ABSTRACT Expansive clay soils are a problem for agriculture and engineering because they are susceptible to change in volume due to seasonal variation in water content and temperature. One of its morphological properties is slickensides, which result from the ability to contract and crack when dry and expand by wetting. The objective of this study was to evaluate the processes of expansion and formation and propagation of cracks due to the change in water content over time. The expansion process was evaluated through simple edometric tests with different external stress values applied to undisturbed soil samples. To evaluate the shrinking process, a device was developed to monitor the process of crack propagation. The mechanisms through which cracks begin and develop were studied using molded soil samples at the liquidity limit and at 1.25 times the liquidity limit with a drying and wetting cycle. Crack initiation conditions and development of geometric crack indices were measured with the water content and drying time. The soil presented medium to high expansion that depends on the overburden and suction applied, and the swelling stress was found to increase as suction increases. The changes in volume due to wetting and the propagation of cracks due to drying developed in three stages: initial, primary, and secondary. In the initial stage, few cracks or swelling occur with gradual variation in water content. As the water content approaches the limit of soil contraction (in the drying process) or the limit of soil saturation (in the wetting process), cracks and expansion developed slowly and approach a secondary stage. In the primary stage, cracks and expansion occurred rapidly with drying or wetting, respectively. Drying and wetting cycles showed similar crack patterns with the appearance of new micro-cracks during each new drying cycle.

Objective:To explore the temporal mechanism of attention in children with attention deficit hyperactivity disorder (ADHD) and controls using a rapid serial visual presentation (RSVP) task in which two letters (T1 and T2) were presented in close temporal proximity among distractors (attentional blink [AB]).Method:Thirty children aged between 9 and 13 years (12 with ADHD combined type and 18 controls) took part in the study. Both groups performed two kinds of RSVP task. In the single task, participants simply had to identify a target letter (T1), whereas in the dual task, they had to identify a target letter (T1) and a probe letter (T2).Results:The ADHD and control groups were equivalent in their single-task performance. However, in the dual-task condition, there were significant between-group differences in the rate of detection of the probe letter (T2) at lag + 1 and lag + 4. The ADHD group exhibited a larger overall AB compared with controls.Conclusion:Our findings provide support for a link between ADHD and attentional blink.

Se ha cuestionado la validez ecológica de expresiones faciales estáticas e intensas en el reconocimiento de emociones. Estudios recientes han propuesto el uso de estímulos de expresiones faciales compatibles con las condiciones naturales de interacción social en las que hay movimiento y variaciones en la intensidad emocional. En esta investigación se comparó el reconocimiento de expresiones faciales estáticas y dinámicas de alegría, miedo, rabia y tristeza, presentadas en cuatro intensidades emocionales (25, 50, 75 y 100%). El estudio incluyó a veinte voluntarios (nueve mujeres y once hombres) con edades comprendidas entre 19 y 31 años. El experimento consistió de dos sesiones, en las cuales los participantes tenían que identificar la emoción de expresiones faciales estáticas (fotografías) y dinámicas (videos) presentadas en la pantalla del ordenador. Los promedios de aciertos fueron sometidos a una Anova para medidas repetidas de modelo: 2 sexos x [2 condiciones x 4 expresiones x 4 intensidades]. Se observó una ventaja para el reconocimiento de expresiones dinámicas de alegría y miedo frente a los estímulos estáticos equivalentes (p < .05). El análisis de las interacciones mostró que las expresiones con intensidad de un 25% fueron reconocidas mejor en la condición dinámica (p < .05). La adición de movimiento contribuyó para el reconocimiento de emociones en los participantes masculinos (p < .05). Se concluyó que el efecto del movimiento varía con el tipo de emoción, intensidad de expresión y sexo del participante. Estos resultados apoyan la hipótesis de que los estímulos dinámicos tienen más validez ecológica y pertinencia en la investigación de las emociones.

Ecological validity of static and intense facial expressions in emotional recognition has been questioned. Recent studies have recommended the use of facial stimuli more compatible to the natural conditions of social interaction, which involves motion and variations in emotional intensity. In this study, we compared the recognition of static and dynamic facial expressions of happiness, fear, anger and sadness, presented in four emotional intensities (25%, 50%, 75% and 100%). Twenty volunteers (9 women and 11 men), aged between 19 and 31 years, took part in the study. The experiment consisted of two sessions in which participants had to identify the emotion of static (photographs) and dynamic (videos) displays of facial expressions on the computer screen. The mean accuracy was submitted to an Anova for repeated measures of model: 2 sexes x [2 conditions x 4 expressions x 4 intensities]. We observed an advantage for the recognition of dynamic expressions of happiness and fear compared to the static stimuli (p < .05). Analysis of interactions showed that expressions with intensity of 25% were better recognized in the dynamic condition (p < .05). The addition of motion contributes to improve recognition especially in male participants (p < .05). We concluded that the effect of the motion varies as a function of the type of emotion, intensity of the expression and sex of the participant. These results support the hypothesis that dynamic stimuli have more ecological validity and are more appropriate to the research with emotions.

Tem sido questionada a validade ecológica de expressões faciais estáticas e intensas no reconhecimento de emoções. Estudos recentes têm proposto o uso de estímulos faciais compatíveis com as condições naturais de interação social em que há movimento e variações na intensidade emocional. No presente estudo, foi comparado o reconhecimento de expressões faciais estáticas e dinâmicas de alegria, medo, raiva e tristeza, apresentadas em quatro intensidades emocionais (25%, 50%, 75% e 100%). Participaram do estudo 20 voluntários (9 mulheres e 11 homens), com idade variando entre 19 e 31 anos. O experimento foi composto por duas sessões, nas quais os participantes deveriam identificar a emoção de expressões faciais estáticas (fotografias) e dinâmicas (vídeos) apresentadas na tela do computador. As médias de acerto foram submetidas a uma Anova para medidas repetidas de modelo: 2 sexos x [2 condições x 4 expressões x 4 intensidades]. Foi observada uma vantagem para o reconhecimento das expressões dinâmicas de alegria e medo em comparação com as equivalentes estáticas (p < .05). A análise das interações mostrou que as expressões com intensidade de 25% foram mais bem reconhecidas na condição dinâmica (p < .05). A adição do movimento contribui para melhorar o reconhecimento das emoções nos participantes do sexo masculino (p < .05). Concluí-se que o efeito do movimento varia em função do tipo da emoção, intensidade da expressão e sexo do participante. Tais resultados sustentam a hipótese de que estímulos dinâmicos possuem maior validade ecológica e adequação à pesquisa com emoções.