Pablo Valdez
Universidad Autónoma de Nuevo León, Facultad de Psicología, Faculty Member
- Professor in Psychobiologyedit
Excessive usage of electronic devices delays bedtime and increases nighttime arousal, reducing sleep duration of adolescents in the morning shift. The impacts of media use before bedtime (MBB) on sleep patterns and components of morning... more
Excessive usage of electronic devices delays bedtime and increases nighttime arousal, reducing sleep duration of adolescents in the morning shift. The impacts of media use before bedtime (MBB) on sleep patterns and components of morning attention were evaluated in 89 adolescents (15.8±0.8 years) using sleep questionnaires and a continuous performance task. Multivariate multiple regression analysis was used to examine relationships ofMBB, chronotype, and genderwith sleep and attention. Smartphoneswere found to be the most frequently used device before bedtime. Attention components were found to be significantly associated with MBB, with a higher frequency of MBB predicting slower reaction times for tonic and phasic alertness and less stable performance of sustained attention. Media usage before bedtime was not significantly associated with patterns of sleep nor sleep quality. This study showed negative impacts ofMBB on most components of morning attention, potentially leading to compromised learning in adolescents.
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Introduction: Sleep deprived people have difficulties to perform daily activities. Their performance depends on three basic cognitive processes: attention, working memory, and executive functions. Objectives: The aim of this study was to... more
Introduction: Sleep deprived people have difficulties to perform daily activities. Their performance depends on three basic cognitive processes: attention, working memory, and executive functions. Objectives: The aim of this study was to identify which specific components of these cognitive processes are more susceptible to a 24-h sleep deprivation period. Material and Methods: Participants were 23 undergraduate students assigned to one of two groups: a control group (n=11, age=18.73±1.62 years) and a sleep deprivation group (n=12, age=18.08±1.16 years). After sleeping freely, control group participants performed a continuous performance task to evaluate the components of attention, a phonological and a visuospatial tasks to record these components of working memory, and a Stroop-like task to assess cognitive inhibition and flexibility, two components of executive functions, at noon for 3 days. Whereas, the sleep deprivation group participants performed the same tasks at noon: after sleeping freely for one night, after a 24-h sleep deprivation, and after one recovery night. Results: After the sleep deprivation, participants had a significant reduction in tonic alertness, selective and sustained attention, components of attention; and in cognitive inhibition, component of executive functions. Conclusion: A 24-h sleep deprivation period reduces several specific components of the basic cognitive processes, which are crucial for performing many everyday activities, thus increasing the risk of errors and accidents.
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Objective: To analyze if the delay of the sleep-wake cycle is the effect of pubertal development, independently of age or school grade. Methods: Girls and boys between 4th and 6th grade were divided into a low pubertal stage and a high... more
Objective: To analyze if the delay of the sleep-wake cycle is the effect of pubertal development, independently of age or school grade. Methods: Girls and boys between 4th and 6th grade were divided into a low pubertal stage and a high pubertal stage group. Age and school grade were controlled to isolate the effect of puberty by pairing the groups on these variables. The regular bedtime, waking time, sleep duration and daytime sleepiness were obtained through questionnaires. A Pubertal Developmental Scale with questions about bodily changes was used to determine pubertal stage. Results: Girls in high pubertal stages reported weekend bedtimes an hour later than girls in low puberty stages (low pubertal stage: 22:36±2:11 h, high pubertal stage: 23:37±1:27 h, U=215, p<0.05); there were no differences on waking time or sleep duration. Boys of different pubertal development did not have differences on any sleep parameter. Girls had a longer sleep duration compared to boys on weekends, but not on weekdays. Discussion: The bedtime delay in girls is the effect of pubertal development, not of age or school grade. There was no effect on boys due to their lower pubertal development at this age. Variability in pubertal development creates disparities in the sleep patterns of pubescent girls, even of the same age and school grade. Acknowledging this delay can help to create school and sports schedules in which young people are fully awake and alert. In research, it is crucial to consider pubertal development while studying sleep in children and adolescents.
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Juvenile delinquents are young people who break the law. They are usually males of low socioeconomic status and low education, and are more exposed to brain damage risk factors, especially drug use, and have a higher prevalence of... more
Juvenile delinquents are young people who break the law. They are usually males of low socioeconomic status and low education, and are more exposed to brain damage risk factors, especially drug use, and have a higher prevalence of attention deficit hyperactivity disorder. These characteristics suggest a delay in the development of the prefrontal cortex of the brain, which is related to neuropsychological functions such as language, memory, attention, and executive functions. To assess the evidence of a delay in the development of prefrontal functions, a search was conducted for studies that evaluated neu-ropsychological functions in inmate juvenile delinquents, comparing them to a control group, and only 14 articles were found with these characteristics. The review showed that, despite methodological issues on task selection and on the composition of control groups, there is evidence that juvenile delinquents have disorders on neuropsychological functions such as language comprehension, visuospatial working memory, selective and sustained attention, and components of executive functions such as cognitive inhibition, cognitive flexibility, and planning. These findings agree with the hypothesis that there is a developmental delay in the prefrontal functions of juvenile delinquents. Understanding the deficits juvenile delinquents have on neuropsychological functions is crucial to design prevention and treatment programs for juvenile delinquency. Trastornos neuropsicológicos en delincuentes juveniles Resumen Los delincuentes juveniles son jóvenes que violan la ley. Por lo general, son hombres de bajo nivel socioeconómico que tienen poca educación, están más expuestos a factores de riesgo de daño cerebral, especialmente el uso de drogas y tienen una mayor prevalencia de TDAH. Estas características sugieren un retraso en el desarrollo de la corteza prefrontal del cerebro, que está relacionada con funciones neuropsicológicas como el lenguaje, la memoria, la atención y las funciones ejecutivas. Para evaluar la evidencia de un retraso en el desarrollo de las funciones prefrontales, se realizó una búsqueda de estudios que evaluaran las funciones neuropsicológicas en delincuentes juveniles internos, comparándolos con un grupo de control y solo se encontraron 14 artículos con estas características. La revisión mostró que, a pesar de los problemas metodológicos en la selección de tareas y en la composición de los grupos de control, existe evidencia de que los
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Attention is a cognitive process crucial for human performance. It has four components: tonic alertness, phasic alertness, selective attention, and sustained attention. All the components of attention show homeostatic (time awake, sleep... more
Attention is a cognitive process crucial for human performance. It has four components: tonic alertness, phasic alertness, selective attention, and sustained attention. All the components of attention show homeostatic (time awake, sleep deprivation) and circadian (time of day) variations. The time course of the circadian rhythms in attention is important to program work and school-related activities. The components of attention reach their lowest levels during nighttime and early hours in the morning, better levels occur around noon, and even higher levels can be observed during afternoon and evening hours. However, this time course can be modulated by chronotype, sleep deprivation, age, or drugs. Homeostatic and circadian variations have also been found in other basic cognitive processes (working memory and executive functions), with a time course similar to that observed for attention. Data reviewed in this paper suggests the need to consider circadian rhythms, age, and chronotype of the person, when programming schedules for work, study, school start time, school testing, psychological testing, and neuropsychological assessment.
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An important property of attention is the limitation to process new information after responding to a stimulus. This property of attention can be evaluated by the Attentional Blink (AB), a phenomenon that consists of a failure to detect... more
An important property of attention is the limitation to process new information after responding to a stimulus. This property of attention can be evaluated by the Attentional Blink (AB), a phenomenon that consists of a failure to detect the second of two targets when the interval between them is 200–500 ms. The aim of the present work is to determine the possible existence of time awake (homeostatic changes) and time of day (circadian rhythm) variations in the AB. Eighteen undergraduate students, 11 men and 7 women, age = 18.06 ± 1.16 years, participated voluntarily in this research. They were recorded in a constant routine protocol during 29 h, in which rectal temperature was recorded every minute, while subjective sleepiness and responses to a Rapid Serial Visual Presentation (RSVP) task, to measure the AB, were recorded every hour. Homeostatic and circadian variations in all parameters of the RSVP task were observed, including changes in the capacity to process a new stimulus (Target 1 accuracy), a second stimulus occurring in a short interval after the first (Target 2 accuracy at lag 2, 200 ms) and to process another successive independent stimulus (Target 2 accuracy at lag 8, 800 ms). The acrophase of these parameters occurred with a phase delay of 2 h compared to the circadian rhythm of rectal temperature. The AB magnitude, an index of the AB, showed a decline with time awake, but no variations with time of day. In conclusion, there are homeostatic and circadian variations in the capacity to process any incoming information, especially in tasks with brief duration stimuli presented at a high frequency.
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Cognitive processes are crucial for human performance. Basic cognitive processes, such as attention, working memory, and executive functions, show homeostatic (time awake, sleep deprivation) and circadian (time of day) variations. Each of... more
Cognitive processes are crucial for human performance. Basic cognitive processes, such as attention, working memory, and executive functions, show homeostatic (time awake, sleep deprivation) and circadian (time of day) variations. Each of these cognitive processes includes several components, which contribute sequentially to the homeostatic and circadian modulation of performance. Sudden (lapses) and gradual changes in cognitive performance occur with sleep deprivation or with time of day. The time course of human cognitive processes throughout the day is relevant to the programming of different human activities. The lowest level of cognitive performance occurs during nighttime and early in the morning, a better level occurs around noon, and even higher levels occur during afternoon and evening hours. However, this time course can be modulated by conditions such as chronotype, sleep deprivation, sleep disorders or medication that affects the central nervous system.
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Cognitive performance is affected by an individual’s characteristics and the environment, as well as by the nature of the task and the amount of practice at it. Mental performance tests range in complexity and include subjective estimates... more
Cognitive performance is affected by an individual’s characteristics and the environment, as well as by the nature of the task and the amount of practice at it. Mental performance tests range in complexity and include subjective estimates of mood, simple objective tests (reaction time), and measures of complex performance that require decisions to be made and priorities set. Mental performance tasks show 2 components, a circadian rhythm and the effects of time awake. The circadian rhythm is in phase with the rhythm of core temperature and there is evidence for a causal link. Increasing time awake results in performance deterioration and is attributed to fatigue. The relative contribution of these 2 components depends upon the task under consideration; simple tasks generally show smaller effects due to increasing time awake. These contributions have been assessed by constant routines and forced desynchronization protocols and have formed the basis of several mathematical models that attempt to predict performance in a variety of field conditions. Mental performance is negatively affected by sleep loss; although short naps are beneficial, sleep inertia limits their value immediately after waking. The processes involved in cognition include attention (tonic and phasic alertness, and selective and sustained attention), working memory (phonological, used for speech, reading, and writing; and visuospatial, used for spatial processing, drawing, and mathematics), and executive function (initiative, decision making, and problem solving). These processes are illuminated by analysis of the regions of the brain involved, the presence of circadian rhythmicity, and the effects of sleep loss. The results from such laboratory- and field-based observations are relevant to the issue of learning in schoolchildren and lead to suggestions for improving their performance.
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Circadian variations have been found in human performance, including the efficiency to execute many tasks, such as sensory, motor, reaction time, time estimation, memory, verbal, arithmetic calculations, and simulated driving tasks.... more
Circadian variations have been found in human performance, including the efficiency to execute many tasks, such as sensory, motor, reaction time, time estimation, memory, verbal, arithmetic calculations, and simulated driving tasks. Performance increases during the day and decreases during the night. Circadian rhythms have been found in three basic neuropsycho-logical processes (attention, working memory, and executive functions), which may explain oscillations in the performance of many tasks. The time course of circadian rhythms in cognitive performance may be modified significantly in patients with brain disorders, due to chronotype, age, alterations of the circadian rhythm, sleep deprivation, type of disorder, and medication. This review analyzes the recent results on circadian rhythms in cognitive performance, as well as the implications of these rhythms for the neuropsychological assessment of patients with brain disorders such as traumatic head injury, stroke, dementia, developmental disorders, and psychiatric disorders.
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Objective. The current study aimed to determine the differences between sleep–wake habits and circadian preference in Mexican adolescents attending classes at a morning shift or an afternoon shift. Methods. The sample consisted of 568... more
Objective. The current study aimed to determine the differences between sleep–wake habits and circadian preference in Mexican adolescents attending classes at a morning shift or an afternoon shift. Methods. The sample consisted of 568 students of a secondary school in Reynosa, northeastern Mexico, of whom 280 were boys and 288 were girls (mean age 14.08 ± 0.72 years, age range 13–16 years). In the morning shift, 287 students attend classes on a schedule from 7:30 to 13:00 and the afternoon shift, 281 students, on a schedule from 13:20 to 19:00. Students completed a general information questionnaire, the Sleep Timing Questionnaire and the Spanish version of the Morningness–Eveningness Questionnaire. Results.
The adolescents who attended the morning shift had earlier bedtime and waking time, but shorter sleep duration than those who attended the afternoon shift. Those oriented to eveningness had later bedtime, waking time, and a shorter sleep duration than those oriented to morningness. Two interactions were found between school shift and chronotype. First, with regard to waking time during weekdays, students who attended the afternoon shift and were oriented to eveningness woke up later than those who attended the morning shift and were oriented to eveningness; during weekdays, there were no differences between the waking time of morning-type and evening-type students who attended the morning shift. Second, with regard to sleep duration on weekdays, students who attended the morning shift and were oriented to eveningness had the shortest sleep duration. Furthermore, there were no differences between sleep duration on weekdays in evening-type and morning-type students of the afternoon shift. Conclusion. Adolescents who attend classes in the morning shift and are oriented to eveningness are the most sleep deprived. Those who attend the afternoon shift will have optimal sleep duration, regardless of their circadian preference.
The adolescents who attended the morning shift had earlier bedtime and waking time, but shorter sleep duration than those who attended the afternoon shift. Those oriented to eveningness had later bedtime, waking time, and a shorter sleep duration than those oriented to morningness. Two interactions were found between school shift and chronotype. First, with regard to waking time during weekdays, students who attended the afternoon shift and were oriented to eveningness woke up later than those who attended the morning shift and were oriented to eveningness; during weekdays, there were no differences between the waking time of morning-type and evening-type students who attended the morning shift. Second, with regard to sleep duration on weekdays, students who attended the morning shift and were oriented to eveningness had the shortest sleep duration. Furthermore, there were no differences between sleep duration on weekdays in evening-type and morning-type students of the afternoon shift. Conclusion. Adolescents who attend classes in the morning shift and are oriented to eveningness are the most sleep deprived. Those who attend the afternoon shift will have optimal sleep duration, regardless of their circadian preference.
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Circadian variations have been found in cognitive processes, such as attention, working memory, and executive functions, which may explain oscillations in the performance of many tasks. These cognitive processes improve during the day and... more
Circadian variations have been found in cognitive processes, such as attention, working memory, and executive functions, which may explain oscillations in the performance of many tasks. These cognitive processes improve during the day and decrease during the night and early hours of the morning. Sleep deprivation further decreases these cognitive processes during daytime hours. This review analyses the recent findings on circadian rhythms in cognitive processes, as well as the implications of these rhythms for school learning.
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Working memory is a basic cognitive process that temporarily maintains the information necessary for the performance of many complex tasks such as reading comprehension, learning and reasoning. Working memory includes two storage... more
Working memory is a basic cognitive process that temporarily maintains the information necessary for the performance of many complex tasks such as reading comprehension, learning and reasoning. Working memory includes two storage components: phonological and visuospatial, and a central executive control. The objective of this study was to identify possible circadian rhythms in phonological and visuospatial storage components of working memory using a constant routine protocol. Participants were eight female undergraduate students, aged 17.5±0.93, range = 16 – 19 years old. They were recorded in the laboratory in a constant routine protocol during 30 h. Rectal temperature was recorded every minute; subjective sleepiness and tiredness, as well as phonological and visuospatial working memory tasks, were assessed each hour. There were circadian variations in correct responses in phonological and visuospatial working memory tasks. Cross-correlation analysis showed a 1-h phase delay of the phonological storage component and a 3-h phase delay of the visuospatial storage component with respect to rectal temperature. This result may explain the changes in the performance of many complex tasks during the day.
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The objective of this study was to identify circadian rhythms in cognitive inhibition and flexibility using a Stroop task. Eight undergraduate student volunteers (age = 17.75 ± 0.46 years; 7 females), participated in this study.... more
The objective of this study was to identify circadian rhythms in cognitive inhibition and flexibility using a Stroop task. Eight undergraduate student volunteers (age = 17.75 ± 0.46 years; 7 females), participated in this study. Participants were recorded in a constant routine protocol for 29 h. Body temperature was recorded every minute, and every 100 min participants completed scales of sleepiness and tiredness and responded to a Stroop task with shifting criteria. This task includes a chart with 48 colors printed with incongruent names. A random half of the words had a point on the left. Participants were instructed to do four actions: (i) read all the words; (ii) name the color in which each word was printed; (iii) read the words marked with a point and name the colors of the unmarked words; and (iv) name the colors of the words marked with a point and read the unmarked words. The time and errors in naming the colors were considered inhibition indices, while performance time and errors upon shifting criteria were considered flexibility indices. Circadian variations were found in inhibition (color-naming) and flexibility (shifting criteria). These cognitive processes also showed decay with time on task. In conclusion, there were circadian variations in two components of executive functions: inhibition and flexibility, modulated by sustained attention (time on task). These results may explain the difficulties experienced at night in problem-solving that requires adjustment of behavior in accordance with environmental demands.
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Changes of schedules larger than 3 h, such as jet lag and shift work, require an adjustment period of several days to resynchronize the sleep-wake cycle and several weeks to resynchronize other circadian rhythms to the new schedule.... more
Changes of schedules larger than 3 h, such as jet lag and shift work, require an adjustment period of several days to resynchronize the sleep-wake cycle and several weeks to resynchronize other circadian rhythms to the new schedule. Initial studies on adaptation to small changes of schedule (1-2 h) found that the sleep-wake cycle adapts to the new schedule in less than 48 h, and such modifications are generally not studied because they may be confounded by a potential masking effect. This article summarizes the few published studies on Daylight Saving Time (DST) and sleep during weekends, two examples of small changes in schedule. There are individual differences in adaptation to daylight saving time, while some persons adjust immediately; other persons require more than 2 weeks. During weekends, people tend to go to bed and wake up later, and to extend their sleep. Delay and extension of sleep depend on factors such as shift of work during weekdays and chronotype (morningness-eveningness). Both DST and sleep during weekends offer the opportunity to study adaptation of the sleep-wake cycle in recurrent, social conditions. Studying these phenomena is also relevant to some socioeconomic issues, like the reportedincrease of traffic accidents and complaints from the population during daylight saving time; or the possible decrease in productivity and absenteeism during the ‘Blue Monday’.
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The objective of this study was to analyze possible circadian variations in two components of executive functions: inhibition and flexibility. Participants were eight undergraduate students, age: 17.75 ± 0.46 years, one male and seven... more
The objective of this study was to analyze possible circadian variations in two components of executive functions: inhibition and flexibility. Participants were eight undergraduate students, age: 17.75 ± 0.46 years, one male and seven female. They were kept in a constant routine protocol for 29 h. Rectal temperature was recorded every minute and responses to a computerized Stroop-like task with shifting criteria were recorded every 100 min. The task had three sections: match, no-match (index of inhibition), and shifting criteria (index of flexibility). There were circadian variations in rectal temperature, inhibition and flexibility. These cognitive processes showed a 1–2 h phase delay with respect to rectal temperature, and were modulated by sustained attention (time on task). The decline of these components of executive functions at night and in the early morning impairs decision-making and problem-solving, thus promoting errors while driving a car or working at night.
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The present article is the adapted version of an electronic symposium organized by the Brazilian Society of Neuroscience and Behavior (SBNeC) which took place on June 14, 2000. The text is divided into three sections: I. The main issues,... more
The present article is the adapted version of an electronic symposium organized by the Brazilian Society of Neuroscience and Behavior (SBNeC) which took place on June 14, 2000. The text is divided into three sections: I. The main issues, II. Chronodrugs, and III. Methods. The first section is dedicated to the perspectives of chronobiology for the next decade, with opinions about the trends of future research being emitted and discussed. The second section deals mostly with drugs acting or potentially acting on the organism's timing systems. In the third section there are considerations about relevant methodological issues concerning data analysis.
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Executive functions are still developing during adolescence. It is important to analyse if juvenile delinquency is related to a delay in the development of these functions. The objective of this study was to analyse cognitive inhibition... more
Executive functions are still developing during adolescence. It is important to analyse if juvenile delinquency is related to a delay in the development of these functions. The objective of this study was to analyse cognitive inhibition and flexibility, two components of executive functions, in juvenile delinquents. Participants were 81 males, 17.46 ± 1.60 years old. Three groups were compared: a juvenile delinquent inmate group (IG), an age-paired group (APG), and an age- and education-paired group (AEPG). A modified Stroop task was used to assess cognitive inhibition and flexibility. The IG and the AEPG (low-education adolescents) had significantly more difficulties than the APG on inhibition; the IG and the AEPG had no significant differences. No group differences were found on flexibility. Since all low-education adolescents have difficulties on inhibition, these difficulties are not an exclusive characteristic of juvenile delinquents. Analysis of cognitive processes in juvenile delinquents must control for education to determine how specific are the difficulties found in these adolescents.
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Objective: To determine the effect of computer and mobile phone use before bedtime on the sleep/wake cycle. Method: A total of 568 junior high school students were registered, 280 (49.30%) males and 288 (50.79%) females, mean age 14.08 ±... more
Objective: To determine the effect of computer and mobile phone use before bedtime on the sleep/wake cycle. Method: A total of 568 junior high school students were registered, 280 (49.30%) males and 288 (50.79%) females, mean age 14.08 ± 0.72 (13-16) years, 287 attended classes on the morning shift from 7:30 to 1:00h and 281 attended the afternoon shift from 13:20 to 19:00h. All participants answered a questionnaire on how they use before bedtime the computer and mobile phone. They were divided into two groups according to the use of each device, a group of higher use (GHU) (4-7 days per week; >105 min per day) and a group of lower use (GLU) (1-3 days per week; <105 min per day). In addition, participants answered a sleep timing questionnaire (STQ), the morgningness-eveningness questionnaire (MEQ) of Horne & Östberg and Epworth Sleepiness Scale (ESS). Results: In the computer GHU, there was a delay on weekday bedtime (GHU: 24.13±1.65; GLU: 23.02±1.16, T=6.90, p<0.001), waki...
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It has been found that juvenile delinquents have a high prevalence of attention deficit and hyperactivity disorder (ADHD) symptoms. The objective of this study was to analyze ADHD symptoms and possible difficulties on the four components... more
It has been found that juvenile delinquents have a high prevalence of attention deficit and hyperactivity disorder (ADHD) symptoms. The objective of this study was to analyze ADHD symptoms and possible difficulties on the four components of attention (tonic alertness, phasic alertness, selective attention and sustained attention) in juvenile delinquents. Participants were 45 males, 15 juvenile delinquents (JDG), 15 non-delinquent adolescents paired by age (PAG) and 15 non-delinquent adolescents paired by age and education level (PAEG). ADHD symptoms were self-reported using the Conners Questionnaire. The components of attention were analyzed using a Continuous Performance Task. There were no group differences on the predominantly inattentive ADHD scale (JDG 4.04±2.13, PAG 2.51±1.42, PAEG 2.93±1.88; H=4.08, NS) but there were differences on the predominantly hyperactive – impulsive ADHD scale (JDG 4.69±2.40, PAG 2.54±1.41, PAEG 2.72±2.05; H=8.58; p<0.05). There were differences on...
Cognitive processes such as attention are diminished in elderly people, compared to younger adults. In this study, attention was analyzed during normal aging using a neuropsychological model with four components: tonic alertness, phasic... more
Cognitive processes such as attention are diminished in elderly people, compared to younger adults. In this study, attention was analyzed during normal aging using a neuropsychological model with four components: tonic alertness, phasic alertness, selective attention and sustained attention. The aim of this study was to analyze changes on the components of attention during aging. Participants were 43 elderly people aged between 60 and 81 years old (21 females, 22 males; age: 72.00 ± 5.83 years), with no history of sensory or neurological disorder that performed all their daily living activities themselves. A continuous performance task was used to assess the components of attention. Age correlated with all components of attention. As age increased, correct responses decreased (tonic alertness: r = -0.43, p<0.01; phasic alertness: r = -0.45, p<0.01; selective attention: r = -0.45, p<0.01) and reaction time increased (tonic alertness r = 0.32, p<0.05; phasic alertness: r =...