Introduction: Psychophysical and electrophysiological techniques have shown that chromatic contrast sensitivity improves between infancy and adolescence. In adults, electrophysiological and psychophysical methods usually agree. However, in infants electrophysiological techniques may underestimate ability to see chromatic contrast (Suttle et al., 2002). It is not known if the discrepancy between electrophysiological and psychophysical methods continues during childhood nor whether the chromatic VEP can be used as an indicator of colour perception in children. Purpose: To investigate the transient L-M chromatic visual evoked potential and its ability to indicate perception (psychophysical thresholds) of chromatic stimuli in children and adults. In particular, to determine whether a discrepancy between VEP and psychophysical L-M thresholds exists during childhood and if so, to gain some understanding about the nature of the discrepancy. Methods: Transient chromatic VEPs were recorded in children (aged 4.5-13 years) and adults (aged 20-40 years). VEP thresholds were compared with psychophysical thresholds (within-subjects comparison). Because the VEPs of the children were less intra-individually repeatable in morphology than those of the adults, post-hoc objective analysis of the VEPs, linear (Fourier) and nonlinear dynamical (Grassberger and Procaccia's (1983) correlation dimension) analyses, was conducted. Results: VEP and psychophysical estimates of chromatic contrast thresholds agreed using a variety of methods in the adults. In the children, however, the objective methods of assessment (extrapolation from Fourier-derived amplitudes and the correlation dimension) were more accurate than the methods that employed subjective evaluations of VEP morphology. Conclusion: The L-M transient chromatic VEPs of both children (aged 4.5-13 years) and adults appear to contain chromatic information, even in the absence of repeatable VEP morphology and should therefore be able to indicate chromatic perception (psychophysical thresholds). However, the chromatic information may be present as a nonlinear dynamical signal, which may require objective methods (Fourier analysis, the correlation dimension) to reveal the chromatic signal. The greater intra-individual variability of VEP morphology in children compared to adults may reflect poorer precision when switching between cortical states in children's brains. Alternatively, interactions between the immature visual system of the children and their general EEG may occur. Children's VEPs should therefore be interpreted differently to adult VEPs.

Introduction: Psychophysical and electrophysiological techniques have shown that chromatic contrast sensitivity improves between infancy and adolescence. In adults, electrophysiological and psychophysical methods usually agree. However, in infants electrophysiological techniques may underestimate ability to see chromatic contrast (Suttle et al., 2002). It is not known if the discrepancy between electrophysiological and psychophysical methods continues during childhood nor whether the chromatic VEP can be used as an indicator of colour perception in children. Purpose: To investigate the transient L-M chromatic visual evoked potential and its ability to indicate perception (psychophysical thresholds) of chromatic stimuli in children and adults. In particular, to determine whether a discrepancy between VEP and psychophysical L-M thresholds exists during childhood and if so, to gain some understanding about the nature of the discrepancy. Methods: Transient chromatic VEPs were recorded in children (aged 4.5-13 years) and adults (aged 20-40 years). VEP thresholds were compared with psychophysical thresholds (within-subjects comparison). Because the VEPs of the children were less intra-individually repeatable in morphology than those of the adults, post-hoc objective analysis of the VEPs, linear (Fourier) and nonlinear dynamical (Grassberger and Procaccia's (1983) correlation dimension) analyses, was conducted. Results: VEP and psychophysical estimates of chromatic contrast thresholds agreed using a variety of methods in the adults. In the children, however, the objective methods of assessment (extrapolation from Fourier-derived amplitudes and the correlation dimension) were more accurate than the methods that employed subjective evaluations of VEP morphology. Conclusion: The L-M transient chromatic VEPs of both children (aged 4.5-13 years) and adults appear to contain chromatic information, even in the absence of repeatable VEP morphology and should therefore be able to indicate chromatic perception (psychophysical thresholds). However, the chromatic information may be present as a nonlinear dynamical signal, which may require objective methods (Fourier analysis, the correlation dimension) to reveal the chromatic signal. The greater intra-individual variability of VEP morphology in children compared to adults may reflect poorer precision when switching between cortical states in children's brains. Alternatively, interactions between the immature visual system of the children and their general EEG may occur. Children's VEPs should therefore be interpreted differently to adult VEPs.

Made available in DSpace on 2016-08-03T16:34:20Z (GMT). No. of bitstreams: 1 LETICIA I_P_S GERTSENCHTEIN.pdf: 506102 bytes, checksum: 777922ec8a932c3175b54a47d293e99c (MD5) Previous issue date: 2011-11-30 / This study investigated the influence of anxiety traits on the performance in cognitive tasks. Thirty-three normal individuals (ages ranging from 18 to 59 years) performed 3 reaction time tasks. The tasks consisted of the identification of 1, 2, or 3 letters sets built from combinations of p, b, q, or d. The mean reaction time for each individual for each stimulus were computed. Anxiety was evaluated through the Spielberger State-Trait Anxiety Inventory (STAI). As expected, mean reaction times increased with the increasing of task difficulty. The scores in both STAI subscales showed a tendency to a negative correlation with reaction time in all three tasks. These results suggest that measures of anxiety must be useful to control sources of variability in psychophysiological studies involving attention tasks. / A influência de traços e sintomas ansiosos sobre o desempenho em tarefas atencionais de dificuldade crescente foi avaliada em 33 participantes de ambos os sexos (18 à 59 anos de idade). O experimento foi constituído de 3 blocos, em que a tarefa proposta consistia na identificação de grupos de uma, duas e três letras. Metade dos sujeitos realizou os testes na seqüência direta e os demais, na seqüência invertida. Os resultados dos três blocos foram correlacionados com os escores das escalas de ansiedade traço e estado de Spielberger. A análise dos dados baseou-se nos tempos médios de reação e no número de respostas válidas para uma, duas e três letras. Os resultados indicaram que os tempos de resposta foram maiores na medida em que a dificuldade da tarefa aumentava. Os resultados mostraram uma tendência à correlação negativa entre os escores das escalas de ansiedade e os tempos de reação em todos os tipos de tarefa. Estes resultados sugerem que a inclusão de avaliações de ansiedade em estudos psicofísicos que envolvam testes de atenção, pode ser útil no controle da variabilidade dos resultados.