Bacterial pathogens adapt to changing environments within their hosts, and the signaling molecule... more Bacterial pathogens adapt to changing environments within their hosts, and the signaling molecule adenosine 3', 5'-cyclic monophosphate (cAMP) facilitates this process. In this study, we characterized in vivo DNA binding and gene regulation by the cAMP-responsive protein CRP in M. bovis BCG as a model for tuberculosis (TB)-complex bacteria. Chromatin immunoprecipitation followed by deep-sequencing (ChIP-seq) showed that CRP associates with ∼900 DNA binding regions, most of which occur within genes. The most highly enriched binding region was upstream of a putative copper transporter gene (ctpB), and crp-deleted bacteria showed increased sensitivity to copper toxicity. Detailed mutational analysis of four CRP binding sites upstream of the virulence-associated Rv0249c-Rv0247c succinate dehydrogenase genes demonstrated that CRP directly regulates Rv0249c-Rv0247c expression from two promoters, one of which requires sequences intragenic to Rv0250c for maximum expression. The high...
Page 1. Resuming after Interruption: Exploring the roles of spatial and goal memory Nicole E. Wer... more Page 1. Resuming after Interruption: Exploring the roles of spatial and goal memory Nicole E. Werner David M. Cades nwerner2@gmu.edudcades@gmu.edu Deborah A. Boehm-Davis Matthew S. Peterson dbdavis@gmu.edumpeters2@gmu.edu ...
Corollary discharge (CD) is hypothesized to provide the movement information (direction and ampli... more Corollary discharge (CD) is hypothesized to provide the movement information (direction and amplitude) required to compensate for the saccade induced disruptions to visual input. Here, we investigated to what extent these conveyed metrics influence perceptual stability in human subjects with a target displacement detection task. Subjects made saccades to targets located at different amplitudes (4°, 6° or 8°) and directions (horizontal or vertical). During the saccade the target disappeared and then reappeared at a shifted location either in the same direction or opposite to the movement vector. Subjects reported the target displacement direction and from these reports we determined the perceptual threshold for shift detection and estimate of target location. Our results indicate that the thresholds for all amplitudes and directions generally scaled with saccade amplitude. Additionally, subjects on average produced hypometric saccades with an estimated CD gain less than one. Finally,...
Multiple object tracking (MOT) is a complex task recruiting a distributed network of brain region... more Multiple object tracking (MOT) is a complex task recruiting a distributed network of brain regions. There are also marked individual differences in MOT performance. A positive causal relationship between the anterior intraparietal sulcus (AIPS), an integral region in the MOT attention network and inter-individual variation in MOT performance has not been previously established. The present study used transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, in order to examine such a causal link. Active anodal stimulation was applied to the right AIPS and the left dorsolateral prefrontal cortex (DLPFC) (and sham stimulation), an area associated with working memory (but not MOT) while participants completed a MOT task. Stimulation to the right AIPS significantly improved MOT accuracy more than the other two conditions. The results confirm a causal role of the AIPS in the MOT task and illustrate that tDCS has the ability to improve MOT performance.
Preview benefit is an attentional phenomenon that enables observers to selectively search through... more Preview benefit is an attentional phenomenon that enables observers to selectively search through new information in the visual field. In a preview search task, objects are presented in two sets, separated by a time interval (preview interval), and with the second set (new objects) containing the target. Event-related brain potentials (ERPs) were used to investigate whether preview benefit occurs via maintenance of inhibition of the old objects during the preview interval. ERPs time-locked to a color probe indicated that the old objects were actively attended rather than inhibited during the preview interval. Follow-up behavioral experiments produced converging results. The results suggest that, although participants might be using inhibition at later stages of the preview interval, they are not maintaining inhibition on the old objects throughout most of the preview interval.
Page 1. Explicit memory for rejected distractors during visual search Melissa R. Beck and Matthew... more Page 1. Explicit memory for rejected distractors during visual search Melissa R. Beck and Matthew S. Peterson Psychology Department, George Mason University, Fairfax, Virginia, USA Walter R. Boot Beckman Institute and Department ...
Page 1. Oculomotor behaviour in visual search for multiple targets Jason S. McCarley, Arthur F. K... more Page 1. Oculomotor behaviour in visual search for multiple targets Jason S. McCarley, Arthur F. Kramer, and Walter R. Boot University of Illinois at Urbana-Champaign, IL, USA Matthew S. Peterson George Mason University, Fairfax, VA, USA ...
Using a novel visual search paradigm McCarley et al. (2003) concluded that the oculomotor system ... more Using a novel visual search paradigm McCarley et al. (2003) concluded that the oculomotor system keeps a history of 3-4 previously attended objects. However, their displays were visually sparse, denying participants structural information which might be used during normal search. This might have underestimated memory capacity. To examine this possibility, we included landmarks in the same search paradigm. Previously examined items were re-examined less frequently when landmarks were present compared to when they were absent. Results indicate that objects in the environment that share no features with search items are used as external support to aid memory in guiding visual search.
Previous research has indicated that saccade target selection during visual search is influenced ... more Previous research has indicated that saccade target selection during visual search is influenced by scanning history. Already inspected items are less likely to be chosen as saccade targets as long as the number intervening saccades is small. Here, we adapted Jacoby's (1991) process dissociation procedure to assess the role of intentional and automatic processes in saccade target selection. Results indicate a large automatic component biasing participants to move their eyes to unexamined locations. However, an intentional component allowed participants to both reinspect old items and aid their selection of new items. A second experiment examined inhibition of return (IOR) as a candidate for the observed automatic component. IOR was found for items that had been previously examined. It is concluded that both automatic and intentional memory traces are available to guide the eyes during search.
A number of studies have suggested that attentional control skills required to perform 2 tasks co... more A number of studies have suggested that attentional control skills required to perform 2 tasks concurrently become impaired with age (A. A. Hartley, 1992; J. M. McDowd & R. J. Shaw, 2000). A. A. Hartley (2001) recently observed that the age-related differences in dual-task performance were larger when the 2 tasks required similar motor responses. The present study examined the extent to which age-related deficits in dual-task performance or time sharing--in particular, dual-task performance of 2 discrimination tasks with similar motor requirements--can be moderated by training. The results indicate that, even when the 2 tasks required similar motor responses, both older and younger adults could learn to perform the tasks faster and more accurately. Moreover, the improvement in performance generalized to new task combinations involving new stimuli. Therefore, it appears that training can substantially improve dual-task processing skills in older adults.
A study was conducted to examine potential age-related differences in the strategic control of ex... more A study was conducted to examine potential age-related differences in the strategic control of exogenous and endogenous saccades within the context of the fixation offset effect (FOE; i.e., faster saccades when a fixation point is removed than when it is left on throughout a trial). Subjects were instructed to make rapid saccades either on the basis of a suddenly appearing peripheral visual stimulus (exogenous saccade) or in response to a tone (endogenous saccade). On half of the trials the fixation point was removed simultaneously with the occurrence of the cue stimulus. Subjects' preparatory set was varied by manipulating the proportion of saccades generated to a visual and auditory stimulus within a trial block. Young and old adults both produced FOEs, and the FOEs were strategically modulated by preparatory set. The data are discussed in terms of aging and oculomotor control.
Bacterial pathogens adapt to changing environments within their hosts, and the signaling molecule... more Bacterial pathogens adapt to changing environments within their hosts, and the signaling molecule adenosine 3', 5'-cyclic monophosphate (cAMP) facilitates this process. In this study, we characterized in vivo DNA binding and gene regulation by the cAMP-responsive protein CRP in M. bovis BCG as a model for tuberculosis (TB)-complex bacteria. Chromatin immunoprecipitation followed by deep-sequencing (ChIP-seq) showed that CRP associates with ∼900 DNA binding regions, most of which occur within genes. The most highly enriched binding region was upstream of a putative copper transporter gene (ctpB), and crp-deleted bacteria showed increased sensitivity to copper toxicity. Detailed mutational analysis of four CRP binding sites upstream of the virulence-associated Rv0249c-Rv0247c succinate dehydrogenase genes demonstrated that CRP directly regulates Rv0249c-Rv0247c expression from two promoters, one of which requires sequences intragenic to Rv0250c for maximum expression. The high...
Page 1. Resuming after Interruption: Exploring the roles of spatial and goal memory Nicole E. Wer... more Page 1. Resuming after Interruption: Exploring the roles of spatial and goal memory Nicole E. Werner David M. Cades nwerner2@gmu.edudcades@gmu.edu Deborah A. Boehm-Davis Matthew S. Peterson dbdavis@gmu.edumpeters2@gmu.edu ...
Corollary discharge (CD) is hypothesized to provide the movement information (direction and ampli... more Corollary discharge (CD) is hypothesized to provide the movement information (direction and amplitude) required to compensate for the saccade induced disruptions to visual input. Here, we investigated to what extent these conveyed metrics influence perceptual stability in human subjects with a target displacement detection task. Subjects made saccades to targets located at different amplitudes (4°, 6° or 8°) and directions (horizontal or vertical). During the saccade the target disappeared and then reappeared at a shifted location either in the same direction or opposite to the movement vector. Subjects reported the target displacement direction and from these reports we determined the perceptual threshold for shift detection and estimate of target location. Our results indicate that the thresholds for all amplitudes and directions generally scaled with saccade amplitude. Additionally, subjects on average produced hypometric saccades with an estimated CD gain less than one. Finally,...
Multiple object tracking (MOT) is a complex task recruiting a distributed network of brain region... more Multiple object tracking (MOT) is a complex task recruiting a distributed network of brain regions. There are also marked individual differences in MOT performance. A positive causal relationship between the anterior intraparietal sulcus (AIPS), an integral region in the MOT attention network and inter-individual variation in MOT performance has not been previously established. The present study used transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, in order to examine such a causal link. Active anodal stimulation was applied to the right AIPS and the left dorsolateral prefrontal cortex (DLPFC) (and sham stimulation), an area associated with working memory (but not MOT) while participants completed a MOT task. Stimulation to the right AIPS significantly improved MOT accuracy more than the other two conditions. The results confirm a causal role of the AIPS in the MOT task and illustrate that tDCS has the ability to improve MOT performance.
Preview benefit is an attentional phenomenon that enables observers to selectively search through... more Preview benefit is an attentional phenomenon that enables observers to selectively search through new information in the visual field. In a preview search task, objects are presented in two sets, separated by a time interval (preview interval), and with the second set (new objects) containing the target. Event-related brain potentials (ERPs) were used to investigate whether preview benefit occurs via maintenance of inhibition of the old objects during the preview interval. ERPs time-locked to a color probe indicated that the old objects were actively attended rather than inhibited during the preview interval. Follow-up behavioral experiments produced converging results. The results suggest that, although participants might be using inhibition at later stages of the preview interval, they are not maintaining inhibition on the old objects throughout most of the preview interval.
Page 1. Explicit memory for rejected distractors during visual search Melissa R. Beck and Matthew... more Page 1. Explicit memory for rejected distractors during visual search Melissa R. Beck and Matthew S. Peterson Psychology Department, George Mason University, Fairfax, Virginia, USA Walter R. Boot Beckman Institute and Department ...
Page 1. Oculomotor behaviour in visual search for multiple targets Jason S. McCarley, Arthur F. K... more Page 1. Oculomotor behaviour in visual search for multiple targets Jason S. McCarley, Arthur F. Kramer, and Walter R. Boot University of Illinois at Urbana-Champaign, IL, USA Matthew S. Peterson George Mason University, Fairfax, VA, USA ...
Using a novel visual search paradigm McCarley et al. (2003) concluded that the oculomotor system ... more Using a novel visual search paradigm McCarley et al. (2003) concluded that the oculomotor system keeps a history of 3-4 previously attended objects. However, their displays were visually sparse, denying participants structural information which might be used during normal search. This might have underestimated memory capacity. To examine this possibility, we included landmarks in the same search paradigm. Previously examined items were re-examined less frequently when landmarks were present compared to when they were absent. Results indicate that objects in the environment that share no features with search items are used as external support to aid memory in guiding visual search.
Previous research has indicated that saccade target selection during visual search is influenced ... more Previous research has indicated that saccade target selection during visual search is influenced by scanning history. Already inspected items are less likely to be chosen as saccade targets as long as the number intervening saccades is small. Here, we adapted Jacoby's (1991) process dissociation procedure to assess the role of intentional and automatic processes in saccade target selection. Results indicate a large automatic component biasing participants to move their eyes to unexamined locations. However, an intentional component allowed participants to both reinspect old items and aid their selection of new items. A second experiment examined inhibition of return (IOR) as a candidate for the observed automatic component. IOR was found for items that had been previously examined. It is concluded that both automatic and intentional memory traces are available to guide the eyes during search.
A number of studies have suggested that attentional control skills required to perform 2 tasks co... more A number of studies have suggested that attentional control skills required to perform 2 tasks concurrently become impaired with age (A. A. Hartley, 1992; J. M. McDowd & R. J. Shaw, 2000). A. A. Hartley (2001) recently observed that the age-related differences in dual-task performance were larger when the 2 tasks required similar motor responses. The present study examined the extent to which age-related deficits in dual-task performance or time sharing--in particular, dual-task performance of 2 discrimination tasks with similar motor requirements--can be moderated by training. The results indicate that, even when the 2 tasks required similar motor responses, both older and younger adults could learn to perform the tasks faster and more accurately. Moreover, the improvement in performance generalized to new task combinations involving new stimuli. Therefore, it appears that training can substantially improve dual-task processing skills in older adults.
A study was conducted to examine potential age-related differences in the strategic control of ex... more A study was conducted to examine potential age-related differences in the strategic control of exogenous and endogenous saccades within the context of the fixation offset effect (FOE; i.e., faster saccades when a fixation point is removed than when it is left on throughout a trial). Subjects were instructed to make rapid saccades either on the basis of a suddenly appearing peripheral visual stimulus (exogenous saccade) or in response to a tone (endogenous saccade). On half of the trials the fixation point was removed simultaneously with the occurrence of the cue stimulus. Subjects' preparatory set was varied by manipulating the proportion of saccades generated to a visual and auditory stimulus within a trial block. Young and old adults both produced FOEs, and the FOEs were strategically modulated by preparatory set. The data are discussed in terms of aging and oculomotor control.
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