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Chantal Kemner - One of the best experts on this subject based on the ideXlab platform.
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neural processing of high and Low Spatial Frequency information in faces changes across development qualitative changes in face processing during adolescence
European Journal of Neuroscience, 2013Co-Authors: Petra H J M Vlamings, Chantal Kemner, Judith C PetersAbstract:Face perception in adults depends on skilled processing of interattribute distances ('configural' processing), which is disrupted for faces presented in inverted orientation (face inversion effect or FIE). Children are not proficient in configural processing, and this might relate to an underlying immaturity to use facial information in Low Spatial Frequency (SF) ranges, which capture the coarse information needed for configural processing. We hypothesized that during adolescence a shift from use of high to Low SF information takes place. Therefore, we studied the influence of SF content on neural face processing in groups of children (9-10 years), adolescents (14-15 years) and young adults (21-29 years) by measuring event-related potentials (ERPs) to upright and inverted faces which varied in SF content. Results revealed that children show a neural FIE in early processing stages (i.e. P1; generated in early visual areas), suggesting a superficial, global facial analysis. In contrast, ERPs of adults revealed an FIE at later processing stages (i.e. N170; generated in face-selective, higher visual areas). Interestingly, adolescents showed FIEs in both processing stages, suggesting a hybrid developmental stage. Furthermore, adolescents and adults showed FIEs for stimuli containing Low SF information, whereas such effects were driven by both Low and high SF information in children. These results indicate that face processing has a protracted maturational course into adolescence, and is dependent on changes in SF processing. During adolescence, sensitivity to configural cues is developed, which aids the fast and holistic processing that is so special for faces.
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is the early modulation of brain activity by fearful facial expressions primarily mediated by coarse Low Spatial Frequency information
Journal of Vision, 2009Co-Authors: Petra H J M Vlamings, Valerie Goffaux, Chantal KemnerAbstract:Rapidly decoding the emotional content of a face is an important skill for successful social behavior. Several Event Related brain Potential (ERP) have indicated that emotional expressions already influence brain activity as early as 100 ms. Some studies hypothesized that this early brain response to fear depends on coarse-magnocellular inputs, which are primarily driven by Low Spatial Frequency (LSF) cues. Until now however, evidence is inconclusive probably due to the divergent methods used to match luminance and contrast across Spatial frequencies and emotional stimuli. In the present study, we measured ERPs to LSF and HSF faces with fearful or neutral expressions when contrast and luminance was matched across SF or not. Our findings clearly show that fearful facial expressions increases the amplitude of P1 (only for contrast–luminance equated images) and N170 in comparison to neutral faces but only in LSF faces, irrespective of contrast or luminance equalization, further suggesting that LSF information plays a crucial role in the early brain responses to fear. Furthermore, we found that, irrespective of luminance or contrast equalization, N170 occurred faster faster when perceiving LSF faces than HSF faces, again emphasizing the primacy of LSF processing in early face perception.
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abnormal Spatial Frequency processing in high functioning children with pervasive developmental disorder pdd
Clinical Neurophysiology, 2007Co-Authors: M A Boeschoten, Chantal Kemner, J L Kenemans, H Van EngelandAbstract:Abstract Objective Basic abnormalities in visual information processing could be associated with the local visual bias often found in subjects with PDD. Therefore, the present study investigated the existence of deficits in Spatial Frequency processing at an early sensory level in children with PDD. Methods Visual evoked potentials (VEPs) and VEP dipole sources elicited by high and Low Spatial Frequency gratings were analyzed in high-functioning children with PDD and matched controls. Results Around 80ms (N80-latency) children with PDD did not show the same robust differences between high and Low Spatial frequencies in VEP amplitude and VEP brain sources as controls, because of atypical processing of high frequencies. Analyses at the P1-latency (130ms) revealed that, although similar inferior–medial brain sources were activated for the processing of both Spatial frequencies in the PDD and control group, source strength in response to both frequencies was weaker in the PDD compared to control group. Moreover, additional superior–lateral brain sources were activated during the processing of both frequencies in the PDD group. Conclusions Decreased specialized processing of high and Low Spatial frequencies might be a robust characteristic of PDD. Early in processing abnormalities in high Spatial Frequency processing seem to occur in PDD. At a later phase in processing there seems to be both atypical high and Low Spatial Frequency processing. Considering that the processing of specific Spatial frequencies plays an important role in the processing of global and local aspects of hierarchical stimuli and faces and of emotions, present data suggest that peculiarities in PDD subjects with respect to these stimuli might be related to an abnormality in more fundamental visual processes. Significance A basic abnormality in visual Frequency processing is established in children with PDD.
Jörn Bonse - One of the best experts on this subject based on the ideXlab platform.
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Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon: the role of carrier generation and relaxation processes
Applied Physics A Solids and Surface, 2014Co-Authors: Thibault J Y Derrien, Sandra Höhm, A Rosenfeld, Jorg Kruger, Tatiana Itina, Jörn BonseAbstract:The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between 0 and ∼4 ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay-dependent decrease of the Low Spatial Frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination is quantified individually.
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rippled area formed by surface plasmon polaritons upon femtosecond laser double pulse irradiation of silicon the role of carrier generation and relaxation processes
arXiv: Materials Science, 2013Co-Authors: Thibault J Y Derrien, Sandra Höhm, A Rosenfeld, Jorg Kruger, Tatiana Itina, Jörn BonseAbstract:The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between $0$ and $\sim 4$ ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay dependent decrease of the Low-Spatial-Frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination are quantified individually.
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sub 100 nm laser induced periodic surface structures upon irradiation of titanium by ti sapphire femtosecond laser pulses in air
Applied Physics A, 2013Co-Authors: Jörn Bonse, Sandra Höhm, A Rosenfeld, Jorg KrugerAbstract:The formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30 fs, λ=790 nm) in an air environment is studied experimentally and theoretically. In the experiments, the dependence on the laser fluence and the number of laser pulses per irradiation spot has been analyzed. For a moderate number of laser pulses (N<1000) and at fluences between ∼0.09 and ∼0.35 J/cm2, predominantly Low-Spatial-Frequency-LIPSS with periods between 400 nm and 800 nm are observed perpendicular to the polarization. In a narrow fluence range between 0.05 and 0.09 J/cm2, high-Spatial-Frequency-LIPSS with sub-100-nm Spatial periods (∼λ/10) can be generated with an orientation parallel to the polarization (N=50). These experimental results are complemented by calculations based on a theoretical LIPSS model and compared to the present literature.
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femtosecond laser induced periodic surface structures
Journal of Laser Applications, 2012Co-Authors: Jörn Bonse, Sandra Höhm, Jorg Kruger, A RosenfeldAbstract:The formation of laser-induced periodic surface structures (LIPSS) in different materials (metals, semiconductors, and dielectrics) upon irradiation with linearly polarized fs-laser pulses (τ ∼ 30–150 fs, λ ∼ 800 nm) in air environment is studied experimentally and theoretically. In metals, predominantly Low-Spatial-Frequency-LIPSS with periods close to the laser wavelength λ are observed perpendicular to the polarization. Under specific irradiation conditions, high-Spatial-Frequency-LIPSS with sub-100-nm Spatial periods (∼λ/10) can be generated. For semiconductors, the impact of transient changes of the optical properties to the LIPSS periods is analyzed theoretically and experimentally. In dielectrics, the importance of transient excitation stages in the LIPSS formation is demonstrated experimentally using (multiple) double-fs-laser-pulse irradiation sequences. A characteristic decrease of the LIPSS periods is observed for double-pulse delays of less than 2 ps.
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femtosecond laser induced periodic surface structures on silica
Journal of Applied Physics, 2012Co-Authors: Sandra Höhm, A Rosenfeld, Jorg Kruger, Jörn BonseAbstract:The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences (τ = 150 fs pulse duration, λ = 800 nm center wavelength, temporal pulse separation Δt < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called Low-Spatial-Frequency LIPSS (LSFL) and high-Spatial-Frequency LIPSS (HSFL)] with different Spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the “dynamics” of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier...
Raymond J Dolan - One of the best experts on this subject based on the ideXlab platform.
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Distinct and convergent visual processing of high and Low Spatial Frequency information in faces
CEREB CORTEX, 2007Co-Authors: Raymond J DolanAbstract:We tested for differential brain response to distinct Spatial Frequency (SF) components in faces. During a functional magnetic resonance imaging experiment, participants were presented with "hybrid" faces containing superimposed Low and high SF information from different identities. We used a repetition paradigm where faces at either SF range were independently repeated or changed across consecutive trials. In addition, we manipulated which SF band was attended. Our results suggest that repetition and attention affected partly overlapping occipitotemporal regions but did not interact. Changes of high SF faces increased responses of the right inferior occipital gyrus (IOG) and left inferior temporal gyrus (ITG), with the latter response being also modulated additively by attention. In contrast, the bilateral middle occipital gyrus (MOG) responded to repetition and attention manipulations of Low SF. A common effect of high and Low SF repetition was observed in the right fusiform gyrus (FFG). FolLow-up connectivity analyses suggested direct influence of the MOG (Low SF), IOG, and ITG (high SF) on the FFG responses. Our results reveal that different regions within occipitotemporal cortex extract distinct visual cues at different SF ranges in faces and that the outputs from these separate processes project forward to the right FFG, where the different visual cues may converge.
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effects of Low Spatial Frequency components of fearful faces on fusiform cortex activity
Current Biology, 2003Co-Authors: Joel S Winston, Patrik Vuilleumier, Raymond J DolanAbstract:Emotive faces elicit neural responses even when they are not consciously perceived [1, 2]. We used faces hybridized from Spatial Frequency-filtered individual stimuli [3] to study processing of facial emotion. Employing event-related functional magnetic resonance imaging (fMRI), we show enhanced fusiform cortex responses to hybrid faces containing fearful expressions when such emotional cues are present in the Low-Spatial Frequency (LSF) range. Critically, this effect is independent of whether subjects use LSF or high-Spatial Frequency (HSF) information to make gender judgments on the hybridized faces. The magnitude of this fusiform enhancement predicts behavioral sLowing in response times when participants report HSF information of the hybrid stimulus in the presence of fear in the unreported LSF components. Thus, emotional modulation of a face-responsive region of fusiform is driven by the Low-Frequency components of the stimulus, an effect independent of subjects' reported perception but evident in an incidental measure of behavioral performance.
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distinct Spatial Frequency sensitivities for processing faces and emotional expressions
Nature Neuroscience, 2003Co-Authors: Patrik Vuilleumier, Jorge L Armony, Jon Driver, Raymond J DolanAbstract:High and Low Spatial Frequency information in visual images is processed by distinct neural channels. Using event-related functional magnetic resonance imaging (fMRI) in humans, we show dissociable roles of such visual channels for processing faces and emotional fearful expressions. Neural responses in fusiform cortex, and effects of repeating the same face identity upon fusiform activity, were greater with intact or high-Spatial-Frequency face stimuli than with Low-Frequency faces, regardless of emotional expression. In contrast, amygdala responses to fearful expressions were greater for intact or Low-Frequency faces than for high-Frequency faces. An activation of pulvinar and superior colliculus by fearful expressions occurred specifically with Low-Frequency faces, suggesting that these subcortical pathways may provide coarse fear-related inputs to the amygdala.
Antoni Valero-cabré - One of the best experts on this subject based on the ideXlab platform.
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Low Frequency transcranial magnetic stimulation of right posterior parietal cortex reduces reaction time to perithreshold Low Spatial Frequency visual stimuli
Scientific Reports, 2020Co-Authors: Seth Elkin-frankston, Richard Rushmore, Antoni Valero-cabréAbstract:Research in humans and animal models suggests that visual responses in early visual cortical areas may be modulated by top-down influences from distant cortical areas, particularly in the frontal and parietal regions. The right posterior parietal cortex is part of a broad cortical network involved in aspects of visual search and attention, but its role in modulating activity in early visual cortical areas is less well understood. This study evaluated the influence of right posterior parietal cortex (PPC) on a direct measure of visual processing in humans. Contrast sensitivity (CS) and detection response times were recorded using a visual detection paradigm to two types of centrally-presented stimuli. Participants were tested on the detection task before, after, and 1 hour after Low-Frequency repetitive transcranial magnetic stimulation (rTMS) to the right PPC or to the scalp vertex. Low-Frequency rTMS to the right PPC did not significantly change measures of contrast sensitivity, but increased the speed at which participants responded to visual stimuli of Low Spatial Frequency. Response times returned to baseline 1-hour after rTMS. These data indicate that Low Frequency rTMS to the right PPC speeds up aspects of early visual processing, likely due to a disinhibition of the homotopic left posterior parietal cortex.
Sandra Höhm - One of the best experts on this subject based on the ideXlab platform.
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Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon: the role of carrier generation and relaxation processes
Applied Physics A Solids and Surface, 2014Co-Authors: Thibault J Y Derrien, Sandra Höhm, A Rosenfeld, Jorg Kruger, Tatiana Itina, Jörn BonseAbstract:The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between 0 and ∼4 ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay-dependent decrease of the Low Spatial Frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination is quantified individually.
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rippled area formed by surface plasmon polaritons upon femtosecond laser double pulse irradiation of silicon the role of carrier generation and relaxation processes
arXiv: Materials Science, 2013Co-Authors: Thibault J Y Derrien, Sandra Höhm, A Rosenfeld, Jorg Kruger, Tatiana Itina, Jörn BonseAbstract:The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between $0$ and $\sim 4$ ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay dependent decrease of the Low-Spatial-Frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination are quantified individually.
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sub 100 nm laser induced periodic surface structures upon irradiation of titanium by ti sapphire femtosecond laser pulses in air
Applied Physics A, 2013Co-Authors: Jörn Bonse, Sandra Höhm, A Rosenfeld, Jorg KrugerAbstract:The formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30 fs, λ=790 nm) in an air environment is studied experimentally and theoretically. In the experiments, the dependence on the laser fluence and the number of laser pulses per irradiation spot has been analyzed. For a moderate number of laser pulses (N<1000) and at fluences between ∼0.09 and ∼0.35 J/cm2, predominantly Low-Spatial-Frequency-LIPSS with periods between 400 nm and 800 nm are observed perpendicular to the polarization. In a narrow fluence range between 0.05 and 0.09 J/cm2, high-Spatial-Frequency-LIPSS with sub-100-nm Spatial periods (∼λ/10) can be generated with an orientation parallel to the polarization (N=50). These experimental results are complemented by calculations based on a theoretical LIPSS model and compared to the present literature.
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femtosecond laser induced periodic surface structures
Journal of Laser Applications, 2012Co-Authors: Jörn Bonse, Sandra Höhm, Jorg Kruger, A RosenfeldAbstract:The formation of laser-induced periodic surface structures (LIPSS) in different materials (metals, semiconductors, and dielectrics) upon irradiation with linearly polarized fs-laser pulses (τ ∼ 30–150 fs, λ ∼ 800 nm) in air environment is studied experimentally and theoretically. In metals, predominantly Low-Spatial-Frequency-LIPSS with periods close to the laser wavelength λ are observed perpendicular to the polarization. Under specific irradiation conditions, high-Spatial-Frequency-LIPSS with sub-100-nm Spatial periods (∼λ/10) can be generated. For semiconductors, the impact of transient changes of the optical properties to the LIPSS periods is analyzed theoretically and experimentally. In dielectrics, the importance of transient excitation stages in the LIPSS formation is demonstrated experimentally using (multiple) double-fs-laser-pulse irradiation sequences. A characteristic decrease of the LIPSS periods is observed for double-pulse delays of less than 2 ps.
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femtosecond laser induced periodic surface structures on silica
Journal of Applied Physics, 2012Co-Authors: Sandra Höhm, A Rosenfeld, Jorg Kruger, Jörn BonseAbstract:The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences (τ = 150 fs pulse duration, λ = 800 nm center wavelength, temporal pulse separation Δt < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called Low-Spatial-Frequency LIPSS (LSFL) and high-Spatial-Frequency LIPSS (HSFL)] with different Spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the “dynamics” of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier...
