Intramodal Processing Research Articles

Fully integrated and broadband Si-rich silicon nitride wavelength converter based on Bragg scattering intermodal four-wave mixing

Intermodal four-wave mixing (FWM) processes have recently attracted significant interest for all-optical signal processing applications thanks to the possibility to control the propagation properties of waves exciting distinct spatial modes of the same waveguide. This allows, in principle, to place signals in different spectral regions and satisfy the phase matching condition over considerably larger bandwidths compared to intramodal processes. However, the demonstrations reported so far have shown a limited bandwidth and suffered from the lack of on-chip components designed for broadband manipulation of different modes. We demonstrate here a silicon-rich silicon nitride wavelength converter based on Bragg scattering intermodal FWM, which integrates mode conversion, multiplexing and de-multiplexing functionalities on-chip. The system enables wavelength conversion between pump waves and a signal located in different telecommunication bands (separated by 60 nm) with a 3 dB bandwidth exceeding 70 nm, which represents, to our knowledge, the widest bandwidth ever achieved in an intermodal FWM-based system.

Synchronisation of Neural Oscillations and Cross-modal Influences.

At any given moment, we receive multiple signals from our different senses. Prior research has shown that signals in one sensory modality can influence neural activity and behavioural performance associated with another sensory modality. Recent human and nonhuman primate studies suggest that such cross-modal influences in sensory cortices are mediated by the synchronisation of ongoing neural oscillations. In this review, we consider two mechanisms proposed to facilitate cross-modal influences on sensory processing, namely cross-modal phase resetting and neural entrainment. We consider how top-down processes may further influence cross-modal processing in a flexible manner, and we highlight fruitful directions for further research.

Tailoring Nonlinear Processes of Orbital Angular Momentum with Dispersion Engineering in Vortex Fibers

Manipulation of nonlinear processes of orbital angular momentum (OAM) modes in optical fibers is an emerging challenge, providing the potential for a wide variety of applications in parametric amplification, high-dimensional entanglement generation, and frequency conversion. The authors demonstrate low-crosstalk intramodal processes for four-wave mixing between OAM modes in an optical-vortex fiber. By engineering the relative group velocity within a spatial dimension, the phase-matching conditions for OAM modes can be tailored. The proposed scheme may also illuminate further possibilities for generating and manipulating OAM states in fiber systems.

Visuohaptic Crossmodal Matching: A Developmental fMRI Study

Research on the development of crossmodal (intersensory) perception of visual and haptic inputs suggests that communication within sensory systems develops earlier than communication across sensory systems. These behavioral changes reflect the development of neural substrates, but little is known about the neural mechanisms that underlie the developmental progression of haptic perception or visuohaptic interactions. To address this gap in knowledge, BOLD fMRI was measured during intramodal (visual-to-visual, haptic-to-haptic) and crossmodal (visual-to-haptic, haptic-to-visual) delayed match-to-sample recognition tasks with novel objects in children aged 7-8.5 years and in young adults. Tasks were further divided into encoding (sample) and matching (test) phases. During matching, adults and children demonstrated similar results. Whole-brain comparisons of intramodal and crossmodal object matching to rest revealed the network of known visuohaptic multisensory substrates, including the lateral occipital complex (LOC) and intraparietal sulcus (IPS). Comparisons of crossmodal versus intramodal conditions (i.e., (HV>VV) ͪ5; (HV>HH), (VH>VV) ͪ5; (VH>HH)) produced significant clusters in the same regions, and further, indicated specific effects of crossmodal directionality. In particular, haptic-to-visual matching tasks activated ventral regions (LOC) in both groups, while visual-to-haptic matching tasks activated dorsal regions (IPS) in adults only. Moreover, in the regions of interest as defined by contrasts with rest, crossmodal matching showed greater activation than intramodal matching. Specifically, results revealed this pattern in LOC during haptic-to-visual matching and in IPS during visual-to-haptic matching. Overall, children were highly similar to adults with the exception of some developmental differences in IPS. These results converge with existing findings on the multisensory nature of the IPS and LOC in adults, and extend our knowledge of the development of haptic perception and crossmodal integration. Critically, the results highlight the dominance of crossmodal over intramodal processing, as well as the different influences of test modality on the dorsal (IPS) and ventral (LOC) sites for visuohaptic object processing. Meeting abstract presented at VSS 2013

Auditory processing in an inter-modal oddball task: Effects of a combined auditory/visual standard on auditory target ERPs

Previous research examining auditory target ERPs in an inter-modal oddball task has shown that early components are affected by intra-modal processes, whilst components in the later part of the ERP, around 200–400 ms, are affected by both inter-modal and intra-modal processes. These findings led to the conclusion that there are separate stages of auditory target processing — an early modality-specific stage and a later context-dependent stage. The present study investigated this further by simultaneously presenting a visual standard stimulus with an auditory standard stimulus in an oddball task. The aim was to determine whether the inclusion of the visual standard stimulus in this task affected the ERP to targets. The auditory–visual oddball task consisted of a regularly presented combined auditory and visual standard stimulus (80%) and an infrequent auditory target (20%). The ERPs to targets in the auditory–visual oddball task were compared to those in an auditory oddball task, which had identical auditory stimuli and no visual standards. The results showed that the early components N100, P200 and N200 did not differ between tasks. This was in line with earlier results, and confirmed that activity up to 200 ms is unaffected by visual standard stimuli. The later components P250, P300 and P350 were larger and showed topographic differences in the auditory–visual oddball task. This was interpreted as reflecting separate inter-modal and intra-modal processes at later stages. In particular, the P300 and P350 components were argued to represent separate inter-modal and intra-modal components. Overall, this study provides further evidence of auditory processing occurring in two stages, an early modality-dependent stage and a later context-dependent stage.

Functional Anatomy of Intra- and Cross-Modal Lexical Tasks

Functional magnetic resonance imaging (fMRI) was used to examine lexical processing in normal adults (20–35 years). Two tasks required only intramodal processing (spelling judgments with visual input and rhyming judgments with auditory input) and two tasks required cross-modal processing between phonologic and orthographic representations (spelling judgments with auditory input and rhyming judgments with visual input). Each task led to greater activation in the unimodal association area concordant with the modality of input, namely fusiform gyrus (BA 19, 37) for written words and superior temporal gyrus (BA 22, 42) for spoken words. Cross-modal tasks generated greater activation in posterior heteromodal regions including the supramarginal and angular gyri (BA 40, 39). Cross-modal tasks generated additional activation in unimodal areas representing the target of conversion, superior temporal gyrus for visual rhyming and fusiform gyrus for auditory spelling. Our findings suggest that the fusiform gyrus processes orthographic word forms, the superior temporal gyrus processes phonologic word forms, and posterior heteromodal regions are involved in the conversion between orthography and phonology.

Inter- and Intramodal Encoding of Auditory and Visual Presentation of Material: Effects on Memory Performance

Different encoding activities during list learning, such as writing down or reading aloud, have a differential effect on memory performance. It has been argued that intermodal processing, that is, auditory processing of visually presented material and vice versa, results in a better performance than intramodal processing. This has been referred to as the ''translation hypothesis:' In this study, we set out to test the translation hypothesis looking at all four possible experimental conditions using visual and auditory presentation and writing and vocalization as encoding activities. The results show a similar memory performance in all conditions apart from the one in which visually presented words had to be written down. That is, in the only condition in which subjects did not hear the words (either via auditory presentation or via their own vocalization), fewer words were remembered. These findings do not support the translation hypothesis and are more in agreement with previous theoretical proposals regarding long-term modality effects.

Inter- and intra-modal processing of sensory-specific stimuli.

Inter- and intra-modal processing was compared with modality-specific forms in two experiments on a group of 40 university students. In Exp. I, the RTs for tactual-to-visual and visual-to-visual processing were compared for 20 subjects, and in Exp. II, the visual-to-tactual and the tactual-to-tactual processing were compared for another group of 20 subjects. Analysis showed that intra-modal processing is faster than inter-modal processing. Further, the "same" RT is faster than the "different" RT. The inter- and intra-modal processing differences are based on the delay in retrieval and recognition across sensory-specific areas.