■ A central question concerning word recognition is whether linguistic categories are processed i... more ■ A central question concerning word recognition is whether linguistic categories are processed in continuous or categorical ways, in particular, whether regular and irregular inflection is stored and processed by the same or by distinct systems. Here, we contribute to this issue by contrasting regular (regular stem, regular suffix) with semi-irregular (regular stem, irregular suffix) and irregular (irregular stem, irregular suffix) participle formation in a visual priming experiment on German verb inflection. We measured ERPs and RTs and manipulated the inflectional and meaning relatedness between primes and targets. Inflected verb targets (e.g., leite, "head") were preceded either by themselves, by their participle ( geleitet, "headed"), by a semantically related verb in the same inflection as the target ( führe, "guide") or in the participle form ( geführt, "guided"), or by an unrelated verb in the same inflection (nenne, "name"). Results showed that behavioral and ERP priming effects were gradually affected by verb regularity. Regular participles produced a widely distributed frontal and parietal effect, irregular participles produced a small left parietal effect, and semi-irregular participles yielded an effect in-between these two in terms of amplitude and topography. The behavioral and ERP effects further showed that the priming because of participles differs from that because of semantic associates for all verb types. These findings argue for a single processing system that generates participle priming effects for regular, semi-irregular, and irregular verb inflection. Together, the findings provide evidence that the linguistic categories of verb inflection are processed continuously. We present a single-system model that can adequately account for such graded effects. ■
Motivated by models that propose material-specific cortical long-term memory representations we e... more Motivated by models that propose material-specific cortical long-term memory representations we expected different topographies of event-related slow waves of the EEG during cued retrieval of two distinct types of information (faces and spatial positions), which are assumed to be processed and stored in topographically distinct cortical areas, i.e., in either the ventral or the dorsal visual pathway. Seventeen participants learned associations either between words and spatial positions or between words and faces. Each word was associated with either one or two positions or faces. In a cued recall test, one day later, participants saw two words and had to decide whether these were linked to each other via an associated spatial position or a face. Slow event-related potentials (ERPs) of the EEG were recorded from 61 scalp electrodes during both acquisition and recall. Response times increased monotonically with the number of faces and positions to be reactivated. Negative slow ERPs sh...
To date, much is known about the neural mechanisms underlying working-memory (WM) maintenance and... more To date, much is known about the neural mechanisms underlying working-memory (WM) maintenance and long-term-memory (LTM) encoding. However, these topics have typically been examined in isolation, and little is known about how these processes might interact. Here, we investigated whether EEG oscillations arising specifically during the delay of a delayed matching-to-sample task reflect successful LTM encoding. Given previous findings of increased alpha and theta power with increasing WM load, together with the assumption that successful memory encoding involves processes that are similar to those that are invoked by increasing WM load, alpha and theta power should be higher for subsequently remembered stimuli. Consistent with this assumption, we found stronger alpha power for subsequently remembered stimuli over occipital-to-parietal scalp sites. Furthermore, stronger theta power was found for subsequently remembered stimuli over parietal-to-central electrodes. These results support the idea that alpha and theta oscillations modulate successful LTM encoding.
The present study investigated the neuroanatomical basis of different solution processes in singl... more The present study investigated the neuroanatomical basis of different solution processes in single-digit multiplication by means of fMRI. Sixteen participants silently produced the solution of three distinct types of multiplication, i.e., problems involving zero (e.g., 3 ⁎ 0), small (e.g., 2 ⁎ 4), or large operands (e.g., 8 ⁎ 7). Zero and small problems are assumed to be solved by rule application and fact retrieval, respectively, and problems with large operands sometimes involve backup strategies when direct retrieval is not sufficient. Small problems, when compared with a high-level baseline not requiring any kind of calculation, activated a network of parietal, subcortical, and frontal areas. This activation pattern supports the hypothesis that arithmetic fact retrieval is mediated by a verbal processing loop including the angular gyrus and the basal ganglia. Problems with larger operands showed increased activation in the anterior cingulate cortex, SMA, and the left inferior frontal gyrus, which could reflect increased conflict during the fact-retrieval process, but also higher demands for controlling and coordinating multiple processing steps when a problem cannot be solved by direct retrieval. Zero problems, in comparison to multiplications with small operands, activated the caudate nucleus and the right inferior frontal cortex, showing that rule application is separable from fact retrieval on a neuroanatomical level, too.
■ Many of our daily decisions are memory based, that is, the attribute information about the deci... more ■ Many of our daily decisions are memory based, that is, the attribute information about the decision alternatives has to be recalled. Behavioral studies suggest that for such decisions we often use simple strategies (heuristics) that rely on controlled and limited information search. It is assumed that these heuristics simplify decision-making by activating long-term memory representations of only those attributes that are necessary for the decision. However, from behavioral studies alone, it is unclear whether using heuristics is indeed associated with limited memory search. The present study tested this assumption by monitoring the activation of specific long-term-memory representations with fMRI while participants made memory-based decisions using the "take-the-best" heuristic. For different decision trials, different numbers and types of information had to be retrieved and processed. The attributes consisted of visual information known to be represented in different parts of the posterior cortex. We found that the amount of information required for a decision was mirrored by a parametric activation of the dorsolateral PFC. Such a parametric pattern was also observed in all posterior areas, suggesting that activation was not limited to those attributes required for a decision. However, the posterior increases were systematically modulated by the relative importance of the information for making a decision. These findings suggest that memory-based decision-making is mediated by the dorsolateral PFC, which selectively controls posterior storage areas. In addition, the systematic modulations of the posterior activations indicate a selective boosting of activation of decisionrelevant attributes. ■
This review summarizes experimental studies that investigated the relationship between DC-recorde... more This review summarizes experimental studies that investigated the relationship between DC-recorded slow event-related potentials (slow waves) of the electroencephalogram (EEG) and the hemodynamic BOLD response, as measured with functional magnetic resonance imaging (f MRI). Slow waves have been found to accompany a large number of cognitive processes in a systematic and topographically specific way, and have thus been successfully employed in psychophysiological experiments to dissociate cognitive functions by means of their slow wave topography. Recently, however, several independent studies, using different experimental paradigms, suggest the existence of another feature of slow waves, i.e., a close relationship with the fMRI BOLD response. Some of these studies found couplings between slow waves and BOLD signals in various brain regions, using simultaneous EEG-f MRI recordings. Others found similar task-related activation patterns of slow waves (i.e., scalp topographies) and BOLD responses (i.e., activated voxel profiles), as well as corresponding parametric increases of signal strength with increasing task difficulty. The close relationship between slow waves and BOLD responses reported here concerns a low frequency range of the EEG signal (b 1 Hz) that has so far received less attention in studies on the correspondence between EEG and f MRI than the higher frequencies, and therefore adds to the various findings obtained at higher EEG frequencies. Implications for the use of slow waves for neuroscientific research are discussed.
The goal of the present study was to investigate the neuroanatomical basis of arithmetic fact ret... more The goal of the present study was to investigate the neuroanatomical basis of arithmetic fact retrieval. The rationale was that areas playing a crucial role in arithmetic fact retrieval should show a systematic increase of activation with increasing retrieval effort. To achieve this goal, we utilized the problem-size effect as this is known to be systematically related to retrieval effort. In contrast to many previous studies, we here took a parametric approach to account for the continuous increase of retrieval effort with problem size. BOLD signals were modeled with problem size as parametric regressor and negative slow waves of the EEG were categorized into six levels of problem size. The fMRI data showed that activation in the angular gyrus and ACC/SMA increased parametrically with problem size. The ERP data showed a systematic amplitude increase with increasing problem size, especially at fronto-central electrodes. Consistent with the fMRI data, source modeling localized this effect to the ACC. While these findings support previous notions about the crucial role of the angular gyrus during fact retrieval, they also provide evidence that the medial frontal cortex is involved when single-digit multiplications are solved. Thus, both parietal and frontal structures seem to be integral parts of a system that enables and controls arithmetic fact retrieval. Hum Brain Mapp 32:51-59,
The neural basis underlying the generation of nouns and verbs is still not completely 16 understo... more The neural basis underlying the generation of nouns and verbs is still not completely 16 understood. In classical generation tasks, specific features of the produced words can hardly 17 be controlled. Therefore, the observed neural correlates of noun and verb production cannot 18 be directly related to differences in specific features of the generated words. The present 19 study seeks to address this issue by using a "minimal-phrase context" to elicit the activation 20 of specific nouns and verbs. With this context, the to-be-generated words were highly 21 constrained, and thus their semantic and other features (visual/action relatedness, word 22 frequency, cloze probability, etc.) are well controlled. Thus, the present paradigm combines 23 the advantages of classical word generation tasks (i.e., active semantic processing) with the 24 advantages of tasks that allow for a high control of the experimental stimuli, such as passive 25 viewing, reading, or lexical decision tasks. In an fMRI study, 17 participants generated verbs 26 with strong motor and nouns with strong visual associations. Both noun and verb 27 generation, compared to a rhyme generation baseline, elicited stronger activation in 28 perisylvian language areas of the temporal and parietal cortex. In addition, stronger 29 activation for nouns was found in the right middle/inferior temporal cortex. This activation 30 supports the claim that noun generation is mediated by visual processing areas. Stronger 31 activation for verb generation was found in the left superior temporal gyrus. Since this area 32 is involved in motion perception, the results suggest that perceptual representations of 33 movements mediate the generation of action verbs. 34 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m w w w . e l s e v i e r . c o m / l o c a t e / b r a i n r e s ARTICLE IN PRESS Please cite this article as: Khader, P.H., et al., Neural correlates of generating visual nouns and motor verbs in a minimal phrase context, Brain Res. (2010),
■ A central question concerning word recognition is whether linguistic categories are processed i... more ■ A central question concerning word recognition is whether linguistic categories are processed in continuous or categorical ways, in particular, whether regular and irregular inflection is stored and processed by the same or by distinct systems. Here, we contribute to this issue by contrasting regular (regular stem, regular suffix) with semi-irregular (regular stem, irregular suffix) and irregular (irregular stem, irregular suffix) participle formation in a visual priming experiment on German verb inflection. We measured ERPs and RTs and manipulated the inflectional and meaning relatedness between primes and targets. Inflected verb targets (e.g., leite, "head") were preceded either by themselves, by their participle ( geleitet, "headed"), by a semantically related verb in the same inflection as the target ( führe, "guide") or in the participle form ( geführt, "guided"), or by an unrelated verb in the same inflection (nenne, "name"). Results showed that behavioral and ERP priming effects were gradually affected by verb regularity. Regular participles produced a widely distributed frontal and parietal effect, irregular participles produced a small left parietal effect, and semi-irregular participles yielded an effect in-between these two in terms of amplitude and topography. The behavioral and ERP effects further showed that the priming because of participles differs from that because of semantic associates for all verb types. These findings argue for a single processing system that generates participle priming effects for regular, semi-irregular, and irregular verb inflection. Together, the findings provide evidence that the linguistic categories of verb inflection are processed continuously. We present a single-system model that can adequately account for such graded effects. ■
Motivated by models that propose material-specific cortical long-term memory representations we e... more Motivated by models that propose material-specific cortical long-term memory representations we expected different topographies of event-related slow waves of the EEG during cued retrieval of two distinct types of information (faces and spatial positions), which are assumed to be processed and stored in topographically distinct cortical areas, i.e., in either the ventral or the dorsal visual pathway. Seventeen participants learned associations either between words and spatial positions or between words and faces. Each word was associated with either one or two positions or faces. In a cued recall test, one day later, participants saw two words and had to decide whether these were linked to each other via an associated spatial position or a face. Slow event-related potentials (ERPs) of the EEG were recorded from 61 scalp electrodes during both acquisition and recall. Response times increased monotonically with the number of faces and positions to be reactivated. Negative slow ERPs sh...
To date, much is known about the neural mechanisms underlying working-memory (WM) maintenance and... more To date, much is known about the neural mechanisms underlying working-memory (WM) maintenance and long-term-memory (LTM) encoding. However, these topics have typically been examined in isolation, and little is known about how these processes might interact. Here, we investigated whether EEG oscillations arising specifically during the delay of a delayed matching-to-sample task reflect successful LTM encoding. Given previous findings of increased alpha and theta power with increasing WM load, together with the assumption that successful memory encoding involves processes that are similar to those that are invoked by increasing WM load, alpha and theta power should be higher for subsequently remembered stimuli. Consistent with this assumption, we found stronger alpha power for subsequently remembered stimuli over occipital-to-parietal scalp sites. Furthermore, stronger theta power was found for subsequently remembered stimuli over parietal-to-central electrodes. These results support the idea that alpha and theta oscillations modulate successful LTM encoding.
The present study investigated the neuroanatomical basis of different solution processes in singl... more The present study investigated the neuroanatomical basis of different solution processes in single-digit multiplication by means of fMRI. Sixteen participants silently produced the solution of three distinct types of multiplication, i.e., problems involving zero (e.g., 3 ⁎ 0), small (e.g., 2 ⁎ 4), or large operands (e.g., 8 ⁎ 7). Zero and small problems are assumed to be solved by rule application and fact retrieval, respectively, and problems with large operands sometimes involve backup strategies when direct retrieval is not sufficient. Small problems, when compared with a high-level baseline not requiring any kind of calculation, activated a network of parietal, subcortical, and frontal areas. This activation pattern supports the hypothesis that arithmetic fact retrieval is mediated by a verbal processing loop including the angular gyrus and the basal ganglia. Problems with larger operands showed increased activation in the anterior cingulate cortex, SMA, and the left inferior frontal gyrus, which could reflect increased conflict during the fact-retrieval process, but also higher demands for controlling and coordinating multiple processing steps when a problem cannot be solved by direct retrieval. Zero problems, in comparison to multiplications with small operands, activated the caudate nucleus and the right inferior frontal cortex, showing that rule application is separable from fact retrieval on a neuroanatomical level, too.
■ Many of our daily decisions are memory based, that is, the attribute information about the deci... more ■ Many of our daily decisions are memory based, that is, the attribute information about the decision alternatives has to be recalled. Behavioral studies suggest that for such decisions we often use simple strategies (heuristics) that rely on controlled and limited information search. It is assumed that these heuristics simplify decision-making by activating long-term memory representations of only those attributes that are necessary for the decision. However, from behavioral studies alone, it is unclear whether using heuristics is indeed associated with limited memory search. The present study tested this assumption by monitoring the activation of specific long-term-memory representations with fMRI while participants made memory-based decisions using the "take-the-best" heuristic. For different decision trials, different numbers and types of information had to be retrieved and processed. The attributes consisted of visual information known to be represented in different parts of the posterior cortex. We found that the amount of information required for a decision was mirrored by a parametric activation of the dorsolateral PFC. Such a parametric pattern was also observed in all posterior areas, suggesting that activation was not limited to those attributes required for a decision. However, the posterior increases were systematically modulated by the relative importance of the information for making a decision. These findings suggest that memory-based decision-making is mediated by the dorsolateral PFC, which selectively controls posterior storage areas. In addition, the systematic modulations of the posterior activations indicate a selective boosting of activation of decisionrelevant attributes. ■
This review summarizes experimental studies that investigated the relationship between DC-recorde... more This review summarizes experimental studies that investigated the relationship between DC-recorded slow event-related potentials (slow waves) of the electroencephalogram (EEG) and the hemodynamic BOLD response, as measured with functional magnetic resonance imaging (f MRI). Slow waves have been found to accompany a large number of cognitive processes in a systematic and topographically specific way, and have thus been successfully employed in psychophysiological experiments to dissociate cognitive functions by means of their slow wave topography. Recently, however, several independent studies, using different experimental paradigms, suggest the existence of another feature of slow waves, i.e., a close relationship with the fMRI BOLD response. Some of these studies found couplings between slow waves and BOLD signals in various brain regions, using simultaneous EEG-f MRI recordings. Others found similar task-related activation patterns of slow waves (i.e., scalp topographies) and BOLD responses (i.e., activated voxel profiles), as well as corresponding parametric increases of signal strength with increasing task difficulty. The close relationship between slow waves and BOLD responses reported here concerns a low frequency range of the EEG signal (b 1 Hz) that has so far received less attention in studies on the correspondence between EEG and f MRI than the higher frequencies, and therefore adds to the various findings obtained at higher EEG frequencies. Implications for the use of slow waves for neuroscientific research are discussed.
The goal of the present study was to investigate the neuroanatomical basis of arithmetic fact ret... more The goal of the present study was to investigate the neuroanatomical basis of arithmetic fact retrieval. The rationale was that areas playing a crucial role in arithmetic fact retrieval should show a systematic increase of activation with increasing retrieval effort. To achieve this goal, we utilized the problem-size effect as this is known to be systematically related to retrieval effort. In contrast to many previous studies, we here took a parametric approach to account for the continuous increase of retrieval effort with problem size. BOLD signals were modeled with problem size as parametric regressor and negative slow waves of the EEG were categorized into six levels of problem size. The fMRI data showed that activation in the angular gyrus and ACC/SMA increased parametrically with problem size. The ERP data showed a systematic amplitude increase with increasing problem size, especially at fronto-central electrodes. Consistent with the fMRI data, source modeling localized this effect to the ACC. While these findings support previous notions about the crucial role of the angular gyrus during fact retrieval, they also provide evidence that the medial frontal cortex is involved when single-digit multiplications are solved. Thus, both parietal and frontal structures seem to be integral parts of a system that enables and controls arithmetic fact retrieval. Hum Brain Mapp 32:51-59,
The neural basis underlying the generation of nouns and verbs is still not completely 16 understo... more The neural basis underlying the generation of nouns and verbs is still not completely 16 understood. In classical generation tasks, specific features of the produced words can hardly 17 be controlled. Therefore, the observed neural correlates of noun and verb production cannot 18 be directly related to differences in specific features of the generated words. The present 19 study seeks to address this issue by using a "minimal-phrase context" to elicit the activation 20 of specific nouns and verbs. With this context, the to-be-generated words were highly 21 constrained, and thus their semantic and other features (visual/action relatedness, word 22 frequency, cloze probability, etc.) are well controlled. Thus, the present paradigm combines 23 the advantages of classical word generation tasks (i.e., active semantic processing) with the 24 advantages of tasks that allow for a high control of the experimental stimuli, such as passive 25 viewing, reading, or lexical decision tasks. In an fMRI study, 17 participants generated verbs 26 with strong motor and nouns with strong visual associations. Both noun and verb 27 generation, compared to a rhyme generation baseline, elicited stronger activation in 28 perisylvian language areas of the temporal and parietal cortex. In addition, stronger 29 activation for nouns was found in the right middle/inferior temporal cortex. This activation 30 supports the claim that noun generation is mediated by visual processing areas. Stronger 31 activation for verb generation was found in the left superior temporal gyrus. Since this area 32 is involved in motion perception, the results suggest that perceptual representations of 33 movements mediate the generation of action verbs. 34 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m w w w . e l s e v i e r . c o m / l o c a t e / b r a i n r e s ARTICLE IN PRESS Please cite this article as: Khader, P.H., et al., Neural correlates of generating visual nouns and motor verbs in a minimal phrase context, Brain Res. (2010),
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