Perception of the intensity and duration of a stimulus within a unified framework: psychophysics and underlying neuronal processing

Every sensory experience is embedded in time, and is accompanied by the perception of the passage of time. The fact that perception of the content of a sensory event and the perception of the time occupied by that event are generated in parallel raises a number of questions: Do these percepts interact with each other? Do they emerge within separate neural populations? Which neuronal mechanism underlies this divergence? In the work of my thesis I explored how the perception of the intensity of a vibrotactile stimulus, interacts with the perception of its duration, in both humans and rats. I have carried out three main studies. Chapter I works out the details of the interaction between vibration amplitude and duration, revealing a symmetric confound: perceived duration depends on stimulus speed, and perceived intensity depends on stimulus duration. Quantification of this interaction allowed us formulate a testable computational model for the generation of both percepts, which posits that a single sensory drive provides input to two distinct downstream centers, which generate the two percepts in parallel. Chapter II addresses the effect of stimulus history. Systems neuroscience has given considerable attention in recent years to the effects of preceding stimuli on the perception of the current stimulus. We now ask whether the interaction found in Study I extends to an interaction in the memory trace of recent stimuli: are the perceptual priors mixed or separate? Through psychophysical testing, we were able to show that perception of the duration and the intensity of stimuli, are biased toward the perceived features of previously presented stimuli, and not their low-level physical properties, and that separate representations of prior perceived duration and prior perceived intensity exist in the brain. Chapter III begins to look for neuronal correlates of perceived duration, through extracellular recordings in behaving rats in Dorso-Lateral Striatum (DLS), a region which receives direct input from primary somatosensory cortex and has previously shown to be involved in time perception. The delayed comparison task, differently from many common behavioral paradigms, has the advantage of dissociating the first stimulus presented to the animal from any decisional and motor processes. This makes it particularly relevant for the search for the neural basis of stimulus duration perception. Moreover, the bias of stimulus intensity on perceived time found on Study I, posits the principle that the interaction between these two features should be present in the neural population that encodes the perception of stimulus duration in a behaviourally-relevant way. Ongoing recordings are showing that the unfolding of trial time can be decoded from the striatal neural activity, but the confound of stimulus speed is not encoded by the population. This findings points toward a role of striatum in representing temporal sequences of events, while questioning its involvement in encoding the perception of stimulus duration

The dynamics of PdO-Pd phase transformation in the presence of water over Si-doped Pd/CeO 2 methane oxidation catalysts

One of the main issues for the catalytic abatement of methane from natural gas fueled vehicles over Pd-based materials is due to the large amount of water vapor in the exhausts, which can severely deactivate the catalyst. In this work, we investigated the effect of water added during methane oxidation on a series of silica doped Pd/ceria catalysts prepared by solution combustion synthesis, using different characterization techniques. The results obtained by coupling Temperature Programmed Oxidation (TPO) experiments and High Resolution Transmission Electron Microscopy (HRTEM) indicate that the mechanism of PdO-Pd-PdO phase transformation over Si-doped catalysts is different in dry and wet conditions. The presence of water not only shifts the onset of PdO decomposition to higher temperature, but also PdO-Pd transition is found to proceed via the formation of multi-domain PdO/Pd particles. This effect is tentatively attributed to the suppression of oxygen exchange induced by the presence of stable hydroxyl groups on silica.Postprint (author's final draft

A sensory integration account for time perception

The connection between stimulus perception and time perception remains unknown. The present study combines human and rat psychophysics with sensory cortical neuronal firing to construct a computational model for the percept of elapsed time embedded within sense of touch. When subjects judged the duration of a vibration applied to the fingertip (human) or whiskers (rat), increasing stimulus intensity led to increasing perceived duration. Symmetrically, increasing vibration duration led to increasing perceived intensity. We modeled spike trains from vibrissal somatosensory cortex as input to dual leaky integrators \u2013 an intensity integrator with short time constant and a duration integrator with long time constant \u2013 generating neurometric functions that replicated the actual psychophysical functions of rats. Returning to human psychophysics, we then confirmed specific predictions of the dual leaky integrator model. This study offers a framework, based on sensory coding and subsequent accumulation of sensory drive, to account for how a feeling of the passage of time accompanies the tactile sensory experience

Real-Time and Real-Fast Performance of General-Purpose and Real-Time Operating Systems in Multithreaded Physical Simulation of Complex Mechanical Systems

Physical simulation is a valuable tool in many fields of engineering for the tasks of design, prototyping, and testing. General-purpose operating systems (GPOS) are designed for real-fast tasks, such as offline simulation of complex physical models that should finish as soon as possible. Interfacing hardware at a given rate (as in a hardware-in-the-loop test) requires instead maximizing time determinism, for which real-time operating systems (RTOS) are designed. In this paper, real-fast and real-time performance of RTOS and GPOS are compared when simulating models of high complexity with large time steps. This type of applications is usually present in the automotive industry and requires a good trade-off between real-fast and real-time performance. The performance of an RTOS and a GPOS is compared by running a tire model scalable on the number of degrees-of-freedom and parallel threads. The benchmark shows that the GPOS present better performance in real-fast runs but worse in real-time due to nonexplicit task switches and to the latency associated with interprocess communication (IPC) and task switch

SIOUX project: a simultaneous multiband camera for exoplanet atmospheres studies

The exoplanet revolution is well underway. The last decade has seen order-of-magnitude increases in the number of known planets beyond the Solar system. Detailed characterization of exoplanetary atmospheres provide the best means for distinguishing the makeup of their outer layers, and the only hope for understanding the interplay between initial composition chemistry, temperature-pressure atmospheric profiles, dynamics and circulation. While pioneering work on the observational side has produced the first important detections of atmospheric molecules for the class of transiting exoplanets, important limitations are still present due to the lack of sys- tematic, repeated measurements with optimized instrumentation at both visible (VIS) and near-infrared (NIR) wavelengths. It is thus of fundamental importance to explore quantitatively possible avenues for improvements. In this paper we report initial results of a feasibility study for the prototype of a versatile multi-band imaging system for very high-precision differential photometry that exploits the choice of specifically selected narrow-band filters and novel ideas for the execution of simultaneous VIS and NIR measurements. Starting from the fundamental system requirements driven by the science case at hand, we describe a set of three opto-mechanical solutions for the instrument prototype: 1) a radial distribution of the optical flux using dichroic filters for the wavelength separation and narrow-band filters or liquid crystal filters for the observations; 2) a tree distribution of the optical flux (implying 2 separate foci), with the same technique used for the beam separation and filtering; 3) an exotic solution consisting of the study of a complete optical system (i.e. a brand new telescope) that exploits the chromatic errors of a reflecting surface for directing the different wavelengths at different foci

Grid Cells Lose Coherence in Realistic Environments

Spatial cognition in naturalistic environments, for freely moving animals, may pose quite different constraints from that studied in artificial laboratory settings. Hippocampal place cells indeed look quite different, but almost nothing is known about entorhinal cortex grid cells, in the wild. Simulating our self-organizing adaptation model of grid cell pattern formation, we consider a virtual rat randomly exploring a virtual burrow, with feedforward connectivity from place to grid units and recurrent connectivity between grid units. The virtual burrow was based on those observed by John B. Calhoun, including several chambers and tunnels. Our results indicate that lateral connectivity between grid units may enhance their “gridness” within a limited strength range, but the overall effect of the irregular geometry is to disable long-range and obstruct short-range order. What appears as a smooth continuous attractor in a flat box, kept rigid by recurrent connections, turns into an incoherent motley of unit clusters, flexible or outright unstable

Vehicle and mission design of a future small payload launcher

This paper presents the conceptual design and performance analysis of a partially reusable space launch vehicle for small payloads. The system uses a multi-stage vehicle with rocket engines, with a reusable first stage capable of glided or powered flight, and expendable upper stage(s) to inject a 500 kg payload in different low Earth orbits. The space access vehicle is designed to be air-launched from a modified aircraft carrier. The aim of the system design is to develop a commercially viable launch system for near-term operation, thus emphasis is placed on the efficient use of high TRL technologies. The vehicle design are analysed using a multi-disciplinary design optimisation approach to evaluate the performance, operational capabilities and design trade-offs

A commercially driven design approach to UK future small payload launch systems

Miniaturisation of satellite componentry, increasingly capable small sensors and substantial increases in processing capacity and transmission bandwidth are driving rapid growth in small payload development and consequential launch demand. The advent of horizontal take-off spaceports opens the door for a new generation of small payload launch systems that will fulfil this demand. However, the key to a launch system's success is its ability to provide a return on the substantial costs of development while delivering pricing levels commensurate with the needs of launch customers. Therefore, commercially led design approaches are needed to refine and optimise the design of the new small payload launch systems required. This approach was embodied in an ongoing UKSA funded NSTP2 project titled Future UK Small Payload Launcher (FSPLUK). The approach is first founded upon a bespoke and specific market assessment. This characterises, segments and quantifies the commercial opportunity and establishes principal desired system performance requirements. An assessment of available technologies at differing TRLs permits initial vehicle configuration options to be developed and technically assessed. Technically viable options are then assessed in terms of commercial viability with the best advanced into more detailed technical assessment and system optimisation. The resultant vehicles are again tested for commercial viability and, if successful, emerge as recommended development avenues. Using these methods, it has been possible to iterate design concepts from apparently simple yet economically sub-optimised stacked launcher systems through several design iterations to a resultant highly flexible and economically efficient conceptual design. The key finding relates to the inter-relationship between payload flexibility, in permitting maximised flight rates from a reasonably complex but highly reusable first stage design, and low disposable upper stage unit cost. This has driven the resultant system to feature an air launched integrated re-usable first stage vehicle, configured with a flexible internal payload bay from which one or more upper stages are deployed. This configuration maximises commercial utility and reusability. The resultant high flight rate allows development costs to be efficiently amortised with minimised direct launch costs. The configuration therefore meets low cost per kg price targets while delivering a positive return on development expenditure over life. It also provides a flight proven vehicle platform with available internal real-estate for application as a hypersonic air test platform for new propulsion systems, such as SABRE. The commercially led approach has created the foundation for viable and economically justifiable development