64 research outputs found
Super-resolution imaging of a low frequency levitated oscillator
We describe the measurement of the secular motion of a levitated nanoparticle
in a Paul trap with a CMOS camera. This simple method enables us to reach
signal-to-noise ratios as good as 10 with a displacement sensitivity
better than 10/Hz. This method can be used to extract trap
parameters as well as the properties of the levitated particles. We demonstrate
continuous monitoring of the particle dynamics on timescales of the order of
weeks. We show that by using the improvement given by super-resolution imaging,
a significant reduction in the noise floor can be attained, with an increase in
the bandwidth of the force sensitivity. This approach represents a competitive
alternative to standard optical detection for a range of low frequency
oscillators where low optical powers are require
An ultra-narrow line width levitated nano-oscillator for testing dissipative wavefunction collapse
Levitated nano-oscillators are seen as promising platforms for testing
fundamental physics and testing quantum mechanics in a new high mass regime.
Levitation allows extreme isolation from the environment, reducing the
decoherence processes that are crucial for these sensitive experiments. A
fundamental property of any oscillator is its line width and mechanical quality
factor, Q. Narrow line widths in the microHertz regime and mechanical Q's as
high as have been predicted for levitated systems, but to date, the
poor stability of these oscillators over long periods have prevented direct
measurement in high vacuum. Here we report on the measurement of an
ultra-narrow line width levitated nano-oscillator, whose line width of
Hz is only limited by residual gas pressure at high vacuum.
This narrow line width allows us to put new experimental bounds on dissipative
models of wavefunction collapse including continuous spontaneous localisation
and Di\'{o}si-Penrose and illustrates its utility for future precision
experiments that aim to test the macroscopic limits of quantum mechanics
Age-related delay in information accrual for faces: Evidence from a parametric, single-trial EEG approach
Background: In this study, we quantified age-related changes in the time-course of face processing
by means of an innovative single-trial ERP approach. Unlike analyses used in previous studies, our
approach does not rely on peak measurements and can provide a more sensitive measure of
processing delays. Young and old adults (mean ages 22 and 70 years) performed a non-speeded
discrimination task between two faces. The phase spectrum of these faces was manipulated
parametrically to create pictures that ranged between pure noise (0% phase information) and the
undistorted signal (100% phase information), with five intermediate steps.
Results: Behavioural 75% correct thresholds were on average lower, and maximum accuracy was
higher, in younger than older observers. ERPs from each subject were entered into a single-trial
general linear regression model to identify variations in neural activity statistically associated with
changes in image structure. The earliest age-related ERP differences occurred in the time window
of the N170. Older observers had a significantly stronger N170 in response to noise, but this age
difference decreased with increasing phase information. Overall, manipulating image phase
information had a greater effect on ERPs from younger observers, which was quantified using a
hierarchical modelling approach. Importantly, visual activity was modulated by the same stimulus
parameters in younger and older subjects. The fit of the model, indexed by R2, was computed at
multiple post-stimulus time points. The time-course of the R2 function showed a significantly slower
processing in older observers starting around 120 ms after stimulus onset. This age-related delay
increased over time to reach a maximum around 190 ms, at which latency younger observers had
around 50 ms time lead over older observers.
Conclusion: Using a component-free ERP analysis that provides a precise timing of the visual
system sensitivity to image structure, the current study demonstrates that older observers
accumulate face information more slowly than younger subjects. Additionally, the N170 appears to
be less face-sensitive in older observers
Weight Consistency Specifies Regularities of Macaque Cortical Networks
To what extent cortical pathways show significant weight differences and whether these differences are consistent across animals (thereby comprising robust connectivity profiles) is an important and unresolved neuroanatomical issue. Here we report a quantitative retrograde tracer analysis in the cynomolgus macaque monkey of the weight consistency of the afferents of cortical areas across brains via calculation of a weight index (fraction of labeled neurons, FLN). Injection in 8 cortical areas (3 occipital plus 5 in the other lobes) revealed a consistent pattern: small subcortical input (1.3% cumulative FLN), high local intrinsic connectivity (80% FLN), high-input form neighboring areas (15% cumulative FLN), and weak long-range corticocortical connectivity (3% cumulative FLN). Corticocortical FLN values of projections to areas V1, V2, and V4 showed heavy-tailed, lognormal distributions spanning 5 orders of magnitude that were consistent, demonstrating significant connectivity profiles. These results indicate that 1) connection weight heterogeneity plays an important role in determining cortical network specificity, 2) high investment in local projections highlights the importance of local processing, and 3) transmission of information across multiple hierarchy levels mainly involves pathways having low FLN values
Abnormal Brain Activation in Neurofibromatosis Type 1: A Link between Visual Processing and the Default Mode Network
Neurofibromatosis type 1 (NF1) is one of the most common single gene disorders affecting the human nervous system with a high incidence of cognitive deficits, particularly visuospatial. Nevertheless, neurophysiological alterations in low-level visual processing that could be relevant to explain the cognitive phenotype are poorly understood. Here we used functional magnetic resonance imaging (fMRI) to study early cortical visual pathways in children and adults with NF1. We employed two distinct stimulus types differing in contrast and spatial and temporal frequencies to evoke relatively different activation of the magnocellular (M) and parvocellular (P) pathways. Hemodynamic responses were investigated in retinotopically-defined regions V1, V2 and V3 and then over the acquired cortical volume. Relative to matched control subjects, patients with NF1 showed deficient activation of the low-level visual cortex to both stimulus types. Importantly, this finding was observed for children and adults with NF1, indicating that low-level visual processing deficits do not ameliorate with age. Moreover, only during M-biased stimulation patients with NF1 failed to deactivate or even activated anterior and posterior midline regions of the default mode network. The observation that the magnocellular visual pathway is impaired in NF1 in early visual processing and is specifically associated with a deficient deactivation of the default mode network may provide a neural explanation for high-order cognitive deficits present in NF1, particularly visuospatial and attentional. A link between magnocellular and default mode network processing may generalize to neuropsychiatric disorders where such deficits have been separately identified
Ultra-Rapid Categorization of Fourier-Spectrum Equalized Natural Images: Macaques and Humans Perform Similarly
BACKGROUND: Comparative studies of cognitive processes find similarities between humans and apes but also monkeys. Even high-level processes, like the ability to categorize classes of object from any natural scene under ultra-rapid time constraints, seem to be present in rhesus macaque monkeys (despite a smaller brain and the lack of language and a cultural background). An interesting and still open question concerns the degree to which the same images are treated with the same efficacy by humans and monkeys when a low level cue, the spatial frequency content, is controlled. METHODOLOGY/PRINCIPAL FINDINGS: We used a set of natural images equalized in Fourier spectrum and asked whether it is still possible to categorize them as containing an animal and at what speed. One rhesus macaque monkey performed a forced-choice saccadic task with a good accuracy (67.5% and 76% for new and familiar images respectively) although performance was lower than with non-equalized images. Importantly, the minimum reaction time was still very fast (100 ms). We compared the performances of human subjects with the same setup and the same set of (new) images. Overall mean performance of humans was also lower than with original images (64% correct) but the minimum reaction time was still short (140 ms). CONCLUSION: Performances on individual images (% correct but not reaction times) for both humans and the monkey were significantly correlated suggesting that both species use similar features to perform the task. A similar advantage for full-face images was seen for both species. The results also suggest that local low spatial frequency information could be important, a finding that fits the theory that fast categorization relies on a rapid feedforward magnocellular signal
Dos and don’ts in response priming research
Response priming is a well-understood but sparsely employed paradigm in cognitive
science. The method is powerful and well-suited for exploring early visuomotor
processing in a wide range of tasks and research fields. Moreover, response
priming can be dissociated from visual awareness, possibly because it is based
on the first sweep of feedforward processing of primes and targets. This makes
it a theoretically interesting device for separating conscious and unconscious
vision. We discuss the major opportunities of the paradigm and give specific
recommendations (e.g., tracing the time-course of priming in parametric
experiments). Also, we point out typical confounds, design flaws, and data
processing artifacts
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