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Eliot Hazeltine
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2021) 33 (7): 1365–1380.
Published: 01 June 2021
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Flexibly shifting attention between stimulus dimensions (e.g., shape and color) is a central component of regulating cognition for goal-based behavior. In the present report, we examine the functional roles of different cortical regions by manipulating two demands on task switching that have been confounded in previous studies—shifting attention between visual dimensions and resolving conflict between stimulus–response representations. Dimensional shifting was manipulated by having participants shift attention between dimensions (either shape or color; dimension shift) or keeping the task-relevant dimension the same (dimension same). Conflict between stimulus–response representations was manipulated by creating conflict between response-driven associations from the previous set of trials and the stimulus–response mappings on the current set of trials (e.g., making a leftward response to a red stimulus during the previous task, but being required to make a rightward response to a red stimulus in the current task; stimulus–response conflict), or eliminating conflict by altering the features of the dimension relevant to the sorting rule (stimulus–response no-conflict). These manipulations revealed activation along a network of frontal, temporal, parietal, and occipital cortices. Specifically, dimensional shifting selectively activated frontal and parietal regions. Stimulus–response conflict, on the other hand, produced decreased activation in temporal and occipital cortices. Occipital regions demonstrated a complex pattern of activation that was sensitive to both stimulus–response conflict and dimensional attention switching. These results provide novel information regarding the distinct role that frontal cortex plays in shifting dimensional attention and posterior cortices play in resolving conflict at the stimulus level.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2020) 32 (4): 590–602.
Published: 01 April 2020
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The stop signal task (SST) is the gold standard experimental model of inhibitory control. However, neither SST condition–contrast (stop vs. go, successful vs. failed stop) purely operationalizes inhibition. Because stop trials include a second, infrequent signal, the stop versus go contrast confounds inhibition with attentional and stimulus processing demands. While this confound is controlled for in the successful versus failed stop contrast, the go process is systematically faster on failed stop trials, contaminating the contrast with a different noninhibitory confound. Here, we present an SST variant to address both confounds and evaluate putative neural indices of inhibition with these influences removed. In our variant, stop signals occurred on every trial, equating the noninhibitory demands of the stop versus go contrast. To entice participants to respond despite the impending stop signals, responses produced before stop signals were rewarded. This also reversed the go process bias that typically affects the successful versus failed stop contrast. We recorded scalp electroencephalography in this new version of the task (as well as a standard version of the SST with infrequent stop signal) and found that, even under these conditions, the properties of the frontocentral stop signal P3 ERP remained consistent with the race model. Specifically, in both tasks, the amplitude of the P3 was increased on stop versus go trials. Moreover, the onset of this P3 occurred earlier for successful compared with failed stop trials in both tasks, consistent with the proposal of the race model that an earlier start of the inhibition process will increase stopping success. Therefore, the frontocentral stop signal P3 represents a neural process whose properties are in line with the predictions of the race model of motor inhibition, even when the SST's confounds are controlled.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2014) 26 (2): 334–351.
Published: 01 February 2014
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People are typically slower when executing two tasks than when only performing a single task. These dual-task costs are initially robust but are reduced with practice. Dux et al. ( 2009 ) explored the neural basis of dual-task costs and learning using fMRI. Inferior frontal junction (IFJ) showed a larger hemodynamic response on dual-task trials compared with single-task trial early in learning. As dual-task costs were eliminated, dual-task hemodynamics in IFJ reduced to single-task levels. Dux and colleagues concluded that the reduction of dual-task costs is accomplished through increased efficiency of information processing in IFJ. We present a dynamic field theory of response selection that addresses two questions regarding these results. First, what mechanism leads to the reduction of dual-task costs and associated changes in hemodynamics? We show that a simple Hebbian learning mechanism is able to capture the quantitative details of learning at both the behavioral and neural levels. Second, is efficiency isolated to cognitive control areas such as IFJ, or is it also evident in sensory motor areas? To investigate this, we restrict Hebbian learning to different parts of the neural model. None of the restricted learning models showed the same reductions in dual-task costs as the unrestricted learning model, suggesting that efficiency is distributed across cognitive control and sensory motor processing systems.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2008) 20 (3): 526–540.
Published: 01 March 2008
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Two studies [Ivry, R. B., Franz, E. A., Kingstone, A., & Johnston, J. C. The psychological refractory period effect following callosotomy: Uncoupling of lateralized response codes. Journal of Experimental Psychology: Human Perception and Performance, 24 , 463–480, 1998; Pashler, H., Luck, S., Hillyard, S. A., Mangun, G. R., O'Brien, S., & Gazzaniga, M. S. Sequential operation of disconnected hemispheres in split-brain patients. NeuroReport, 5 , 2381–2384, 1994] reported robust dual-task costs in split-brain patients even when the two tasks were associated with separate cerebral hemispheres. Although the patients failed to demonstrate specific forms of interference observed in control participants, the timing of the two responses suggested that performance was constrained such that the responses could not be initiated independently. Alternatively, the split-brain participants may have adopted a strategy in which the second response was withheld until the first was initiated. The present study revisits this phenomenon using a procedure in which the stimuli for both tasks are presented simultaneously and neither is given priority over the other. Under these conditions, neurologically intact participants show robust dual-task costs that are mediated by compatibility effects between the responses of the two hands. In contrast, the split-brain participants show greatly reduced dual-task costs and compatibility effects. The minimal dual-task costs observed in the current study indicate that previous dual-task costs in split-brain patients may be strategic, reflecting experimental instructions to prioritize one task, rather than reflect fundamental constraints of the cognitive architecture.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2002) 14 (6): 836–837.
Published: 15 August 2002
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2000) 12 (Supplement 2): 118–129.
Published: 01 November 2000
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The flanker task, introduced by Eriksen and Eriksen [Eriksen, B. A., & Eriksen, C. W. (1974). Effects of noise letters upon the identification of a target letter in a nonsearch task. Perception & Psychophysics, 16 , 143-149], provides a means to selectively manipulate the presence or absence of response competition while keeping other task demands constant. We measured brain activity using functional magnetic resonance imaging (fMRI) during performance of the flanker task. In accordance with previous behavioral studies, trials in which the flanking stimuli indicated a different response than the central stimulus were performed significantly more slowly than trials in which all the stimuli indicated the same response. This reaction time effect was accompanied by increases in activity in four regions: the right ventrolateral prefrontal cortex, the supplementary motor area, the left superior parietal lobe, and the left anterior parietal cortex. The increases were not due to changes in stimulus complexity or the need to overcome previously learned associations between stimuli and responses. Correspondences between this study and other experiments manipulating response interference suggest that the frontal foci may be related to response inhibition processes whereas the posterior foci may be related to the activation of representations of the inappropriate responses.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (1995) 7 (4): 497–510.
Published: 01 October 1995
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The brain localization of motor sequence learning was studied in normal subjects with positron emission tomography. Subjects performed a serial reaction time (SRT) task by responding to a series of stimuli that occurred at four different spatial positions. The stimulus locations were either determined randomly or according to a 6-element sequence that cycled continuously. The SRT task was performed under two conditions. With attentional interference from a secondary counting task there was no development of awareness of the sequence. Learning-related increases of cerebral blood flow were located in contralateral motor effector areas including motor cortex, supplementary motor area, and putamen, consistent with the hypothesis that nondeclarative motor learning occurs in cerebral areas that control limb movements. Additional cortical sites included the rostral prefrontal cortex and parietal cortex. The SRT learning task was then repeated with a new sequence and no attentional interference. In this condition, 7 of 12 subjects developed awareness of the sequence. Learning-related blood flow increases were present in right dorsolateral prefrontal cortex, right premotor cortex, right ventral putamen, and biparieto-occipital cortex. The right dorsolateral prefrontal and parietal areas have been previously implicated in spatial working memory and right prefrontal cortex is also implicated in retrieval tasks of verbal episodic memory. Awareness of the sequence at the end of learning was associated with greater activity in bilateral parietal, superior temporal, and right premotor cortex. Motor learning can take place in different cerebral areas, contingent on the attentional demands of the task.