First sight: Donald Duck, suspended in front of a coloured pattern displayed on a computer screen is used to evaluate a 7 weeks-old infant's sight. Scientists at the Smith-Kettlewell Institute in San Francisco record electrical activity in the brains of infants in response to visual stimuli displayed on a computer. The toy is used to engage the baby's attention whilst the pattern changes at a controlled rate - in colour, brightness or size. The infant's response to these changes is measured through electrodes taped to her head. The method gives a measure of visual development, when images become too faint to provoke a response in the brain.