What's that on Your Phone? Effects of Mobile Device Task Type on Pedestrian Performance.

BACKGROUND: The number of accidents due to distracted pedestrian is on the rise and many governments and institutions are enacting public policies which restrict texting while walking. However, pedestrians do more than just texting when they use their mobile devices on the go. OBJECTIVE: Exploring pedestrian multitasking, this paper aims to examine the effects of mobile device task type on pedestrian performance outcomes. METHOD: We performed two studies in lab simulations where 78 participants were asked to perform different tasks on a mobile device (playing a game, reading, writing an email, texting one person, group texting) while performing a pedestrian visual discrimination task while either standing or walking on a treadmill. Behavioral performance as well as neurophysiological data are collected. RESULTS: Results show that compared to a no-phone control, multitasking with any of the tasks on a mobile device leads to poor performance on a pedestrian visual discrimination task. Playing a game is the most cognitively demanding task and leads to the greatest performance degradation. CONCLUSION: Our studies show that multitasking with a mobile device has the potential to negatively impact pedestrian safety, regardless of task type. However, the impacts of different mobile device tasks are not all equivalent. More research is needed to tease out the different effects of these various tasks and to design mobile applications which effectively and safely capture pedestrians' attention. APPLICATION: Public policy, infrastructure, and smart technologies can be used to mitigate the negative effects of mobile multitasking. A more thorough understanding of mobile device task-specific factors at play can help tailor these counter-measures to better aid distracted pedestrians.

Could Neurotracker be used as a clinical marker of recovery following pediatric mild traumatic brain injury? An exploratory study.

PRIMARY OBJECTIVE: This study aimed to explore the potential for the Neurotracker, a perceptual-cognitive, multiple-object tracking test, and train paradigm, as a marker of functional recovery after mild traumatic brain injury (mTBI). It is hypothesized that Neurotracker could serve as a proxy for assessing cerebral functioning. RESEARCH DESIGN: A comparative, 6 time points, longitudinal study design was used to compare Neurotracker performance between children and adolescents who were clinically recovered from mTBI and healthy controls. METHODS AND PROCEDURES: Clinical measures were collected at the initial and final visits. Neurotracker trainings were performed at each of the 6 visits. Speed thresholds (Neurotracker performance) were recorded at each visit. MAIN OUTCOMES AND RESULTS: A two-way repeated measures ANOVA suggested no differences between the groups but a significant time effect was apparent. CONCLUSIONS: Clinically recovered children and adolescents exhibit similar training abilities to control subjects on this task. These results support further investigations using Neurotracker as a marker of recovery following mTBI.

Multiple object-tracking isolates feedback-specific load in attention and learning.

Feedback is beneficial for learning. Nevertheless, it remains unclear whether (i) feedback draws attentional resources when integrated and (ii) the benefits of feedback for learning can be demonstrated using an attention-based task. We therefore (i) isolated feedback-specific load from task-specific load via individual differences in attention resource capacity and (ii) examined the effect of trial-by-trial feedback (i.e., present vs. absent) on learning a multiple object-tracking (MOT) paradigm. We chose MOT because it is a robust measure of attention resource capacity. In Study 1 participants tracked one (i.e., lowest attentional load condition) through four target items (i.e., highest load condition) among eight total items. One group (n = 32) received trial-by-trial feedback whereas the other group (n = 32) did not. The absence of feedback resulted in better MOT performance compared with the presence of feedback. Moreover, the difference in MOT capability between groups increased as the task-specific attentional load increased. These findings suggest that feedback integration requires attentional resources. Study 2 examined whether the absence (n = 19) or presence (n = 19) of feedback affects learning on the same MOT task across four testing days. When holding task-specific load constant, improvement in MOT was greater with feedback than without. Although this study is the first to isolate feedback-specific load in attention with MOT, more evidence is needed to demonstrate how the benefits of feedback translate to improvement on an attention-based task. These findings encourage future research to further explore the interaction between feedback, attention and learning.

Training with a three-dimensional multiple object-tracking (3D-MOT) paradigm improves attention in students with a neurodevelopmental condition: a randomized controlled trial.

The efficacy of attention training paradigms is influenced by many factors, including the specificity of targeted cognitive processes, accuracy of outcome measures, accessibility to specialized populations, and adaptability to user capability. These issues are increasingly significant when working with children diagnosed with neurodevelopmental conditions that are characterized by attentional difficulties. This study investigated the efficacy of training attention in students with neurodevelopmental conditions using a novel three-dimensional Multiple Object-Tracking (3D-MOT) task. All students (ages 6-18 years) performed the Conners Continuous Performance Task (CPT-3) as a baseline measure of attention. They were then equally and randomly assigned to one of three groups: a treatment group, (3D-MOT); an active control group (visual strategy/math-based game, 2048); and a treatment as usual group. Students were trained on their respective tasks for a total of 15 training sessions over a five-week period and then reassessed on the CPT-3. Results showed that post-training CPT-3 performance significantly improved from baseline for participants in the treatment group only. This improvement indicates that training with 3D-MOT increased attentional abilities in students with neurodevelopmental conditions. These results suggest that training attention with a non-verbal, visual-based task is feasible in a school setting and accessible to atypically developing students with attentional difficulties.

Different effects of aging and gender on the temporal resolution in attentional tracking.

The current study examined the role of temporal resolution of attention in the decline in multiple object tracking abilities with healthy aging. The temporal resolution of attention is known to limit attentional tracking of one and multiple targets (Holcombe & Chen, 2013). Here, we examined whether aging is associated with a lower temporal resolution of attention when tracking one target, the efficiency of splitting attention across multiple targets, or both. Stimuli comprised three concentric rings containing five or 10 equally spaced dots. While maintaining central fixation, younger and older participants tracked a target dot on one, two, or three rings while the rings rotated around fixation in random directions for 5 s. Rotational speed was varied to estimate speed or temporal frequency thresholds in six conditions. Results showed that younger and older participants had similar temporal frequency thresholds for tracking one target, but the addition of one and two more targets reduced thresholds more in the older group compared to the younger group. Gender also affected performance, with men having higher temporal frequency thresholds than women, independently of the number of targets. These findings indicate that the temporal resolution of attention for a single target depends on gender but is not affected by aging, whereas aging specifically affects the efficiency of dividing attention across multiple targets.

Head-Eye Coordination Increases with Age and Varies across Countries.

PURPOSE: Head movements in older people may contribute to their dizziness and equilibrium problems. Head gain is the ratio of head movement to total movement (head + eye) when executing a saccade to an eccentric target. Two studies have investigated the relationship between head gain and age but have provided conflicting results. METHODS: We report head gain data collected from research laboratories and optician stores. Our sample sizes are much larger (n = 657 for laboratory, n = 64,458 for optician stores), permitting more detailed analyses. RESULTS: The head-eye coefficient, expressed as 100 times the square root of head gain, was bimodal with one mode of primarily eye movers and one mode of eye-and-head movers. Head-eye coefficient increased with age and was invariant with eye correction and gender. We also found an effect of nation that seemed associated with gross domestic product or by latitude (in the northern hemisphere) and log population density. DISCUSSION: Assuming that head movements and visual distortions contribute to dizziness and equilibrium problems, our study suggests that customizing eyewear based on age and country may help in reducing the prevalence of problems associated with head and/or eye movements.

An expansive, cone-specific nonlinearity enabling the luminance motion system to process color-defined motion.

To conclude that there is a dedicated color motion system, the hypothesis that the luminance motion pathway is processing color motion due to some nonlinearity must be rejected. Many types of nonlinearities have been considered. Cavanagh and Anstis (1991) considered interunit variability in equiluminance, but they found that adding a color-defined modulation to a luminance-defined drifting modulation increased the contribution to motion. This color contribution to motion cannot be due to interunit variability in equiluminance alone because such a luminance artifact would increase the effective luminance contrast for some luminance-sensitive units and decrease it for the others, resulting in no additional contribution to motion on average. Cavanagh and Anstis considered this color contribution to motion as evidence of a dedicated color motion system, but here we show that such a color contribution to motion varies with the phase difference between the luminance and color modulations, which would not be expected if luminance- and color-defined motion were processed separately. Specifically, the contribution to motion was greater when the luminance and color modulations were aligned (i.e., 0 degrees or 180 degrees phase difference), than when they were not (90 degrees or 270 degrees phase difference). Such a luminance-color phase interaction was also observed when spatially interleaving luminance and color information, which suggests that the interaction occurs after some spatial integration (i.e., not at the photoreceptors). To our knowledge, this luminance-color phase interaction cannot be explained by any previously considered nonlinearity. However, it can be explained by an expansive nonlinearity occurring before the summation of the L- and M-cone pathways (i.e., before ganglion cells) and after some spatial integration (i.e., after the photoreceptors). We conclude that there is a nonlinearity that has not been considered before, enabling some color motion processing by the luminance motion system.

Gender comparison of perceptual-cognitive learning in young athletes.

Elite athletes demonstrate higher perceptual cognitive abilities compared to non-athletes and those capacities can be trained. A recent study showed that differences were observed between male and female athletes in their cognitive abilities whereby male athletes showed superior perceptual abilities compared to female athletes. The purpose of this study was to investigate whether there were gender differences in athletes' perceptual cognitive learning using a 3D-MOT tracking task. The study was performed on 72 young people from 16 to 22 years of age; athlete males and females and non-athlete males and females were distributed in four distinct groups. Five sessions comprised of three thresholds were performed with each participant. Results indicated that all participants benefited from training and significantly increased their speed thresholds. Initial scores showed that male athletes achieved higher speed thresholds than any other groups. Furthermore, after 5 weeks, female athletes obtained higher speed thresholds in comparison to their non-athlete counterparts. In conclusion, engaging in sporting activity is associated with improved perceptual-cognitive abilities and learning. The results support the notion that competitive sport-related activity is beneficial for perceptual-cognitive functions and emphasizes the benefits of participating in sport-related activities for improved brain function with an even greater impact for females.

"Extended Descriptive Risk-Averse Bayesian Model" a More Comprehensive Approach in Simulating Complex Biological Motion Perception.

The ability to perceive biological motion is crucial for human survival, social interactions, and communication. Over the years, researchers have studied the mechanisms and neurobiological substrates that enable this ability. In a previous study, we proposed a descriptive Bayesian simulation model to represent the dorsal pathway of the visual system, which processes motion information. The model was inspired by recent studies that questioned the impact of dynamic form cues in biological motion perception and was trained to distinguish the direction of a soccer ball from a set of complex biological motion soccer-kick stimuli. However, the model was unable to simulate the reaction times of the athletes in a credible manner, and a few subjects could not be simulated. In this current work, we implemented a novel disremembering strategy to incorporate neural adaptation at the decision-making level, which improved the model's ability to simulate the athletes' reaction times. We also introduced receptive fields to detect rotational optic flow patterns not considered in the previous model to simulate a new subject and improve the correlation between the simulation and experimental data. The findings suggest that rotational optic flow plays a critical role in the decision-making process and sheds light on how different individuals perform at different levels. The correlation analysis of human versus simulation data shows a significant, almost perfect correlation between experimental and simulated angular thresholds and slopes, respectively. The analysis also reveals a strong relation between the average reaction times of the athletes and the simulations.

Immediate fall prevention: the missing key to a comprehensive solution for falling hazard in older adults.

The world is witnessing an unprecedented demographic shift due to increased life expectancy and declining birth rates. By 2050, 20% of the global population will be over 60, presenting significant challenges like a shortage of caregivers, maintaining health and independence, and funding extended retirement. The technology that caters to the needs of older adults and their caregivers is the most promising candidate to tackle these issues. Although multiple companies and startups offer various aging solutions, preventive technology, which could prevent trauma, is not a big part of it. Trauma is the leading cause of morbidity, disability, and mortality in older adults, and statistics constitute traumatic fall accidents as its leading cause. Therefore, an immediate preventive technology that anticipates an accident on time and prevents it must be the first response to this hazard category to decrease the gap between life expectancy and the health/wellness expectancy of older adults. The article outlines the challenges of the upcoming aging crisis and introduces falls as one major challenge. After that, falls and their mechanisms are investigated, highlighting the cognitive functions and their relation to falls. Moreover, since understanding predictive cognitive mechanisms is critical to an effective prediction-interception design, they are discussed in more detail, signifying the role of cognitive decline in balance maintenance. Furthermore, the landscape of available solutions for falling and its shortcomings is inspected. Finally, immediate fall prevention, the missing part of a wholesome solution, and its barriers are introduced, and some promising methodologies are proposed.

Investigating sensitivity to multi-domain prediction errors in chronic auditory phantom perception.

The perception of a continuous phantom in a sensory domain in the absence of an external stimulus is explained as a maladaptive compensation of aberrant predictive coding, a proposed unified theory of brain functioning. If this were true, these changes would occur not only in the domain of the phantom percept but in other sensory domains as well. We confirm this hypothesis by using tinnitus (continuous phantom sound) as a model and probe the predictive coding mechanism using the established local-global oddball paradigm in both the auditory and visual domains. We observe that tinnitus patients are sensitive to changes in predictive coding not only in the auditory but also in the visual domain. We report changes in well-established components of event-related EEG such as the mismatch negativity. Furthermore, deviations in stimulus characteristics were correlated with the subjective tinnitus distress. These results provide an empirical confirmation that aberrant perceptions are a symptom of a higher-order systemic disorder transcending the domain of the percept.

Amplifying pathological detection in EEG signaling pathways through cross-dataset transfer learning.

Pathology diagnosis based on EEG signals and decoding brain activity holds immense importance in understanding neurological disorders. With the advancement of artificial intelligence methods and machine learning techniques, the potential for accurate data-driven diagnoses and effective treatments has grown significantly. However, applying machine learning algorithms to real-world datasets presents diverse challenges at multiple levels. The scarcity of labeled data, especially in low regime scenarios with limited availability of real patient cohorts due to high costs of recruitment, underscores the vital deployment of scaling and transfer learning techniques. In this study, we explore a real-world pathology classification task to highlight the effectiveness of data and model scaling and cross-dataset knowledge transfer. As such, we observe varying performance improvements through data scaling, indicating the need for careful evaluation and labeling. Additionally, we identify the challenges of possible negative transfer and emphasize the significance of some key components to overcome distribution shifts and potential spurious correlations and achieve positive transfer. We see improvement in the performance of the target model on the target (NMT) datasets by using the knowledge from the source dataset (TUAB) when a low amount of labeled data was available. Our findings demonstrated that a small and generic model (e.g. ShallowNet) performs well on a single dataset, however, a larger model (e.g. TCN) performs better in transfer learning when leveraging a larger and more diverse dataset.

No second-order motion system sensitive to high temporal frequencies.

It has been shown that the perception of contrast-defined motion (i.e., a second-order stimulus) at high temporal frequencies cannot be explained solely by global distortion products (i.e., luminance artifacts due to preprocessing nonlinearities) processed by the first-order system. However, previous studies rejecting the first-order pathway hypothesis have assumed that the preprocessing nonlinearities are identical for all first-order motion units. If this is not the case, then introducing a nonlinearity within the stimulus could neutralize the global (i.e., mean) distortion product but would leave residual distortion products. We neutralized either global only or both global and residual distortion products by superimposing a luminance modulation onto the contrast modulation. At a temporal frequency too high for features to be tracked (15 Hz), we found a substantial texture (i.e., contrast-modulated) contribution to motion when neutralizing only global distortion products but not when neutralizing both global and residual distortion products. Furthermore, we found that the texture contribution to motion at this high temporal frequency, when it was not completely neutralized, depended on the phase difference between luminance and contrast modulations, which implied some common processing before the motion extraction stage. We concluded that the texture contribution to motion at high temporal frequencies was due to nonuniform preprocessing nonlinearities within the visual system, enabling first-order motion units to process distortion products, and not due to a dedicated second-order motion system.

No dedicated second-order motion system.

The existence of a second-order motion system distinct from both the first-order and feature tracking motion systems remains controversial even though many consider it well established. In the present study, the texture contribution to motion was measured within and beyond the spatial acuity of attention by presenting the stimuli in the near periphery where the spatial resolution of attention is low. The logic was that when moving elements are too close one to another for attention to individually select them (i.e., crowding), it is not possible to track them. To test the existence of a dedicated second-order motion system, the texture contribution to motion was measured when neutralizing both the feature tracking motion system and the contribution of the first-order motion system due to preprocessing nonlinearities introducing residual distortion products. When the contribution of distortion products was not neutralized, texture substantially contributed to motion for spatial frequencies within and beyond the spatial acuity of attention. When neutralizing the contribution of distortion products, texture substantially contributed to motion for spatial frequencies within the spatial acuity of attention, but not for spatial frequencies beyond the spatial acuity of attention. We conclude that there is no dedicated second-order motion system; the texture contribution to motion is mediated solely by the first-order (due to residual distortion products) and feature tracking (at frequencies within spatiotemporal acuity of attention) motion systems.

Is the Contralateral Delay Activity (CDA) a robust neural correlate for Visual Working Memory (VWM) tasks? A reproducibility study.

Visual working memory (VWM) allows us to actively store, update, and manipulate visual information surrounding us. While the underlying neural mechanisms of VWM remain unclear, contralateral delay activity (CDA), a sustained negativity over the hemisphere contralateral to the positions of visual items to be remembered, is often used to study VWM. To investigate if the CDA is a robust neural correlate for VWM tasks, we reproduced eight CDA-related studies with a publicly accessible EEG data set. We used the raw EEG data from these eight studies and analyzed all of them with the same basic pipeline to extract CDA. We were able to reproduce the results from all the studies and show that with a basic automated EEG pipeline we can extract a clear CDA signal. We share insights from the trends observed across the studies and raise some questions about the CDA decay and the CDA during the recall phase, which surprisingly, none of the eight studies did address. Finally, we also provide reproducibility recommendations based on our experience and challenges in reproducing these studies.

Distinctive patterns of Multiple Object-Tracking performance trajectories in youth with deficits in attention, learning, and intelligence.

There is a significant overlap in symptomology between individuals with deficits in attention and learning, which is explained by the co-dependent dynamic between the two cognitive constructs. Within this dynamic, attentional resources are allocated to salient stimuli while learning mechanisms distinguish relevant from irrelevant information. Moreover, individuals with deficits in higher-order cognition (i.e., intelligence) can demonstrate difficulties in attention and learning. The Multiple Object-Tracking (MOT) task is a sensitive and versatile measure of attention that has characterized individual differences in attention as a function of higher-order cognition. Exploiting the traditional MOT task's ability to characterize the allocation of attentional resources to task demands, the current study compared learning exhibited on an attention-based task across neurodevelopmental conditions defined by deficits in attention (attention-deficit/hyperactivity disorder; ADHD), learning (specific learning disorder; SLD), and intelligence (intellectual developmental disorder; IDD). Children and adolescents (N = 101) completed 15 sessions on a Multiple Object-Tracking (MOT) task where performance trajectories were analyzed using latent growth curve modeling and conditioned by the presence of ADHD, SLD, or IDD while controlling for performance on a separate measure of attention, age, and sex. The sample, characterized by below-average IQ and problematic levels of attention, exhibited an effect of learning on MOT. However, individuals with an IDD diagnosis demonstrated decreased baseline MOT capability while ADHD and SLD profiles exhibited decreased slopes, relative to other neurodevelopmental conditions. Taken together, the results demonstrate distinct linear performance trajectories between neurodevelopmental conditions defined by deficits in attention, learning, and intelligence. The current study provides additional evidence to repurpose the traditional MOT task as a descriptor of attention and discusses alternative uses for the paradigm. Overall, these results suggest an eclectic approach that considers attention, learning, and higher-order cognition when diagnosing ADHD, SLD, or IDD.

Characterizing Attention Resource Capacity in Autism: A Multiple Object Tracking Study.

The extant literature aimed at characterizing attentional capability in autistics has presented inconsistent findings. This inconsistency and uncertainty may be the product of different theoretical and methodological approaches used to define attention in autism. In the current study, we investigate whether the allocation of attentional resources to task demands, and attention resource capacity, differs between autistics with no comorbid attention-deficit diagnosis (n = 55) and age-matched neurotypicals (n = 55). We compared differences in capacity and the allocation of resources by manipulating attentional load in a Multiple Object-Tracking (MOT) task, a robust, versatile, and ecological measure of selective, sustained, and distributed attention. While autistics demonstrated lower MOT performance, this difference disappeared when we accounted for fluid reasoning intelligence. Additionally, the similarity in the trend of MOT performance at increasing levels of attentional load between autistics and neurotypicals suggests no differences in the allocation of attentional resources to task demands. Taken together, our study suggests that higher-order cognitive abilities, such as intelligence, should be considered when characterizing attention across the autistic population in research. Similarly, our findings highlight the importance of considering cognitive competence when assessing attentional capabilities in autistic individuals, which could have significant implications for clinical diagnosis, treatment, and support.

Can Three-Dimensional Multiple Object Tracking Training Be Used to Improve Simulated Driving Performance? A Pilot Study in Young and Older Adults.

Driving ability has been shown to be dependent on perceptual-cognitive abilities such as visual attention and speed of processing. There is mixed evidence suggesting that training these abilities may improve aspects of driving performance. This preliminary study investigated the feasibility of training three-dimensional multiple object tracking (3D-MOT)-a dynamic, speeded tracking task soliciting selective, sustained and divided attention as well as speed of processing-to improve measures of simulated driving performance in older and younger adults. A sample of 20 young adults (23-33 years old) and 14 older adults (65-76 years old) were randomly assigned to either a 3D-MOT training group or an active control group trained on a perceptual discrimination task as well as 2048. Participants were tested on a driving scenario with skill-testing events previously identified as optimal for cross-sectional comparisons of driving ability. Results replicated previously identified differences in driving behaviour between age groups. A possible trend was observed for the 3D-MOT trained group, especially younger adults, to increase the distance at which they applied their maximum amount of braking in response to dangerous events. This measure was associated with less extreme braking during events, implying that these drivers may have been making more controlled stops. Limitations of sample size and task realism notwithstanding, the present experiment offers preliminary evidence that 3D-MOT training might transfer to driving performance through quicker detection of or reaction to dangerous events and provides a rationale for replication with a larger sample size.

A Protocol for Remote Cognitive Training Developed for Use in Clinical Populations During the COVID-19 Pandemic.

Many traumatic brain injury (TBI) survivors face scheduling and transportation challenges when seeking therapeutic interventions. The COVID-19 pandemic created a shift in the use of at-home spaces for work, play, and research, inspiring the development of online therapeutic options. In the current study, we determined the feasibility of an at-home cognitive training tool (NeuroTrackerX) that uses anaglyph three-dimensional (3D) glasses and three-dimensional multiple object tracking (3D-MOT) software. We recruited 20 adults (10 female; mean age = 68.3 years, standard deviation [SD] = 6.75) as the at-home training group. We assessed cognitive health status for participants using a self-report questionnaire and the Mini-Mental State Examination (MMSE), and all participants were deemed cognitively healthy (MMSE >26). At-home participants loaned the necessary equipment (e.g., 3D glasses, computer equipment) from the research facilities and engaged in 10 training sessions over 5 weeks (two times per week). Participant recruitment, retention, adherence, and experience were used as markers of feasibility. For program validation, 20 participants (10 female; mean age = 63.39 years, SD = 12.22), who had previously completed at least eight sessions of the in-lab 3D-MOT program, were randomly selected as the control group. We assessed individual session scores, overall improvement, and learning rates between groups. Program feasibility is supported by high recruitment and retention, 90% participant adherence, and participants' ease of use of the program. Validation of the program is supported. Groups showed no differences in session scores (p > 0.05) and percentage improvement (p > 0.05) despite the differences in screen size and 3D technology. Participants in both groups showed significant improvements in task performance across the training sessions (p < 0.001). NeuroTrackerX provides a promising at-home option for cognitive training in cognitively healthy adults and may be a promising avenue as an at-home therapeutic for TBI survivors. This abstract was previously published on clinicaltrials.gov and can be found at: https://www.clinicaltrials.gov/ct2/show/NCT05278273.

Beyond performance: the role of task demand, effort, and individual differences in ab initio pilots.

Aviation safety depends on the skill and expertise of pilots to meet the task demands of flying an aircraft in an effective and efficient manner. During flight training, students may respond differently to imposed task demands based on individual differences in capacity, physiological arousal, and effort. To ensure that pilots achieve a common desired level of expertise, training programs should account for individual differences to optimize pilot performance. This study investigates the relationship between task performance and physiological correlates of effort in ab initio pilots. Twenty-four participants conducted a flight simulator task with three difficulty levels and were asked to rate their perceived demand and effort using the NASA TLX. We recorded heart rate, EEG brain activity, and pupil size to assess changes in the participants' mental and physiological states across different task demands. We found that, despite group-level correlations between performance error and physiological responses, individual differences in physiological responses to task demands reflected different levels of participant effort and task efficiency. These findings suggest that physiological monitoring of student pilots might provide beneficial insights to flight instructors to optimize pilot training at the individual level.