Word contexts enhance the neural representation of individual letters in early visual cortex

Visual context facilitates perception, but how this is neurally implemented remains unclear. One example of contextual facilitation is found in reading, where letters are more easily identified when embedded in a word. Bottom-up models explain this word advantage as a post-perceptual decision bias, while top-down models propose that word contexts enhance perception itself. Here, we arbitrate between these accounts by presenting words and nonwords and probing the representational fidelity of individual letters using functional magnetic resonance imaging. In line with top-down models, we find that word contexts enhance letter representations in early visual cortex. Moreover, we observe increased coupling between letter information in visual cortex and brain activity in key areas of the reading network, suggesting these areas may be the source of the enhancement. Our results provide evidence for top-down representational enhancement in word recognition, demonstrating that word contexts can modulate perceptual processing already at the earliest visual regions

A hierarchy of linguistic predictions during natural language comprehension

Understanding spoken language requires transforming ambiguous acoustic streams into a hierarchy of representations, from phonemes to meaning. It has been suggested that the brain uses prediction to guide the interpretation of incoming input. However, the role of prediction in language processing remains disputed, with disagreement about both the ubiquity and representational nature of predictions. Here, we address both issues by analyzing brain recordings of participants listening to audiobooks, and using a deep neural network (GPT-2) to precisely quantify contextual predictions. First, we establish that brain responses to words are modulated by ubiquitous predictions. Next, we disentangle model-based predictions into distinct dimensions, revealing dissociable neural signatures of predictions about syntactic category (parts of speech), phonemes, and semantics. Finally, we show that high-level (word) predictions inform low-level (phoneme) predictions, supporting hierarchical predictive processing. Together, these results underscore the ubiquity of prediction in language processing, showing that the brain spontaneously predicts upcoming language at multiple levels of abstraction

Using benthic foraminifera to reconstruct the benthic environment during sapropel formation

Date du colloque : 03/2008International audienc

The suppression of repetition enhancement: A review

Repetition suppression is generally accepted as the neural correlate of behavioural priming and is often used to selectively identify the neuronal representations associated with a stimulus. However, this does not explain the large number of repetition enhancement effects observed under very similar conditions. Based on a review of a large set of studies we propose several variables biasing repetition effects towards enhancement instead of suppression. On the one hand, there are stimulus variables which influence the direction of repetition effects: visibility, e. g. in the case of degraded stimuli perceptual learning occurs; novelty, e. g. in case of unfamiliar stimuli a novel network formation process occurs; and timing intervals, e. g. repetition effects are sensitive to stimulus onset asynchronies. On the other hand, repetition effects are not solely automatic processes, triggered by particular types or sequences of stimuli. The brain is continuously and actively filtering, attending to and interpreting the information provided by our senses. Consequently, internal state variables like attention, expectation and explicit memory modulate repetition effects towards enhancement versus suppression. Current models i.e. the accumulation, fatigue and sharpening models of repetition suppression have so far left out top-down factors and cannot or can only partially account for repetition enhancement effects. Instead we propose that models which incorporate both stimulus bottom-up and cognitive top-down factors are called for in order to better understand repetition effects. A good candidate is the predictive coding model in which sensory evidence is interpreted according to subjective biases and statistical accounts of past encounters

Mapping the CMB Sky: The BOOMERANG experiment

We describe the BOOMERanG experiment, a stratospheric balloon telescope intended to measure the Cosmic Microwave Background anisotropy at angular scales between a few degrees and ten arcminutes. The experiment has been optimized for a long duration (7 to 14 days) flight circumnavigating Antarctica at the end of 1998. A test flight was performed on Aug.30, 1997 in Texas. The level of performance achieved in the test flight was satisfactory and compatible with the requirements for the long duration flight.Comment: 11 pages, 6 figure

Manipulating word awareness dissociates feed-forward from feedback models of language-perception interactions

Previous studies suggest that linguistic material can modulate visual perception, but it is unclear at which level of processing these interactions occur. Here we aim to dissociate between two competing models of language–perception interactions: a feed-forward and a feedback model. We capitalized on the fact that the models make different predictions on the role of feedback. We presented unmasked (aware) or masked (unaware) words implying motion (e.g. “rise,” “fall”), directly preceding an upward or downward visual motion stimulus. Crucially, masking leaves intact feed-forward information processing from low- to high-level regions, whereas it abolishes subsequent feedback. Under this condition, participants remained faster and more accurate when the direction implied by the motion word was congruent with the direction of the visual motion stimulus. This suggests that language–perception interactions are driven by the feed-forward convergence of linguistic and perceptual information at higher-level conceptual and decision stages

The BOOMERANG North America Instrument: a balloon-borne bolometric radiometer optimized for measurements of cosmic background radiation anisotropies from 0.3 to 4 degrees

We describe the BOOMERANG North America (BNA) instrument, a balloon-borne bolometric radiometer designed to map the Cosmic Microwave Background (CMB) radiation with 0.3 deg resolution over a significant portion of the sky. This receiver employs new technologies in bolometers, readout electronics, millimeter-wave optics and filters, cryogenics, scan and attitude reconstruction. All these subsystems are described in detail in this paper. The system has been fully calibrated in flight using a variety of techniques which are described and compared. It has been able to obtain a measurement of the first peak in the CMB angular power spectrum in a single balloon flight, few hours long, and was a prototype of the BOOMERANG Long Duration Balloon (BLDB) experiment.Comment: 40 pages, 22 figures, submitted to Ap

Both 3,3′,5-triiodothyronine and 3,5-diodo-L-thyronine are able to repair mitochondrial DNA damage but by different mechanisms

This study evaluated the effect of 3,5-diiodo-L-thyronine (T2) and 3,5,3′-triiodo-L-thyronine (T3) on rat liver mitochondrial DNA (mtDNA) oxidative damage and repair and to investigate their ability to induce protective effects against oxidative stress. Control rats, rats receiving a daily injection of T2 (N+T2) for 1 week and rats receiving a daily injection of T3 (N+T3) for 1 week, were used throughout the study. In the liver, mtDNA oxidative damage [by measuring mtDNA lesion frequency and expression of DNA polymerase γ (POLG)], mtDNA copy number, mitochondrial biogenesis [by measuring amplification of mtDNA/nDNA and expression of peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α)], and oxidative stress [by measuring serum levels of 8-hydroxy-2′-deoxyguanosine (8-OHdG)] were detected. T2 reduces mtDNA lesion frequency and increases the expression of POLG, and it does not change the mtDNA copy number, the expression of PGC-1α, or the serum levels of 8-OHdG. Therefore, T2, by stimulating the major mtDNA repair enzyme, maintains genomic integrity. Similar to T2, T3 decreases mtDNA lesion frequency but increases the serum levels of 8-OHdG, and it decreases the expression of POLG. Moreover, as expected, T3 increases the mtDNA copy number and the expression of PGC-1α. Thus, in T3-treated rats, the increase of 8-OHdG and the decrease of POLG indicate that there is increased oxidative damage and that the decreased mtDNA lesion frequency might be a consequence of increased mitochondrial biogenesis. These data demonstrate that both T2 and T3 are able to decrease in the liver mtDNA oxidative damage, but they act via different mechanisms

Towards T1-limited magnetic resonance imaging using Rabi beats

Two proof-of-principle experiments towards T1-limited magnetic resonance imaging with NV centers in diamond are demonstrated. First, a large number of Rabi oscillations is measured and it is demonstrated that the hyperfine interaction due to the NV's 14N can be extracted from the beating oscillations. Second, the Rabi beats under V-type microwave excitation of the three hyperfine manifolds is studied experimentally and described theoretically.Comment: 6 pages, 8 figure

The High Frequency Instrument of Planck: Requirements and Design

The Planck satellite is a project of the European Space Agency based on a wide international collaboration, including United States and Canadian laboratories. It is dedicated to the measurement of the anisotropy of the Cosmic Microwave Background (CMB) with unprecedented sensitivity and angular resolution. The detectors of its High frequency Instrument (HFI) are bolometers cooled down to 100 mK. Their sensitivity will be limited by the photon noise of the CMB itself at low frequencies, and of the instrument background at high frequencies. The requirements on the measurement chain are directly related to the strategy of observation used for the satellite. Due to the scanning on the sky, time features of the measurement chain are directly transformed into angular features in the sky maps. This impacts the bolometer design as well as other elements: For example, the cooling system must present outstanding temperature stability, and the amplification chain must show, down to very low frequencies, a flat noise spectrum