Rafael Doti

Multisensory Integration Central Processing Modifies Peripheral Systems

Multisensory integration in humans is thought to be essentially a brain phenomenon, but theories are silent as to the possible involvement of the peripheral nervous system. We provide evidence that this approach is insufficient. We report novel tactile-auditory and tactilevisual interactions in humans, demonstrating that a facilitating sound or visual stimulus that is exactly synchronous with an excitatory tactile signal presented at the lower leg increases the peripheral representation of that excitatory signal. These results demonstrate that during multisensory integration, the brain not only continuously binds information obtained from the senses, but also acts directly on that information by modulating activity at peripheral levels. We also discuss a theoretical framework to explain this novel interaction.

Negative refraction angular characterization in one-dimensional photonic crystals.

Background Photonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs. Methodology/Principal Findings By using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snells law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone. Conclusions/Significance Since both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.

The bifoil photodyne: a photonic crystal oscillator

Optical tweezers is an example how to use light to generate a physical force. They have been used to levitate viruses, bacteria, cells, and sub cellular organisms. Nonetheless it would be beneficial to use such force to develop a new kind of applications. However the radiation pressure usually is small to think in moving larger objects. Currently, there is some research investigating novel photonic working principles to generate a higher force. Here, we studied theoretically and experimentally the induction of electromagnetic forces in one-dimensional photonic crystals when light impinges on the off-axis direction. The photonic structure consists of a micro-cavity like structure formed of two one-dimensional photonic crystals made of free-standing porous silicon, separated by a variable air gap and the working wavelength is 633 nm. We show experimental evidence of this force when the photonic structure is capable of making auto-oscillations and forced-oscillations. We measured peak displacements and velocities ranging from 2 up to 35 microns and 0.4 up to 2.1 mm/s with a power of 13 mW. Recent evidence showed that giant resonant light forces could induce average velocity values of 0.45 mm/s in microspheres embedded in water with 43 mW light power.

Effective Tactile Noise Facilitates Visual Perception

The fulcrum principle establishes that a subthreshold excitatory signal (entering in one sense) that is synchronous with a facilitation signal (entering in a different sense) can be increased (up to a resonant-like level) and then decreased by the energy and frequency content of the facilitating signal. As a result, the sensation of the signal changes according to the excitatory signal strength. In this context, the sensitivity transitions represent the change from subthreshold activity to a firing activity in multisensory neurons. Initially the energy of their activity (supplied by the weak signals) is not enough to be detected but when the facilitating signal enters the brain, it generates a general activation among multisensory neurons, modifying their original activity. In our opinion, the result is an integrated activation that promotes sensitivity transitions and the signals are then perceived. In other words, the activity created by the interaction of the excitatory signal (e.g., visual) and the facilitating signal (tactile noise) at some specific energy, produces the capability for a central detection of an otherwise weak signal. In this work we investigate the effect of an effective tactile noise on visual perception. Specifically we show that tactile noise is capable of decreasing luminance modulated thresholds.

Inducing forced and auto-oscillations in one-dimensional photonic crystals with light

Abstract. We induced forced and auto-oscillations in one-dimensional photonic crystals (1-D-PCs) with localized defects when light impinges transversally to the defect layer. The photonic structure used consists of a microcavity-like structure formed of two 1-D-PCs made of free-standing porous silicon, separated by a variable air gap (the defect) and the working wavelength is 633 nm. The force generation was made evident by driving a laser light by means of a chopper; the light hit the photonic structure and induced a vibration and the vibration was characterized by using a very sensitive vibrometer. For example, we measured peak displacements and velocities ranging from 2 to 167  μm and 0.4 to 2.1  mm/s with a power light level from 2.6 to 13 mW. In comparison, recent evidence showed that giant resonant light forces could induce average velocity values of 0.45  mm/s in microspheres embedded in water with a 43-mW light power.

Theoretical and experimental study of electromagnetic forces induced in one-dimensional photonic crystals

We studied theoretically and experimentally the induction of electromagnetic forces in one-dimensional photonic crystals with localized defects when light impinges transversally to the defect layer. The theoretical calculations indicate that the electromagnetic forces increases at a certain frequency that coincide with a defect photonic state. The photonic structure consists of a microcavity like structure formed of two one-dimensional photonic crystals made of free-standing porous silicon, separated by variable air gap and the working wavelength is 633 nm. The force generation is made evident by driving a laser light by means of a chopper; the light hits the photonic structure and induces a vibration and the vibration is characterized by using a very sensitive vibrometer.

A photonic self-oscillator based on porous silicon

Abstract We induced mechanical self-oscillations in a microcavity structure made of porous silicon onedimensional photonic crystals (PSi-1DPC) with an air gap. The electromagnetic force generated within the whole photonic structure, by light with a wavelength of 633 nm, is enough to overcome energy losses and sustain selfoscillations. From these mechano-optical measurements we estimated the stiffness and Young’s modulus of porous silicon and compared the results with values reported elsewhere and with values estimated herein by a mechanical method.We obtained good agreement between all values.

Inducing forced and auto oscillations in one-dimensional photonic crystals with light

We induced forced and auto oscillations in one-dimensional photonic crystals with localized defects when light impinges transversally to the defect layer. The photonic structure consists of a microcavity like structure formed of two onedimensional photonic crystals made of free-standing porous silicon, separated by variable air gap and the working wavelength is 633 nm. The force generation is made evident by driving a laser light by means of a chopper; the light hits the photonic structure and induces a vibration and the vibration is characterized by using a very sensitive vibrometer. Moreover we measured peak displacements and velocities ranging from 2 up to 35 microns and 0.4 up to 2.1 mm/s with a power of 13 mW. Recent evidence showed that giant resonant light forces could induce average velocity values of 0.45 mm/s in microspheres embedded in water with 43 mW light power.

The Fulcrum Principle Between Parasympathetic and Sympathetic Peripheral Systems: Auditory Noise Can Modulate Body’s Peripheral Temperature

The Fulcrum principle represents a mechanism that improves our capability to extract information from the external world. It describes the interaction between at least two physiological signals, namely excitatory and facilitation. The excitatory signal can be present in any sensory system, motor, or reflex mechanism and normally is too weak to be detected by the central nervous system and/or to enact a change on the physiological, behavioral, cognitive, etc., state of a human subject. Simultaneously, the facilitation signal can be present in any sensory system, motor or reflex mechanism and it is its energy and frequency content that may create a general activation between the central nervous system and peripheral nervous systems. Consequently, the excitatory signal can be detected and/or the physiological, behavioral, cognitive, etc., state of a human subject can be changed. Herein, we present an example of such principle where auditory noise can induce transitions between sympathetic and parasympathetic nervous systems, which are part of the autonomic nervous system.

Evaluation of a Thermal Image for Pedestrian Modeling Using the Least-Action Principle

Living labs provide the possibility of doing real-time research in an ecological context corresponding to normal daily activities. In particular, it is important to know how humans respond to environmental changes and different scenarios. The appropriate characterization of individual human displacement dynamics within a crowd remains illusive and for this reason there is a great interest in exploring behaviors with general physical models. In this work, we present a theoretical and experimental study of the natural movement of pedestrians when passing through a limited and known area of a shopping center. The modeling problem for the motion of a single pedestrian is complex and extensive; therefore, we focus on the need to design models taking into account mechanistic aspects of human locomotion. The theoretical study used mean values of pedestrian characteristics, e.g., density, velocity, and number of obstacles. We propose a human pedestrian trajectory model by using the least-action principle, and we compared it with experimental results. The experimental study is conducted in a Living Lab inside a shopping center using infrared cameras. For this experiment, we collected highly accurate trajectories allowing us to quantify pedestrian crowd dynamics. The experiments included 20 runs distributed over 5 days with up to 25 test persons.