Salience Signals Research Articles

Secondary Saliency Tracking-Based Sensorless Control for Concentrated Winding SPMSM

Sensorless ac drives have been widely adopted in many industry applications. However, the characteristic of strong multiple saliencies is still a main drawback impeding applying sensorless control over several types of machine, e.g., surface-mounted permanent magnet synchronous machine with concentrated windings (cwSPMSM). This work proposes a novel secondary saliency tracking (SST) algorithm to implement the sensorless control exclusively for such machines at low speed range. The saliency signals of a typical cwSPMSM under consideration are experimentally investigated. The stator background and physical mechanism of its strong multiple saliencies are explained in detail. Instead of processing the primary saliency signal, secondary saliency signal that has a better signal to noise ratio and more precise resolution is processed by a specially designed bandpass filter, and an adaptive notch filter for speed and rotor position estimation. Finally, the effectiveness and accuracy of the newly proposed SST method are verified by experimental results.

Associative Learning Through Acquired Salience.

Most associative learning studies describe the salience of stimuli as a fixed learning-rate parameter. Presumptive saliency signals, however, have also been linked to motivational and attentional processes. An interesting possibility, therefore, is that discriminative stimuli could also acquire salience as they become powerful predictors of outcomes. To explore this idea, we first characterized and extracted the learning curves from mice trained with discriminative images offering varying degrees of structural similarity. Next, we fitted a linear model of associative learning coupled to a series of mathematical representations for stimulus salience. We found that the best prediction, from the set of tested models, was one in which the visual salience depended on stimulus similarity and a non-linear function of the associative strength. Therefore, these analytic results support the idea that the net salience of a stimulus depends both on the items' effective salience and the motivational state of the subject that learns about it. Moreover, this dual salience model can explain why learning about a stimulus not only depends on the effective salience during acquisition but also on the specific learning trajectory that was used to reach this state. Our mathematical description could be instrumental for understanding aberrant salience acquisition under stressful situations and in neuropsychiatric disorders like schizophrenia, obsessive-compulsive disorder, and addiction.

Basal forebrain motivational salience signal enhances cortical processing and decision speed.

The basal forebrain (BF) contains major projections to the cerebral cortex, and plays a well-documented role in arousal, attention, decision-making, and in modulating cortical activity. BF neuronal degeneration is an early event in Alzheimer’s disease (AD) and dementias, and occurs in normal cognitive aging. While the BF is best known for its population of cortically projecting cholinergic neurons, the region is anatomically and neurochemically diverse, and also contains prominent populations of non-cholinergic projection neurons. In recent years, increasing attention has been dedicated to these non-cholinergic BF neurons in order to better understand how non-cholinergic BF circuits control cortical processing and behavioral performance. In this review, we focus on a unique population of putative non-cholinergic BF neurons that encodes the motivational salience of stimuli with a robust ensemble bursting response. We review recent studies that describe the specific physiological and functional characteristics of these BF salience-encoding neurons in behaving animals. These studies support the unifying hypothesis whereby BF salience-encoding neurons act as a gain modulation mechanism of the decision-making process to enhance cortical processing of behaviorally relevant stimuli, and thereby facilitate faster and more precise behavioral responses. This function of BF salience-encoding neurons represents a critical component in determining which incoming stimuli warrant an animal’s attention, and is therefore a fundamental and early requirement of behavioral flexibility.

Direct Evidence for Active Suppression of Salient-but-Irrelevant Sensory Inputs

Researchers have long debated whether attentional capture is purely stimulus driven or purely goal driven. In the current study, we tested a hybrid account, called the signal-suppression hypothesis, which posits that stimuli automatically produce a bottom-up salience signal, but that this signal can be suppressed via top-down control processes. To test this account, we used a new capture-probe paradigm in which participants searched for a target shape while ignoring an irrelevant color singleton. On occasional probe trials, letters were briefly presented inside the search shapes, and participants attempted to report these letters. Under conditions that promoted capture by the irrelevant singleton, accuracy was greater for the letter inside the singleton distractor than for letters inside nonsingleton distractors. However, when the conditions were changed to avoid capture by the singleton, accuracy for the letter inside the irrelevant singleton was reduced below the level observed for letters inside nonsingleton distractors, an indication of active suppression of processing at the singleton location.

Parietal cortex integrates contextual and saliency signals during the encoding of natural scenes in working memory.

The Brief presentation of a complex scene entails that only a few objects can be selected, processed indepth, and stored in memory. Both low-level sensory salience and high-level context-related factors (e.g., the conceptual match/mismatch between objects and scene context) contribute to this selection process, but how the interplay between these factors affects memory encoding is largely unexplored. Here, during fMRI we presented participants with pictures of everyday scenes. After a short retention interval, participants judged the position of a target object extracted from the initial scene. The target object could be either congruent or incongruent with the context of the scene, and could be located in a region of the image with maximal or minimal salience. Behaviourally, we found a reduced impact of saliency on visuospatial working memory performance when the target was out-of-context. Encoding-related fMRI results showed that context-congruent targets activated dorsoparietal regions, while context-incongruent targets de-activated the ventroparietal cortex. Saliency modulated activity both in dorsal and ventral regions, with larger context-related effects for salient targets. These findings demonstrate the joint contribution of knowledge-based and saliency-driven attention for memory encoding, highlighting a dissociation between dorsal and ventral parietal regions.

Trend salience, investor behaviours and momentum profitability

Trend extrapolation in financial markets has been well documented, however it is contentious as to which trends will be extrapolated or mean reverted. This paper examines whether investors are more likely to extrapolate trends that they perceive to be salient, thereby providing an empirical test of the behavioural models of momentum. We employ an investment strategy that exploits trend salience by considering both the magnitude and the persistence of recent return performance. Consistent with behavioural models of momentum, an investment strategy based on trend salience significantly outperforms traditional momentum strategies and is not explained by the four-factor model. The relative performance of the trend salience signal is robust across different investment horizons and size-sorted portfolios, although is time-varying; the strategy does not outperform momentum in “down” markets or periods of high volatility in the formation period where trends are more difficult to identify.

Altered basolateral amygdala encoding in an animal model of schizophrenia.

It has been proposed that schizophrenia results, in part, from the inappropriate or spurious attribution of salience to cues in the environment. We have recently reported neural correlates of salience in the basolateral amygdala (ABL) of rats during learning in an odor-guided discrimination task. Here we tested whether this dopamine-dependent salience signal is altered in rats with neonatal ventral hippocampal lesions (NVHLs), a rodent model of schizophrenia. We found that ABL signals related to violations in reward prediction were only mildly affected by NVHL; however, neurons in rats with NVHLs showed significantly stronger selectivity during odor sampling, particularly for the more salient large-reward cue. The elevated cue-evoked activity in NVHL rats was correlated with heightened orienting behavior and also with changes in firing to the shifts in reward, suggesting that it reflected abnormal signaling of the large reward-predicting cue's salience. These results are broadly consistent with the proposal that schizophrenics suffer from enhanced signaling of salience.

Sensorless Control for SPMSM With Concentrated Windings Using Multisignal Injection Method

Surface-mounted permanent magnet synchronous machine with concentrated windings (cwSPMSM) is a high-performance drive machine and has been adopted in many applications. The difficulty of implementing its sensorless control at low and zero speeds is its multiple saliencies, which is much more significant than most other ac machines. The traditional decoupling methods provide successful results only under the condition that high-order saliencies are not stronger than half of the primary saliency. Furthermore, the behavior of the multiple saliencies is principally frequency dependent. Based on the characteristics of such machines, this paper proposes a multisignal injection method for realizing sensorless control. This method injects multiple high-frequency signals with different frequencies and magnitudes into the machine. Different frequency components in the response current signals are demodulated and then combined together to get the clear primary saliency signal, which is used to identify the rotor position. This new method was validated using a cwSPMSM at low speed. The experimental results proved the effectiveness and accuracy of the new method.

Enhanced consumption of salient solutions following pedunculopontine tegmental lesions

Rats with lesions of the pedunculopontine tegmental nucleus (PPTg) reliably overconsume high concentration sucrose solution. This effect is thought to be indicative of response-perseveration or loss of behavioral control in conditions of high excitement. While these theories have anatomical and behavioral support, they have never been explicitly tested. Here, we used a contact lickometer to examine the microstructure of drinking behavior to gain insight into the behavioral changes during overconsumption. Rats received either excitotoxic (ibotenic acid) damage to all PPTg neuronal subpopulations or selective depletion of the cholinergic neuronal sub-population (diphtheria toxin–urotensin II (Dtx–UII) lesions). We offered rats a variety of pleasant, neutral and aversive tastants to assess the generalizability and specificity of the overconsumption effect. Ibotenic-lesioned rats consumed significantly more 20% sucrose than sham controls, and did so through licking significantly more times. However, the behavioral microstructure during overconsumption was unaffected by the lesion and showed no indications of response-perseveration. Furthermore, the overconsumption effect did not generalize to highly consumed saccharin. In contrast, while only consuming small amounts of quinine solution, ibotenic-lesioned rats had significantly more licks and bursts for this tastant. Selective depletion of cholinergic PPTg neurons had no effect on consumption of any tastant. We then assessed whether it is the salience of the solution which determines overconsumption by ibotenic-lesioned rats. While maintained on free-food, ibotenic-lesioned rats had normal consumption of sucrose and hypertonic saline. After mild food deprivation ibotenic PPTg-lesioned rats overconsumed 20% sucrose. Subsequently, after dietary-induced sodium deficiency, lesioned rats consumed significantly more saline than controls. These results establish that it is the salience of the solution which is the determining factor leading to overconsumption following excitotoxic PPTg lesion. They also find no support for response-perseveration contributing to this effect. Results are discussed in terms of altered dopamine (DA) and salience signaling.

Visual search for singleton targets redundantly defined in two feature dimensions: Coactive processing of color-motion targets?

In 2 visual search experiments, the role of feature contrast/saliency signals in generating detection responses to singleton feature targets in visual search was investigated using the redundant-target paradigm. Experiment 1 showed that coactive integration of dimensional signals is not restricted to targets defined on the color and orientation dimensions; rather, targets involving any of the combinations of color, orientation, and motion, are integrated coactively, as evidenced by violations of Miller's (1982) race model inequality. Experiment 2 replicated the findings of Experiment 1 for color-motion targets, with the target items' luminance adjusted, individually for each observer, to that of the distractors. The evidence for coactive processing of motion (saliency) with color and, respectively, orientation (saliency) signals suggests that, at variance with a recent suggestion by Li (2002; Koene & Zhaoping, 2007), signal integration in feature search tasks occurs at a stage following initial feature coding in primary visual cortex (V1), even though feature contrast computations in V1 may well contribute to saliency coding. In sum, the results suggest that detection responses were based on an integrated, overall-saliency representation indicating the presence of an odd-one-out item in the display, consistent with the dimension-weighting account of visual search (Müller et al., 1995, 2003).

Social neuroscience in psychiatry: pathways to discovering neurobiological risk and resilience.

Cacioppo et al 1 provide a thoughtful overview of the ways in which social neuroscience can significantly advance our understanding and treatment of mental disorders. They touch on the way gene regulation, epigenetics and the environment can alter neurodevelopmental trajectories and in turn influence social behavior and social functioning. We would like to emphasize here the importance of future research exploring dynamic social brain changes taking place during adolescence 2,3 as a possible key to understanding the emergence of mental disorders at this critical stage of maturation, when risk for such disorders peaks. Recent work in our laboratory shows that attenuated growth of the hippocampus and attenuated reduction in putamen volume during age 12 to 16 years are associated with the onset of depression 4. Sex is also a significant factor, since exaggerated amygdala growth in females and attenuated growth in males seems to increase the risk of depression. Taking account of the neurodevelopmental background for boys and girls, relevant to all aspects of cognition, including social cognition, is a necessary prerequisite to understanding mental disorders and their neurobiology. The prominence of social themes in the characterization of autism spectrum disorders (ASD) also warrants brief discussion. Our recent work on ASD 5 is relevant in being an interdisciplinary study involving biology and engineering, and in linking statistical approaches to biology. Importantly, while the emphasis of most studies has been on discovery of neurobiological risk markers for such disorders, in our study we also identified several single-nucleotide polymorphisms (SNPs) that protected against ASD, that is, might be associated with resilience to development of the disorder. For example, we found that the SNP rs12317962 protected against ASD 5. This SNP lies in the gene KCNMB4, encoding a potassium channel involved in neuronal excitability, which is highly expressed in the fusiform gyrus and key social brain regions, namely the superior temporal, cingulate and orbitofrontal cortices. Other SNPs, such as variation in rs3796863 in CD38, a gene linked to ASD and known to be involved in oxytocin secretion, has also been linked with activation of the amygdala and in particular the fusiform gyrus, during visual processing of social stimuli in healthy young men 6. We are in the processes of furthering this research in ASD by examining the influence of allelic variation on brain regions using neuroimaging. Schizophrenia is another disorder that involves deficits in social cognition. Recent theories propose that aberrations in dopaminergic and glutamatergic subcortical-amygdala-prefrontal circuits give rise to dysregulation of salience signaling, causing impairments in emotion-related perception, learning and memory 7, similar to the model of Phillips et al 8 described by Cacioppo et al 1 in the context of depression. Interdisciplinary research of Walter et al 9 shows that carriers for the psychosis risk variant of the SNP rs1344706 (gene ZNF804A) have abnormal neural activation in the medial prefrontal and left temporo-parietal cortex, as well as in regions of the mirror neuron system, during a theory of mind task. This potential intermediate phenotype derived from functional imaging may have implications for biological treatment of social cognitive impairments in schizophrenia. One thing that is clear from Cacioppo et al's paper 1 is that, across disorders, common social brain regions are dysfunctional: the amygdala, orbitofrontal cortex, medial prefrontal cortex, superior temporal sulcus, anterior insula and anterior cingulate. Yet, the way in which they deviate from normal functioning (hypo- vs. hyper-activation/mixture of both) depends on the illness being studied and the social processes in question. Therefore, we should study not only across disciplines but also across mental disorders, and in the context of carefully controlled treatment interventions, to provide insights into both risk and resilience factors associated with developing particular disorders. Oxytocin has been proposed as a potential adjunctive treatment for the social cognitive and behavioural deficits common in social anxiety disorder, ASD, schizophrenia, and borderline personality disorder 10. While there are several oxytocin-related risk alleles that have been linked to social brain functioning, there is little insight into the mechanisms of the actions of oxytocin in the brain. This is a promising avenue for future research in psychiatry. In conclusion, Cacioppo et al's paper on social neuroscience and mental disorders provides us much food for thought. There is a need for dynamic interdisciplinary (rather than just multidisciplinary) exchange between biological and other sciences; assessing changes in trajectories of brain structure and function; linking these dynamic changes to genes that may bestow risk or resilience to development of illness; and examining the impact of interventions that modulate social cognition. All of these approaches and their combination present exciting ways forward in understanding some of the most challenging and complex disorders affecting human beings.

From features to dimensions: cognitive and motor development in pop-out search in children and young adults.

In an experiment involving a total of 124 participants, divided into eight age groups (6-, 8-, 10-, 12-, 14-, 16-, 18-, and 20-year-olds) the development of the processing components underlying visual search for pop-out targets was tracked. Participants indicated the presence or absence of color or orientation feature singleton targets. Observers also solved a detection task, in which they responded to the onset of search arrays. There were two main results. First, analyses of inter-trial effects revealed differences in the search strategies of the 6-year-old participants compared to older age groups. Participants older than 8 years based target detection on feature-less dimensional salience signals (indicated by cross-trial RT costs in target dimension change relative to repetition trials), the 6-year-olds accessed the target feature to make a target present or absent decision (cross-trial RT costs in target feature change relative to feature repetition trials). The result agrees with predictions derived from the Dimension Weighting account and previous investigations of inter-trial effects in adult observers (Müller et al., 1995; Found and Müller, 1996). The results are also in line with theories of cognitive development suggesting that the ability to abstract specific visual features into feature categories is developed after the age of 7 years. Second, overall search RTs decreased with increasing age in a decelerated fashion. RT differences between consecutive age groups can be explained by sensory-motor maturation up to the age of 10 years (as indicated by RTs in the onset detection task). Expedited RTs in older age groups (10-, vs. 12-year-olds; 14- vs. 16-year-olds), but also in the 6- vs. 8-year-olds, are due to the development of search-related (cognitive) processes. Overall, the results suggest that the level of adult performance in visual search for pop-out targets is achieved by the age of 16.

Salience-based integration of redundant signals in visual pop-out search: Evidence from behavioral and electrophysiological measures

Behavioral and electrophysiological evidence is presented suggesting that, in visual search for feature singleton targets, multidimensional signals are integrated at a preselective stage of processing. Observers searched for a target that was consistently defined by the same features, but differed from the variable context either nonredundantly by one or redundantly by two dimensionally different features. The behavioral results showed reaction time redundancy gains and evidence of coactive processing, and the electrophysiological analyses revealed the latency of the N2pc component of the event-related potential (ERP) to be expedited by redundant relative to nonredundant displays, while the response-related lateralized readiness potential (LRP) remained unaffected. These findings suggest that target signal integration in singleton search paradigms occurs pre-attentively, that is, prior to focal-attentional target selection, with observers basing their responses on the detection of featureless saliency signals, even under conditions in which the target features remain constant and are known in advance. These results have implications for theories assuming top-down influences in feature detection.

Motivational Salience Signal in the Basal Forebrain Is Coupled with Faster and More Precise Decision Speed

Author SummaryHumans and animals face the constant challenge of identifying the subset of incoming sensory stimuli that are most behaviorally relevant and prioritizing behavioral responses accordingly. Critical to this decision is the ability to determine whether a stimulus is motivationally salient—that is, whether the stimulus predicts important behavioral outcomes such as reward or punishment. While it is generally assumed that motivational salience is related to faster decision speed and shorter reaction time, it remains unclear how motivational salience actually modulates the decision-making process. This study investigates how the motivational salience signal in the basal forebrain controls the fundamental properties of the decision-making process—decision speed and its variability. In rats performing a reward-biased simple reaction time task, we show that the basal forebrain motivational salience signal is associated with a faster and also precise decision speed. In support of a causal role for this association, artificially augmenting this basal forebrain motivational salience signal by electrical stimulation also leads to faster and more precise reaction times. These results suggest that decision speed and its variability are jointly determined by an early and previously unrecognized step in the decision-making process, dictated largely by the motivational salience signal encoded by poorly understood noncholinergic neurons in the basal forebrain.

Enhanced distraction by magnocellular salience signals in schizophrenia

Research on schizophrenia has provided evidence of both impaired attentional control and dysfunctional magnocellular sensory processing. The present study tested the hypothesis that these impairments may be related, such that people with schizophrenia would be differentially distracted by stimuli that strongly activate the magnocellular pathway. To accomplish this, we used a visual attention paradigm from the basic cognitive neuroscience literature designed to assess the capture of attention by salient but irrelevant stimuli. Participants searched for a target shape in an array of non-target shapes. On some trials, a salient distractor was presented that either selectively activated the parvocellular system (parvo-biased distractors) or activated both the magnocellular and parvocellular systems (magno+parvo distractors). For both manual reaction times and eye movement measures, the magno+parvo distractors captured attention more strongly than the parvo-biased distractors in people with schizophrenia, but the opposite pattern was observed in matched healthy control participants. These results indicate that attentional control deficits in schizophrenia may arise, at least in part, by means of an interaction with magnocellular sensory dysfunction.

Trend Salience, Investor Behaviors and Momentum Profitability

Trend extrapolation in financial markets has been well documented, however it is contentious as to which trends will be extrapolated or mean reverted. We examine whether investors are more likely to extrapolate trends that they perceive to be salient by examining an investment strategy that considers both the magnitude and the strength of the trend. Consistent with behavioral models of momentum, our investment strategy based on trend salience significantly outperforms traditional momentum strategies and is not explained by the Carhart [1997] four-factor model. The relative performance of the trend salience signal is robust across different investment horizons and size-sorted portfolios, although is time-varying; the strategy does not outperform momentum in down markets where volatility is high and salient trends are more difficult to identify.

Dissociation between saliency signals and activity in early visual cortex

Saliency is a measure that describes how attention is guided by local stimulus properties. Some hypotheses assign its computation to specific topographically organized areas of early human visual cortex. However, in most stimuli, saliency is correlated with luminance contrast, which in turn is known to correlate with activity in these early areas. Thus, any observed correlation of local activity with saliency might be due to the area encoding luminance contrast. Here we disentangle encoding of local luminance contrast and saliency by using stimuli where the two properties are uncorrelated. First, we conducted an eye-tracking study to verify that both negative and positive contrast modifications located in individual quadrants of the visual field increase saliency. Second, subjects viewed identical stimuli while fMRI signals were recorded. We find that positive contrast modifications induce a robust increase of activity in V1-V3 and hV4. However, negative contrast modifications lead to a reduced (V1, V2) or comparable (V3, hV4) activity level compared to unmodified quadrants. Furthermore, even with linear multivariate pattern-classification techniques, it is not possible to decode the location of the salient quadrant independent of the type of the contrast modification. Instead, decoding of the contrast-modified location is only possible separately for the two modification types in V1-V3. These findings suggest that the BOLD activity in V1-V3 is dominated by contrast-dependent processes and does not include the contrast invariance necessary for the computation of feature-invariant saliency.

Representations of Distinct Salience Signals in the Nucleus Accumbens

Processing salient events is an essential component of adaptive behavior. To navigate a changing world, organisms must learn which events are meaningful and determine the appropriate behavioral response. Many regions throughout the brain, including affective subcortical and executive cortical

Computational heterogeneity in the human mesencephalic dopamine system

Recent evidence in animals has indicated that the mesencephalic dopamine system is heterogeneous anatomically, molecularly, and functionally, and it has been suggested that the dopamine system comprises distinct functional systems. Identifying and characterizing these systems in humans will have widespread ramifications for understanding drug addiction and mental health disorders. Model-based studies in humans have suggested an analogous computational heterogeneity, in which dopaminergic targets in striatum encode both experience-based learning signals and counterfactual learning signals that are based on hypothetical information. We used brainstem-tailored fMRI to identify mesencephalic sources of experiential and counterfactual learning signals. Participants completed a decision-making task based on investing in markets. This sequential investment task generated experience-based learning signals, in the form of temporal difference (TD) reward prediction errors, and counterfactual learning signals, in the form of “fictive errors.” Fictive errors are reinforcement learning signals based on hypothetical information about “what could have been.” An additional learning signal was constructed to be relatable to a motivational salience signal. Blood oxygenation level dependent responses in regions of substantia nigra (SN) and ventral tegmental area (VTA), where dopamine neurons are located, coded for TD and fictive errors, and additionally were related to the motivational salience signal. These results are highly consistent with animal electrophysiology and provide direct evidence that human SN and VTA heterogeneously handle important reward-harvesting computations.Electronic supplementary materialThe online version of this article (doi:10.3758/s13415-013-0191-5) contains supplementary material, which is available to authorized users.

Visual Salience Improves Spatial Working Memory via Enhanced Parieto-Temporal Functional Connectivity

In everyday life, the brain is bombarded with a multitude of concurrent and competing stimuli. Only some of these enter consciousness and memory. Attention selects relevant signals for in-depth processing depending on current goals, but also on the intrinsic properties of stimuli. We combined behavior, computational modeling, and functional imaging to investigate mechanisms supporting access to memory based on intrinsic sensory properties. During fMRI scanning, human subjects were presented with pictures of naturalistic scenes that entailed high levels of competition between possible target objects. Following a retention interval of 8 s, participants judged the location (same/different) of a target object extracted from the initial scene. We found that memory performance at retrieval increased with increasing object salience at encoding, indicating a "prior entry" for salient information. fMRI analyses revealed encoding-related activation in the posterior parietal cortex, selectively for salient objects that were later remembered. Moreover, parietal cortex showed increased functional coupling with the medial-temporal lobe, for remembered objects only. These findings reveal a parietotemporal circuit that integrates available sensory cues (based on attention-grabbing saliency signals) and current memory requirements (storing objects' locations) to encode object-related spatial information in working memory.