Publications by authors named "Leandro L Di Stasi"

28 Publications

  • Page 1 of 1

Visual Feedback Effectiveness in Reducing Over Speeding of Moped-Riders.

Front Psychol 2021 11;12:611603. Epub 2021 Mar 11.

Department of General Psychology, University of Padua, Padua, Italy.

The use of assistance systems aimed at reducing road fatalities is spreading, especially for car drivers, but less effort has been devoted to developing and testing similar systems for powered two-wheelers (PTWs). Considering that over speeding represents one of the main causal factors in road crashes and that riders are more vulnerable than drivers, in the present study we investigated the effectiveness of an assistance system which signaled speed limit violations during a simulated moped-driving task, in optimal and poor visibility conditions. Participants performed four conditions of simulated riding: one baseline condition without Feedback, one Fog condition in which visual feedback was provided so as to indicate to the participants when a speed limit (lower than that indicated by the traffic signals) was exceeded, and two post-Feedback conditions with and without Fog, respectively, in which no feedback was delivered. Results showed that participants make fewer speeding violations when the feedback is not provided, after 1 month, and regardless of the visibility condition. Finally, the feedback has been proven effective in reducing speed violations in participants with an aggressive riding style, as measured in the baseline session.
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http://dx.doi.org/10.3389/fpsyg.2021.611603DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7990878PMC
March 2021

A cross-cultural comparison of visual search strategies and response times in road hazard perception testing.

Accid Anal Prev 2020 Dec 5;148:105785. Epub 2020 Nov 5.

Mind, Brain, and Behavior Research Center, University of Granada, Granada, Spain.

Road hazard perception is considered the most prominent higher-order cognitive skill related to traffic-accident involvement. Regional cultures and social rules that govern acceptable behavior may influence drivers' interpretation of a traffic situation and, consequently, the correct identification of potentially hazardous situations. Here, we aimed to compare hazard perception skills among four European countries that differ in their traffic culture, policies to reduce traffic risks, and fatal crashes: Ukraine, Italy, Spain, and Sweden. We developed a static hazard perception test in which driving scenes with different levels of braking affordance were presented while drivers' gaze was recorded. The test required drivers to indicate the action they would undertake: to brake vs. to keep driving. We assessed 218 young adult drivers. Multilevel models revealed that the scenes' levels of braking affordance (i.e., road hazard) modulated drivers' behavior. As the levels of braking affordance increased, drivers' responses became faster and their gaze entropy decreased (i.e., visual search strategy became less erratic). The country of origin influenced these effects. Ukrainian drivers were the fastest and Swedish drivers were the slowest to respond. For all countries, the decrement in response times was less marked in the case of experienced drivers. Also, Spanish drivers showed the most structured (least erratic) visual search strategy, whereas the Italians had the most rigid (most constant) one. These results suggest that road hazard perception can be defined cross-culturally, with cultural factors (e.g., traffic climate, legislation) modulating response times and visual search strategies. Our results also support the idea that a multimodal assessment methodology is possible for mass testing of road hazard perception and its outcomes would be relevant to understand how different traffic cultures shape driving behavior.
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http://dx.doi.org/10.1016/j.aap.2020.105785DOI Listing
December 2020

EEG Theta Power Activity Reflects Workload among Army Combat Drivers: An Experimental Study.

Brain Sci 2020 Mar 28;10(4). Epub 2020 Mar 28.

Mind, Brain, and Behavior Research Center-CIMCYC, University of Granada, Campus de Cartuja s/n, 18071 Granada; Spain.

We aimed to evaluate the effects of mental workload variations, as a function of the road environment, on the brain activity of army drivers performing combat and non-combat scenarios in a light multirole vehicle dynamic simulator. Forty-one non-commissioned officers completed three standardized driving exercises with different terrain complexities (low, medium, and high) while we recorded their electroencephalographic (EEG) activity. We focused on variations in the theta EEG power spectrum, a well-known index of mental workload. We also assessed performance and subjective ratings of task load. The theta EEG power spectrum in the frontal, temporal, and occipital areas were higher during the most complex scenarios. Performance (number of engine stops) and subjective data supported these findings. Our findings strengthen previous results found in civilians on the relationship between driver mental workload and the theta EEG power spectrum. This suggests that EEG activity can give relevant insight into mental workload variations in an objective, unbiased fashion, even during real training and/or operations. The continuous monitoring of the warfighter not only allows instantaneous detection of over/underload but also might provide online feedback to the system (either automated equipment or the crew) to take countermeasures and prevent fatal errors.
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http://dx.doi.org/10.3390/brainsci10040199DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7226148PMC
March 2020

Nasal skin temperature reveals changes in arousal levels due to time on task: An experimental thermal infrared imaging study.

Appl Ergon 2019 Nov 18;81:102870. Epub 2019 Jun 18.

Mind, Brain, and Behavior Research Center-CIMCYC, University of Granada, Campus de Cartuja s/n, 18071 Granada, Spain; Joint Center University of Granada - Spanish Army Training and Doctrine Command, C/ Gran Via de Colon, 48, 18071 Granada, Spain. Electronic address:

Infrared thermography, thanks to technological developments and lowering prices, is now getting considerable attention as a potential arousal monitor in the safety industry. Nasal skin temperature might be a valid index to track physiological variations due to reduced arousal levels, and its use could prevent a drowsiness-related deterioration of performance. However, the few studies that have investigated nasal skin temperature in applied settings have had inconsistent results. Here, we assessed the validity of nasal skin temperature to monitor changes in arousal levels (from alertness to drowsiness). The participants performed a 2-h simulated driving task while we simultaneously recorded their nasal skin temperature, brain activity (we used frontal delta electroencephalographic [EEG] activity as the reference index of alertness), and driving performance (speeding time). For those variables, we calculated growth curve models. We also collected subjective ratings of alertness and fatigue before and after the driving session. We found that the nasal skin temperature showed a cubic trajectory (it increased for the first 75 min, and then it began to decrease, but such deceleration gradually diminished over time). As expected, frontal delta EEG activity showed an inverted U-shaped quadratic trend (EEG power increased for the first hour and half, and gradually decreased during the last thirty minutes). The speeding time exhibited a similar pattern of change. Subjective sleepiness and fatigue increased after the task. Overall, our results suggest that nasal skin temperature seems to be a valid measure of arousal variations while performing a complex and dynamic everyday task.
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http://dx.doi.org/10.1016/j.apergo.2019.06.001DOI Listing
November 2019

Validation of Electroencephalographic Recordings Obtained with a Consumer-Grade, Single Dry Electrode, Low-Cost Device: A Comparative Study.

Sensors (Basel) 2019 Jun 23;19(12). Epub 2019 Jun 23.

Mind, Brain, and Behavior Research Center, University of Granada, 18071 Granada, Spain.

The functional validity of the signal obtained with low-cost electroencephalography (EEG) devices is still under debate. Here, we have conducted an in-depth comparison of the EEG-recordings obtained with a medical-grade golden-cup electrodes ambulatory device, the SOMNOwatch + EEG-6, vs those obtained with a consumer-grade, single dry electrode low-cost device, the NeuroSky MindWave, one of the most affordable devices currently available. We recorded EEG signals at Fp1 using the two different devices simultaneously on 21 participants who underwent two experimental phases: a 12-minute resting state task (alternating two cycles of closed/open eyes periods), followed by 60-minute virtual-driving task. We evaluated the EEG recording quality by comparing the similarity between the temporal data series, their spectra, their signal-to-noise ratio, the reliability of EEG measurements (comparing the closed eyes periods), as well as their blink detection rate. We found substantial agreement between signals: whereas, qualitatively, the NeuroSky MindWave presented higher levels of noise and a biphasic shape of blinks, the similarity metric indicated that signals from both recording devices were significantly correlated. While the NeuroSky MindWave was less reliable, both devices had a similar blink detection rate. Overall, the NeuroSky MindWave is noise-limited, but provides stable recordings even through long periods of time. Furthermore, its data would be of adequate quality compared to that of conventional wet electrode EEG devices, except for a potential calibration error and spectral differences at low frequencies.
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http://dx.doi.org/10.3390/s19122808DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6630628PMC
June 2019

The effects of flight complexity on gaze entropy: An experimental study with fighter pilots.

Appl Ergon 2019 May 11;77:92-99. Epub 2019 Feb 11.

Mind, Brain, and Behavior Research Center-CIMCYC, University of Granada, Campus de Cartuja s/n, 18071, Granada, Spain; Joint Center University of Granada - Spanish Army Training and Doctrine Command, C/ Gran Via de Colon, 48, 18071, Granada, Spain. Electronic address:

We studied the effects of task load variations as a function of flight complexity on combat pilots' gaze behavior (i.e., entropy) while solving in-flight emergencies. The second company of the Spanish Army Attack Helicopter Battalion (n = 15) performed three sets of standardized flight exercises with different levels of complexity (low [recognition flights], medium and high [emergency flights]). Throughout the flight exercises we recorded pilots' gaze entropy, as well as pilots' performance (assessed by an expert flight instructor) and subjective ratings of task load (assessed by the NASA-Task Load Index). Furthermore, we used pilots' electroencephalographic (EEG) activity as a reference physiological index for task load variations. We found that pilots' gaze entropy decreased ∼2% (i.e., visual scanning became less erratic) while solving the emergency flight exercises, showing a significant decreasing trend with increasing complexity (p < .05). This is in consonance with the ∼12% increase in the frontal theta band of their EEG spectra during said exercises. Pilots' errors and subjective ratings of task load increased as flight complexity increased (p-values < .05). Gaze data suggest that pilots used nondeterministic visual patterns when the aircraft was in an error-free state (low complexity), and changed their scanning behavior, becoming more deterministic, once emergencies occurred (medium/high complexity). Overall, our findings indicate that gaze entropy can serve as a sensitive index of task load in aviation settings.
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http://dx.doi.org/10.1016/j.apergo.2019.01.012DOI Listing
May 2019

Detecting Mental Workload in Surgical Teams Using a Wearable Single-Channel Electroencephalographic Device.

J Surg Educ 2019 Jul - Aug;76(4):1107-1115. Epub 2019 Jan 26.

Mind, Brain, and Behavior Research Center, University of Granada, Granada, Spain; Joint Center University of Granada-Spanish Army Training and Doctrine Command, Spain.

Objective: To assess the sensitivity of an electroencephalographic (EEG)-based index, the prefrontal beta power, to quantify the mental workload in surgeons in real scenarios. Such EEG-based index might offer unique and unbiased measures of overload, a crucial factor when designing learning and training surgical programs.

Design: The experiment followed a 2 × 2 × 2 within subjects design with 3 factors: (1) Surgical Role during the surgery (primary surgeon vs. assistant surgeon), (2) the Surgical Procedure (laparo-endoscopic single-site [LESS] surgery vs. multiport laparoscopic surgery [MPS]), and (3) the Suturing Techniques (interrupted vs. continuous suture).

Setting: The study was carried out at the Advanced Multi-Purpose Simulation and Technological Innovation Complex situated at IAVANTE (Granada, Spain).

Methods: Four surgical teams (primary surgeon and assistant surgeon, experts in MPS) performed 8 surgical exercises on porcine models, under different task complexities. They performed 2 suturing techniques (continuous and interrupted), employing a low complex procedure (MPS) and a high complex procedure (LESS). Surgeons acted as the primary surgeon during half of the exercises, and, as the assistant surgeon, during the rest of them. Simultaneously, we monitored EEG prefrontal EEG beta power spectra of both surgeons, using 2 synchronized wearable EEG devices. We also collected performance and subjective data.

Results: Surgical complexity modulated prefrontal beta power. LESS surgery caused significant higher prefrontal beta power for both suturing techniques for both surgical roles which indicates higher demands than MPS. Perceived task complexity, overall surgical evaluation, and laparoscopic execution time confirmed EEG-based results. Finally, subjective ratings of surgical complexity differentiated between surgical roles within the same exercise, even when prefrontal beta power did not.

Conclusions: To detect mental overload when surgeons are engaged with complex surgeries, real or simulated, is still guesswork. EEG-based indices have great potential as objective and nonintrusive measures to assess mental overload in surgeons. Furthermore, EEG-based indices might play a relevant role in monitoring surgeons and residents' cognitive state during their training.
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http://dx.doi.org/10.1016/j.jsurg.2019.01.005DOI Listing
July 2020

Intraocular pressure increases after complex simulated surgical procedures in residents: an experimental study.

Surg Endosc 2019 01 2;33(1):216-224. Epub 2018 Jul 2.

Mind, Brain, and Behavior Research Center - CIMCYC, University of Granada, Campus de Cartuja s/n, 18071, Granada, Spain.

Background: Surgeons' overload is one of the main causes of medical errors that might compromise patient safety. Due to the drawbacks of current options to monitor surgeons' load, new, sensitive, and objective indices of task (over)load need to be considered and tested. In non-health-care scenarios, intraocular pressure (IOP) has been proved to be an unbiased physiological index, sensitive to task complexity (one of the main variables related to overload), and time on task. In the present study, we assessed the effects of demanding and complex simulated surgical procedures on surgical and medical residents' IOP.

Methods: Thirty-four surgical and medical residents and healthcare professionals took part in this study (the experimental group, N = 17, and the control group, N = 17, were matched for sex and age). The experimental group performed two simulated bronchoscopy procedures that differ in their levels of complexity. The control group mimicked the same hand-eye movements and posture of the experimental group to help control for the potential effects of time on task and re-measurement on IOP. We measured IOP before and after each procedure, surgical performance during procedures, and perceived task complexity.

Results: IOP increased as consequence of performing the most complex procedure only in the experimental group. Consistently, residents performed worse and reported higher perceived task complexity for the more complex procedure.

Conclusions: Our data show, for the first time, that IOP is sensitive to residents' task load, and it could be used as a new index to easily and rapidly assess task (over)load in healthcare scenarios. An arousal-based explanation is given to describe IOP variations due to task complexity.
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http://dx.doi.org/10.1007/s00464-018-6297-7DOI Listing
January 2019

Monitoring driver fatigue using a single-channel electroencephalographic device: A validation study by gaze-based, driving performance, and subjective data.

Accid Anal Prev 2017 Dec 13;109:62-69. Epub 2017 Oct 13.

Mind, Brain, and Behavior Research Center, University of Granada, Granada, Spain; College of Nursing and Health Innovation, Arizona State University, Phoenix, AZ, USA. Electronic address:

Driver fatigue can impair performance as much as alcohol does. It is the most important road safety concern, causing thousands of accidents and fatalities every year. Thanks to technological developments, wearable, single-channel EEG devices are now getting considerable attention as fatigue monitors, as they could help drivers to assess their own levels of fatigue and, therefore, prevent the deterioration of performance. However, the few studies that have used single-channel EEG devices to investigate the physiological effects of driver fatigue have had inconsistent results, and the question of whether we can monitor driver fatigue reliably with these EEG devices remains open. Here, we assessed the validity of a single-channel EEG device (TGAM-based chip) to monitor changes in mental state (from alertness to fatigue). Fifteen drivers performed a 2-h simulated driving task while we recorded, simultaneously, their prefrontal brain activity and saccadic velocity. We used saccadic velocity as the reference index of fatigue. We also collected subjective ratings of alertness and fatigue, as well as driving performance. We found that the power spectra of the delta EEG band showed an inverted U-shaped quadratic trend (EEG power spectra increased for the first hour and half, and decreased during the last thirty minutes), while the power spectra of the beta band linearly increased as the driving session progressed. Coherently, saccadic velocity linearly decreased and speeding time increased, suggesting a clear effect of fatigue. Subjective data corroborated these conclusions. Overall, our results suggest that the TGAM-based chip EEG device is able to detect changes in mental state while performing a complex and dynamic everyday task as driving.
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http://dx.doi.org/10.1016/j.aap.2017.09.025DOI Listing
December 2017

Quantifying the cognitive cost of laparo-endoscopic single-site surgeries: Gaze-based indices.

Appl Ergon 2017 Nov 27;65:168-174. Epub 2017 Jun 27.

Mind, Brain, and Behavior Research Center, University of Granada, 18071 Granada, Spain.

Background: Despite the growing interest concerning the laparo-endoscopic single-site surgery (LESS) procedure, LESS presents multiple difficulties and challenges that are likely to increase the surgeon's cognitive cost, in terms of both cognitive load and performance. Nevertheless, there is currently no objective index capable of assessing the surgeon cognitive cost while performing LESS. We assessed if gaze-based indices might offer unique and unbiased measures to quantify LESS complexity and its cognitive cost. We expect that the assessment of surgeon's cognitive cost to improve patient safety by measuring fitness-for-duty and reducing surgeons overload.

Methods: Using a wearable eye tracker device, we measured gaze entropy and velocity of surgical trainees and attending surgeons during two surgical procedures (LESS vs. multiport laparoscopy surgery [MPS]). None of the participants had previous experience with LESS. They performed two exercises with different complexity levels (Low: Pattern Cut vs. High: Peg Transfer). We also collected performance and subjective data.

Results: LESS caused higher cognitive demand than MPS, as indicated by increased gaze entropy in both surgical trainees and attending surgeons (exploration pattern became more random). Furthermore, gaze velocity was higher (exploration pattern became more rapid) for the LESS procedure independently of the surgeon's expertise. Perceived task complexity and laparoscopic accuracy confirmed gaze-based results.

Conclusion: Gaze-based indices have great potential as objective and non-intrusive measures to assess surgeons' cognitive cost and fitness-for-duty. Furthermore, gaze-based indices might play a relevant role in defining future guidelines on surgeons' examinations to mark their achievements during the entire training (e.g. analyzing surgical learning curves).
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http://dx.doi.org/10.1016/j.apergo.2017.06.008DOI Listing
November 2017

Gaze-based Technology as a Tool for Surgical Skills Assessment and Training in Urology.

Urology 2017 Sep 27;107:26-30. Epub 2017 Jun 27.

Mind, Brain, and Behavior Research Center, University of Granada, Granada, Spain; College of Nursing and Health Innovation, Arizona State University, Phoenix, AZ. Electronic address:

Objective: To assess the sensitivity of gaze-based metrics in detecting cognitive demands imposed by surgical procedures. We analyzed urologists' gaze entropy and velocity while performing 2 standardized high-fidelity simulated stone procedures with different levels of complexity.

Methods: Using a wearable eye tracker device (mounted onto an eyeglass frame), we measured gaze entropy and velocity in 15 urologists, members of the Andalusian health-care system, while they performed an extraction of a stone in the bladder (low complexity) and an extraction of a stone in the lumbar ureter (high complexity). We also collected performance and subjective data.

Results: Gaze entropy and velocity were significantly higher when surgeons performed the most complex surgical procedure: the visual exploration pattern became less stereotyped (ie, more random) and faster. Surgeons' performance and perceived task complexity differed accordingly, confirming the gaze-based results.

Conclusion: Gaze-based metrics might have great potential as objective and nonintrusive indices to assess surgeons' cognitive (over)load, potentially being a complementary assessment tool to quantify the learning curve for surgical procedures.
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http://dx.doi.org/10.1016/j.urology.2017.06.030DOI Listing
September 2017

Abnormal Capillary Vasodynamics Contribute to Ictal Neurodegeneration in Epilepsy.

Sci Rep 2017 02 27;7:43276. Epub 2017 Feb 27.

Barrow Neurological Institute, 350 W Thomas Rd, Phoenix, AZ 85013, USA.

Seizure-driven brain damage in epilepsy accumulates over time, especially in the hippocampus, which can lead to sclerosis, cognitive decline, and death. Excitotoxicity is the prevalent model to explain ictal neurodegeneration. Current labeling technologies cannot distinguish between excitotoxicity and hypoxia, however, because they share common molecular mechanisms. This leaves open the possibility that undetected ischemic hypoxia, due to ictal blood flow restriction, could contribute to neurodegeneration previously ascribed to excitotoxicity. We tested this possibility with Confocal Laser Endomicroscopy (CLE) and novel stereological analyses in several models of epileptic mice. We found a higher number and magnitude of NG2+ mural-cell mediated capillary constrictions in the hippocampus of epileptic mice than in that of normal mice, in addition to spatial coupling between capillary constrictions and oxidative stressed neurons and neurodegeneration. These results reveal a role for hypoxia driven by capillary blood flow restriction in ictal neurodegeneration.
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http://dx.doi.org/10.1038/srep43276DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5327474PMC
February 2017

Gaze entropy reflects surgical task load.

Surg Endosc 2016 11 16;30(11):5034-5043. Epub 2016 Mar 16.

Mind, Brain, and Behavior Research Center (CIMCYC), University of Granada, Campus de Cartuja s/n, 18071, Granada, Spain.

Background: Task (over-)load imposed on surgeons is a main contributing factor to surgical errors. Recent research has shown that gaze metrics represent a valid and objective index to asses operator task load in non-surgical scenarios. Thus, gaze metrics have the potential to improve workplace safety by providing accurate measurements of task load variations. However, the direct relationship between gaze metrics and surgical task load has not been investigated yet. We studied the effects of surgical task complexity on the gaze metrics of surgical trainees.

Methods: We recorded the eye movements of 18 surgical residents, using a mobile eye tracker system, during the performance of three high-fidelity virtual simulations of laparoscopic exercises of increasing complexity level: Clip Applying exercise, Cutting Big exercise, and Translocation of Objects exercise. We also measured performance accuracy and subjective rating of complexity.

Results: Gaze entropy and velocity linearly increased with increased task complexity: Visual exploration pattern became less stereotyped (i.e., more random) and faster during the more complex exercises. Residents performed better the Clip Applying exercise and the Cutting Big exercise than the Translocation of Objects exercise and their perceived task complexity differed accordingly.

Conclusions: Our data show that gaze metrics are a valid and reliable surgical task load index. These findings have potential impacts to improve patient safety by providing accurate measurements of surgeon task (over-)load and might provide future indices to assess residents' learning curves, independently of expensive virtual simulators or time-consuming expert evaluation.
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http://dx.doi.org/10.1007/s00464-016-4851-8DOI Listing
November 2016

Driving time modulates accommodative response and intraocular pressure.

Physiol Behav 2016 10 24;164(Pt A):47-53. Epub 2016 May 24.

College of Nursing and Health Innovation, Arizona State University, Phoenix, AZ, USA; Mind, Brain, and Behavior Research Center [CIMCYC], University of Granada, Granada, Spain; Joint Center University of Granada - Spanish Army Training and Doctrine Command, Spain. Electronic address:

Driving is a task mainly reliant on the visual system. Most of the time, while driving, our eyes are constantly focusing and refocusing between the road and the dashboard or near and far traffic. Thus, prolonged driving time should produce visual fatigue. Here, for the first time, we investigated the effects of driving time, a common inducer of driver fatigue, on two ocular parameters: the accommodative response (AR) and the intraocular pressure (IOP). A pre/post-test design has been used to assess the impact of driving time on both indices. Twelve participants (out of 17 recruited) completed the study (5 women, 24.42±2.84years old). The participants were healthy and active drivers with no visual impairment or pathology. They drove for 2h in a virtual driving environment. We assessed AR and IOP before and after the driving session, and also collected subjective measures of arousal and fatigue. We found that IOP and AR decreased (i.e., the accommodative lag increased) after the driving session (p=0.03 and p<0.001, respectively). Moreover, the nearest distances tested (20cm, 25cm, and 33cm) induced the highest decreases in AR (corrected p-values<0.05). Consistent with these findings, the subjective levels of arousal decreased and levels of fatigue increased after the driving session (all p-values<0.001). These results represent an innovative step towards an objective, valid, and reliable assessment of fatigue-impaired driving based on visual fatigue signs.
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http://dx.doi.org/10.1016/j.physbeh.2016.05.043DOI Listing
October 2016

Effects of long and short simulated flights on the saccadic eye movement velocity of aviators.

Physiol Behav 2016 Jan 24;153:91-6. Epub 2015 Oct 24.

Barrow Neurological Institute, Phoenix, AZ, USA; Department of Ophthalmology, State University of New York, Downstate Medical Center, Brooklyn, NY, USA. Electronic address:

Aircrew fatigue is a major contributor to operational errors in civil and military aviation. Objective detection of pilot fatigue is thus critical to prevent aviation catastrophes. Previous work has linked fatigue to changes in oculomotor dynamics, but few studies have studied this relationship in critical safety environments. Here we measured the eye movements of US Marine Corps combat helicopter pilots before and after simulated flight missions of different durations.We found a decrease in saccadic velocities after long simulated flights compared to short simulated flights. These results suggest that saccadic velocity could serve as a biomarker of aviator fatigue.
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http://dx.doi.org/10.1016/j.physbeh.2015.10.024DOI Listing
January 2016

Seeing red on the road.

Perception 2015 ;44(1):87-92

Human and animal research has found that red perception is associated with specific behavioral reactions, generally characterized by intense responses. Here, we explored whether red cars are perceived as more dangerous than other colored cars. One hundred Spanish drivers examined several road scenarios which involved hazardous cars with different colors: red, green, yellow, black, gray, and white. Driver's behavior (response time and probability of braking) and the perceived level of risk for each scenario were analyzed. Although car color affected participants' response times, contrary to expectations, red cars did not elicit faster responses or higher perceived levels of risk.
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http://dx.doi.org/10.1068/p7811DOI Listing
November 2015

Characteristics of Spontaneous Square-Wave Jerks in the Healthy Macaque Monkey during Visual Fixation.

PLoS One 2015 11;10(6):e0126485. Epub 2015 Jun 11.

Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ, United States of America; Department of Ophthalmology, State University of New York Downstate Medical Center, Brooklyn, NY, United States of America.

Saccadic intrusions (SIs), predominantly horizontal saccades that interrupt accurate fixation, include square-wave jerks (SWJs; the most common type of SI), which consist of an initial saccade away from the fixation target followed, after a short delay, by a return saccade that brings the eye back onto target. SWJs are present in most human subjects, but are prominent by their increased frequency and size in certain parkinsonian disorders and in recessive, hereditary spinocerebellar ataxias. SWJs have been also documented in monkeys with tectal and cerebellar etiologies, but no studies to date have investigated the occurrence of SWJs in healthy nonhuman primates. Here we set out to determine the characteristics of SWJs in healthy rhesus macaques (Macaca mulatta) during attempted fixation of a small visual target. Our results indicate that SWJs are common in healthy nonhuman primates. We moreover found primate SWJs to share many characteristics with human SWJs, including the relationship between the size of a saccade and its likelihood to be part of a SWJ. One main discrepancy between monkey and human SWJs was that monkey SWJs tended to be more vertical than horizontal, whereas human SWJs have a strong horizontal preference. Yet, our combined data indicate that primate and human SWJs play a similar role in fixation correction, suggesting that they share a comparable coupling mechanism at the oculomotor generation level. These findings constrain the potential brain areas and mechanisms underlying the generation of fixational saccades in human and nonhuman primates.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126485PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4466238PMC
April 2016

The influence of traffic signal solutions on self-reported road-crossing behavior.

Span J Psychol 2015 Jan 7;17:E103. Epub 2015 Jan 7.

Universidad de Granada (Spain).

Injury to pedestrians is a major safety hazard in many countries. Since the beginning of the last century, modern cities have been designed around the use of motor vehicles despite the unfavourable interactions between the vehicles and pedestrians. This push towards urbanization resulted in a substantial number of crashes and fatalities involving pedestrians every day, all over the world. Thus, improving the design of urban cities and townships is a pressing issue for modern society. The study presented here provides a characterization of pedestrian safety problems, with the emphasis on signalized crosswalks (i.e. traffic signal) design solutions. We tested the impact of seven different traffic light configurations (steady [green, yellow, and red], flashing [green, yellow, and red], and light off) on pedestrian self-reported road-crossing behavior, using a 11-point scale -ranging from 0 ("I never cross in this situation") to 10 ("I always cross in this situation"). Results showed that mandatory solutions (steady green vs. steady red) are the best solutions to avoid unsafe pedestrian behaviors while crossing controlled intersections (frequency of crossing: Mgreen = 9.4 ± 1 vs. Mred = 2.6 ± 2). These findings offer important guidelines for the design of future traffic signals for encouraging a pedestrian/transit-friendly environment.
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http://dx.doi.org/10.1017/sjp.2014.105DOI Listing
January 2015

Task complexity modulates pilot electroencephalographic activity during real flights.

Psychophysiology 2015 Jul 25;52(7):951-6. Epub 2015 Feb 25.

Mind, Brain, and Behavior Research Center (CIMCYC), University of Granada, Granada, Spain.

Most research connecting task performance and neural activity to date has been conducted in laboratory conditions. Thus, field studies remain scarce, especially in extreme conditions such as during real flights. Here, we investigated the effects of flight procedures of varied complexity on the in-flight EEG activity of military helicopter pilots. Flight procedural complexity modulated the EEG power spectrum: highly demanding procedures (i.e., takeoff and landing) were associated with higher EEG power in the higher frequency bands, whereas less demanding procedures (i.e., flight exercises) were associated with lower EEG power over the same frequency bands. These results suggest that EEG recordings may help to evaluate an operator's cognitive performance in challenging real-life scenarios, and thus could aid in the prevention of catastrophic events.
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http://dx.doi.org/10.1111/psyp.12419DOI Listing
July 2015

Sleep disturbances of adult women suffering from fibromyalgia: a systematic review of observational studies.

Sleep Med Rev 2015 Jun 7;21:86-99. Epub 2014 Oct 7.

Mind, Brain, and Behavior Research Center-CIMCYC, University of Granada, Spain.

Although sleep complaints are often reported in patients with fibromyalgia syndrome (FMS), there is no conclusive evidence that these complaints represent symptomatic disorders of sleep physiology. Thus, the question of the role of sleep disturbances as an etiological or maintenance factor in FMS remains open. This study identifies the subjective and objective characteristics of sleep disturbances in adult women diagnosed with FMS. We carried out a systematic review of publications since 1990, the publication year of the American College of Rheumatology criteria of FMS. We selected empirical studies comparing sleep characteristics of adult women with FMS and healthy women or women with rheumatic diseases. We identified 42 articles. Patients with FMS were more likely to exhibit sleep complaints and also a less efficient, lighter and fragmented sleep. The evidence of a FMS signature on objective measures of sleep is inconsistent, however, as the majority of studies lacks statistical power. Current evidence cannot confirm the role played by sleep physiology in the pathogenesis or maintenance of FMS symptoms; nonetheless, it is clear that sleep disturbances are present in this syndrome.
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http://dx.doi.org/10.1016/j.smrv.2014.09.001DOI Listing
June 2015

Effects of driving time on microsaccadic dynamics.

Exp Brain Res 2015 Feb 23;233(2):599-605. Epub 2014 Nov 23.

Barrow Neurological Institute, Phoenix, AZ, USA,

Driver fatigue is a common cause of car accidents. Thus, the objective detection of driver fatigue is a first step toward the effective management of fatigue-related traffic accidents. Here, we investigated the effects of driving time, a common inducer of driver fatigue, on the dynamics of fixational eye movements. Participants drove for 2 h in a virtual driving environment while we recorded their eye movements. Microsaccade velocities decreased with driving time, suggesting a potential effect of fatigue on microsaccades during driving.
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http://dx.doi.org/10.1007/s00221-014-4139-yDOI Listing
February 2015

Intersaccadic drift velocity is sensitive to short-term hypobaric hypoxia.

Eur J Neurosci 2014 Apr 28;39(8):1384-90. Epub 2014 Jan 28.

Hypoxia, defined as decreased availability of oxygen in the body's tissues, can lead to dyspnea, rapid pulse, syncope, visual dysfunction, mental disturbances such as delirium or euphoria, and even death. It is considered to be one of the most serious hazards during flight. Thus, early and objective detection of the physiological effects of hypoxia is critical to prevent catastrophes in civil and military aviation. The few studies that have addressed the effects of hypoxia on objective oculomotor metrics have had inconsistent results, however. Thus, the question of whether hypoxia modulates eye movement behavior remains open. Here we examined the effects of short-term hypobaric hypoxia on the velocity of saccadic eye movements and intersaccadic drift of Spanish Air Force pilots and flight engineers, compared with a control group that did not experience hypoxia. Saccadic velocity decreased with time-on-duty in both groups, in correlation with subjective fatigue. Intersaccadic drift velocity increased in the hypoxia group only, suggesting that acute hypoxia diminishes eye stability, independently of fatigue. Our results suggest that intersaccadic drift velocity could serve as a biomarker of acute hypoxia. These findings may also contribute to our understanding of the relationship between hypoxia episodes and central nervous system impairments.
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http://dx.doi.org/10.1111/ejn.12482DOI Listing
April 2014

Task difficulty in mental arithmetic affects microsaccadic rates and magnitudes.

Eur J Neurosci 2014 Jan 7;39(2):287-94. Epub 2013 Nov 7.

Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ, USA.

Microsaccades are involuntary, small-magnitude saccadic eye movements that occur during attempted visual fixation. Recent research has found that attention can modulate microsaccade dynamics, but few studies have addressed the effects of task difficulty on microsaccade parameters, and those have obtained contradictory results. Further, no study to date has investigated the influence of task difficulty on microsaccade production during the performance of non-visual tasks. Thus, the effects of task difficulty on microsaccades, isolated from sensory modality, remain unclear. Here we investigated the effects of task difficulty on microsaccades during the performance of a non-visual, mental arithmetic task with two levels of complexity. We found that microsaccade rates decreased and microsaccade magnitudes increased with increased task difficulty. We propose that changes in microsaccade rates and magnitudes with task difficulty are mediated by the effects of varying attentional inputs on the rostral superior colliculus activity map.
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http://dx.doi.org/10.1111/ejn.12395DOI Listing
January 2014

Saccadic eye movement metrics reflect surgical residents' fatigue.

Ann Surg 2014 Apr;259(4):824-9

*Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ †Cognitive Ergonomics Group, Mind, Brain, and Behavior Research Center (CIMCYC), University of Granada, Granada, Spain ‡Joint Center University of Granada-Spanish Army Training and Doctrine Command, Spain §Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ ¶St. Joseph's Hospital and Medical Center, Phoenix, AZ ‖Learning, Emotion and Decision Group, Mind, Brain, and Behavior Research Center (CIMCYC), University of Granada, Granada, Spain.

Objective: Little is known about the effects of surgical residents' fatigue on patient safety. We monitored surgical residents' fatigue levels during their call day using (1) eye movement metrics, (2) objective measures of laparoscopic surgical performance, and (3) subjective reports based on standardized questionnaires.

Background: Prior attempts to investigate the effects of fatigue on surgical performance have suffered from methodological limitations, including inconsistent definitions and lack of objective measures of fatigue, and nonstandardized measures of surgical performance. Recent research has shown that fatigue can affect the characteristics of saccadic (fast ballistic) eye movements in nonsurgical scenarios. Here we asked whether fatigue induced by time-on-duty (~24 hours) might affect saccadic metrics in surgical residents. Because saccadic velocity is not under voluntary control, a fatigue index based on saccadic velocity has the potential to provide an accurate and unbiased measure of the resident's fatigue level.

Methods: We measured the eye movements of members of the general surgery resident team at St. Joseph's Hospital and Medical Center (Phoenix, AZ) (6 males and 6 females), using a head-mounted video eye tracker (similar configuration to a surgical headlight), during the performance of 3 tasks: 2 simulated laparoscopic surgery tasks (peg transfer and precision cutting) and a guided saccade task, before and after their call day. Residents rated their perceived fatigue level every 3 hours throughout their 24-hour shift, using a standardized scale.

Results: Time-on-duty decreased saccadic velocity and increased subjective fatigue but did not affect laparoscopic performance. These results support the hypothesis that saccadic indices reflect graded changes in fatigue. They also indicate that fatigue due to prolonged time-on-duty does not result necessarily in medical error, highlighting the complicated relationship among continuity of care, patient safety, and fatigued providers.

Conclusions: Our data show, for the first time, that saccadic velocity is a reliable indicator of the subjective fatigue of health care professionals during prolonged time-on-duty. These findings have potential impacts for the development of neuroergonomic tools to detect fatigue among health professionals and in the specifications of future guidelines regarding residents' duty hours.
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http://dx.doi.org/10.1097/SLA.0000000000000260DOI Listing
April 2014

Microsaccade and drift dynamics reflect mental fatigue.

Eur J Neurosci 2013 Aug 15;38(3):2389-98. Epub 2013 May 15.

Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ, USA.

Our eyes are always in motion. Even during periods of relative fixation we produce so-called 'fixational eye movements', which include microsaccades, drift and tremor. Mental fatigue can modulate saccade dynamics, but its effects on microsaccades and drift are unknown. Here we asked human subjects to perform a prolonged and demanding visual search task (a simplified air traffic control task), with two difficulty levels, under both free-viewing and fixation conditions. Saccadic and microsaccadic velocity decreased with time-on-task whereas drift velocity increased, suggesting that ocular instability increases with mental fatigue. Task difficulty did not influence eye movements despite affecting reaction times, performance errors and subjective complexity ratings. We propose that variations in eye movement dynamics with time-on-task are consistent with the activation of the brain's sleep centers in correlation with mental fatigue. Covariation of saccadic and microsaccadic parameters moreover supports the hypothesis of a common generator for microsaccades and saccades. We conclude that changes in fixational and saccadic dynamics can indicate mental fatigue due to time-on-task, irrespective of task complexity. These findings suggest that fixational eye movement dynamics have the potential to signal the nervous system's activation state.
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http://dx.doi.org/10.1111/ejn.12248DOI Listing
August 2013

Saccadic velocity as an arousal index in naturalistic tasks.

Neurosci Biobehav Rev 2013 Jun 26;37(5):968-75. Epub 2013 Mar 26.

Department of Neurobiology, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, AZ 85013, USA.

Experimental evidence indicates that saccadic metrics vary with task difficulty and time-on-task in naturalistic scenarios. We explore historical and recent findings on the correlation of saccadic velocity with task parameters in clinical, military, and everyday situations, and its potential role in ergonomics. We moreover discuss the hypothesis that changes in saccadic velocity indicate variations in sympathetic nervous system activation; that is, variations in arousal.
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http://dx.doi.org/10.1016/j.neubiorev.2013.03.011DOI Listing
June 2013

Effect of directional speech warnings on road hazard detection.

Traffic Inj Prev 2011 Dec;12(6):630-5

Learning, Emotion, and Decision Group, Department of Experimental Psychology, University of Granada, Campus de Cartuja, Granada, Spain.

Background: In the last 2 decades, cognitive science and the transportation psychology field have dedicated a lot of effort to designing advanced driver support systems. Verbal warning systems are increasingly being implemented in modern automobiles in an effort to increase road safety.

Objective: The study presented here investigated the impact of directional speech alert messages on the participants' speed to judge whether or not naturalistic road scenes depicted a situation of impending danger.

Method: Thirty-eight volunteers performed a computer-based key-press reaction time task.

Results: Findings indicated that semantic content of verbal warning signals can be used for increasing driving safety and improving hazard detection. Furthermore, the classical result regarding signal accuracy is confirmed: directional informative speech messages lead to faster hazard detection compared to drivers who received a high rate of false alarms.

Conclusion: Notwithstanding some study limitations (lack of driver experience and low ecological validity), this evidence could provide important information for the specification of future Human-Machine-interaction (HMI) design guidelines.
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http://dx.doi.org/10.1080/15389588.2011.620661DOI Listing
December 2011

Saccadic peak velocity sensitivity to variations in mental workload.

Aviat Space Environ Med 2010 Apr;81(4):413-7

Applied Cognitive Research Unit/Psychology III, Technische Universitaet Dresden, Dresden, Germany.

Introduction: For research and applications in the field of (neuro)ergonomics, it is of increasing importance to have reliable methods for measuring mental workload. In the present study we examined the hypothesis that saccadic eye movements can be used for an online assessment of mental workload.

Methods: Saccadic main sequence (amplitude, duration and peak velocity) was used as a diagnostic measure of mental workload in a virtual driving task with three complexity levels. We tested 18 drivers in the SIRCA driving simulator while their eye movements were recorded. The Wickens' multiple resources model was used as theoretical framework. Changes in mental workload between the complexity levels were evaluated multidimensionally, using subjective rating, performance in a secondary task, and other behavioral indices.

Results: Saccadic peak velocity decreased (7.2 visual degrees/s) as the mental workload increased, as measured by scores of mental workload test (15.2 scores) and the increase of the reaction time on the secondary task (46 ms).

Discussion: Saccadic peak velocity is affected by variations in mental workload during ecologically valid tasks. We conclude that saccadic peak velocity could be a useful diagnostic index for the assessment of operators' mental workload and attentional state in hazardous environments.
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http://dx.doi.org/10.3357/asem.2579.2010DOI Listing
April 2010