are still largely unknown. It has recently been shown that, following brain tumors, damage to different brain regions causes a variety of deficits at different levels in the perception and interpretation of emotions and intentions. However, the effects of different tumor histologies and, more importantly, the effects of surgery on these functions have not been examined. The performance of 66 patients affected by high-grade glioma (HGG), LGG, and meningioma on 4 tasks tapping different levels of perception and interpretations of emotion and intentions was assessed before, immediately after, and (for LGG patients) 4 months following surgery. Results showed that HGG patie...
Episodic memory provides information about the ''when'' of events as well as ''what'' and ''where... more Episodic memory provides information about the ''when'' of events as well as ''what'' and ''where'' they happened. Using functional imaging, we investigated the domain specificity of retrieval-related processes following encoding of complex, naturalistic events. Subjects watched a 42-min TV episode, and 24 h later, made discriminative choices of scenes from the clip during fMRI. Subjects were presented with two scenes and required to either choose the scene that happened earlier in the film (Temporal), or the scene with a correct spatial arrangement (Spatial), or the scene that had been shown (Object). We identified a retrieval network comprising the precuneus, lateral and dorsal parietal cortex, middle frontal and medial temporal areas. The precuneus and angular gyrus are associated with temporal retrieval, with precuneal activity correlating negatively with temporal distance between two happenings at encoding. A dorsal fronto-parietal network engages during spatial retrieval, while antero-medial temporal regions activate during object-related retrieval. We propose that access to episodic memory traces involves different processes depending on task requirements. These include memory-searching within an organised knowledge structure in the precuneus (Temporal task), online maintenance of spatial information in dorsal fronto-parietal cortices (Spatial task) and combining scene-related spatial and non-spatial information in the hippocampus (Object task). Our findings support the proposal of process-specific dissociations of retrieval.
Patients affected by brain tumours may show behavioural and emotional regulation deficits, someti... more Patients affected by brain tumours may show behavioural and emotional regulation deficits, sometimes showing flattened affect and sometimes experiencing a true 'change' in personality. However, little evidence is available to the surgeon as to what changes are likely to occur with damage at specific sites, as previous studies have either relied on single cases or provided only limited anatomical specificity, mostly reporting associations rather than dissociations of symptoms. We investigated these aspects in patients undergoing surgery for the removal of cerebral tumours. We argued that many of the problems described can be ascribed to the onset of difficulties in one or more of the different levels of the process of mentalizing (i.e. abstracting and reflecting upon) emotion and intentions, which impacts on everyday behaviour. These were investigated in terms of (i) emotion recognition; (ii) Theory of Mind; (iii) alexithymia; and (iv) self-maturity (personality disorder). We...
The Quarterly journal of experimental psychology, 1975
The systems underlying word recognition were investigated in a single case study of a patient (K.... more The systems underlying word recognition were investigated in a single case study of a patient (K.F.) with an acquired dyslexia. His reading performance was related to parts of speech, word frequency and word concreteness, and his reading errors were analysed. There was a very striking difference between his ability to read concrete and abstract words. Furthermore visual errors, which could
Verbal initiation, suppression and strategy generation/use are cognitive processes widely held to... more Verbal initiation, suppression and strategy generation/use are cognitive processes widely held to be supported by the frontal cortex. The Hayling Test was designed to tap these cognitive processes within the same sentence completion task. There are few studies specifically investigating the neural correlates of the Hayling Test but it has been primarily used to detect frontal lobe damage. This study investigates the components of the Hayling Test in a large sample of patients with unselected focal frontal (n = 60) and posterior (n = 30) lesions. Patients and controls (n = 40) matched for education, age and sex were administered the Hayling Test as well as background cognitive tests. The standard Hayling Test clinical measures (initiation response time, suppression response time, suppression errors and overall score), composite errors scores and strategy-based responses were calculated. Lesions were analysed by classical frontal/posterior subdivisions as well as a finer-grained front...
Ninety-one patients with cerebral lesions were tested on a task involving two conditions. In the ... more Ninety-one patients with cerebral lesions were tested on a task involving two conditions. In the first condition (response initiation) subjects were read a sentence from which the last word was omitted and were required to give a word which completed the sentence reasonably. In the second condition (response suppression) subjects were asked to produce a word unrelated to the sentence. Patients with frontal lobe involvement showed longer response latencies in the first condition and produced more words which were related to the sentence in the second, in comparison to patients with lesions elsewhere. Moreover, in the second condition patients with frontal lobe lesions produced fewer words which showed the use of a strategy during response preparation. Performance on the initiation and suppression conditions was unrelated at the group or single case level. The relationships between response initiation, suppression and strategy use are discussed.
Journal of the International Neuropsychological Society, 2015
Part B of the Trail Making Test (TMT-B) is one of the most widely used neuropsychological tests o... more Part B of the Trail Making Test (TMT-B) is one of the most widely used neuropsychological tests of "executive" function. A commonly held assumption is that the TMT-B can be used to detect frontal executive dysfunction. However, so far, research evidence has been limited and somewhat inconclusive. In this retrospective study, performance on the TMT-B of 55 patients with known focal frontal lesions, 27 patients with focal non-frontal lesions and 70 healthy controls was compared. Completion time and the number of errors made were examined. Patients with frontal and non-frontal lesions performed significantly worse than healthy controls for both completion time and the number of errors. However, there was no significant difference for both completion time and the number of errors when patients with frontal and non-frontal lesions were compared. Performance was also not significantly different between patients with focal lesions within different regions of the frontal lobe (orbital, left lateral, right lateral, medial). Our findings suggest that the TMT-B is a robust test for detection of brain dysfunction. However, its capacity for detecting frontal executive dysfunction appears rather limited. Clinicians should be cautious when drawing conclusions from performance on the TMT-B alone. (JINS, 2015, 21, 1-6)
Neuropsychological group study methodology is considered one of the primary methods to further un... more Neuropsychological group study methodology is considered one of the primary methods to further understanding of the organisation of frontal 'executive' functions. Typically, patients with frontal lesions caused by stroke or tumours have been grouped together to obtain sufficient power. However, it has been debated whether it is methodologically appropriate to group together patients with neurological lesions of different aetiologies. Despite this debate, very few studies have directly compared the performance of patients with different neurological aetiologies on neuropsychological measures. The few that did included patients with both anterior and posterior lesions.
Two views on the semantics of concrete words are that their core mental representations are featu... more Two views on the semantics of concrete words are that their core mental representations are feature-based or are reconstructions of sensory experience. We argue that neither of these approaches is capable of representing the semantics of abstract words, which involve the representation of possibly hypothetical physical and mental states, the binding of entities within a structure, and the possible use of embedding (or recursion) in such structures. Brain based evidence in the form of dissociations between deficits related to concrete and abstract semantics corroborates the hypothesis. Neuroimaging evidence suggests that left lateral inferior frontal cortex supports those processes responsible for the representation of abstract words.
This study examined the performance of 41 patients with focal prefrontal cortical lesions and 38 ... more This study examined the performance of 41 patients with focal prefrontal cortical lesions and 38 healthy controls on a task-switching procedure. Three different conditions were evaluated: single tasks without switches and two switching tasks with the currently relevant task signalled either 1500 ms (Long Cue) or 200 ms (Short Cue) before the stimulus. Patients with Superior Medial lesions showed both a general slowing of reaction time (RT) and a significantly increased switch cost as measured by RT. No other prefrontal group showed this increased reaction time switch cost. Increased error rates in the switching conditions, on the other hand, were observed in patients with Inferior Medial lesions and, to a lesser extent, ones with Superior Medial lesions. Patients with left dorsolateral lesions (9/46v) showed slower learning of the task as indicated by a high error rate early on. Several different processes are involved in task-switching and these are selectively disrupted by lesions...
This paper considers evidence provided by large neuropsychological group studies and meta-analyse... more This paper considers evidence provided by large neuropsychological group studies and meta-analyses of functional imaging experiments on the location in frontal cortex of the subprocesses involved in the carrying out of task-switching paradigms. The function of the individual subprocesses is also considered in the light of analyses of the performance of normal subjects.
The British Journal for the Philosophy of Science, 1995
BJPS owes a great debt of gratitude to all of its referees. Though most of the refereeing is done... more BJPS owes a great debt of gratitude to all of its referees. Though most of the refereeing is done by members of the editorial advisory panel and the editorial team, a number of other individuals are asked to read submissions. We would like to thank the following referees of papers during the period April 1995 to July 1996.
Traditional accounts of sequential behavior assume that schemas and goals play a causal role in t... more Traditional accounts of sequential behavior assume that schemas and goals play a causal role in the control of behavior. In contrast, M. argued that, at least in routine behavior, schemas and goals are epiphenomenal. The authors evaluate the Botvinick and Plaut account by contrasting the simple recurrent network model of Botvinick and Plaut with their own more traditional hierarchically structured interactive activation model (R. P. . The authors present a range of arguments and additional simulations that demonstrate theoretical and empirical difficulties for both Botvinick and Plaut's model and their theoretical position. The authors conclude that explicit hierarchically organized and causally efficacious schema and goal representations are required to provide an adequate account of the flexibility of sequential behavior. We are grateful to Nicolas Ruh for many helpful discussions of the simple recurrent network (SRN) model, particularly in relation to the role of the training set in shaping the model's attractors and the role of the resulting context representations in the SRN model's implementation of choice. We are also grateful to Gordon Brown for his comments on the effect of rate of production on error profiles, to Matthew Botvinick for providing additional details of his implementation of the SRN model and for insightful comments on an earlier draft of this article, and to Padraic Monaghan for insightful comments on an earlier draft of this article.
A recurrent connectionist network was trained to output semantic feature vectors when presented w... more A recurrent connectionist network was trained to output semantic feature vectors when presented with letter strings. When damaged, the network exhibited characteristics that resembled several of the phenomena found in deep dyslexia and semantic-access dyslexia. Damaged networks sometimes settled to the semantic vectors for semantically similar but visually dissimilar words. With severe damage, a forced-choice decision between categories was possible even when the choice of the particular semantic vector within the category was not possible. The damaged networks typically exhibited many mixed visual and semantic errors in which the output corresponded to a word that was both visually and semantically similar. Surprisingly, damage near the output sometimes caused pure visual errors. Indeed, the characteristic error pattern of deep dyslexia occurred with damage to virtually any part of the network.
SYNOPSIS Neuropsychological studies of schizophrenia typically apply a small number of tests to a... more SYNOPSIS Neuropsychological studies of schizophrenia typically apply a small number of tests to a large group of patients. This approach has at least two drawbacks. First, the heterogeneity of the condition will lead to group means which may not reflect the behaviour of any individual. Secondly, it is difficult to infer the nature of the underlying cognitive impairments from a small number of tests, since good performance on a particular test depends on many different cognitive processes. In these circumstances it is more appropriate to apply the methods of cognitive neuropsychology where a large number of tests are used on a single case. This approach has proved fruitful in the study of neurological patients. We have intensively studied 5 chronic schizophrenic patients. These patients varied greatly in terms of overall ability. However, all patients, whatever their overall ability, performed badly on tests sensitive to frontal lobe lesions. This result suggests impairment of the supervisory attentional system in these patients. In addition, one patient suffered from a visual agnosia.
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