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Brittenham C, Gordon J, Zemon VM, Siper PM. Objective frequency analysis of transient visual evoked potentials in autistic children. Autism Res 2021; 15:464-480. [PMID: 34908250 DOI: 10.1002/aur.2654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 12/02/2021] [Accepted: 12/05/2021] [Indexed: 11/06/2022]
Abstract
Visual evoked potentials (VEPs) provide a means to examine neural mechanisms in autism with high temporal resolution. Conventional VEP analysis relies on subjective inspection of a few points (peaks and troughs) in the time-domain waveform. The current study applied power spectral analysis and magnitude-squared coherence (MSC) statistics (frequency-domain measures) to VEPs recorded during 1-minute runs and with a recently developed short-duration technique that allow for objective examination of the responses (Zemon & Gordon, European Journal of Neuroscience, 2018, 48, 1765-1788) from nonautistic and autistic children. Results indicate that, for both groups, early time-domain measures (P60 , N75 , P100 ) are highly correlated with middle- and high-frequency (14-28 and 30-48 Hz, respectively) mechanisms, and late measures are highly correlated with a low-frequency (6-12 Hz) mechanism. One frequency-domain measure (power in the middle-frequency band) is capable of predicting the key amplitude measure (N75 -P100 ) with high accuracy. MSC and power measures were combined to yield separate measures of signal and noise strength to evaluate alternate hypotheses in autism. Linear mixed-effects modeling demonstrated selective differences in early time-domain and middle-to-high frequency-domain measures in autistic children as compared to nonautistic children given both recording techniques, implicating weaker excitatory input to the cortex. Receiver-operating-characteristic curve analysis showed predictive diagnostic accuracy for middle- and high-frequency bands based on MSC. These findings support the value of frequency analysis measures (power spectral analysis and MSC) in the objective examination of neural differences in autism. LAY SUMMARY: Visual evoked potentials (VEPs) are used to assess neural mechanisms. Typically, VEPs are analyzed by subjective examination of time-series waveforms; but here objective techniques were applied to quantify VEP frequency components to investigate neural differences between autistic and nonautistic children. The objective measures demonstrate group differences in brain function that point to weaker excitatory input to the cortex in autism.
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Affiliation(s)
- Chloe Brittenham
- Department of Psychology, The Graduate Center, City University of New York, New York, New York, USA
| | - James Gordon
- Department of Psychology, Hunter College, New York, New York, USA
| | - Vance M Zemon
- Ferkauf Graduate School of Psychology, Yeshiva University, Bronx, New York, USA
| | - Paige M Siper
- Seaver Autism Center for Research and Treatment, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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Stefanics G, Heinzle J, Czigler I, Valentini E, Stephan KE. Timing of repetition suppression of event-related potentials to unattended objects. Eur J Neurosci 2020; 52:4432-4441. [PMID: 29802671 PMCID: PMC7818225 DOI: 10.1111/ejn.13972] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 04/03/2018] [Accepted: 05/16/2018] [Indexed: 12/11/2022]
Abstract
Current theories of object perception emphasize the automatic nature of perceptual inference. Repetition suppression (RS), the successive decrease of brain responses to repeated stimuli, is thought to reflect the optimization of perceptual inference through neural plasticity. While functional imaging studies revealed brain regions that show suppressed responses to the repeated presentation of an object, little is known about the intra-trial time course of repetition effects to everyday objects. Here, we used event-related potentials (ERPs) to task-irrelevant line-drawn objects, while participants engaged in a distractor task. We quantified changes in ERPs over repetitions using three general linear models that modeled RS by an exponential, linear, or categorical "change detection" function in each subject. Our aim was to select the model with highest evidence and determine the within-trial time-course and scalp distribution of repetition effects using that model. Model comparison revealed the superiority of the exponential model indicating that repetition effects are observable for trials beyond the first repetition. Model parameter estimates revealed a sequence of RS effects in three time windows (86-140, 322-360, and 400-446 ms) and with occipital, temporoparietal, and frontotemporal distribution, respectively. An interval of repetition enhancement (RE) was also observed (320-340 ms) over occipitotemporal sensors. Our results show that automatic processing of task-irrelevant objects involves multiple intervals of RS with distinct scalp topographies. These sequential intervals of RS and RE might reflect the short-term plasticity required for optimization of perceptual inference and the associated changes in prediction errors and predictions, respectively, over stimulus repetitions during automatic object processing.
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Affiliation(s)
- Gabor Stefanics
- Translational Neuromodeling Unit (TNU)Institute for Biomedical EngineeringUniversity of Zurich & ETH ZurichZurichSwitzerland
- Laboratory for Social and Neural Systems ResearchDepartment of EconomicsUniversity of ZurichZurichSwitzerland
| | - Jakob Heinzle
- Translational Neuromodeling Unit (TNU)Institute for Biomedical EngineeringUniversity of Zurich & ETH ZurichZurichSwitzerland
| | - István Czigler
- Institute of Cognitive Neuroscience and PsychologyResearch Center for Natural SciencesHungarian Academy of SciencesBudapestHungary
| | | | - Klaas E. Stephan
- Translational Neuromodeling Unit (TNU)Institute for Biomedical EngineeringUniversity of Zurich & ETH ZurichZurichSwitzerland
- Wellcome Trust Centre for NeuroimagingUniversity College LondonLondonUK
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3
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Zemon VM, Gordon J. Quantification and statistical analysis of the transient visual evoked potential to a contrast‐reversing pattern: A frequency‐domain approach. Eur J Neurosci 2018; 48:1765-1788. [DOI: 10.1111/ejn.14049] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 05/27/2018] [Accepted: 06/13/2018] [Indexed: 11/27/2022]
Affiliation(s)
- Vance M. Zemon
- Ferkauf Graduate School of PsychologyYeshiva University New York New York
| | - James Gordon
- Department of PsychologyHunter CollegeCity University of New York New York New York
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Crosse MJ, Di Liberto GM, Bednar A, Lalor EC. The Multivariate Temporal Response Function (mTRF) Toolbox: A MATLAB Toolbox for Relating Neural Signals to Continuous Stimuli. Front Hum Neurosci 2016; 10:604. [PMID: 27965557 PMCID: PMC5127806 DOI: 10.3389/fnhum.2016.00604] [Citation(s) in RCA: 271] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Accepted: 11/11/2016] [Indexed: 01/05/2023] Open
Abstract
Understanding how brains process sensory signals in natural environments is one of the key goals of twenty-first century neuroscience. While brain imaging and invasive electrophysiology will play key roles in this endeavor, there is also an important role to be played by noninvasive, macroscopic techniques with high temporal resolution such as electro- and magnetoencephalography. But challenges exist in determining how best to analyze such complex, time-varying neural responses to complex, time-varying and multivariate natural sensory stimuli. There has been a long history of applying system identification techniques to relate the firing activity of neurons to complex sensory stimuli and such techniques are now seeing increased application to EEG and MEG data. One particular example involves fitting a filter—often referred to as a temporal response function—that describes a mapping between some feature(s) of a sensory stimulus and the neural response. Here, we first briefly review the history of these system identification approaches and describe a specific technique for deriving temporal response functions known as regularized linear regression. We then introduce a new open-source toolbox for performing this analysis. We describe how it can be used to derive (multivariate) temporal response functions describing a mapping between stimulus and response in both directions. We also explain the importance of regularizing the analysis and how this regularization can be optimized for a particular dataset. We then outline specifically how the toolbox implements these analyses and provide several examples of the types of results that the toolbox can produce. Finally, we consider some of the limitations of the toolbox and opportunities for future development and application.
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Affiliation(s)
- Michael J Crosse
- School of Engineering, Trinity Centre for Bioengineering and Trinity College Institute of Neuroscience, Trinity College DublinDublin, Ireland; Department of Pediatrics and Department of Neuroscience, Albert Einstein College of MedicineThe Bronx, NY, USA
| | - Giovanni M Di Liberto
- School of Engineering, Trinity Centre for Bioengineering and Trinity College Institute of Neuroscience, Trinity College Dublin Dublin, Ireland
| | - Adam Bednar
- School of Engineering, Trinity Centre for Bioengineering and Trinity College Institute of Neuroscience, Trinity College DublinDublin, Ireland; Department of Biomedical Engineering and Department of Neuroscience, University of RochesterRochester, NY, USA
| | - Edmund C Lalor
- School of Engineering, Trinity Centre for Bioengineering and Trinity College Institute of Neuroscience, Trinity College DublinDublin, Ireland; Department of Biomedical Engineering and Department of Neuroscience, University of RochesterRochester, NY, USA
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Kiiski HSM, Ní Riada S, Lalor EC, Gonçalves NR, Nolan H, Whelan R, Lonergan R, Kelly S, O'Brien MC, Kinsella K, Bramham J, Burke T, Ó Donnchadha S, Hutchinson M, Tubridy N, Reilly RB. Delayed P100-Like Latencies in Multiple Sclerosis: A Preliminary Investigation Using Visual Evoked Spread Spectrum Analysis. PLoS One 2016; 11:e0146084. [PMID: 26726800 PMCID: PMC4699709 DOI: 10.1371/journal.pone.0146084] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 12/11/2015] [Indexed: 01/21/2023] Open
Abstract
Conduction along the optic nerve is often slowed in multiple sclerosis (MS). This is typically assessed by measuring the latency of the P100 component of the Visual Evoked Potential (VEP) using electroencephalography. The Visual Evoked Spread Spectrum Analysis (VESPA) method, which involves modulating the contrast of a continuous visual stimulus over time, can produce a visually evoked response analogous to the P100 but with a higher signal-to-noise ratio and potentially higher sensitivity to individual differences in comparison to the VEP. The main objective of the study was to conduct a preliminary investigation into the utility of the VESPA method for probing and monitoring visual dysfunction in multiple sclerosis. The latencies and amplitudes of the P100-like VESPA component were compared between healthy controls and multiple sclerosis patients, and multiple sclerosis subgroups. The P100-like VESPA component activations were examined at baseline and over a 3-year period. The study included 43 multiple sclerosis patients (23 relapsing-remitting MS, 20 secondary-progressive MS) and 42 healthy controls who completed the VESPA at baseline. The follow-up sessions were conducted 12 months after baseline with 24 MS patients (15 relapsing-remitting MS, 9 secondary-progressive MS) and 23 controls, and again at 24 months post-baseline with 19 MS patients (13 relapsing-remitting MS, 6 secondary-progressive MS) and 14 controls. The results showed P100-like VESPA latencies to be delayed in multiple sclerosis compared to healthy controls over the 24-month period. Secondary-progressive MS patients had most pronounced delay in P100-like VESPA latency relative to relapsing-remitting MS and controls. There were no longitudinal P100-like VESPA response differences. These findings suggest that the VESPA method is a reproducible electrophysiological method that may have potential utility in the assessment of visual dysfunction in multiple sclerosis.
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Affiliation(s)
- Hanni S. M. Kiiski
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- School of Engineering, Trinity College Dublin, Dublin, Ireland
- * E-mail:
| | - Sinéad Ní Riada
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- School of Engineering, Trinity College Dublin, Dublin, Ireland
| | - Edmund C. Lalor
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- School of Engineering, Trinity College Dublin, Dublin, Ireland
| | - Nuno R. Gonçalves
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- School of Engineering, Trinity College Dublin, Dublin, Ireland
| | - Hugh Nolan
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- School of Engineering, Trinity College Dublin, Dublin, Ireland
| | - Robert Whelan
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- Cognitive and Behavioural Neuroscience Research Group, School of Psychology, UCD College of Human Sciences, University College Dublin, Dublin, Ireland
| | - Róisín Lonergan
- Department of Neurology, St. Vincent’s University Hospital, Dublin, Ireland
| | - Siobhán Kelly
- Department of Neurology, St. Vincent’s University Hospital, Dublin, Ireland
| | - Marie Claire O'Brien
- Cognitive and Behavioural Neuroscience Research Group, School of Psychology, UCD College of Human Sciences, University College Dublin, Dublin, Ireland
| | - Katie Kinsella
- Department of Neurology, St. Vincent’s University Hospital, Dublin, Ireland
| | - Jessica Bramham
- Cognitive and Behavioural Neuroscience Research Group, School of Psychology, UCD College of Human Sciences, University College Dublin, Dublin, Ireland
| | - Teresa Burke
- Cognitive and Behavioural Neuroscience Research Group, School of Psychology, UCD College of Human Sciences, University College Dublin, Dublin, Ireland
- School of Nursing and Human Sciences, Dublin City University, Dublin, Ireland
| | - Seán Ó Donnchadha
- Cognitive and Behavioural Neuroscience Research Group, School of Psychology, UCD College of Human Sciences, University College Dublin, Dublin, Ireland
| | - Michael Hutchinson
- Department of Neurology, St. Vincent’s University Hospital, Dublin, Ireland
| | - Niall Tubridy
- Department of Neurology, St. Vincent’s University Hospital, Dublin, Ireland
| | - Richard B. Reilly
- Neural Engineering Group, Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland
- School of Engineering, Trinity College Dublin, Dublin, Ireland
- School of Medicine, Trinity College Dublin, Dublin, Ireland
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Gonçalves NR, Whelan R, Foxe JJ, Lalor EC. Towards obtaining spatiotemporally precise responses to continuous sensory stimuli in humans: a general linear modeling approach to EEG. Neuroimage 2014; 97:196-205. [PMID: 24736185 DOI: 10.1016/j.neuroimage.2014.04.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Revised: 03/05/2014] [Accepted: 04/02/2014] [Indexed: 11/28/2022] Open
Abstract
Noninvasive investigation of human sensory processing with high temporal resolution typically involves repeatedly presenting discrete stimuli and extracting an average event-related response from scalp recorded neuroelectric or neuromagnetic signals. While this approach is and has been extremely useful, it suffers from two drawbacks: a lack of naturalness in terms of the stimulus and a lack of precision in terms of the cortical response generators. Here we show that a linear modeling approach that exploits functional specialization in sensory systems can be used to rapidly obtain spatiotemporally precise responses to complex sensory stimuli using electroencephalography (EEG). We demonstrate the method by example through the controlled modulation of the contrast and coherent motion of visual stimuli. Regressing the data against these modulation signals produces spatially focal, highly temporally resolved response measures that are suggestive of specific activation of visual areas V1 and V6, respectively, based on their onset latency, their topographic distribution and the estimated location of their sources. We discuss our approach by comparing it with fMRI/MRI informed source analysis methods and, in doing so, we provide novel information on the timing of coherent motion processing in human V6. Generalizing such an approach has the potential to facilitate the rapid, inexpensive spatiotemporal localization of higher perceptual functions in behaving humans.
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Affiliation(s)
- Nuno R Gonçalves
- Trinity Centre for Bioengineering and School of Engineering, Trinity College Dublin, Dublin 2, Ireland; Department of Psychology, University of Cambridge, Cambridge, UK
| | - Robert Whelan
- School of Psychology, University College Dublin, Dublin 4, Ireland
| | - John J Foxe
- Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland; The Sheryl and Daniel R. Tishman Cognitive Neurophysiology Laboratory, Children's Evaluation and Rehabilitation Center, Departments of Pediatrics and Neuroscience, Albert Einstein College of Medicine, Rose F. Kennedy Intellectual and Developmental Disabilities Research Center, 1225 Morris Park Avenue, Bronx, NY 10461, USA
| | - Edmund C Lalor
- Trinity Centre for Bioengineering and School of Engineering, Trinity College Dublin, Dublin 2, Ireland; Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland.
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7
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Frey HP, Molholm S, Lalor EC, Russo NN, Foxe JJ. Atypical cortical representation of peripheral visual space in children with an autism spectrum disorder. Eur J Neurosci 2013; 38:2125-38. [PMID: 23692590 DOI: 10.1111/ejn.12243] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Accepted: 04/03/2013] [Indexed: 11/30/2022]
Abstract
A key feature of early visual cortical regions is that they contain discretely organized retinotopic maps. Titration of these maps must occur through experience, and the fidelity of their spatial tuning will depend on the consistency and accuracy of the eye movement system. Anomalies in fixation patterns and the ballistics of eye movements are well documented in autism spectrum disorder (ASD), with off-center fixations a hallmark of the phenotype. We hypothesized that these atypicalities might affect the development of visuo-spatial maps and specifically that peripheral inputs might receive altered processing in ASD. Using high-density recordings of visual evoked potentials (VEPs) and a novel system-identification approach known as VESPA (visual evoked spread spectrum analysis), we assessed sensory responses to centrally and peripherally presented stimuli. Additionally, input luminance was varied to bias responsiveness to the magnocellular system, given previous suggestions of magnocellular-specific deficits in ASD. Participants were 22 ASD children (7-17 years of age) and 31 age- and performance-IQ-matched neurotypical controls. Both VEP and VESPA responses to central presentations were indistinguishable between groups. In contrast, peripheral presentations resulted in significantly greater early VEP and VESPA amplitudes in the ASD cohort. We found no evidence that anomalous enhancement was restricted to magnocellular-biased responses. The extent of peripheral response enhancement was related to the severity of stereotyped behaviors and restricted interests, cardinal symptoms of ASD. The current results point to differential visuo-spatial cortical mapping in ASD, shedding light on the consequences of peculiarities in gaze and stereotyped visual behaviors often reported by clinicians working with this population.
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Affiliation(s)
- Hans-Peter Frey
- Department of Pediatrics and Neuroscience, The Sheryl and Daniel R Tishman Cognitive Neurophysiology Laboratory, Children's Evaluation and Rehabilitation Center, Albert Einstein College of Medicine, Bronx, NY, USA
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8
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Lalor EC, De Sanctis P, Krakowski MI, Foxe JJ. Visual sensory processing deficits in schizophrenia: is there anything to the magnocellular account? Schizophr Res 2012; 139:246-52. [PMID: 22704644 PMCID: PMC3393820 DOI: 10.1016/j.schres.2012.05.022] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Revised: 05/01/2012] [Accepted: 05/28/2012] [Indexed: 10/28/2022]
Abstract
Visual processing studies have repeatedly shown impairment in patients with schizophrenia compared to healthy controls. Electroencephalography (EEG) and, specifically, visual evoked potential (VEP) studies have identified an early marker of this impairment in the form of a decrement in the P1 component of the VEP in patients and their clinically unaffected first-degree relatives. Much behavioral and neuroimaging research has implicated specific dysfunction of either the subcortical magnocellular pathway or the cortical visual dorsal stream in this impairment. In this study, EEG responses were obtained to the contrast modulation of checkerboard stimuli using the VESPA (Visual Evoked Spread Spectrum Analysis) method. This was done for a high contrast condition and, in order to bias the stimuli towards the magnocellular pathway, a low contrast condition. Standard VEPs were also obtained using high contrast pattern reversing checkerboards. Responses were measured using high-density electrical scalp recordings in 29 individuals meeting DSM-IV criteria for schizophrenia and in 18 control subjects. Replicating previous research, a large (Cohen's d=1.11) reduction in the P1 component of the VEP was seen in patients when compared with controls with no corresponding difference in the VESPA response to high contrast stimuli. In addition, the low-contrast VESPA displayed no difference between patients and controls. Furthermore, no differences were seen between patients and controls for the C1 components of either the VEP or the high-contrast VESPA. Based on the differing acquisition methods between VEP and VESPA, we discuss these results in terms of contrast gain control and the possibility of dysfunction at the cortical level with initial afferent activity into V1 along the magnocellular pathway being intact when processing is biased towards that pathway using low contrast stimuli.
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Affiliation(s)
- Edmund C. Lalor
- The Cognitive Neurophysiology Laboratory, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, New York 10962, USA,Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland,School of Engineering, Trinity College Dublin, Dublin 2, Ireland,Trinity Centre for Bioengineering, Trinity College Dublin, Dublin 2, Ireland
| | - Pierfilippo De Sanctis
- The Cognitive Neurophysiology Laboratory, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, New York 10962, USA,The Sheryl and Daniel R. Tishman Cognitive Neurophysiology Laboratory, Children’s Evaluation and Rehabilitation Center (CERC), Departments of Pediatrics and Neuroscience, Albert Einstein College of Medicine, Van Etten Building – Wing 1C, 1225 Morris Park Avenue, Bronx, New York 10461, USA
| | - Menahem I. Krakowski
- The Cognitive Neurophysiology Laboratory, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, New York 10962, USA
| | - John J. Foxe
- The Cognitive Neurophysiology Laboratory, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, New York 10962, USA,Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland,The Sheryl and Daniel R. Tishman Cognitive Neurophysiology Laboratory, Children’s Evaluation and Rehabilitation Center (CERC), Departments of Pediatrics and Neuroscience, Albert Einstein College of Medicine, Van Etten Building – Wing 1C, 1225 Morris Park Avenue, Bronx, New York 10461, USA
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Generation of the VESPA response to rapid contrast fluctuations is dominated by striate cortex: evidence from retinotopic mapping. Neuroscience 2012; 218:226-34. [PMID: 22683721 DOI: 10.1016/j.neuroscience.2012.05.067] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 05/04/2012] [Accepted: 05/29/2012] [Indexed: 11/22/2022]
Abstract
The VESPA (visual-evoked spread spectrum analysis) method derives an impulse response function of the visual system from scalp electroencephalographic (EEG) data using the controlled modulation of some feature of a visual stimulus. Recent research using VESPA responses to modulations of stimulus contrast has provided new insights into both early visual attention mechanisms and the specificity of visual-processing deficits in schizophrenia. To allow a fuller interpretation of these and future findings, it is necessary to further characterize the VESPA in terms of its underlying cortical generators. To that end, we here examine spatio-temporal variations in the components of the VESPA as a function of stimulus location. We found that the first two VESPA components (C1/P1) each have a posterior dorsal midline focus and reverse in polarity across the horizontal meridian, consistent with retinotopic projections to calcarine cortex (V1) for the stimulus locations tested. Furthermore, the focal scalp topography of the VESPA was strikingly constant across the entire C1-P1 timeframe (50-120 ms) for each stimulus location, with negligible global scalp activity visible at the zero-crossing dividing the two. This indicates a common focal source underpinning both components, which was further supported by a significant correlation between C1 and P1 amplitudes across subjects (r=0.54; p<0.05). These results, along with factors implicit in the method of derivation of the contrast-VESPA, lead us to conclude that these responses are dominated by activity from striate cortex. We discuss the implications of this finding for previous and future research using the VESPA.
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