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The response to prism deviations in human infants
P M Riddell1, A M Horwood, S M Houston
1Baby Vision Laboratory Department of Psychology University of Reading 3 Earley Gate, Whiteknights, Reading, RG6 6AL, UK. p.m. riddell@reading.ac.uk
Insights
Infants can make corrective eye movements to large prisms much earlier than previously thought, challenging existing theories on infant visual development and disparity detection.
Area of Science:
- Developmental Psychology
- Neuroscience
- Ophthalmology
Background:
- Infants previously thought unable to correct eye movements for small prisms before 14-16 weeks.
- Three hypotheses explained this inability: degraded sensory capacity, learning through practice, or maturational factors linked to stereopsis.
Purpose of the Study:
- To test hypotheses on early infant visual responses to prisms.
- To determine if infants respond to larger prisms at younger ages.
Main Methods:
- Tested 192 infants aged 2-52 weeks with a larger prism in the dark.
- Recorded corrective eye movements in response to prismatic deviation.
Main Results:
- 63% of 5-8 week olds showed corrective eye movements with a larger prism.
- Response percentage and speed increased with infant age.
- Infants demonstrate corrective eye movements to large prismatic deviations earlier than 14-16 weeks.
Conclusions:
- Infant visual systems can process larger prismatic deviations earlier than previously believed.
- Findings challenge existing hypotheses regarding sensory capacity, learning, and stereopsis onset.
- Early corrective eye movements indicate a more developed visual response system in young infants.
Abstract:
Previous research has suggested that infants are unable to make a corrective eye movement in response to a small base-out prism placed in front of one eye before 14-16 weeks [1]. Three hypotheses have been proposed to explain this early inability, and each of these makes different predictions for the time of onset of a response to a larger prism. The first proposes that infants have a 'degraded sensory capacity' and so require a larger retinal disparity (difference in the position of the image on the retina of each eye) to stimulate disparity detectors [2]. This predicts that infants might respond at an earlier age than previously reported [1] when tested using a larger prism. The second hypothesis proposes that infants learn to respond to larger retinal disparities through practice with small disparities [3]. According to this theory, using a larger prism will not result in developmentally earlier responses, and may even delay the response. The third hypothesis proposes that the ability to respond to prismatic deviation depends on maturational factors indicated by the onset of stereopsis (the ability to detect depth in an image on the basis of retinal disparity cues only) [4] [5], predicting that the size of the prism is irrelevant. To differentiate between these hypotheses, we tested 192 infants ranging from 2 to 52 weeks of age using a larger prism. Results showed that 63% of infants of 5-8 weeks of age produced a corrective eye movement in response to placement of a prism in front of the eye when in the dark. Both the percentage of infants who produced a response, and the speed of the response, increased with age. These results suggest that infants can make corrective eye movements in response to large prismatic deviations before 14-16 weeks of age. This, in combination with other recent results [6], discounts previous hypotheses.