L Sewall | PubMed Health

PubMed1991

Stimulus determinants of achromatic constancy.

Achromatic constancy refers to the invariance of either lightness or brightness despite changes in illumination intensity. Previous results disagree as to the extent to which constancy occurs with fixed luminance ratio conditions. This may reflect a lack of distinction between lightness and brightness. We measured both lightness and brightness constancy with fixed luminance ratios between test and annular fields under conditions varying in stimulus duration and adaptation. Lightness constancy occurred for all ratios under sustained viewing conditions and irrespective of adaptation level. Brightness constancy occurred for high-contrast stimuli and under sustained viewing conditions. These results support a bidimensional description of achromatic stimuli and suggest that lightness and brightness are the outcomes of two functionally distinct processes.

Color Perception↗

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Strength training for children.

The indications for progressive resistive strength training for prepubescent children in sports training and rehabilitation have been a source of controversy. Eighteen prepubescent children, two at Tanner Stage II and the remainder at Tanner Stage I, were studied. Examination included anthropometric upper and lower extremity strength and flexibility measurements. The study group participated in progressive resistive strength training sessions on machines three times per week. The study group had a mean increase in strength of 42.9%, whereas strength in the control group increased 9.5% (p less than 0.05). The study group had a mean increase in flexibility of 4.5% compared with 3.6% in the control group. The study group showed a mean decrease in body weight during the training period of 0.51% and then gained 3.48% over the subsequent 9 weeks. The control group's body weight increased an average of 6.66% during the 18 weeks. There were no injuries during the training period. It is concluded that prepubescent children can make significant gains in muscle strength in response to progressive resistive training.

Body Weight↗