Alternative method of implementation of all-optical NOR and NAND gates using quantum-dot semiconductor optical amplifiers in non-interferometer structure

Present communication deals with the design and analysis of all-optical NOR and NAND gates using Quantum dot Semiconductor Optical Amplifiers (QDSOA). The design uses no interferometer structure but cross gain modulation is utilized for operation. The structures are simple and simulations at a rate of 1 Tb/s are processed. For unsaturated gain 30 dB, the logic gates show high values of ER (29.82 dB, 16.93 dB), CR (29.6 dB, 21.33 dB), and Q (25.4 dB, 13.2 dB). This ensures practical feasibility and high quality of the proposed gates.

Invariant neural subspaces maintained by feedback modulation

Sensory systems reliably process incoming stimuli in spite of changes in context. Most recent models accredit this context invariance to an extraction of increasingly complex sensory features in hierarchical feedforward networks. Here, we study how context-invariant representations can be established by feedback rather than feedforward processing. We show that feedforward neural networks modulated by feedback can dynamically generate invariant sensory representations. The required feedback can be implemented as a slow and spatially diffuse gain modulation. The invariance is not present on the level of individual neurons, but emerges only on the population level. Mechanistically, the feedback modulation dynamically reorients the manifold of neural activity and thereby maintains an invariant neural subspace in spite of contextual variations. Our results highlight the importance of population-level analyses for understanding the role of feedback in flexible sensory processing.

Attention biases preferential choice by enhancing an option's value

Does attending to an option lead to liking it? Though attention induced valuation is often hypothesized, evidence for this causal link has remained elusive. We test this hypothesis across two studies by manipulating attention during a preferential decision and its perceptual analog. In a free-viewing task, we found attention biased choice and eye movement pattern in the preferential decision more than during the perceptual analog. In a controlled-viewing task, we again found attention had a larger effect on choice in the preferential decision than its perceptual analog. Computational modeling of the data reveals that attention impacted preference by discounting the unattended option’s value. These results support the attention-induced valuation hypothesis. We suggest that attention impacts preference via a normalization process where an option's representation is scaled by its spatial and temporal neighbors. Attention provides a gain modulation on this representation at the sensory and value processing levels.

Hyperdirect connectivity of opercular speech network to the subthalamic nucleus

The importance of the basal ganglia in modulating cognitive and motor behaviors is well known, yet how the basal ganglia participate in the uniquely human behavior of speech is poorly understood. The subthalamic nucleus (STN) is well positioned to facilitate two basal ganglia functions critical for speech: motor learning and gain modulation. Using a novel paradigm to study cortical-subcortical interactions during speech in patients undergoing awake DBS surgery, we found evidence for a left opercular hyperdirect pathway in humans by stimulating in the STN and examining antidromic evoked activity in the left temporal, parietal and frontal opercular cortex. These high resolution cortical and subcortical mapping data provided evidence for hyperdirect connectivity between Broca area (typically corresponding to pars triangularis and pars opercularis of the inferior frontal gyrus) and the STN. In addition, we observed evoked potentials consistent with the presence of monosynaptic projections from areas of opercular speech cortex that are primarily sensory, including auditory cortex, to the STN. These connections may be unique to humans, evolving alongside the ability for speech.