Unattended Locations Research Articles

Design Considerations for Implementing an Optimal Battery Management System of a Wireless Sensor Node

Nowadays, researchers' preferably giving more attention to the power consumption of a sensor node as it is the main criteria in all Wireless Sensor Networks (WSNs). Wireless Sensor Nodes of a network have some major constraints due to their limited energy, storage capacity, computing power and frequent battery replacement factor, when they meant to collect the information from an unattended location using various sensors. Hence the proposed research implements a novel power management system by introducing pack of two solar powered batteries and an automatic battery switching system with LabVIEW based real time data acquisition. The proposed approach avoids the frequent replacement of batteries in the sensor node about 90%. Hill stations, barren region, and unattended location may include the implemented WSN.

The relationship between contrast detection and saccadic reaction times with attention.

Visual spatial attention can increase contrast sensitivity and decrease saccadic or manual reaction times (RTs) in attended compared to unattended locations. As stimulus contrast also influences saccadic RT, we asked whether the effect of attention on saccadic RT can be accounted for by the change in contrast sensitivity. We used a dual task paradigm that recorded saccadic RTs and psychophysical responses to targets of various contrast. On each trial, subjects were presented with a central fixation stimulus, which also carried an endogenous cue (an arrow) to the target's radial direction but not its eccentricity. Across trials, the cue was 75% valid, 12.5 % invalid and 12.5 % neutral (no arrow). Circular gratings m-scaled for eccentricity were flashed for 8 ms in one of 8 radial directions around fixation, at either 3 or 6 deg eccentricity, with one of 9 contrasts. The subjects' tasks were to (1) saccade to the location where the target flashed and (2) respond via button press if the target flashed at the nearer (3 deg) or the farther (6 deg) eccentricity. Saccadic RTs and psychophysical responses to targets at the different contrast levels were analyzed to assess the effects of cueing. Valid cueing produced a factor of 1.2 increase in contrast sensitivity, relative to invalid-cue trials. Valid cueing also reduced saccadic RTs for contrast levels at and above the detection threshold. However, the effect of cueing on saccadic RT is accounted for only partly by the increase in psychophysical contrast sensitivity. A comparison of RT vs. contrast for valid and invalid cueing shows a combined effect: a shift consistent with the observed change in contrast sensitivity, and an overall change in latency of roughly 20 msec. Attention appears to influence saccadic RTs in more than one way. Meeting abstract presented at VSS 2014

On the Role of Suppression in Spatial Attention: Evidence from Negative BOLD in Human Subcortical and Cortical Structures

There is clear evidence that spatial attention increases neural responses to attended stimuli in extrastriate visual areas and, to a lesser degree, in earlier visual areas. Other evidence shows that neurons representing unattended locations can also be suppressed. However, the extent to which enhancement and suppression is observed, their stimulus dependence, and the stages of the visual system at which they are expressed remains poorly understood. Using fMRI we set out to characterize both the task and stimulus dependence of neural responses in the lateral geniculate nucleus (LGN), primary visual cortex (V1), and visual motion area (V5) in humans to determine where suppressive and facilitatory effects of spatial attention are expressed. Subjects viewed a lateralized drifting grating stimulus, presented at multiple stimulus contrasts, and performed one of three tasks designed to alter the spatial location of their attention. In retinotopic representations of the stimulus location, we observed increasing attention-dependent facilitation and decreasing dependence on stimulus contrast moving up the visual hierarchy from the LGN to V5. However, in the representations of unattended locations of the LGN and V1, we observed suppression, which was not significantly dependent on the attended stimulus contrast. These suppressive effects were also found in the pulvinar, which has been frequently associated with attention. We provide evidence, therefore, for a spatially selective suppressive mechanism that acts at a subcortical level.

Combining spatial and temporal expectations to improve visual perception.

The importance of temporal expectations in modulating perceptual functions is increasingly recognized. However, the means through which temporal expectations can bias perceptual information processing remains ill understood. Recent theories propose that modulatory effects of temporal expectations rely on the co-existence of other biases based on receptive-field properties, such as spatial location. We tested whether perceptual benefits of temporal expectations in a perceptually demanding psychophysical task depended on the presence of spatial expectations. Foveally presented symbolic arrow cues indicated simultaneously where (location) and when (time) target events were more likely to occur. The direction of the arrow indicated target location (80% validity), while its color (pink or blue) indicated the interval (80% validity) for target appearance. Our results confirmed a strong synergistic interaction between temporal and spatial expectations in enhancing visual discrimination. Temporal expectation significantly boosted the effectiveness of spatial expectation in sharpening perception. However, benefits for temporal expectation disappeared when targets occurred at unattended locations. Our findings suggest that anticipated receptive-field properties of targets provide a natural template upon which temporal expectations can operate in order to help prioritize goal-relevant events from early perceptual stages.

A Robust User Authentication Scheme Using Dynamic Identity in Wireless Sensor Networks

In modern, wireless sensor networks (WSNs) stand for the next evolutionary and innovative development step in utilities, industrial, building, home, shipboard, and transportation systems automation. The feature of WSNs is easy to deploy and has wide range of applications. Therefore, in distributed and unattended locations, WSNs are deployed to allow a legitimated user to login to the network and access data. Consequently, the authentication between users and sensor nodes has become one of the important security issues. In 2009, M. L. Das proposed a two-factor authentication for WSNs. Based on one-way hash function and exclusive-OR operation, the scheme is well-suited for resource constrained environments. Later, Khan and Algahathbar pointed out the flaws and vulnerabilities of Das's scheme and proposed an alternative scheme. However, Vaidya et al. found that both Das's and Khan–Algahathbar's schemes are vulnerable to various attacks including stolen smart card attacks. Further, Vaidya et al. proposed an improved two-factor user authentication to overcome the security weakness of both schemes. In this paper, we show that Vaidya et al.'s scheme still exposes to a malicious insider attack that seriously threatens the security of WSNs. Furthermore, we propose an improve scheme that mends those vulnerabilities.

Attention and Specificity in Unconscious Perceptual Learning

Practicing perceptual tasks improves performance. This is known as perceptual learning (PL). Visual PL is highly specific to trained stimulus locations, indicating neural plasticity in early retinotopic visual regions. Attention facilitates PL, but would it also affect PL of stimuli that observers remain unaware of? Here, we first measured performance on a texture discrimination task used commonly in PL studies. In seven subsequent training sessions, similar textures were presented monocularly and suppressed from awareness by continuous flash suppression, where monocular stimuli are rendered invisible by dynamic displays presented to the other eye. Observers performed an attentional task on dominant-eye stimuli; texture discrimination targets were presented at attended and unattended locations in the suppressed eye. In a final session, we assessed texture discrimination again. We expected PL (improved texture discrimination) to be greatest at locations that were attended during training. Surprisingly, we found significant PL at both attended and unattended locations. Control experiments ruled out the possibility that improvements were due to either repeated testing or training on the dominant eye's task. As observers were unaware of the texture stimuli during training, this finding indicates that attention can facilitate PL without awareness, and furthermore, can generalize it to untrained locations.

RTMS of Medial Parieto-occipital Cortex Interferes with Attentional Reorienting during Attention and Reaching Tasks

Unexpected changes in the location of a target for an upcoming action require both attentional reorienting and motor planning update. In both macaque and human brain, the medial posterior parietal cortex is involved in both phenomena but its causal role is still unclear. Here we used on-line rTMS over the putative human V6A (pV6A), a reach-related region in the dorsal part of the anterior bank of the parieto-occipital sulcus, during an attention and a reaching task requiring covert shifts of attention and planning of reaching movements toward cued targets in space. We found that rTMS increased RTs to invalidly cued but not to validly cued targets during both the attention and reaching task. Furthermore, we found that rTMS induced a deviation of reaching endpoints toward visual fixation and that this deviation was larger for invalidly cued targets. The results suggest that reorienting signals are used by human pV6A area to rapidly update the current motor plan or the ongoing action when a behaviorally relevant object unexpectedly occurs in an unattended location. The current findings suggest a direct involvement of the action-related dorso-medial visual stream in attentional reorienting and a more specific role of pV6A area in the dynamic, on-line control of reaching actions.

Blocking the Link between Stimulus and Response at Previously Attended Locations: Evidence for Inhibitory Tagging Mechanism

Inhibition of return (IOR) refers to a slower response to a target appearing at the previously attended location (also called the cued location) than to a target appearing at an unattended location (uncued location). Inhibitory tagging (IT) involving the attentional executive network is suggested to function by blocking or disconnecting the link between a stimulus representation and the corresponding response mapping at the cued location. Data from behavioral and neuroscience studies are integrated to discuss the IT theory. Behaviorally, the IT effect can be measured by the comparisons of the priming or conflict effects at the cued location versus effects at the uncued location. It has been suggested that IT can reduce or even eliminate the priming effect in semantic priming tasks and the conflict effect in the Stroop (either color-word or spatial Stroop) and the Flanker interference tasks at previously attended locations. Neural correlates of IT are also summarized. Specifically, the posterior parietal lobe, the anterior cingulate cortex (ACC), and the prefrontal cortex (PFC) are suggested to be involved in IT. Reduced event-related potentials (ERPs) components at the cued location provided evidences for IT; these included the N450 component, which is related to conflict resolution processing, and the N400 component, which is related to semantic priming processing, Finally, some comments and prospective remarks on IT are given. Keywords: Attentional network, inhibition of return (IOR), inhibitory tagging (IT), spatial cueing procedure, stimulus-response link.

Electrophysiological Correlates of Stimulus-driven Reorienting Deficits after Interference with Right Parietal Cortex during a Spatial Attention Task: A TMS-EEG Study

TMS interference over right intraparietal sulcus (IPS) causally disrupts behaviorally and EEG rhythmic correlates of endogenous spatial orienting before visual target presentation [Capotosto, P., Babiloni, C., Romani, G. L., & Corbetta, M. Differential contribution of right and left parietal cortex to the control of spatial attention: A simultaneous EEG-rTMS study. Cerebral Cortex, 22, 446-454, 2012; Capotosto, P., Babiloni, C., Romani, G. L., & Corbetta, M. Fronto-parietal cortex controls spatial attention through modulation of anticipatory alpha rhythms. Journal of Neuroscience, 29, 5863-5872, 2009]. Here we combine data from our previous studies to examine whether right parietal TMS during spatial orienting also impairs stimulus-driven reorienting or the ability to efficiently process unattended stimuli, that is, stimuli outside the current focus of attention. Healthy volunteers (n = 24) performed a Posner spatial cueing task while their EEG activity was being monitored. Repetitive TMS (rTMS) was applied for 150 msec simultaneously to the presentation of a central arrow directing spatial attention to the location of an upcoming visual target. Right IPS-rTMS impaired target detection, especially for stimuli presented at unattended locations; it also caused a modulation of the amplitude of parieto-occipital positive ERPs peaking at about 480 msec (P3) post-target. The P3 significantly decreased for unattended targets and significantly increased for attended targets after right IPS-rTMS as compared with sham stimulation. Similar effects were obtained for left IPS stimulation albeit in a smaller group of volunteers. We conclude that disruption of anticipatory processes in right IPS has prolonged effects that persist during target processing. The P3 decrement may reflect interference with postdecision processes that are part of stimulus-driven reorienting. Right IPS is a node of functional interaction between endogenous spatial orienting and stimulus-driven reorienting processes in human vision.

Differential effects of exogenous and endogenous attention on second-order texture contrast sensitivity

The visual system can use a rich variety of contours to segment visual scenes into distinct perceptually coherent regions. However, successfully segmenting an image is a computationally expensive process. Previously we have shown that exogenous attention--the more automatic, stimulus-driven component of spatial attention--helps extract contours by enhancing contrast sensitivity for second-order, texture-defined patterns at the attended location, while reducing sensitivity at unattended locations, relative to a neutral condition. Interestingly, the effects of exogenous attention depended on the second-order spatial frequency of the stimulus. At parafoveal locations, attention enhanced second-order contrast sensitivity to relatively high, but not to low second-order spatial frequencies. In the present study we investigated whether endogenous attention-the more voluntary, conceptually-driven component of spatial attention--affects second-order contrast sensitivity, and if so, whether its effects are similar to those of exogenous attention. To that end, we compared the effects of exogenous and endogenous attention on the sensitivity to second-order, orientation-defined, texture patterns of either high or low second-order spatial frequencies. The results show that, like exogenous attention, endogenous attention enhances second-order contrast sensitivity at the attended location and reduces it at unattended locations. However, whereas the effects of exogenous attention are a function of the second-order spatial frequency content, endogenous attention affected second-order contrast sensitivity independent of the second-order spatial frequency content. This finding supports the notion that both exogenous and endogenous attention can affect second-order contrast sensitivity, but that endogenous attention is more flexible, benefitting performance under different conditions.

Temporary inhibitory tagging at previously attended locations: Evidence from event‐related potentials

Recent studies propose that a mechanism termed "inhibitory tagging" acts upon the processing of the target at the attended location by temporarily blocking the stimulus-response mapping. Here we combined the cue-target paradigm with the Stroop task and measured event-related potential (ERP) responses to the color of a color word presented at the previously attended (cued) or unattended (uncued) location. We found that the conflict-related N450 effect emerged later and had a smaller size at the cued than the uncued location. The overall ERP responses to the target showed lower P1 and N1 amplitude at the cued than the uncued location. Although the P1/N1 effect may reflect deficient perceptual processing of the target, the delay of the N450 suggests that the link between perceptual processing and response activation is temporarily blocked at the previously attended location.

Anxiety modulates the effects of emotion and attention on early vision

At attended locations emotion and attention interact to benefit contrast sensitivity, a basic visual dimension. Whether there are associated costs at unattended locations is unknown. Furthermore, emotion and attention affect response time, and anxiety modulates these effects. We investigated how trait-anxiety influences the interaction of emotion and attention on contrast sensitivity. On each trial, non-predictive pre-cues (neutral or fearful faces) directed exogenous attention to four contrast-varying, tilted stimuli (Gabor patches). Attention was cued toward the target (valid), a distracter (invalid), or distributed over all locations. Observers discriminated target orientation, and completed self-report measures of anxiety. Effects of fearful expressions were mediated by trait anxiety. Only high-trait-anxious individuals showed decreased target contrast sensitivity after attention was diverted to a distracter by a fearful cue, and anxiety score correlated with degree of impairment across participants. This indicates that increasing anxiety exacerbates threat-related attentional costs to visual perception, hampering processing at non-threat-related locations.

Persistent affective biases in human amygdala response following implicit priming with negative emotion concepts

To what extent do past experiences shape our behaviors, perceptions, and thoughts even without explicit knowledge of these influences? Behavioral research has demonstrated that various cognitive processes can be influenced by conceptual representations implicitly primed during a preceding and unrelated task. Here we investigated whether emotion processing might also be influenced by prior incidental exposure to negative semantic material and which neural substrates would mediate these effects. During a first (priming) task, participants performed a variant of the hangman game with either negative or neutral emotion-laden words. Subsequently, they performed a second, unrelated visual task with fearful and neutral faces presented at attended or unattended locations. Participants were generally not aware of any relationships between the two tasks. We found that priming with emotional words enhanced amygdala sensitivity to faces in the subsequent visual task, while decreasing discriminative responses to threat. Furthermore, the magnitude of the induced bias in behavior and amygdala activation was predicted by the effectiveness of semantic access observed in the priming task. This demonstrates that emotional processing can be modulated by implicit influence of environmental information processed at an earlier time, independently of volitional control.

Attentional Modulations Related to Spatial Gating but Not to Allocation of Limited Resources in Primate V1

Attention can modulate neural responses in sensory cortical areas and improve behavioral performance in perceptual tasks. However, the nature and purpose of these modulations remain under debate. Here weused voltage-sensitive dye imaging (VSDI) to measure V1 population responses while monkeys performed a difficult detection task under focal or distributed attention. We found that V1 responses at attended locations are significantly elevated relative to actively ignored or irrelevant locations, consistent with the hypothesis that an important goal of attention in V1 is to highlight task-relevant information. Surprisingly, these modulations were indistinguishable under focal and distributed attention, suggesting a minor or no role for attention as a mechanism for allocating limited representational resources in V1. The response elevation at attended locations is additive, is widespread, and starts shortly before stimulus onset. This elevation could contribute to spatial gating by biasing competition in subsequent processing stages in favor of attended stimuli.

Nonverbal spatially selective attention in 4- and 5-year-old children

Under some conditions 4- and 5-year-old children can differentially process sounds from attended and unattended locations. In fact, the latency of spatially selective attention effects on auditory processing as measured with event-related potentials (ERPs) is quite similar in young children and adults. However, it is not clear if developmental differences in the polarity, distribution, and duration of attention effects are best attributed to acoustic characteristics, availability of non-spatial attention cues, task demands, or domain. In the current study adults and children were instructed to attend to one of two simultaneously presented soundscapes (e.g., city sounds or night sounds) to detect targets (e.g., car horn or owl hoot) in the attended channel only. Probes presented from the same location as the attended soundscape elicited a larger negativity by 80 ms after onset in both adults and children. This initial negative difference (Nd) was followed by a larger positivity for attended probes in adults and another negativity for attended probes in children. The results indicate that the neural systems by which attention modulates early auditory processing are available for young children even when presented with nonverbal sounds. They also suggest important interactions between attention, acoustic characteristics, and maturity on auditory evoked potentials.

Hemispheric asymmetry in the efficiency of attentional networks

Despite the fact that hemispheric asymmetry of attention has been widely studied, a clear picture of this complex phenomenon is still lacking. The aim of the present study was to provide an efficient and reliable measurement of potential hemispheric asymmetries of three attentional networks, i.e. alerting, orienting and executive attention. Participants (N=125) were tested with the Lateralized Attention Network Test (LANT) that allowed us to investigate the efficiency of the networks in both visual fields (VF). We found a LVF advantage when a target occurred in an unattended location, which seems to reflect right hemisphere superiority in control of the reorienting of attention. Furthermore, a LVF advantage in conflict resolution was observed, which may indicate hemispheric asymmetry of the executive network. No VF effect for alerting was found. The results, consistent with the common notion of general right hemisphere dominance for attention, provide a more detailed account of hemispheric asymmetries of the attentional networks than previous studies using the LANT task.

Increased Sensitivity to Perceptual Interference in Adults with Attention Deficit Hyperactivity Disorder

Difficulty with selective attention is a frequent complaint of adult patients with ADHD, but selective attention tasks have not provided robust evidence of attentional dysfunction in this group. Two experiments examine this puzzle by distinguishing between failures of spatial selection and problems due to sensitivity to perceptual interference. In Experiment 1, we measured the level of perceptual interference generated by targets in crowded displays with nearby distractors by comparing luminance thresholds in both distractor-present (noise) and distractor-absent (clean) displays. ADHD and control participants had comparable thresholds for clean displays, but ADHD individuals had elevated thresholds to crowded displays. These effects could be explained in two distinct ways. Deficits may have arisen from amplified visual interference in the noise condition, or from abnormalities in top-down attentional processes that reduce visual interference. Experiment 2 adjusted for individual perceptual differences with clean and noise displays, before measuring visual interference resolution at attended versus unattended locations. ADHD and control groups had comparable interference resolution at attended locations. These results suggest that perceptual interference rather than spatial attention deficits may account for some deficits in ADHD. This putative deficit in sensory function highlights a potential early-stage perceptual processing deficit in ADHD distinct from selective attention.

Anxiety and deficient inhibition of threat distractors: Spatial attention span and time course

We investigated whether anxiety facilitates detection of threat stimuli outside the focus of overt attention, and the time course of the interference produced by threat distractors. Threat or neutral word distractors were presented in attended (foveal) and unattended (parafoveal) locations followed by an unrelated probe word at 300 ms (Experiments 1 and 2) or 1000 ms (Experiment 2) stimulus–onset asynchrony (SOA) in a lexical decision task. Results showed: (1) no effects of trait anxiety on selective saccades to the parafoveal threat distractors; (2) interference with probe processing (i.e., slowed lexical decision times) following a foveal threat distractor at 300 ms SOA for all participants, regardless of anxiety, but only for high-anxiety participants at 1000 ms SOA; and (3) no interference effects of parafoveal threat distractors. These findings suggest that anxiety does not enhance preattentive semantic processing of threat words. Rather, anxiety leads to delays in the inhibitory control of attended task-irrelevant threat stimuli.

Subliminal access to abstract face representations does not rely on attention

The present study used masked repetition priming to examine whether face representations can be accessed without attention. Two experiments using a face recognition task (fame judgement) presented masked repetition and control primes in spatially unattended locations prior to target onset. Experiment 1 (n=20) used the same images as primes and as targets and Experiment 2 (n=17) used different images of the same individual as primes and targets. Repetition priming was observed across both experiments regardless of whether spatial attention was cued to the location of the prime. Priming occurred for both famous and non-famous targets in Experiment 1 but was only reliable for famous targets in Experiment 2, suggesting that priming in Experiment 1 indexed access to view-specific representations whereas priming in Experiment 2 indexed access to view-invariant, abstract representations. Overall, the results indicate that subliminal access to abstract face representations does not rely on attention.

The neural processing of fearful faces without attention and consciousness: An event-related potential study

To investigate whether the non-conscious processing of fearful faces exist in unattended condition, event-related potentials (ERPs) were recorded in a facial expression detection task. Participants were asked to discriminate the facial expressions (fearful or neutral) at the attended location. Unattended faces were associated with a response that was either congruent or in conflict with the response to the attended face. ERP results showed that the trials with response conflict between attended and unattended faces enhanced the amplitude of the P3 component when the neutral face was presented at attended location and the fearful face was presented at the unattended location. Our findings imply that the non-conscious fearful faces can be processed in the unattended condition.