Visual Search Performance Research Articles

Research on similarity bias in dual objective visual search based on nuclear power human-machine interface icons

Using icons from nuclear power interface as the research object, this study explored how icon similarity affected the performance of dual objective visual search. Firstly, the process of generating similarity bias was described from the perspective of human cognitive processing. The feature attributes of nuclear power icons were extracted, and then associated and mapped with similarity bias attributes. Secondly, a total of 16 instruction icons, device icons, and component icons were selected to propose icon coding logic for different similarity dimensions, and similarity experimental materials were designed. Finally, a dual objective search experiment with a 4 × 4 matrix was conducted to explore the impact of graph similarity on search performance and to determine the priority of perceptual similarity, semantic similarity, and memory similarity. High-level (H) similarity between the two targets resulted in superior visual search performance (p = 0.01 between the response times of similarity high and medium/low). Improving experiential familiarity enhanced search performance in cases of low-level (L) (p = 0.021) and medium-level (M) (p ≤ 0.009) icon similarity, but had no significant impact on search performance in cases of high-level (H) similarity (p ≥ 0.269). Compared to semantic similarity, enhancing perceptual similarity was more likely to improve search performance(p = 0.024).

The impact of point symbol similarity on visual search on maps

ABSTRACT The study presented in this paper investigates the impact of the similarity level of cartographic point symbols on visual search performance. Specifically, we explore the application of an algorithm for quantitatively assessing symbols’ shape similarity, and apply the results of such automated analysis in a simple target search task on a map with distractors of varying similarity levels. Our primary hypothesis posits that the more similar the target symbol and distractors, the more challenging the visual search becomes in terms of search efficiency and eye metric performance. In a controlled laboratory experiment utilizing eye-tracking device, 33 participants were recruited, and 60 map stimuli were tested with each participant. The results confirmed the hypothesis assumptions. However, symbols based on a round shape were consistently the easiest to find at every similarity level. Eye movement analysis revealed differences in absolute pupil size between male and female participants, possibly associated with cognitive load, although without affecting search time performance. Interestingly, scan-path speed decreased with an increasing level of similarity between the target symbol and distractors. The practical implication of this study lies in the potential development of tools to assist map designers in selecting symbols with low similarity, thereby ensuring improved map readability.

Visual search of illusory contours: The role of illusory contour clarity.

Illusory contours demonstrate an important function of the visual system-object inference from incomplete boundaries, which can arise from factors such as low luminance, camouflage, or occlusion. Illusory contours can be perceived with varying degrees of clarity depending on the features of their inducers. The present study aimed to evaluate whether illusory contour clarity influences visual search efficiency. Experiment 1 compared visual search performance for Kanizsa illusory stimuli and nonillusory inducer stimuli when manipulating inducer size as a clarity factor. Experiment 2 examined the effects of illusory contour clarity on visual search by manipulating the number of rings with missing arcs (i.e., line ends) comprising the inducers, for both illusory and nonillusory stimuli. To investigate whether surface alterations had an impact on visual search in Experiment 1, Experiment 3 examined search performance for Kanizsa-like stimuli formed from "smoothed" inducers compared with standard Kanizsa figures. The results of Experiments 1 and 2 indicated that while Kanizsa produced inefficient search, this was not contingent on the clarity of the illusory contours. Experiment 3 suggested that surface alterations of Kanizsa figures did impact visual search performance. Together, the results indicated that illusory contour clarity did not have much bearing on search performance. In certain conditions, Kanizsa figures even facilitated search compared with nonillusory stimuli, suggesting that rather than contour inference, surface features might have greater relevance in guiding visual attention.

Alpha transcranial alternating current stimulation as add-on to neglect training: a randomized trial

Abstract Visuospatial neglect is a common and debilitating condition following unilateral stroke, significantly impacting cognitive functioning and daily life. There is an urgent need for effective treatments that can provide clinically relevant and sustained benefits. In addition to traditional stroke treatment, non-invasive brain stimulation, such as transcranial alternating current stimulation, shows promise as a complementary approach to enhance stroke recovery. In the current study, we aimed to evaluate the additive effects of multi-session transcranial alternating current stimulation at alpha frequency when combined with visual scanning training in chronic stroke patients with visuospatial neglect. In this double-blind randomized controlled trial, we compared the effects of active transcranial alternating current stimulation at alpha frequency to sham (placebo) transcranial alternating current stimulation, both combined with visual scanning training. Both groups received eighteen 40-minute training sessions over a 6-week period. A total of 22 chronic visuospatial neglect patients participated in the study (active group n = 12, sham group n = 10). The median age was 61.0 years, with a median time since stroke of 36.1 months. We assessed the patients at six time-points: at baseline, after the first, ninth and eighteenth training sessions, as well as 1 week and 3 months following the completion of the combined neuromodulation intervention. The primary outcome measure was the change in performance on a visual search task, specifically the star cancellation task. Secondary outcomes included performance on a visual detection task, two line bisection tasks and three tasks evaluating visuospatial neglect in daily living. We found significantly improved visual search (primary outcome) and visual detection performance in the neglected side in the active transcranial alternating current stimulation group, compared to the sham transcranial alternating current stimulation group. We did not observe stimulation effects on line bisection performance nor in daily living. Time effects were observed on all but one outcome measures. Multi-session transcranial alternating current stimulation combined with visual scanning training may be a more effective treatment for chronic visuospatial neglect than visual scanning training alone. These findings provide valuable insights into novel strategies for stroke recovery, even long after the injury, with the aim of enhancing cognitive rehabilitation outcomes and improving the overall quality of life for individuals affected by this condition. Trial registration: ClinicalTrials.gov; registration number: NCT05466487; https://clinicaltrials.gov/ct2/show/NCT05466487

Skeuomorphic or flat? The effects of icon style on visual search and recognition performance

Although there have been many previous studies on icon visual search and recognition performance, only a few have considered the effects of both the internal and external characteristics of icons. In this behavioral study, we employed a visual search task and a semantic recognition task to explore the effects of icon style, semantic distance (SD), and task difficulty on users’ performance in perceiving and identifying icons. First, we created and filtered 64 new icons, which were divided into four different groups (flat design & close SD, flat design & far SD, skeuomorphic design & close SD, skeuomorphic design & far SD) through expert evaluation. A total of 40 participants (13 men and 27 women, ages ranging from 19 to 25 years, mean age = 21.9 years, SD=1.93) were asked to perform an icon visual search task and an icon recognition task after a round of learning. Participants’ accuracy and response time were measured as a function of the following independent variables: two icon styles (flat or skeuomorphic style), two levels of SD (close or far), and two levels of task difficulty (easy or difficult). The results showed that flat icons had better visual search performance than skeuomorphic icons; this beneficial effect increased as the task difficulty increased. However, in the icon recognition task, participants’ performance in recalling skeuomorphic icons was significantly better than that in recalling flat icons. Furthermore, a strong interaction effect between icon style and task difficulty was observed for response time. As the task difficulty decreased, the difference in recognition performance between these two different icon styles increased significantly. These findings provide valuable guidance for the design of icons in human–computer interaction interfaces.

Group efficiency based on the termination rule in the multiple-targets visual search task.

In practical visual search fields, observers often encounter errors that result from an unknown number of targets, which may induce reduced accuracy and speed. Our current study addresses the potential enhancement of collaborative search efficiency as a dyad to mitigate such incurred search costs. Utilizing the capacity coefficient, we evaluated search efficiency and explored the interplay of task difficulty and termination rule in collaborative visual search. Our prediction that collaborative benefits increased with elevated task difficulty was not supported in Experiment 1, where participants were tasked with judging the presence of any target. In contrast, Experiment 2 demonstrated that dyads exhibited greater search efficiency during exhaustive searches for multiple targets with elevated task difficulty. Notably, our findings indicated an advantage in dyad searches compared to baseline predictions from individual searches. Our results underscored the significance of task difficulty and termination rules in leveraging human resources for improved collaborative visual search performance.

Top-Down Priors Disambiguate Target and Distractor Features in Simulated Covert Visual Search.

Several models of visual search consider visual attention as part of a perceptual inference process, in which top-down priors disambiguate bottom-up sensory information. Many of these models have focused on gaze behavior, but there are relatively fewer models of covert spatial attention, in which attention is directed to a peripheral location in visual space without a shift in gaze direction. Here, we propose a biologically plausible model of covert attention during visual search that helps to bridge the gap between Bayesian modeling and neurophysiological modeling by using (1) top-down priors over target features that are acquired through Hebbian learning, and (2) spatial resampling of modeled cortical receptive fields to enhance local spatial resolution of image representations for downstream target classification. By training a simple generative model using a Hebbian update rule, top-down priors for target features naturally emerge without the need for hand-tuned or predetermined priors. Furthermore, the implementation of covert spatial attention in our model is based on a known neurobiological mechanism, providing a plausible process through which Bayesian priors could locally enhance the spatial resolution of image representations. We validate this model during simulated visual search for handwritten digits among nondigit distractors, demonstrating that top-down priors improve accuracy for estimation of target location and classification, relative to bottom-up signals alone. Our results support previous reports in the literature that demonstrated beneficial effects of top-down priors on visual search performance, while extending this literature to incorporate known neural mechanisms of covert spatial attention.

Site- and frequency-specific enhancement of visual search performance with online individual alpha frequency (IAF) repetitive transcranial magnetic stimulation (rTMS) to the inferior frontal junction.

In this study, repetitive transcranial magnetic stimulation was applied to either the right inferior frontal junction or the right inferior parietal cortex during a difficult aerial reconnaissance search task to test its capacity to improve search performance. Two stimulation strategies previously found to enhance cognitive performance were tested: The first is called "addition by subtraction," and the second condition utilizes a direct excitatory approach by applying brief trains of high-frequency repetitive transcranial magnetic stimulation immediately before task trials. In a within-subjects design, participants were given active or sham repetitive transcranial magnetic stimulation at either 1Hz or at 1Hz above their individual peak alpha frequency (IAF + 1, mean 11.5Hz), delivered to either the right inferior frontal junction or the right inferior parietal cortex, both defined with individualized peak functional magnetic resonance imaging (fMRI) activation obtained during the visual search task. Results indicated that among the 13 participants who completed the protocol, only active IAF + 1 stimulation to inferior frontal junction resulted in significant speeding of reaction time compared to sham. This site- and frequency-specific enhancement of performance with IAF + 1 repetitive transcranial magnetic stimulation applied immediately prior to task trials provides evidence for the involvement of inferior frontal junction in guiding difficult visual search, and more generally for the use of online repetitive transcranial magnetic stimulation directed at specific functional networks to enhance visual search performance.

Selectively maintaining an object's feature in visual working memory: A comparison between highly discriminable and fine-grained features.

Selectively maintaining information is an essential function of visual working memory (VWM). Recent VWM studies have mainly focused on selective maintenance of objects, leaving the mechanisms of selectively maintaining an object's feature in VWM unknown. Based on the interactive model of perception and VWM, we hypothesized that there are distinct selective maintenance mechanisms for objects containing fine-grained features versus objects containing highly discriminable features. To test this hypothesis, we first required participants to memorize a dual-feature object (colored simple shapes vs. colored polygons), and informed them about the target feature via a retro-cue. Then a visual search task was added to examine the fate of the irrelevant feature. The selective maintenance of an object's feature predicted that the irrelevant feature should be removed from the active state of VWM and should not capture attention when presented as a distractor in the visual search task. We found that irrelevant simple shapes impaired performance in the visual search task (Experiment 1). However, irrelevant polygons did not affect visual search performance (Experiment 2), and this could not be explained by decay of polygons (Experiment 3) or by polygons not capturing attention (Experiment 4). These findings suggest that VWM adopts dissociable mechanisms to selectively maintain an object's feature, depending on the feature's perceptual characteristics.

The impact of clock timing on VDT visual search performance under time constraint.

Conducting Visual Display Terminal (VDT) visual search tasks under time constraint has broad applications in fields such as security checks, medical diagnostics, and rescue operations. While excessive time pressure can impair performance, moderate time pressure can motivate individuals to complete tasks and increase productivity. Investigating the positive impact of time pressure on visual search tasks has become a crucial area of study. Clock timing plays a vital role in the visual interface, influencing the perception of time pressure and impacting visual search performance. However, existing research has paid little attention to the induction of time pressure and the impact of clock timing in VDT visual interfaces on visual search performance. Hence, the objective of this study is to investigate the impact of clock timing on VDT visual search performance under time constraint. The content of the experimental tasks was determined through a pilot experiment. The formal experiment was conducted in two phases over six sessions. Participants were tasked with locating the letter "E" embedded within the distractor letter "F," displayed with a clock area above the interface. The first phase of experiments included conditions of no clock, 4-min clock timing, and 4-min countdown clock timing. In the second phase of the experiment, the clock display method was a countdown clock, with three experiments conducted featuring long time, medium time, and short time. Search speed and accuracy were used as primary performance evaluation metrics to examine the impact of clock timing methods and duration on visual search performance. Twenty-one undergraduate students participated in the formal experiment. In the first phase of experiments, participants demonstrated significantly faster reaction times (RTs) in tasks where a clock display was present compared to tasks without (ANOVA, F(2, 60) = 4.588, P = 0.014). However, there were no significant differences in accuracy rates across different timing conditions (ANOVA, F(2, 60) = 0.146, P = 0.865), and no significant correlation between RTs and accuracy was found (Kendall's R = 0.11, P = 0.914). During the second phase, RTs decreased significantly as time constraints became more stringent (ANOVA, F(2, 60) = 7.564, P < 0.05). Conversely, accuracy rates decreased significantly under shorter time constraints (ANOVA, F(2, 60) = 4.315, P < 0.05), with a negative correlation observed between RTs and accuracy (Kendall's R = 0.220, P < 0.01). Compared to conditions without clock displays, having clock displays significantly improved the speed of the visual search task, although the difference in accuracy was not statistically significant. In the context of shorter clock countdown limits, Shorter timing constraints resulted in faster search speeds but also led to reduced accuracy and increased fatigue. Overall, a correlation exists between search speed and accuracy in visual tasks, where higher speed often correlates with lower accuracy. These findings provide valuable insights into clock timing design for visual search interfaces under time pressure.

Age-related differences in resting-state, task-related, and structural brain connectivity: graph theoretical analyses and visual search performance.

Previous magnetic resonance imaging (MRI) research suggests that aging is associated with a decrease in the functional interconnections within and between groups of locally organized brain regions (modules). Further, this age-related decrease in the segregation of modules appears to be more pronounced for a task, relative to a resting state, reflecting the integration of functional modules and attentional allocation necessary to support task performance. Here, using graph-theoretical analyses, we investigated age-related differences in a whole-brain measure of module connectivity, system segregation, for 68 healthy, community-dwelling individuals 18-78years of age. We obtained resting-state, task-related (visual search), and structural (diffusion-weighted) MRI data. Using a parcellation of modules derived from the participants' resting-state functional MRI data, we demonstrated that the decrease in system segregation from rest to task (i.e., reconfiguration) increased with age, suggesting an age-related increase in the integration of modules required by the attentional demands of visual search. Structural system segregation increased with age, reflecting weaker connectivity both within and between modules. Functional and structural system segregation had qualitatively different influences on age-related decline in visual search performance. Functional system segregation (and reconfiguration) influenced age-related decline in the rate of visual evidence accumulation (drift rate), whereas structural system segregation contributed to age-related slowing of encoding and response processes (nondecision time). The age-related differences in the functional system segregation measures, however, were relatively independent of those associated with structural connectivity.

Individual differences in visual search: A systematic review of the link between visual search performance and traits or abilities

Visual search (VS) comprises a class of tasks that we typically perform several times during a day and requires intentionally scanning (with or without moving the eyes) the environment for a specific target (be it an object or a feature) among distractor stimuli. Experimental research in lab-based or real-world settings has offered insight into its underlying neurocognitive mechanisms from a nomothetic point of view. A lesser-known but rapidly growing body of quasi-experimental and correlational research has explored the link between individual differences and VS performance. This combines different research traditions and covers a wide range of individual differences in studies deploying a vast array of VS tasks. As such, it is a challenge to determine whether any associations highlighted in single studies are robust when considering the wider literature. However, clarifying such relationships systematically and comprehensively would help build more accurate models of VS, and it would highlight promising directions for future research. This systematic review provides an up to date and comprehensive synthesis of the existing literature investigating associations between common indices of performance in VS tasks and measures of individual differences mapped onto four categories of cognitive abilities (short-term working memory, fluid reasoning, visual processing and processing speed) and seven categories of traits (Big Five traits, trait anxiety and autistic traits). Consistent associations for both traits (in particular, conscientiousness, autistic traits and trait anxiety – the latter limited to emotional stimuli) and cognitive abilities (particularly visual processing) were identified. Overall, however, informativeness of future studies would benefit from checking and reporting the reliability of all measurement tools, applying multiplicity correction, using complementary techniques, study preregistration and testing why, rather than only if, a robust relation between certain individual differences and VS performance exists.

The Effect of Icon Color Combinations in Information Interfaces on Task Performance under Varying Levels of Cognitive Load

In human–computer interaction interfaces, icons serve as highly symbolic elements that convey information and significantly influence the performance of visual search and other tasks. Thus, the selection of appropriate colors plays a crucial role in the design of human–computer interfaces. This study aimed to investigate the effects of icon color combinations on human visual search task performance across various cognitive load conditions. The experiment was divided into two parts, involving a cognitive load test experiment and an icon search task, wherein the former required participants to select the target icon from 16 de-colored icons, and the latter involved selecting the target icon from 16 color combinations of 8 colors (background colors: black, red, blue, and purple; foreground colors: white, yellow, green, and turquoise). A total of 20 participants (11 females and 9 males, all aged between 18 and 24 years) were recruited for this experiment to perform both tasks sequentially. Through a comprehensive consideration of factors such as the NASA-TLX scale, retrieval time, etc., the experimental results revealed that cognitive load increased with time pressure, resulting in varying optimal color combinations for different cognitive load levels. Additionally, background colors did not affect task response time under different cognitive loads, whereas white foreground color was superior to turquoise foreground color in a medium cognitive load environment. Meanwhile, our results recommend prioritizing white-on-black as the preferred color combination, given that it demonstrated excellent cognitive performance in all three cognitive load environments. Conversely, white-on-blue is not recommended as a color combination for the design of high cognitive load environments. Concerning medium cognitive load environments, yellow-on-red or white-on-purple color combinations were preferred. Finally, in low cognitive load environments, white-on-purple is recommended as the primary color combination. Overall, this study provides a theoretical reference for the future design of interactive interface icons across various contexts.

Psychopathic traits and attentional control: Antisociality associated with poorer real-world cognitive functioning and egocentricity associated with poorer low-prevalence visual search performance due to quitting early

Attentional control is the process that enables focusing on executing goals without succumbing to distraction, and it is implicated in meaningful outcomes such as driving safety, perspective-taking, and emotion regulation. Across three studies we investigated the relationship between psychopathic traits (egocentricity, callousness, and antisocial tendencies) and: a) subjective experiences of attentional control in real-world contexts, b) performance on a task that differentiates proactive from reactive attentional control, and c) performance on a real-world relevant task that demands endogenous maintenance of a goal with minimal scaffolding from the task (low prevalence visual search). A strong and consistent finding was that antisocial tendencies were associated with poorer subjective real-world attentional control. Psychopathic traits were not reliability associated with individual differences in either proactive or reactive attentional control. Egocentricity was associated with poorer performance in low prevalence visual search, but this was mediated by a reduced quitting threshold (i.e., giving up on searching for the target earlier). This likely reflects reduced motivation rather than impaired ability. Altogether, there was no evidence for psychopathic traits being associated with enhanced attentional control. The differential relationships between different psychopathic traits and attentional control highlights the importance of distinguishing them.

Beyond the Wizard of Oz: Negative Effects of Imperfect Machine Learning to Examine the Impact of Reliability of Augmented Reality Cues on Visual Search Performance.

Despite knowing exactly what an object looks like, searching for it in a person's visual field is a time-consuming and error-prone experience. In Augmented Reality systems, new algorithms are proposed to speed up search time and reduce human errors. However, these algorithms might not always provide 100% accurate visual cues, which might affect users' perceived reliability of the algorithm and, thus, search performance. Here, we examined the detrimental effects of automation bias caused by imperfect cues presented in the Augmented Reality head-mounted display using the YOLOv5 machine learning model. 53 participants in the two groups received either 100% accurate visual cues or 88.9% accurate visual cues. Their performance was compared with the control condition, which did not include any additional cues. The results show how cueing may increase performance and shorten search times. The results also showed that performance with imperfect automation was much worse than perfect automation and that, consistent with automation bias, participants were frequently enticed by incorrect cues.

Investigating the Effect of Contextual Cueing with Face Stimuli on Electrophysiological Measures in Younger and Older Adults.

Extracting repeated patterns from our surroundings plays a crucial role in contextualizing information, making predictions, and guiding our behavior implicitly. Previous research showed that contextual cueing enhances visual search performance in younger adults. In this study, we investigated whether contextual cueing could also improve older adults' performance and whether age-related differences in the neural processes underlying implicit contextual learning could be detected. Twenty-four younger and 25 older participants performed a visual search task with contextual cueing. Contextual information was generated using repeated face configurations alongside random new configurations. We measured RT difference between new and repeated configurations; ERPs to uncover the neural processes underlying contextual cueing for early (N2pc), intermediate (P3b), and late (r-LRP) processes; and multiscale entropy and spectral power density analyses to examine neural dynamics. Both younger and older adults showed similar contextual cueing benefits in their visual search efficiency at the behavioral level. In addition, they showed similar patterns regarding contextual information processing: Repeated face configurations evoked decreased finer timescale entropy (1-20 msec) and higher frequency band power (13-30 Hz) compared with new configurations. However, we detected age-related differences in ERPs: Younger, but not older adults, had larger N2pc and P3b components for repeated compared with new configurations. These results suggest that contextual cueing remains intact with aging. Although attention- and target-evaluation-related ERPs differed between the age groups, the neural dynamics of contextual learning were preserved with aging, as both age groups increasingly utilized more globally grouped representations for repeated face configurations during the learning process.

Testing the contributions of proactive target and distractor templates in visual search performance

ABSTRACT When searching for objects with particular visual features, performance is sometimes improved by the presence of a salient colour distractor, such as a red item among green objects. Attention to such distractors is thought to be suppressed when the visual system expects their specific features (e.g., redness), but a complication with this view is that distractor expectancies are generally accompanied by anticipated target features, with their own associated attentional facilitation. We tested the role of these mechanisms by separately manipulating the colour specificity of salient distractors and of targets, and thus the ability to build up feature-specific templates for each type of search item. Experiment 1 employed singleton distractors appearing in unpredictable colours, preventing the formation of a feature-specific suppression template. Nevertheless, evidence of suppression was unchanged, suggesting that it does not require a fixed, predictable distractor. In Experiment 2, the singleton colour remained fixed while the target colour varied. Without a constant target colour, markers of singleton suppression were effectively abolished. The pattern of results suggests that observed suppression effects are largely driven by global enhancement of the expected target colour, possibly in combination with a second-order suppression mechanism that is not dependent on specific distractor features.

A novel gaze-based visual search task for children with CVI: A twin study

Visual search is often impaired in children with cerebral visual impairment (CVI), but the current assessment of visual search performance is limited. This study aimed to investigate underlying visual search processes in detail by including gaze-based measurements. Twin brothers (age 11.8 years), one diagnosed with CVI and one with neurotypical development, underwent a newly developed conjunction visual search task while simultaneously their gaze was recorded. In addition to speed and accuracy, we analyzed additional timing and spatial parameters of the search process before and after their initial fixation in the target area. The twin with CVI had good visual sensory functions, but impaired search performance indicated by longer search time and larger search areas. Also, it was observed that in more difficult task conditions, he tended to miss the target, even when fixating on it. These results point towards higher-order visual deficits. This study gives insight into the visual search challenges of a child with CVI. Mapping the search process in detail provided new and distinctive information that can shape more tailored support. Coupling verbal and nonverbal gaze-based outcomes is a promising first step towards a more inclusive nonverbal and nonmotor assessment.

Reduced spatial attentional distribution in older adults.

Older adults show decline in visual search performance, but the underlying cause remains unclear. It has been suggested that older adults' altered performance may be related to reduced spatial attention to peripheral visual information compared with younger adults. In this study, 18 younger (M = 21.6 years) and 16 older (M = 69.1 years) participants performed pop-out and serial visual search tasks with variously sized gaze-contingent artificial central scotomas (3°, 5°, or 7° diameter). By occluding central vision, we measured how attention to the periphery was contributing to the search performance. We also tested the effect of target eccentricity on search times and eye movements. We hypothesized that, if attention is reduced primarily in the periphery in older adults, we would observe longer search times for more eccentric targets and with central occlusion. During the pop-out search, older adults showed a steeper decline in search performance with increasing eccentricity and central scotoma size compared with younger adults. In contrast, during the serial search, older adults had longer search times than younger adults overall, independent of target eccentricity and scotoma size. Longer search times were attributed to higher cost-per-item slopes, indicating increased difficulty in simultaneously processing complex symbols made up of separable features in aging, possibly stemming from challenges in spatially binding individual features. Altogether, our findings point to fewer attentional resources of simultaneous visual processing to distribute over space or separable features of objects, consistent with decreased dorsal visual stream functioning in aging.

Neurochemical Predictors of Generalized Learning Induced by Brain Stimulation and Training.

Methods of cognitive enhancement for humans are most impactful when they generalize across tasks. However, the extent to which such "transfer" is possible via interventions is widely debated. In addition, the contribution of excitatory and inhibitory processes to such transfer is unknown. Here, in a large-scale neuroimaging individual differences study with humans (both sexes), we paired multitasking training and noninvasive brain stimulation (transcranial direct current stimulation, tDCS) over multiple days and assessed performance across a range of paradigms. In addition, we varied tDCS dosage (1.0 and 2.0 mA), electrode montage (left or right prefrontal regions), and training task (multitasking vs a control task) and assessed GABA and glutamate concentrations via ultrahigh field 7T magnetic resonance spectroscopy. Generalized benefits were observed in spatial attention, indexed by visual search performance, when multitasking training was combined with 1.0 mA stimulation targeting either the left or right prefrontal cortex (PFC). This transfer effect persisted for ∼30 d post intervention. Critically, the transferred benefits associated with right prefrontal tDCS were predicted by pretraining concentrations of glutamate in the PFC. Thus, the effects of this combined stimulation and training protocol appear to be linked predominantly to excitatory brain processes.