International School for Advanced Studies

About: International School for Advanced Studies is a education organization based out in Trieste, Friuli-Venezia Giulia, Italy. It is known for research contribution in the topics: Galaxy & Dark matter. The organization has 3751 authors who have published 13433 publications receiving 588454 citations. The organization is also known as: SISSA & Scuola Internazionale Superiore di Studi Avanzati.

Transient storage of a tactile memory trace in primary somatosensory cortex.

Abstract: Working memory is known to involve prefrontal cortex and posterior regions of association cortex (eg, the inferior temporal lobes) Here, we investigate the potential role of primary somatosensory cortex (SI) in a working memory task with tactile stimuli Subjects were required to compare the frequencies of two vibrations separated by a retention interval of 1500 msec Their performance was significantly disrupted when we delivered a pulse of transcranial magnetic stimulation (TMS) to the contralateral SI early (300 or 600 msec) in the retention interval TMS did not affect tactile working memory if delivered to contralateral SI late in the retention interval (at 900 or 1200 msec), nor did TMS affect performance if delivered to the ipsilateral SI at any time point Primary sensory cortex thus seems to act not only as a center for on-line sensory processing but also as a transient storage site for information that contributes to working memory

Cosmic evolution of quasar clustering: implications for the host haloes

Abstract: We present detailed clustering measurements from the 2dF Quasi-Stellar Object Redshift Survey (2QZ) in the redshift range 0.8 < z < 2.1. Using a flux-limited sample of ∼14 000 objects with effective redshift z eff = 1.47, we estimate the quasar projected correlation function for separations 1 < r/ h −1 Mpc < 20. We find that the two-point correlation function in real space is well approximated by a power law with slope γ = 1.5 ± 0.2 and comoving correlation length r 0 = 4.8 +0.9 h −1 Mpc. Splitting the sample into three subsets based on redshift, we find evidence for an increase of the clustering amplitude with look-back time. For a fixed γ ,e v olution of r0 is detected at the 3.6σ confidence level. The ratio between the quasar correlation function and the mass autocorrelation function (derived adopting the concordance cosmological model) is found to be scale-independent. For a linear mass-clustering amplitude σ 8 = 0.8, the ‘bias parameter’ decreases from b � 3.9 at z eff = 1.89 to b � 1.8 at z eff = 1.06. From the observed abundance and clustering, we infer how quasars populate dark matter

The representational capacity of the distributed encoding of information provided by populations of neurons in primate temporal visual cortex

Abstract: It has been shown that it is possible to read, from the firing rates of just a small population of neurons, the code that is used in the macaque temporal lobe visual cortex to distinguish between different faces being looked at. To analyse the information provided by populations of single neurons in the primate temporal cortical visual areas, the responses of a population of 14 neurons to 20 visual stimuli were analysed in a macaque performing a visual fixation task. The population of neurons analysed responded primarily to faces, and the stimuli utilised were all human and monkey faces. Each neuron had its own response profile to the different members of the stimulus set. The mean response of each neuron to each stimulus in the set was calculated from a fraction of the ten trials of data available for every stimulus. From the remaining data, it was possible to calculate, for any population response vector, the relative likelihoods that it had been elicited by each of the stimuli in the set. By comparison with the stimuli actually shown, the mean percentage correct identification was computed and also the mean information about the stimuli, in bits, that the population of neurons carried on a single trial. When the decoding algorithm used for this calculation approximated an optimal, Bayesian estimate of the relative likelihoods, the percentage correct increased from 14 correct (chance was 5 correct) with one neuron to 67 with 14 neurons. The information conveyed by the population of neurons increased approximately linearly from 0.33 bits with one neuron to 2.77 bits with 14 neurons. This leads to the important conclusion that the number of stimuli that can be encoded by a population of neurons in this part of the visual system increases approximately exponentially as the number of cells in the sample increases (in that the log of the number of stimuli increases almost linearly). This is in contrast to a local encoding scheme (of 'grandmother' cells), in which the number of stimuli encoded increases linearly with the number of cells in the sample. Thus one of the potentially important properties of distributed representations, an exponential increase in the number of stimuli that can be represented, has been demonstrated in the brain with this population of neurons. When the algorithm used for estimating stimulus likelihood was as simple as could be easily implemented by neurons receiving the population's output (based on just the dot product between the population response vector and each mean response vector), it was still found that the 14-neuron population produced 66 correct guesses and conveyed 2.30 bits of information, or 83 of the information that could be extracted with the nearly optimal procedure. It was also shown that, although there was some redundancy in the representation (with each neuron contributing to the information carried by the whole population 60 of the information it carried alone, rather than 100), this is due to the fact that the number of stimuli in the set was limited (it was 20). The data are consistent with minimal redundancy for sufficiently large and diverse sets of stimuli. The implication for brain connectivity of the distributed encoding scheme, which was demonstrated here in the case of faces, is that a neuron can receive a great deal of information about what is encoded by a large population of neurons if it is able to receive its inputs from a random subset of these neurons, even of limited numbers (e.g. hundreds).

Galaxy properties from the ultraviolet to the far‐infrared: Λ cold dark matter models confront observations

Abstract: We combine a semi-analytic model of galaxy formation with simple analytic recipes describing the absorption and re-emission of starlight by dust in the interstellar medium of galaxies. We use the resulting models to predict galaxy counts and luminosity functions from the far-ultraviolet (FUV) to the submillimetre, from redshift five to the present, and compare with an extensive compilation of observations. We find that in order to reproduce the rest-UV and optical luminosity functions at high redshift, we must assume an evolving normalization in the dust-to-metal ratio, implying that galaxies of a given bolometric luminosity (or metal column density) must be less extinguished than their local counterparts. In our best-fitting model, we find remarkably good agreement with observations from rest ∼1500 A to m. At longer wavelengths, most dramatically in the submillimetre, our models underpredict the number of bright galaxies by a large factor. The models reproduce the observed total IR luminosity function fairly well. We show the results of varying several ingredients of the models, including various aspects of the dust attenuation recipe, the dust emission templates and the cosmology. We use our models to predict the integrated extragalactic background light, and compare with an observationally motivated extragalactic background light EBL model and with other available observational constraints.