The ability to select between possible responses to a given situation is central to human cogniti... more The ability to select between possible responses to a given situation is central to human cognition. The goal of this study was to distinguish between brain areas representing candidate responses and areas selecting between competing response alternatives. Event-related fMRI data were acquired while 10 healthy adults performed a task used to examine response competition: the Eriksen flanker task. Left parietal cortex was activated by either of two manipulations that increased the need to maintain a representation of possible responses. In contrast, lateral prefrontal and rostral anterior cingulate cortices were specifically engaged by the need to select among competing response alternatives. These findings support the idea that parietal cortex is involved in activating possible responses on the basis of learned stimulus-response associations, and that prefrontal cortex is recruited when there is a need to select between competing responses.
Neuro-Behavioral Determinants of Interlimb Coordination, 2004
We argue that bimanual coordination and interference depends critically on how these actions are ... more We argue that bimanual coordination and interference depends critically on how these actions are represented on a cognitive level. We first review the literature on spatial interactions, focusing on the difference between movements directed at visual targets and movements cued symbolically. Interactions manifest during response planning are limited to the latter condition. These results suggest that interactions in the formation of the trajectories of the two hands are associated with processes involved in response selection, rather than interactions in the motor system. Neuropsychological studies involving callosotomy patients argue that these interactions arise from transcallosal interactions between cortically-based spatial codes. The second half of the chapter examines temporal constraints observed in bimanual movements. We propose that most bimanual movements are marked by a common event structure, an explicit representation that ensures temporal coordination of the movements. The translation of an abstract event structure into a movement with a particular timing pattern is associated with cerebellar function, although the resulting temporal coupling during bimanual movements may be due to the operation of other subcortical mechanisms. For rhythmic movements that do not entail an event structure, timing may be an emergent property. Under such conditions, both spatial and temporal coupling can be absent. The emphasis on abstract levels of constraint makes clear that limitations in bimanual coordination overlap to a considerable degree with those observed in other domains of cognition.
Simultaneous reaching movements made with the two hands can show a considerable increase in react... more Simultaneous reaching movements made with the two hands can show a considerable increase in reaction time (RT) when they differ in terms of direction or extent, compared to when the movements involve the same direction and extent. This cost has been attributed to cross-talk in the specification of the motor parameters for the two hands. However, a recent study [Diedrichsen, Hazeltine, Kennerley, & Ivry, (2001). Psychological Science, 12, 493-498] indicates that when reaching movements are cued by the onset of the target endpoint, no compatibility effects are observed. To determine why directly cued movements are immune from interference, we varied the stimulus onset asynchrony for the two movements and used different combinations of directly cued and symbolically cued movements. In two experiments, compatibility effects were only observed when both movements were symbolically cued. No difference was found between compatible and incompatible movements when both movements were directly cued or when one was directly cued and the other was symbolically cued. These results indicate that interference is not related to the specification of movement parameters but instead emerges from processes associated with response selection. Moreover, the data suggest that cross-talk, when present, primarily shortens the RT of the second movement on compatible trials rather than lengthening this RT on incompatible trials.
Hazeltine et al.-Timing mechanisms discrimination task. Furthermore, acuity on the perception tas... more Hazeltine et al.-Timing mechanisms discrimination task. Furthermore, acuity on the perception task was not correlated with performance on a non-temporal motor task (see also Ref. 5), suggesting that the correlation reflects an overlap in the neural systems subserving these tasks. Neural substrates Given the correlational nature of these studies, it is important to look for converging evidence supporting the common Copyright
Research Update Research News Recently, Boyd and Winstein tested three groups of individuals with... more Research Update Research News Recently, Boyd and Winstein tested three groups of individuals with damage to unilateral sensorimotor areas on a version of the serial reaction time task performed with the ipsilesional hand. Only when the individuals were provided in advance with explicit knowledge of the motor sequence were they able to benefit behaviorally from the sequence. Despite aspects of the experimental procedure and the subject selection that make it difficult to draw strong conclusions, these results add to growing evidence that sensorimotor structures contribute to the formation of abstract representations that affect more than ipsilateral effectors.
The authors theorize that 2 neurocognitive sequence-learning systems can be distinguished in seri... more The authors theorize that 2 neurocognitive sequence-learning systems can be distinguished in serial reaction time experiments, one dorsal (parietal and supplementary motor cortex) and the other ventral (temporal and lateral prefrontal cortex). Dorsal system learning is implicit and associates noncategorized stimuli within dimensional modules. Ventral system learning can be implicit or explicit. It also allows associating events across dimensions and therefore is the basis of cross-task integration or interference, depending on degree of cross-task correlation of signals. Accordingly, lack of correlation rather than limited capacity is responsible for dual-task effects on learning. The theory is relevant to issues of attentional effects on learning; the representational basis of complex, sequential skills; hippocampalversus basal ganglia-based learning; procedural versus declarative memory; and implicit versus explicit memory.
The neurocognitive architecture for response selection is uncertain. Some theorists suggest that ... more The neurocognitive architecture for response selection is uncertain. Some theorists suggest that it is mediated by an amodal central mechanism, whereas others propose a set of independent control mechanisms. In a functional neuroimaging experiment, we investigated the nature of response selection by examining how its underlying brain mechanisms are aVected by stimulus modality. To do this, we used a modiWed Xanker task, in which the target and Xanker (distractor) stimuli diVered in time rather than space, making it accessible for both visual and auditory stimuli. As in the traditional Xanker task, larger reaction times were observed for incongruent than congruent trials (i.e., a congruency eVect) for both modalities. Congruency aVected brain activation for both modalities in prefrontal cortex, parietal cortex, and the putamen. Modality-dependent activation was found in additional prefrontal and parietal regions for the visual modality and in left inferior prefrontal cortex for the auditory modality. Modality-dependent activity speciWcally related to response congruency was also found in sensory cortical regions. These data suggest that modality aVects the brain regions throughout the cortex mediating response selection even for conceptually identical stimuli and tasks. They are consistent with the hypothesis that (at least partially) independent brain networks mediate response selection and that input modality may be a powerful factor for organizing neural activity to support task performance.
The present experiment examined the effects of input/output modality pairings on dual-task perfor... more The present experiment examined the effects of input/output modality pairings on dual-task performance using the psychological refractory period (PRP) procedure. Four groups of participants performed two tasks composed of the same sets of inputs (visual and auditory) and the same sets of outputs (manual and vocal), but with different input/output modality pairings. Whereas modality pairings had only small effects on single-task reaction times, they had large effects on dual-task reaction times. The modality pairing effect cannot stem from differences in the difficulty of stimulus classification or response execution, because these task demands were the same across groups. The effect also does not appear to result from changes in stimulus-response compatibility. The present findings suggest dualtask interference arises not only from postponement of central operations (due to a central bottleneck), but also from a slowing of central operations whose magnitude is sensitive to the input/output modality pairings.
Proceedings of the National Academy of Sciences, 2001
To compare neural activity produced by visual events that escape or reach conscious awareness, we... more To compare neural activity produced by visual events that escape or reach conscious awareness, we used event-related MRI and evoked potentials in a patient who had neglect and extinction after focal right parietal damage, but intact visual fields. This neurological disorder entails a loss of awareness for stimuli in the field contralateral to a brain lesion when stimuli are simultaneously presented on the ipsilateral side, even though early visual areas may be intact, and single contralateral stimuli may still be perceived. Functional MRI and event-related potential study were performed during a task where faces or shapes appeared in the right, left, or both fields. Unilateral stimuli produced normal responses in V1 and extrastriate areas. In bilateral events, left faces that were not perceived still activated right V1 and inferior temporal cortex and evoked nonsignificantly reduced N1 potentials, with preserved face-specific negative potentials at 170 ms. When left faces were perce...
Neuronal recording and neuroimaging studies have shown that the primary motor area (M1) not only ... more Neuronal recording and neuroimaging studies have shown that the primary motor area (M1) not only participates in motor execution, but is also engaged during movement preparation. The purpose of the present study was to map the distribution of the preparation-and execution-related activity within the contralateral M1 using functional magnetic resonance imaging. Eleven subjects performed a delayed sequential finger movement task, in which a CUE signal indicated a movement sequence in advance of an imperative GO signal. The hemodynamic response related to the CUE and GO signals decreased in a linear fashion across the central sulcus, with activity greater along the lateral extent compared to the medial extent. This decrease was especially evident in the epoch following the CUE. Our data reveal a pattern of functional organization within M1 related to the preparation and execution of movement sequences.
The present study used the flanker task [Percept. Psychophys. 16 (1974) 143] to identify neural s... more The present study used the flanker task [Percept. Psychophys. 16 (1974) 143] to identify neural structures that support response selection processes, and to determine which of these structures respond differently depending on the type of stimulus material associated with the response. Participants performed two versions of the flanker task while undergoing event-related functional magnetic resonance imaging (fMRI). Both versions of the task required participants to respond to a central stimulus regardless of the responses associated with simultaneously presented flanking stimuli, but one used colored circle stimuli and the other used letter stimuli. Competition-related activation was identified by comparing Incongruent trials, in which the flanker stimuli indicated a different response than the central stimulus, to Neutral stimuli, in which the flanker stimuli indicated no response. A region within the right inferior frontal gyrus exhibited significantly more competition-related activation for the color stimuli, whereas regions within the middle frontal gyri of both hemispheres exhibited more competition-related activation for the letter stimuli. The border of the right middle frontal and inferior frontal gyri and the anterior cingulate cortex (ACC) were significantly activated by competition for both types of stimulus materials. Posterior foci demonstrated a similar pattern: left inferior parietal cortex showed greater competition-related activation for the letters, whereas right parietal cortex was significantly activated by competition for both materials. These findings indicate that the resolution of response competition invokes both material-dependent and material-independent processes. Published by Elsevier Science Ltd.
Do voluntary (endogenous) and involuntary (exogenous) attention have the same perceptual conseque... more Do voluntary (endogenous) and involuntary (exogenous) attention have the same perceptual consequences? Here we used fMRI to examine activity in the fusiform face area (FFA-a region in ventral visual cortex responsive to faces) and frontal-parietal areas (dorsal regions involved in spatial attention) under voluntary and involuntary spatial cueing conditions. The trial and stimulus parameters were identical for both cueing conditions. However, the cue predicted the location of an upcoming target face in the voluntary condition but was nonpredictive in the involuntary condition. The predictable cue condition led to increased activity in the FFA compared to the nonpredictable cue condition. These results show that voluntary attention leads to more activity in areas of the brain associated with face processing than involuntary attention, and they are consistent with differential behavioral effects of attention on recognition-related processes.
Two split-brain patients, a patient with callosal agenesis, and 6 age-matched control participant... more Two split-brain patients, a patient with callosal agenesis, and 6 age-matched control participants were tested on a bimanual force production task. The participants produced isometric responses with their index fingers, attempting to match the target force specified by a visual stimulus. On unimanual trials, the stimuli were presented in either the left or right visual field and the response was made with the ipsilateral hand. On bimanual trials, two stimuli were presented, one on each side, and the target forces could be either identical or different. Bimanual responses of the control subjects showed strong evidence of coupling. Forces produced by one hand were influenced by the forces produced by the other hand with positive correlations observed for all target force combinations. These assimilation effects and correlations were greatly attenuated in the acallosal group, with similar results observed for the split-brain patients and participant with callosal agenesis. Furthermore,...
Journal of Experimental Psychology: Human Perception and Performance, 2008
The dependence of the Simon effect on the correspondence of the previous trial can be explained b... more The dependence of the Simon effect on the correspondence of the previous trial can be explained by the conflict-monitoring theory, which holds that a control system adjusts automatic activation from irrelevant stimulus information (conflict adaptation) on the basis of the congruency of the previous trial. The authors report on 4 experiments showing that conflict adaptation is mediated by task structure as well as previous congruency. Experiment 1 showed that for 2 completely segregated sets of stimulus-response pairs there was no conflict adaptation across sets. However, if the stimulus sets overlapped for 2 separate response sets, conflict adaptation could be observed across the response sets. Experiment 2 showed that this effect was not due to the use of stimulus-response sets lateralized to 1 hemisphere each. Experiment 3 showed that if response sets are common for 2 separate stimulus sets, then conflict adaptation can again be observed across sets. Finally, Experiment 4 showed local control effects in the absence of confounding feature-overlap effects. These results indicate that deployment of control as evidenced by conflict adaptation reflects task structure.
Journal of Experimental Psychology: Human Perception & Performance, 2003
Four experiments were conducted to identify the locus of interference observed during the prepara... more Four experiments were conducted to identify the locus of interference observed during the preparation of bimanual reaching movements. Target locations were specified by color, and the right-hand and left-hand targets could be either the same or a different color. Movements of different amplitudes (Experiment 1) or different directions (Experiment 2) to targets of the same color were initiated more quickly than symmetric movements to targets of different colors. These results indicate that costs observed during bimanual movements arise during target selection rather than during motor programming. Experiments 3 and 4 further examined the interference associated with target selection. Reaction time costs were found with unimanual movements when the target was presented among distractors associated with responses for the other hand. Interference observed during bimanual reaching appears to reflect difficulty in segregating the response rules assigned to each hand.
The ability to select between possible responses to a given situation is central to human cogniti... more The ability to select between possible responses to a given situation is central to human cognition. The goal of this study was to distinguish between brain areas representing candidate responses and areas selecting between competing response alternatives. Event-related fMRI data were acquired while 10 healthy adults performed a task used to examine response competition: the Eriksen flanker task. Left parietal cortex was activated by either of two manipulations that increased the need to maintain a representation of possible responses. In contrast, lateral prefrontal and rostral anterior cingulate cortices were specifically engaged by the need to select among competing response alternatives. These findings support the idea that parietal cortex is involved in activating possible responses on the basis of learned stimulus-response associations, and that prefrontal cortex is recruited when there is a need to select between competing responses.
Neuro-Behavioral Determinants of Interlimb Coordination, 2004
We argue that bimanual coordination and interference depends critically on how these actions are ... more We argue that bimanual coordination and interference depends critically on how these actions are represented on a cognitive level. We first review the literature on spatial interactions, focusing on the difference between movements directed at visual targets and movements cued symbolically. Interactions manifest during response planning are limited to the latter condition. These results suggest that interactions in the formation of the trajectories of the two hands are associated with processes involved in response selection, rather than interactions in the motor system. Neuropsychological studies involving callosotomy patients argue that these interactions arise from transcallosal interactions between cortically-based spatial codes. The second half of the chapter examines temporal constraints observed in bimanual movements. We propose that most bimanual movements are marked by a common event structure, an explicit representation that ensures temporal coordination of the movements. The translation of an abstract event structure into a movement with a particular timing pattern is associated with cerebellar function, although the resulting temporal coupling during bimanual movements may be due to the operation of other subcortical mechanisms. For rhythmic movements that do not entail an event structure, timing may be an emergent property. Under such conditions, both spatial and temporal coupling can be absent. The emphasis on abstract levels of constraint makes clear that limitations in bimanual coordination overlap to a considerable degree with those observed in other domains of cognition.
Simultaneous reaching movements made with the two hands can show a considerable increase in react... more Simultaneous reaching movements made with the two hands can show a considerable increase in reaction time (RT) when they differ in terms of direction or extent, compared to when the movements involve the same direction and extent. This cost has been attributed to cross-talk in the specification of the motor parameters for the two hands. However, a recent study [Diedrichsen, Hazeltine, Kennerley, & Ivry, (2001). Psychological Science, 12, 493-498] indicates that when reaching movements are cued by the onset of the target endpoint, no compatibility effects are observed. To determine why directly cued movements are immune from interference, we varied the stimulus onset asynchrony for the two movements and used different combinations of directly cued and symbolically cued movements. In two experiments, compatibility effects were only observed when both movements were symbolically cued. No difference was found between compatible and incompatible movements when both movements were directly cued or when one was directly cued and the other was symbolically cued. These results indicate that interference is not related to the specification of movement parameters but instead emerges from processes associated with response selection. Moreover, the data suggest that cross-talk, when present, primarily shortens the RT of the second movement on compatible trials rather than lengthening this RT on incompatible trials.
Hazeltine et al.-Timing mechanisms discrimination task. Furthermore, acuity on the perception tas... more Hazeltine et al.-Timing mechanisms discrimination task. Furthermore, acuity on the perception task was not correlated with performance on a non-temporal motor task (see also Ref. 5), suggesting that the correlation reflects an overlap in the neural systems subserving these tasks. Neural substrates Given the correlational nature of these studies, it is important to look for converging evidence supporting the common Copyright
Research Update Research News Recently, Boyd and Winstein tested three groups of individuals with... more Research Update Research News Recently, Boyd and Winstein tested three groups of individuals with damage to unilateral sensorimotor areas on a version of the serial reaction time task performed with the ipsilesional hand. Only when the individuals were provided in advance with explicit knowledge of the motor sequence were they able to benefit behaviorally from the sequence. Despite aspects of the experimental procedure and the subject selection that make it difficult to draw strong conclusions, these results add to growing evidence that sensorimotor structures contribute to the formation of abstract representations that affect more than ipsilateral effectors.
The authors theorize that 2 neurocognitive sequence-learning systems can be distinguished in seri... more The authors theorize that 2 neurocognitive sequence-learning systems can be distinguished in serial reaction time experiments, one dorsal (parietal and supplementary motor cortex) and the other ventral (temporal and lateral prefrontal cortex). Dorsal system learning is implicit and associates noncategorized stimuli within dimensional modules. Ventral system learning can be implicit or explicit. It also allows associating events across dimensions and therefore is the basis of cross-task integration or interference, depending on degree of cross-task correlation of signals. Accordingly, lack of correlation rather than limited capacity is responsible for dual-task effects on learning. The theory is relevant to issues of attentional effects on learning; the representational basis of complex, sequential skills; hippocampalversus basal ganglia-based learning; procedural versus declarative memory; and implicit versus explicit memory.
The neurocognitive architecture for response selection is uncertain. Some theorists suggest that ... more The neurocognitive architecture for response selection is uncertain. Some theorists suggest that it is mediated by an amodal central mechanism, whereas others propose a set of independent control mechanisms. In a functional neuroimaging experiment, we investigated the nature of response selection by examining how its underlying brain mechanisms are aVected by stimulus modality. To do this, we used a modiWed Xanker task, in which the target and Xanker (distractor) stimuli diVered in time rather than space, making it accessible for both visual and auditory stimuli. As in the traditional Xanker task, larger reaction times were observed for incongruent than congruent trials (i.e., a congruency eVect) for both modalities. Congruency aVected brain activation for both modalities in prefrontal cortex, parietal cortex, and the putamen. Modality-dependent activation was found in additional prefrontal and parietal regions for the visual modality and in left inferior prefrontal cortex for the auditory modality. Modality-dependent activity speciWcally related to response congruency was also found in sensory cortical regions. These data suggest that modality aVects the brain regions throughout the cortex mediating response selection even for conceptually identical stimuli and tasks. They are consistent with the hypothesis that (at least partially) independent brain networks mediate response selection and that input modality may be a powerful factor for organizing neural activity to support task performance.
The present experiment examined the effects of input/output modality pairings on dual-task perfor... more The present experiment examined the effects of input/output modality pairings on dual-task performance using the psychological refractory period (PRP) procedure. Four groups of participants performed two tasks composed of the same sets of inputs (visual and auditory) and the same sets of outputs (manual and vocal), but with different input/output modality pairings. Whereas modality pairings had only small effects on single-task reaction times, they had large effects on dual-task reaction times. The modality pairing effect cannot stem from differences in the difficulty of stimulus classification or response execution, because these task demands were the same across groups. The effect also does not appear to result from changes in stimulus-response compatibility. The present findings suggest dualtask interference arises not only from postponement of central operations (due to a central bottleneck), but also from a slowing of central operations whose magnitude is sensitive to the input/output modality pairings.
Proceedings of the National Academy of Sciences, 2001
To compare neural activity produced by visual events that escape or reach conscious awareness, we... more To compare neural activity produced by visual events that escape or reach conscious awareness, we used event-related MRI and evoked potentials in a patient who had neglect and extinction after focal right parietal damage, but intact visual fields. This neurological disorder entails a loss of awareness for stimuli in the field contralateral to a brain lesion when stimuli are simultaneously presented on the ipsilateral side, even though early visual areas may be intact, and single contralateral stimuli may still be perceived. Functional MRI and event-related potential study were performed during a task where faces or shapes appeared in the right, left, or both fields. Unilateral stimuli produced normal responses in V1 and extrastriate areas. In bilateral events, left faces that were not perceived still activated right V1 and inferior temporal cortex and evoked nonsignificantly reduced N1 potentials, with preserved face-specific negative potentials at 170 ms. When left faces were perce...
Neuronal recording and neuroimaging studies have shown that the primary motor area (M1) not only ... more Neuronal recording and neuroimaging studies have shown that the primary motor area (M1) not only participates in motor execution, but is also engaged during movement preparation. The purpose of the present study was to map the distribution of the preparation-and execution-related activity within the contralateral M1 using functional magnetic resonance imaging. Eleven subjects performed a delayed sequential finger movement task, in which a CUE signal indicated a movement sequence in advance of an imperative GO signal. The hemodynamic response related to the CUE and GO signals decreased in a linear fashion across the central sulcus, with activity greater along the lateral extent compared to the medial extent. This decrease was especially evident in the epoch following the CUE. Our data reveal a pattern of functional organization within M1 related to the preparation and execution of movement sequences.
The present study used the flanker task [Percept. Psychophys. 16 (1974) 143] to identify neural s... more The present study used the flanker task [Percept. Psychophys. 16 (1974) 143] to identify neural structures that support response selection processes, and to determine which of these structures respond differently depending on the type of stimulus material associated with the response. Participants performed two versions of the flanker task while undergoing event-related functional magnetic resonance imaging (fMRI). Both versions of the task required participants to respond to a central stimulus regardless of the responses associated with simultaneously presented flanking stimuli, but one used colored circle stimuli and the other used letter stimuli. Competition-related activation was identified by comparing Incongruent trials, in which the flanker stimuli indicated a different response than the central stimulus, to Neutral stimuli, in which the flanker stimuli indicated no response. A region within the right inferior frontal gyrus exhibited significantly more competition-related activation for the color stimuli, whereas regions within the middle frontal gyri of both hemispheres exhibited more competition-related activation for the letter stimuli. The border of the right middle frontal and inferior frontal gyri and the anterior cingulate cortex (ACC) were significantly activated by competition for both types of stimulus materials. Posterior foci demonstrated a similar pattern: left inferior parietal cortex showed greater competition-related activation for the letters, whereas right parietal cortex was significantly activated by competition for both materials. These findings indicate that the resolution of response competition invokes both material-dependent and material-independent processes. Published by Elsevier Science Ltd.
Do voluntary (endogenous) and involuntary (exogenous) attention have the same perceptual conseque... more Do voluntary (endogenous) and involuntary (exogenous) attention have the same perceptual consequences? Here we used fMRI to examine activity in the fusiform face area (FFA-a region in ventral visual cortex responsive to faces) and frontal-parietal areas (dorsal regions involved in spatial attention) under voluntary and involuntary spatial cueing conditions. The trial and stimulus parameters were identical for both cueing conditions. However, the cue predicted the location of an upcoming target face in the voluntary condition but was nonpredictive in the involuntary condition. The predictable cue condition led to increased activity in the FFA compared to the nonpredictable cue condition. These results show that voluntary attention leads to more activity in areas of the brain associated with face processing than involuntary attention, and they are consistent with differential behavioral effects of attention on recognition-related processes.
Two split-brain patients, a patient with callosal agenesis, and 6 age-matched control participant... more Two split-brain patients, a patient with callosal agenesis, and 6 age-matched control participants were tested on a bimanual force production task. The participants produced isometric responses with their index fingers, attempting to match the target force specified by a visual stimulus. On unimanual trials, the stimuli were presented in either the left or right visual field and the response was made with the ipsilateral hand. On bimanual trials, two stimuli were presented, one on each side, and the target forces could be either identical or different. Bimanual responses of the control subjects showed strong evidence of coupling. Forces produced by one hand were influenced by the forces produced by the other hand with positive correlations observed for all target force combinations. These assimilation effects and correlations were greatly attenuated in the acallosal group, with similar results observed for the split-brain patients and participant with callosal agenesis. Furthermore,...
Journal of Experimental Psychology: Human Perception and Performance, 2008
The dependence of the Simon effect on the correspondence of the previous trial can be explained b... more The dependence of the Simon effect on the correspondence of the previous trial can be explained by the conflict-monitoring theory, which holds that a control system adjusts automatic activation from irrelevant stimulus information (conflict adaptation) on the basis of the congruency of the previous trial. The authors report on 4 experiments showing that conflict adaptation is mediated by task structure as well as previous congruency. Experiment 1 showed that for 2 completely segregated sets of stimulus-response pairs there was no conflict adaptation across sets. However, if the stimulus sets overlapped for 2 separate response sets, conflict adaptation could be observed across the response sets. Experiment 2 showed that this effect was not due to the use of stimulus-response sets lateralized to 1 hemisphere each. Experiment 3 showed that if response sets are common for 2 separate stimulus sets, then conflict adaptation can again be observed across sets. Finally, Experiment 4 showed local control effects in the absence of confounding feature-overlap effects. These results indicate that deployment of control as evidenced by conflict adaptation reflects task structure.
Journal of Experimental Psychology: Human Perception & Performance, 2003
Four experiments were conducted to identify the locus of interference observed during the prepara... more Four experiments were conducted to identify the locus of interference observed during the preparation of bimanual reaching movements. Target locations were specified by color, and the right-hand and left-hand targets could be either the same or a different color. Movements of different amplitudes (Experiment 1) or different directions (Experiment 2) to targets of the same color were initiated more quickly than symmetric movements to targets of different colors. These results indicate that costs observed during bimanual movements arise during target selection rather than during motor programming. Experiments 3 and 4 further examined the interference associated with target selection. Reaction time costs were found with unimanual movements when the target was presented among distractors associated with responses for the other hand. Interference observed during bimanual reaching appears to reflect difficulty in segregating the response rules assigned to each hand.
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Papers by E. Hazeltine