Prefrontal GABA and glutamate-glutamine levels affect sustained attention.

Attention levels fluctuate during the course of daily activities. However, factors underlying sustained attention are still unknown. We investigated mechanisms of sustained attention using psychological, neuroimaging, and neurochemical approaches. Participants were scanned with functional magnetic resonance imaging (fMRI) while performing gradual-onset, continuous performance tasks (gradCPTs). In gradCPTs, narrations or visual scenes gradually changed from one to the next. Participants pressed a button for frequent Go trials as quickly as possible and withheld responses to infrequent No-go trials. Performance was better for the visual gradCPT than for the auditory gradCPT, but the 2 were correlated. The dorsal attention network was activated during intermittent responses, regardless of sensory modality. Reaction-time variability of gradCPTs was correlated with signal changes (SCs) in the left fronto-parietal regions. We also used magnetic resonance spectroscopy (MRS) to measure levels of glutamate-glutamine (Glx) and γ-aminobutyric acid (GABA) in the left prefrontal cortex (PFC). Glx levels were associated with performance under undemanding situations, whereas GABA levels were related to performance under demanding situations. Combined fMRI-MRS results demonstrated that SCs of the left PFC were positively correlated with neurometabolite levels. These findings suggest that a neural balance between excitation and inhibition is involved in attentional fluctuations and brain dynamics.

The function of REM and NREM sleep on memory distortion and consolidation.

During rapid eye movement (REM) sleep, newly consolidated memories can be distorted to adjust the existing memory base in memory integration. However, only a few studies have demonstrated the role of REM sleep in memory distortion. The present study aims to clarify the role of REM sleep in the facilitation of memory distortion, that is, hindsight bias, compared to non-rapid eye movement (NREM) sleep and wake states. The split-night paradigm was used to segregate REM and NREM sleep. The hypotheses are (1) hindsight bias-memory distortion-is more substantial during REM-rich sleep (late-night sleep) than during NREM-rich sleep (early-night sleep); (2) memory stabilization is more substantial during NREM-rich sleep (early-night sleep) than during REM-rich sleep (late-night sleep); and (3) memory distortion takes longer time than memory stabilization. The results of the hindsight bias test show that more memory distortions were observed after the REM condition in comparison to the NREM condition. Contrary to the hindsight bias, the correct response in the word-pair association test was observed more in the NREM than in the REM condition. The difference in the hindsight bias index between the REM and NREM conditions was identified only one week later. Comparatively, the difference in correct responses in the word-pair association task between the conditions appeared three hours later and one week later. The present study found that (1) memory distortion occurs more during REM-rich sleep than during NREM-rich sleep, while memory stabilization occurs more during NREM-rich sleep than during REM-rich sleep. Moreover, (2) the newly encoded memory could be stabilized immediately after encoding, but memory distortion occurs over several days. These results suggest that the roles of NREM and REM sleep in memory processes could be different.

Effect of Visual Attention on Binocular Fusion Limits.

We examined the effect of visual attention on binocular fusion limits by using Posner's spatial cueing paradigm that entails cued shifts of attentional focus. Results showed that attention decreases the fusion limit. Observers perceived diplopia of a binocular line within +/-26.5 arcmin disparity (+/- correspond to uncrossed and crossed, respectively) more frequently when it was oriented to the line than when cued attention was directed elsewhere. We discuss the results in terms of attention increasing spatial resolution and contrast sensitivity.

Differential Contributions of GABA Concentration in Frontal and Parietal Regions to Individual Differences in Attentional Blink.

UNLABELLED: Selective attention plays an important role in identifying transient objects in a complex visual scene. Attentional control ability varies with observers. However, it is unclear what neural mechanisms are responsible for individual differences in attentional control ability. The present study used the following attentional blink paradigm: when two targets are to be identified in rapid serial visual presentation, the processing of the first target interrupts the identification of the second one appearing within 500 ms after the first-target onset. It has been assumed that the reduction of the second-target accuracy is mainly due to a transient inhibition of attentional reorienting from the first to the second target, which is modulated by the GABA system. Using magnetic resonance spectroscopy, we investigated whether individual variation of attentional blink magnitude is associated with GABA concentrations in the left prefrontal cortex (PFC), right posterior-parietal cortex (PPC), and visual cortex (VC) of humans. GABA concentrations in the PFC were related negatively to attentional blink magnitude and positively to the first-target accuracy. GABA concentrations in the PPC were positively correlated with attentional blink magnitude. However, GABA concentrations in the VC did not contribute to attentional blink magnitude and first-target accuracy. Our results suggest that frontoparietal inhibitory mechanisms are closely linked with individual differences in attentional processing and that functional roles of the GABAergic system in selective attention differ between the PFC and PPC. SIGNIFICANCE STATEMENT: Selective attention is the process of picking up task-relevant information in the environment. Attentional blink reflects time constraints of visual attention. It has been assumed that attentional blink is induced by the inhibition of attentional reorienting to other objects. This study used magnetic resonance spectroscopy to noninvasively measure concentrations of GABA, the principal inhibitory neurotransmitter, in the human brain. We show that a neural interaction between GABA concentrations in the prefrontal and posterior parietal regions accounts for the interindividual variability of attentional blink magnitude. Our results provide direct evidence that the GABAergic system in the frontoparietal networks is responsible for temporal aspects of attentional control ability.

Dynamic Transitions Between Brain States Predict Auditory Attentional Fluctuations.

Achievement of task performance is required to maintain a constant level of attention. Attentional level fluctuates over the course of daily activities. However, brain dynamics leading to attentional fluctuation are still unknown. We investigated the underlying mechanisms of sustained attention using functional magnetic resonance imaging (fMRI). Participants were scanned with fMRI while performing an auditory, gradual-onset, continuous performance task (gradCPT). In this task, narrations gradually changed from one to the next. Participants pressed a button for frequent Go trials (i.e., male voices) as quickly as possible and withheld responses to infrequent No-go trials (i.e., female voices). Event-related analysis revealed that frontal and temporal areas, including the auditory cortex, were activated during successful and unsuccessful inhibition of predominant responses. Reaction-time (RT) variability throughout the auditory gradCPT was positively correlated with signal changes in regions of the dorsal attention network: superior frontal gyrus and superior parietal lobule. Energy landscape analysis showed that task-related activations could be clustered into different attractors: regions of the dorsal attention network and default mode network. The number of alternations between RT-stable and erratic periods increased with an increase in transitions between attractors in the brain. Therefore, we conclude that dynamic transitions between brain states are closely linked to auditory attentional fluctuations.

Differential contributions of the intraparietal sulcus and the inferior parietal lobe to attentional blink: evidence from transcranial magnetic stimulation.

When two targets (T1 and T2) are to be identified in rapid serial visual presentation, the response to T1 induces impairment of T2 report if T2 appears within 500 msec after T1 (attentional blink: AB). AB is thought to reflect temporal limitations of attention which affect target perception. Recent research suggests that the intraparietal sulcus (IPS) contributes to an attentional set associated with task goals, whereas the inferior parietal lobe (IPL) is associated with the disengagement and reorienting of attention to a relevant stimulus presented outside the current focus of attention. We investigated respective involvement of the IPS and the IPL in AB using transcranial magnetic stimulation (TMS). The results of Experiment 1 showed that the magnitude of AB deficit decreased TMS disrupted activity of the IPS after T1 onset. In addition, an increased AB deficit occurred when TMS was delivered over the IPS or IPL after T2 onset. In Experiment 2, where participants were instructed to ignore T1, they showed an AB-like T2 deficit only when TMS was delivered to the IPS after a T2 onset. Findings are discussed in terms of hypotheses about the respective roles of the IPS, in realizing an attentional set, and the IPL, in contributing to a disengagement of attention (from T1 to T2) during an AB period.

[The integration of spatial frequency-based information in scene perception: evidence from spatially incongruent images].

Humans can recognize a complex natural scene even when it appears only briefly. The rapid recognition of natural scenes is accomplished by parallel processing of information based on multiple spatial frequencies and integration of this information. Previous studies have revealed the time course of integration of frequency-based information. However, it is still unclear how frequency-based information is integrated. There are two possible levels for the integration: One involves spatial integration of images and constructs a unified image, and the other entails semantic integration associated with the scene context level irrespective of spatial arrangements. We investigated the categorization accuracy of the low + high-pass images, in which a left-right mirror reversed low-pass image was superimposed on a nonreversed high-pass image or vice versa. In this context, the low+high-pass images were semantically integrable but spatially incongruent. The results indicated that accuracy of the low+high-pass images did not exceed the expected accuracy level estimated from separate presentations. This finding suggests that frequency-based information can be integrated spatially.

A frame at a different depth than a photograph enhances the apparent depth in the photograph.

Two experiments showed that a photo frame placed at a distance from the photo itself enhances the apparent depth of contents within the photo. In Experiment 1, 32 observers rated the apparent depth of 60 successively presented photos of scenes with pictorial depth cues. In a separate block of trials, the photos were presented either with a frame in front of each photo or without a frame. Observers also assessed apparent depth of the same 60 photos by choosing the photo that had greater apparent depth when a framed and a frameless photo of the same scene were presented side by side. We found that mean depth ratings were higher for framed than for frameless photos, and framed photos were chosen more often than frameless photos. In Experiment 2, 12 observers rated the apparent depth of 20 different photos that were successively presented with or without a frame. The frame was placed in front of, at the same distance as, or behind each photo. Mean ratings for front-framed and behind-framed photos were higher than those for equidistant-framed or frameless photos, and mean ratings increased with the distance between the photo and the frame. We hypothesize that having to process the relative depth between a photo and a frame reduces the effectiveness of flatness information provided by the photo.

Common principles underlie the fluctuation of auditory and visual sustained attention.

Sustained attention plays an important role in adaptive behaviours in everyday activities. As previous studies have mostly focused on vision, and attentional resources have been thought to be specific to sensory modalities, it is still unclear how mechanisms of attentional fluctuations overlap between visual and auditory modalities. To reduce the effects of sudden stimulus onsets, we developed a new gradual-onset continuous performance task (gradCPT) in the auditory domain and compared dynamic fluctuation of sustained attention in vision and audition. In the auditory gradCPT, participants were instructed to listen to a stream of narrations and judge the gender of each narration. In the visual gradCPT, they were asked to observe a stream of scenery images and indicate whether the scene was a city or mountain. Our within-individual comparison revealed that auditory and visual attention are similar in terms of the false alarm rate and dynamic properties including fluctuation frequency. Absolute timescales of the fluctuation in the two modalities were comparable, notwithstanding the difference in stimulus onset asynchrony. The results suggest that fluctuations of visual and auditory attention are underpinned by common principles and support models with a more central, modality-general controller.

Usability of liquid crystal displays for research in the temporal characteristics of perception and attention.

Recently, the use of liquid crystal displays (LCDs) in computer monitors has increased in popularity. Can LCDs produce results similar to those obtained in cathode-ray tube (CRT) displays in studies of temporal attention and perception tasks? Performance in two tasks (metacontrast masking and attentional blink) was examined using an LCD, a CRT oscilloscope, and a raster scan CRT display. Experiment 1 focused on metacontrast masking where a typical metacontrast function emerged irrespective of monitor type. Experiments 2 and 3 examined whether differences in monitors influence the attentional blink. Again, all displays elicited similar performance profiles for both the attentional blink and the trade-off between identification accuracy of the two targets. Although our results may not generalize to all LCD applications and all experimental paradigms, they indicate that LCDs can reproduce results similar to those found in metacontrast masking and attentional blink studies that were originally identified with CRT displays.

Age-related differences in effects of non-driving related tasks on takeover performance in automated driving.

INTRODUCTION: During SAE level 3 automated driving, the driver's role changes from active driver to fallback-ready driver. Drowsiness is one of the factors that may degrade driver's takeover performance. This study aimed to investigate effects of non-driving related tasks (NDRTs) to counter driver's drowsiness with a Level 3 system activated and to improve successive takeover performance in a critical situation. A special focus was placed on age-related differences in the effects. METHOD: Participants of three age groups (younger, middle-aged, older) drove the Level 3 system implemented in a high-fidelity motion-based driving simulator for about 30 min under three experiment conditions: without NDRT, while watching a video clip, and while switching between watching a video clip and playing a game. The Karolinska Sleepiness Scale and eyeblink duration measured driver drowsiness. At the end of the drive, the drivers had to take over control of the vehicle and manually change the lane to avoid a collision. Reaction time and steering angle variability were measured to evaluate the two aspects of driving performance. RESULTS: For younger drivers, both single and multiple NDRT engagements countered the development of driver drowsiness during automated driving, and their takeover performance was equivalent to or better than their performance without NDRT engagement. For older drivers, NDRT engagement did not affect the development of drowsiness but degraded takeover performance especially under the multiple NDRT engagement condition. The results for middle-aged drivers fell at an intermediate level between those for younger and older drivers. Practical Applications: The present findings do not support general recommendations of NDRT engagement to counter drowsiness during automated driving. This study is especially relevant to the automotive industry's search for options that will ensure the safest interfaces between human drivers and automation systems.

The Role of Low-Spatial Frequency Components in the Processing of Deceptive Faces: A Study Using Artificial Face Models.

Interpreting another's true emotion is important for social communication, even in the face of deceptive facial cues. Because spatial frequency components provide important clues for recognizing facial expressions, we investigated how we use spatial frequency information from deceptive faces to interpret true emotion. We conducted two different tasks: a face-generating experiment in which participants were asked to generate deceptive and genuine faces by tuning the intensity of happy and angry expressions (Experiment 1) and a face-classification task in which participants had to classify presented faces as either deceptive or genuine (Experiment 2). Low- and high-spatial frequency (LSF and HSF) components were varied independently. The results showed that deceptive happiness (i.e., anger is the hidden expression) involved different intensities for LSF and HSF. These results suggest that we can identify hidden anger by perceiving unbalanced intensities of emotional expression between LSF and HSF information contained in deceptive faces.

Effects of scheduled manual driving on drowsiness and response to take over request: A simulator study towards understanding drivers in automated driving.

Because current automated vehicles have operational limitations, it is important to ensure that the fallback-ready driver is able to perform appropriately when required to take over control of the vehicle. However, time-related increase in driver drowsiness is well-known, and drowsy driving can affect response to take-over request (TOR). It was previously reported that a scheduled period of manual driving during automated driving was beneficial in maintaining driver arousal level. The present driving simulator study investigates the effects of scheduled manual driving on driver drowsiness and performance, as well as age differences therein. A total of 115 participants, whose gender was balanced and age was distributed uniformly from 20 to 70 years, drove an automated vehicle for 31 min, and a TOR was prompted before a collision event. A between-subjects design comprised two conditions: with versus without a scheduled 10-min interval of manual driving that ended 10 min before TOR. The Karolinska Sleepiness Scale and eyeblink durations estimated from electrooculograms (EOG) were used to subjectively and objectively measure participant's drowsiness. Reaction time, standard deviation of steering wheel angle, and minimum Time-to-Collison (TTC) were extracted to measure driver performance in response to TOR. The alleviating effect on drowsiness of 10-min scheduled manual driving became non-significant after another 10-min period of automated driving. Although the scheduled manual driving had no significant effect for younger drivers, older drivers reacted significantly more slowly in both steering and braking at the critical event. These findings provide essential insights for human-vehicle interactions: Scheduled manual driving cannot maintain drivers' arousal level for 10 min afterwards, and for older drivers, it would be better to avoid unnecessary task-switching between manual and automated driving.

Recovery from object substitution masking induced by transient suppression of visual motion processing: a repetitive transcranial magnetic stimulation study.

Object substitution masking is a form of visual backward masking in which a briefly presented target is rendered invisible by a lingering mask that is too sparse to produce lower image-level interference. Recent studies suggested the importance of an updating process in a higher object-level representation, which should rely on the processing of visual motion, in this masking. Repetitive transcranial magnetic stimulation (rTMS) was used to investigate whether functional suppression of motion processing would selectively reduce substitution masking. rTMS-induced transient functional disruption of cortical area V5/MT+, which is important for motion analysis, or V1, which is reciprocally connected with V5/MT+, produced recovery from masking, whereas sham stimulation did not. Furthermore, masking remained undiminished following rTMS over the region 2 cm posterior to V5/MT+, ruling out nonspecific effects of real stimulation and confirming regional specificity of the rTMS effect. The results suggest that object continuity via the normal function of the visual motion processing system might in part contribute to this masking. The relation of these findings to the reentrant processing view of object substitution masking and other visual phenomena is discussed.

The edge artifact in the point-spread function-based PET reconstruction at different sphere-to-background ratios of radioactivity.

OBJECTIVE: The aim of this study was to quantitatively evaluate the edge artifacts in PET images reconstructed using the point-spread function (PSF) algorithm at different sphere-to-background ratios of radioactivity (SBRs). METHODS: We used a NEMA IEC body phantom consisting of six spheres with 37, 28, 22, 17, 13 and 10 mm in inner diameter. The background was filled with (18)F solution with a radioactivity concentration of 2.65 kBq/mL. We prepared three sets of phantoms with SBRs of 16, 8, 4 and 2. The PET data were acquired for 20 min using a Biograph mCT scanner. The images were reconstructed with the baseline ordered subsets expectation maximization (OSEM) algorithm, and with the OSEM + PSF correction model (PSF). For the image reconstruction, the number of iterations ranged from one to 10. The phantom PET image analyses were performed by a visual assessment of the PET images and profiles, a contrast recovery coefficient (CRC), which is the ratio of SBR in the images to the true SBR, and the percent change in the maximum count between the OSEM and PSF images (Δ % counts). RESULTS: In the PSF images, the spheres with a diameter of 17 mm or larger were surrounded by a dense edge in comparison with the OSEM images. In the spheres with a diameter of 22 mm or smaller, an overshoot appeared in the center of the spheres as a sharp peak in the PSF images in low SBR. These edge artifacts were clearly observed in relation to the increase of the SBR. The overestimation of the CRC was observed in 13 mm spheres in the PSF images. In the spheres with a diameter of 17 mm or smaller, the Δ % counts increased with an increasing SBR. The Δ % counts increased to 91 % in the 10-mm sphere at the SBR of 16. CONCLUSIONS: The edge artifacts in the PET images reconstructed using the PSF algorithm increased with an increasing SBR. In the small spheres, the edge artifact was observed as a sharp peak at the center of spheres and could result in overestimation.

Involvement of V5/MT+ in object substitution masking: evidence from repetitive transcranial magnetic stimulation.

The visibility of a briefly presented target can be reduced by a subsequent weak mask that does not touch it, when the target is encoded in low spatiotemporal resolution. This phenomenon, called object substitution masking, has recently been proposed to reflect information updating in object-level representation, with perception of the target and the mask belonging to a single object through apparent motion. We investigated this issue by applying repetitive transcranial magnetic stimulation over V5/MT+, specialized in visual motion processing. The transient functional disruption of V5/MT+ produced by repetitive transcranial magnetic stimulation attenuated object substitution masking, while sham stimulation did not. Our results suggest that object substitution masking is mediated by normal functioning of V5/MT+. We conclude that repetitive transcranial magnetic stimulation of V5/MT+ impaired perceived object continuity and reduced object substitution masking accordingly.

Attentive tracking of moving objects in real 3D space.

Results of earlier multiple object tracking (MOT) studies imply that humans can track several moving targets in a 2D environment simultaneously. Recently, a study suggested that stereoscopic depth has positive effect on tracking multiple objects when the objects are presented separately on multiple planes. However, it remains unclear whether or not humans can track moving targets in a real 3D environment. In this study, we investigated this issue displaying four targets and four distractors on near and/or far depth planes separated physically by 6, 10 or 50 cm using a half-mirror and two CRT-monitors. In addition we also tested whether participants could track the targets when either a target or a distractor changed depth during tracking. Our results suggested that performance dropped if the targets were presented on both depth planes especially when the distance between the planes was 50 cm. In addition, participants could track a depth-changed target if targets were presented on both planes before the start of a motion phase regardless of whether the initial state of targets distribution randomly varied or not, whereas they failed to track the target if all targets were presented on a single plane before MOT. In conclusion, humans have the ability to set attention on a wide range for MOT in a real 3D environment, with the provision that the efficiency of the tracking is critically dependent not only on the distance in depth but also on an initial state of distribution of the targets without the predictability of the initial state.

Pupillometric evidence for the locus coeruleus-noradrenaline system facilitating attentional processing of action-triggered visual stimuli.

It has been argued that attentional processing of visual stimuli is facilitated by a voluntary action that triggers the stimulus onset. However, the relationship between action-induced facilitation of attention and the neural substrates has not been well established. The present study investigated whether the locus coeruleus-noradrenaline (LC-NA) system is involved in this facilitation effect. A rapid serial visual presentation paradigm was used to assess the dynamics of transient attention in humans. Participants were instructed to change a digit stream to a letter stream by pressing a button and specifying successive targets of four letters. Pupil dilation was measured as an index of LC-NA function. Accuracy of target identification was better when the temporal delay between participants' key press and target onset was 800 ms than when targets appeared just after the key press or when targets appeared without key press. Accuracy of target identification was positively correlated with both the peak amplitude of pupil dilation and the pupil size at the time of the key press. These results indicate that target identification in the visual task is closely linked to pupil dilation. We conclude that the LC-NA system plays an important role in the facilitation of transient attention driven by voluntary action.

Peristomal pagetoid spread of urothelial carcinoma of the ureter.

Patients with ostomy including urinary stoma often develop peristomal complications, especially skin damage. The patient in this case was a 69-year old female with a history of urothelial carcinoma of the bladder and left ureter who underwent transurethral resection of a bladder tumor, nephroureterectomy and cystectomy combined with ureterocutaneostomy. Later, she had recurrence of urothelial carcinoma in the remaining ureter that spread to the peristomal epidermis, with a skin appearance resembling Paget's disease. We report this case based on its clinical significance since we believe it is the first description of this condition in the literature.

Attention-free integration of spatial frequency-based information in natural scenes.

The integration of visual image information provided by low and high spatial frequency channels is critical to rapid perception of natural scenes. However, little is known about the role of attention in integrating this information. In two experiments, using attention-demanding tasks, we examined the advantage of integration, i.e. the superior categorization accuracies for images, using a wide range of different spatial frequencies. In Experiment 1, a spatially central to-be-identified letter and a peripheral filtered image of a natural scene appeared simultaneously. In Experiment 2, the letter and the image were presented sequentially at the same spatial location. In both experiments results consistently showed an advantage of integration in categorization behavior that was not influenced by attention-demanding tasks. This finding suggests that the integration of frequency-based information in natural scenes is attention-free.