Simon P Kelly

CUNY Graduate Center, New York, New York, United States

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Publications (42)194.74 Total impact

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    ABSTRACT: The P300 component of the human event-related potential has been the subject of intensive experimental investigation across a five-decade period, owing to its apparent relevance to a wide range of cognitive functions and its sensitivity to numerous brain disorders, yet its exact contribution to cognition remains unresolved. Here, we carry out key analyses of the P300 elicited by transient auditory and visual targets to examine its potential role as a ‘decision variable’ signal that accumulates evidence to a decision bound. Consistent with the latter, we find that the P300 reaches a stereotyped amplitude immediately prior to response execution and that its rate of rise scales with target detection difficulty and accounts for trial-to-trial variance in RT. Computational simulations of an accumulation-to-bound decision process faithfully captured P300 dynamics when its parameters were set by model fits to the RT distributions. Thus, where the dominant explanatory accounts have conceived of the P300 as a unitary neural event, our data reveal it to be a dynamically evolving neural signature of decision formation. These findings place the P300 at the heart of a mechanistically principled framework for understanding decision-making in both the typical and atypical human brain.
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    ABSTRACT: The P300 component of the human event-related potential has been the subject of intensive experimental investigation across a five-decade period, owing to its apparent relevance to a wide range of cognitive functions and its sensitivity to numerous brain disorders. Yet, its exact contribution to cognition remains unresolved. Here, we carry out key analyses of the P300 elicited by transient auditory and visual targets to examine its potential role as a 'decision variable' signal that accumulates evidence to a decision bound. Consistent with the latter, we find that the P300 reaches a stereotyped amplitude immediately prior to response execution and that it's rate of rise scales with target detection difficulty and accounts for trial-to-trial variance in reaction time (RT). Computational simulations of an accumulation-to-bound decision process faithfully captured P300 dynamics when its parameters were set by model fits to the RT distributions. Thus, where the dominant explanatory accounts have conceived of the P300 as a unitary neural event, our data reveal it to be a dynamically evolving neural signature of decision formation. These findings place the P300 at the heart of a mechanistically principled framework for understanding decision making in both the typical and atypical human brain. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    European Journal of Neuroscience 04/2015; DOI:10.1111/ejn.12936 · 3.67 Impact Factor
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    ABSTRACT: Surround suppression is a well-known example of contextual interaction in visual cortical neurophysiology, whereby the neural response to a stimulus presented within a neuron's classical receptive field is suppressed by surrounding stimuli. Human psychophysical reports present an obvious analog to the effects seen at the single-neuron level: stimuli are perceived as lower-contrast when embedded in a surround. Here we report on a visual paradigm that provides relatively direct, straight-forward indices of surround suppression in human electrophysiology, enabling us to reproduce several well-known neurophysiological and psychophysical effects, and to conduct new analyses of temporal trends and retinal location effects. Steady-state visual evoked potentials (SSVEP) elicited by flickering "foreground" stimuli were measured in the context of various static surround patterns. Early visual cortex geometry and retinotopic organization were exploited to enhance SSVEP amplitude. The foreground response was strongly suppressed as a monotonic function of surround contrast. Further, suppression was stronger for surrounds of matching orientation than orthogonally-oriented ones, and stronger at peripheral than foveal locations. These patterns were reproduced in psychophysical reports of perceived contrast, and peripheral electrophysiological suppression effects correlated with psychophysical effects across subjects. Temporal analysis of SSVEP amplitude revealed short-term contrast adaptation effects that caused the foreground signal to either fall or grow over time depending on the relative contrast of the surround, consistent with stronger adaptation of the suppressive drive. This electrophysiology paradigm has clinical potential in indexing not just visual deficits but possibly gain control deficits expressed more widely in the disordered brain. Copyright © 2014, Journal of Neurophysiology.
    Journal of Neurophysiology 11/2014; 113(4):jn.00774.2014. DOI:10.1152/jn.00774.2014 · 3.04 Impact Factor
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    ABSTRACT: Children born with very low birth weight perform poorly on executive function and attention measures. Any difficulties with sustained attention may underpin impairments in performance on tasks measuring higher order cognitive control. Previous sustained attention research in very low birth weight cohorts has used tasks that involve arousing stimuli, potentially spoiling the measure of sustained attention. The aim of this study was to compare the performance of very low birth weight and normal birth weight children on a well-controlled task of sustained attention. The Fixed and Random versions of the Sustained Attention to Response Task were given to 17 very low birth weight and 18 normal birth weight children. The very low birth weight group performed the Fixed and Random Sustained Attention to Response Tasks in a similar manner as the normal birth weight group on all measures except for the omission error and Slow Frequency Area under the Spectra variables on the Fixed Sustained Attention to Response Task. These measures index lapses in sustained attention that may be underpinned by declining arousal. The very low birth weight group showed no response inhibition deficits. Omission errors and slow-timescale response-time variability on predictable tasks may thus present sensitive indices of difficulties with sustained attention and arousal associated with premature birth and low birth weight.
    Frontiers in Human Neuroscience 10/2014; DOI:10.1080/09297049.2014.964193 · 2.90 Impact Factor
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    ABSTRACT: Healthy subjects typically exhibit a subtle bias of visuospatial attention favouring left space that is commonly termed 'pseudoneglect'. This bias is attenuated, or shifted rightwards, with decreasing alertness over time, consistent with theoretical models proposing that pseudoneglect is a result of the right hemisphere's dominance in regulating attention. Although this 'time-on-task effect' for spatial bias is observed when averaging across whole samples of healthy participants, Benwell, Thut, Learmonth & Harvey (2013b) recently presented evidence that the direction and magnitude of bias exhibited by the participant early in the task (left biased, no bias, or right biased) was a stable trait that predicted the direction of the subsequent time-on-task shift in spatial bias. That is, the spatial bias of participants who were initially left biased shifted in a rightward direction with time, whereas that of participants who were initially right biased shifted in a leftward direction. If valid, the data of Benwell et al. are potentially important and may demand a re-evaluation of current models of the neural networks governing spatial attention. Here we use two novel spatial attention tasks in an attempt to confirm the results of Benwell et al.. We show that rather than being indicative of true participant subtypes, these data patterns are likely driven, at least in part, by 'regression towards the mean' arising from the analysis method employed. Although evidence supports the contention that trait-like individual differences in spatial bias exist within the healthy population, no clear evidence is yet available for participant/observer subtypes in the direction of time-on-task shift in spatial biases.
    Neuropsychologia 09/2014; 64. DOI:10.1016/j.neuropsychologia.2014.09.017 · 3.45 Impact Factor
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    Simon P. Kelly, Redmond G. O'Connell
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    ABSTRACT: In the last two decades, animal neurophysiology research has made great strides towards explaining how the brain can enable adaptive action in the face of noisy sensory information. In particular, this work has identified neural signals that perform the role of a 'decision variable' which integrates sensory information in favor of a particular outcome up to an action-triggering threshold, consistent with long-standing predictions from mathematical psychology. This has provoked an intensive search for similar neural processes at work in the human brain. In this paper we review the progress that has been made in tracing the dynamics of perceptual decision formation in humans using functional imaging and electrophysiology. We highlight some of the limitations that non-invasive recording techniques place on our ability to make definitive judgments regarding the role that specific signals play in decision making. Finally, we provide an overview of our own work in this area which has focussed on two perceptual tasks – intensity change detection and motion discrimination – performed under continuous-monitoring conditions, and highlight the insights gained thus far. We show that through simple paradigm considerations such as avoiding sudden intensity transients at evidence onset, a neural instantiation of the theoretical decision variable can be directly traced in the form of a centro-parietal positivity (CPP) in the standard event-related potential (ERP). We recapitulate evidence for the domain-general nature of the CPP process, being divorced from the sensory and motor requirements of the task, and re-plot data of both tasks highlighting this aspect as well as its relationship to decision outcome and reaction time. We discuss the implications of these findings for mechanistically principled research on normal and abnormal decision making in humans.
    Journal of Physiology-Paris 09/2014; DOI:10.1016/j.jphysparis.2014.08.003 · 2.35 Impact Factor
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    Simon P Kelly, Redmond G O'Connell
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    ABSTRACT: We frequently need to make timely decisions based on sensory evidence that is weak, ambiguous, or noisy resulting from conditions in the external environment (e.g., a cluttered visual scene) or within the brain itself (e.g., inattention, neural noise). Here we examine how externally and internally driven variations in the quality of sensory evidence affect the build-to-threshold dynamics of a supramodal "decision variable" signal and, hence, the timing and accuracy of decision reports in humans. Observers performed a continuous-monitoring version of the prototypical two-alternative dot-motion discrimination task, which is known to strongly benefit from sequential sampling and temporal accumulation of evidence. A centroparietal positive potential (CPP), which we previously established as a supramodal decision signal based on its invariance to motor or sensory parameters, exhibited two key identifying properties associated with the "decision variable" long described in sequential sampling models: (1) its buildup rate systematically scaled with sensory evidence strength across four levels of motion coherence, consistent with temporal integration; and (2) its amplitude reached a stereotyped level at the moment of perceptual report executions, consistent with a boundary-crossing stopping criterion. The buildup rate of the CPP also strongly predicted reaction time within coherence levels (i.e., independent of physical evidence strength), and this endogenous variation was linked with attentional fluctuations indexed by the level of parieto-occipital α-band activity preceding target onset. In tandem with the CPP, build-to-threshold dynamics were also observed in an effector-selective motor preparation signal; however, the buildup of this motor-specific process significantly lagged that of the supramodal process.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 12/2013; 33(50):19434-19441. DOI:10.1523/JNEUROSCI.3355-13.2013 · 6.75 Impact Factor
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    ABSTRACT: Here we summarize the points raised in our dialogue with Ales and colleagues on the cortical generators of the early visual evoked potential (VEP), and offer observations on the results of additional simulations that were run in response to our original comment. For small stimuli placed at locations in the upper and lower visual field for which the human VEP has been well characterized, simulated scalp projections of each of the visual areas V1, V2 and V3 invert in polarity. However, the empirically measured, earliest VEP component, "C1," matches the simulated V1 generators in terms of polarity and topography, but not the simulated V2 and V3 generators. We thus conclude that, 1) consistent with the title of Ales et al (2010a), polarity inversion on its own is not a sufficient criterion for inferring neuroelectric sources in primary visual cortex; but 2) inconsistent with additional claims made in Ales et al (2010a), the simulated topographies provide additional evidence for - not against - the tenet that the C1 component is generated in V1.
    NeuroImage 06/2013; 82. DOI:10.1016/j.neuroimage.2013.05.112 · 6.36 Impact Factor
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    ABSTRACT: Objective. The steady-state visual evoked potential (SSVEP) is an electroencephalographic response to flickering stimuli generated partly in primary visual area V1. The typical 'cruciform' geometry and retinotopic organization of V1 is such that certain neighboring visual regions project to neighboring cortical regions of opposite orientation. Here, we explored ways to exploit this organization in order to boost scalp SSVEP amplitude via oscillatory summation. Approach. We manipulated flicker-phase offsets among angular segments of a large annular stimulus in three ways, and compared the resultant SSVEP power to a conventional condition with no temporal phase offsets. (1) We divided the annulus into standard octants for all subjects, and flickered upper horizontal octants with opposite temporal phase to the lower horizontal ones, and left vertical octants opposite to the right vertical ones; (2) we individually adjusted the boundaries between the eight contiguous segments of the standard octants condition to coincide with cruciform-consistent, early-latency topographical shifts in pattern-pulse multifocal visual-evoked potentials (PPMVEP) derived for each of 32 equal-sized segments; (3) we assigned phase offsets to stimulus segments following an automatic algorithm based on the relative amplitudes of vertically- and horizontally-oriented PPMVEP components. Main results. The three flicker-phase manipulations resulted in a significant enhancement of normalized SSVEP power of (1) 202%, (2) 383%, and (3) 300%, respectively. Significance. We have thus demonstrated a means to obtain more reliable measures of visual evoked activity purely through consideration of cortical geometry. This principle stands to impact both basic and clinical research using SSVEPs.
    Journal of Neural Engineering 04/2013; 10(3):036003. DOI:10.1088/1741-2560/10/3/036003 · 3.42 Impact Factor
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    ABSTRACT: In theoretical accounts of perceptual decision-making, a decision variable integrates noisy sensory evidence and determines action through a boundary-crossing criterion. Signals bearing these very properties have been characterized in single neurons in monkeys, but have yet to be directly identified in humans. Using a gradual target detection task, we isolated a freely evolving decision variable signal in human subjects that exhibited every aspect of the dynamics observed in its single-neuron counterparts. This signal could be continuously tracked in parallel with fully dissociable sensory encoding and motor preparation signals, and could be systematically perturbed mid-flight during decision formation. Furthermore, we found that the signal was completely domain general: it exhibited the same decision-predictive dynamics regardless of sensory modality and stimulus features and tracked cumulative evidence even in the absence of overt action. These findings provide a uniquely clear view on the neural determinants of simple perceptual decisions in humans.
    Nature Neuroscience 10/2012; DOI:10.1038/nn.3248 · 14.98 Impact Factor
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    ABSTRACT: The VESPA (visual-evoked spread spectrum analysis) method estimates the impulse response of the visual system using a continuously varying stimulus. It has been used recently to address both basic cognitive and neurophysiologic questions as well as those surrounding clinical populations. Although the components of the average VESPA response are highly reminiscent of the early components of the visual-evoked potential (VEP) when measured over midline occipital locations, the two responses are acquired in different ways and, thus, they cannot be regarded as being equivalent. To further characterize the relationship between the VESPA and the VEP and the generative mechanisms underlying them, we recorded EEG from 31 subjects in response to checkerboard-based VEP and VESPA stimuli. We found that, across subjects, the amplitudes of the VEP C1 component and the VESPA C1 component were highly correlated, whereas the VEP P1 and the VESPA P1 bore no statistical relationship. Furthermore, we found that C1 and P1 amplitudes were significantly correlated in the VESPA but not in the VEP. We believe these findings point to the presence of common generators underlying the VESPA C1 and the VEP C1. We argue further that the VESPA P1, in light of its strong relationship to the VESPA C1, likely reflects further activation of the same cortical generators. Given the lack of correlation between the VEP P1 and each of these three other components, it is likely that the underlying generators of this particular component are more varied and widespread, as suggested previously. We discuss the implications of these relationships for basic and clinical research using the VESPA and for the assessment of additive-evoked versus phase-reset contributions to the VEP.
    Experimental Brain Research 05/2012; 220(2):191-9. DOI:10.1007/s00221-012-3129-1 · 2.17 Impact Factor
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    ABSTRACT: Recently, a forward-model simulation study demonstrated that the upper and lower visual field projections to extrastriate visual cortical areas V2 and V3 have polarity-inverted electrical scalp projections, a property famously associated with potentials generated in primary visual cortex (V1) (Ales et al., 2010a). The authors use this finding, along with other findings from fMRI-constrained source modeling, to argue that the initial component "C1" of the human visual evoked potential may not be generated in V1 as has been widely believed, but may instead come from V2/V3. Here, we examine the validity of this claim with respect to the full set of anatomical and electrophysiological factors comprising the unabridged "cruciform" model linking C1 to V1. We find that the simulations in their current form do not present a valid test of the model, nor are their results inconsistent with it. We also review non-human primate neurophysiology findings that support the C1-V1 principle, and that can and should be taken into account in assessing the validity of constrained source models of human EEG in general.
    NeuroImage 04/2012; 76(1). DOI:10.1016/j.neuroimage.2012.03.081 · 6.36 Impact Factor
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    ABSTRACT: Caffeine and L-theanine, both naturally occurring in tea, affect the ability to make rapid phasic deployments of attention to locations in space as reflected in behavioural performance and alpha-band oscillatory brain activity (8-14 Hz). However, surprisingly little is known about how these compounds affect an aspect of attention that has been more popularly associated with tea, namely vigilant attention: the ability to maintain focus on monotonous tasks over protracted time-periods. Twenty-seven participants performed the Sustained Attention to Response Task (SART) over a two-hour session on each of four days, on which they were administered caffeine (50 mg), theanine (100 mg), the combination, or placebo in a double-blind, randomized, cross-over fashion. Concurrently, we recorded oscillatory brain activity through high-density electroencephalography (EEG). We asked whether either compound alone, or both in combination, would affect performance of the task in terms of reduced error rates over time, and whether changes in alpha-band activity would show a relationship to such changes in performance. When treated with placebo, participants showed a rise in error rates, a pattern that is commonly observed with increasing time-on-task, whereas after caffeine and theanine ingestion, error rates were significantly reduced. The combined treatment did not confer any additional benefits over either compound alone, suggesting that the individual compounds may confer maximal benefits at the dosages employed. Alpha-band oscillatory activity was significantly reduced on ingestion of caffeine, particularly in the first hour. This effect was not changed by addition of theanine in the combined treatment. Theanine alone did not affect alpha-band activity.
    Neuropharmacology 02/2012; 62(7):2320-7. DOI:10.1016/j.neuropharm.2012.01.020 · 4.82 Impact Factor
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    ABSTRACT: Oscillatory entrainment mechanisms are invoked during attentional processing of rhythmically occurring stimuli, whereby their phase alignment regulates the excitability state of neurons coding for anticipated inputs. These mechanisms have been examined in the delta band (1-3 Hz), where entrainment frequency matches the stimulation rate. Here, we investigated entrainment for subdelta rhythmic stimulation, recording from intracranial electrodes over human auditory cortex during an intersensory audiovisual task. Audiovisual stimuli were presented at 0.67 Hz while participants detected targets within one sensory stream and ignored the other. It was found that entrainment operated at twice the stimulation rate (1.33 Hz), and this was reflected by higher amplitude values in the FFT spectrum, cyclic modulation of alpha-amplitude, and phase-amplitude coupling between delta phase and alpha power. In addition, we found that alpha-amplitude was relatively increased in auditory cortex coincident with to-be-ignored auditory stimuli during attention to vision. Thus, the data suggest that entrainment mechanisms operate within a delimited passband such that for subdelta task rhythms, oscillatory harmonics are invoked. The phase of these delta-entrained oscillations modulates alpha-band power. This may in turn increase or decrease responsiveness to relevant and irrelevant stimuli, respectively.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 12/2011; 31(50):18556-67. DOI:10.1523/JNEUROSCI.2164-11.2011 · 6.75 Impact Factor
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    ABSTRACT: The neural processing of biological motion (BM) is of profound experimental interest since it is often through the movement of another that we interpret their immediate intentions. Neuroimaging points to a specialized cortical network for processing biological motion. Here, high-density electrical mapping and source-analysis techniques were employed to interrogate the timing of information processing across this network. Participants viewed point-light-displays depicting standard body movements (e.g. jumping), while event-related potentials (ERPs) were recorded and compared to ERPs to scrambled motion control stimuli. In a pair of experiments, three major phases of BM-specific processing were identified: 1) The earliest phase of BM-sensitive modulation was characterized by a positive shift of the ERP between 100 and 200 ms after stimulus onset. This modulation was observed exclusively over the right hemisphere and source-analysis suggested a likely generator in close proximity to regions associated with general motion processing (KO/hMT). 2) The second phase of BM-sensitivity occurred from 200 to 350 ms, characterized by a robust negative-going ERP modulation over posterior middle temporal regions bilaterally. Source-analysis pointed to bilateral generators at or near the posterior superior temporal sulcus (STS). 3) A third phase of processing was evident only in our second experiment, where participants actively attended the BM aspect of the stimuli, and was manifest as a centro-parietal positive ERP deflection, likely related to later cognitive processes. These results point to very early sensory registration of biological motion, and highlight the interactive role of the posterior STS in analyzing the movements of other living organisms.
    NeuroImage 05/2011; 56(1):373-83. DOI:10.1016/j.neuroimage.2011.01.058 · 6.36 Impact Factor
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    ABSTRACT: The N1 component of the auditory evoked potential (AEP) is a robust and easily recorded metric of auditory sensory-perceptual processing. In patients with schizophrenia, a diminution in the amplitude of this component is a near-ubiquitous finding. A pair of recent studies has also shown this N1 deficit in first-degree relatives of schizophrenia probands, suggesting that the deficit may be linked to the underlying genetic risk of the disease rather than to the disease state itself. However, in both these studies, a significant proportion of the relatives had other psychiatric conditions. As such, although the N1 deficit represents an intriguing candidate endophenotype for schizophrenia, it remains to be shown whether it is present in a group of clinically unaffected first-degree relatives. In addition to testing first-degree relatives, we also sought to replicate the N1 deficit in a group of first-episode patients and in a group of chronic schizophrenia probands. Subject groups consisted of 35 patients with schizophrenia, 30 unaffected first-degree relatives, 13 first-episode patients, and 22 healthy controls. Subjects sat in a dimly lit room and listened to a series of simple 1,000-Hz tones, indicating with a button press whenever they heard a deviant tone (1,500 Hz; 17% probability), while the AEP was recorded from 72 scalp electrodes. Both chronic and first-episode patients showed clear N1 amplitude decrements relative to healthy control subjects. Crucially, unaffected first-degree relatives also showed a clear N1 deficit. This study provides further support for the proposal that the auditory N1 deficit in schizophrenia is linked to the underlying genetic risk of developing this disorder. In light of recent studies, these results point to the N1 deficit as an endophenotypic marker for schizophrenia. The potential future utility of this metric as one element of a multivariate endophenotype is discussed.
    European Archives of Psychiatry and Clinical Neuroscience 12/2010; 261(5):331-9. DOI:10.1007/s00406-010-0176-0 · 3.36 Impact Factor
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    ABSTRACT: When preparing to make a saccadic eye movement in a cued direction, perception of stimuli at the target location is enhanced, just as it is when attention is covertly deployed there. Accordingly, the timing and anatomical sources of preparatory brain activity accompanying shifts of covert attention and saccade preparation tend to exhibit a large degree of overlap. However, there is evidence that preparatory processes are modulated by the foreknowledge of visual distractor competition during covert attention, and it is unknown whether eye movement preparation undergoes equivalent modulation. Here we examine preparatory processes in the electroencephalogram of human participants during four blocked versions of a spatial cueing task, requiring either covert detection or saccade execution, and either containing a distractor or not. As in previous work, a typical pattern of spatially selective occipital, parietal and frontal activity was seen in all task versions. However, whereas distractor presence called on an enhancement of spatially selective visual cortical modulation during covert attention, it instead called on increased activity over frontomedial oculomotor areas in the case of overt saccade preparation. We conclude that, although advance orienting signals may be similar in character during overt and covert conditions, the pattern by which these signals are modulated to ameliorate the behavioral costs of distractor competition is highly distinct, pointing to a degree of separability between the overt and covert systems.
    European Journal of Neuroscience 05/2010; 31(9):1690-700. DOI:10.1111/j.1460-9568.2010.07219.x · 3.67 Impact Factor
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    ABSTRACT: Attending to a specific spatial location modulates responsivity of neurons with receptive fields processing that part of the environment. A major outstanding question is whether attentional modulation operates differently for the foveal (central) representation of the visual field than it does for the periphery. Indeed, recent animal electrophysiological recordings suggest that attention differentially affects spatial integration for central and peripheral receptive fields in primary visual cortex. In human electroencephalographic recordings, spatial attention to peripheral locations robustly modulates activity in early visual regions, but it has been claimed that this mechanism does not operate in foveal vision. Here, however, we show clear early attentional modulation of foveal stimulation with the same timing and cortical sources as seen for peripheral stimuli, demonstrating that attentional gain control operates similarly across the entire field of view. These results imply that covertly attending away from the center of gaze, which is a common paradigm in behavioral and electrophysiological studies of attention, results in a precisely timed push-pull mechanism. While the amplitude of the initial response to stimulation at attended peripheral locations is significantly increased beginning at 80 ms, the amplitude of the response to foveal stimulation begins to be attenuated.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 03/2010; 30(13):4547-51. DOI:10.1523/JNEUROSCI.5217-09.2010 · 6.75 Impact Factor
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    ABSTRACT: Cueing relevant spatial locations in advance of a visual target results in modulated processing of that target as a consequence of anticipatory attentional deployment, the neural signatures of which remain to be fully elucidated. A set of electrophysiological processes has been established as candidate markers of the invocation and maintenance of attentional bias in humans. These include spatially-selective event-related potential (ERP) components over the lateral parietal (around 200-300 ms post-cue), frontal (300-500 ms) and ventral visual (> 500 ms) cortex, as well as oscillatory amplitude changes in the alpha band (8-14 Hz). Here, we interrogated the roles played by these anticipatory processes in attentional orienting by testing for links with subsequent behavioral performance. We found that both target discriminability (d') and reaction times were significantly predicted on a trial-by-trial basis by lateralization of alpha-band amplitude in the 500 ms preceding the target, with improved speed and accuracy resulting from a greater relative decrease in alpha over the contralateral visual cortex. Reaction time was also predicted by a late posterior contralateral positivity in the broad-band ERP in the same time period, but this did not influence d'. In a further analysis we sought to identify the control signals involved in generating the anticipatory bias, by testing earlier broad-band ERP amplitude for covariation with alpha lateralization. We found that stronger alpha biasing was associated with a greater bilateral frontal positivity at approximately 390 ms but not with differential amplitude across hemispheres in any time period. Thus, during the establishment of an anticipatory spatial bias, while the expected target location is strongly encoded in lateralized activity in parietal and frontal areas, a distinct non-spatial control process seems to regulate the strength of the bias.
    European Journal of Neuroscience 11/2009; 30(11):2224-34. DOI:10.1111/j.1460-9568.2009.06980.x · 3.67 Impact Factor

Publication Stats

2k Citations
194.74 Total Impact Points

Institutions

  • 2011–2014
    • CUNY Graduate Center
      New York, New York, United States
  • 2010–2014
    • City University of New York - York College
      New York, New York, United States
  • 2007–2014
    • Trinity College Dublin
      • School of Psychology
      Dublin, Leinster, Ireland
    • St. Vincents University Hospital
      Dublin, Leinster, Ireland
  • 2012–2013
    • City College of New York
      • Department of Biomedical Engineering
      New York, New York, United States
  • 2007–2011
    • Nathan Kline Institute
      Orangeburg, New York, United States
  • 2009–2010
    • Columbia University
      • Center for Neurobiology and Behavior
      New York, New York, United States
  • 2006–2009
    • St. Vincent Hospital
      Green Bay, Wisconsin, United States
  • 2008
    • St. Vincent’s Hospital, Fairview
      Dublin, Leinster, Ireland
  • 2004–2007
    • University College Dublin
      • School of Electrical, Electronic and Mechanical Engineering
      Dublin, Leinster, Ireland