The corneal reflection technique and the visual preference method: Sources of error

doi:10.1016/0022-0965(75)90101-0

Journal of Experimental Child Psychology

Volume 20, Issue 2, October 1975, Pages 240-247

https://doi.org/10.1016/0022-0965(75)90101-0 Get rights and content

Abstract

Corneal reflection techniques for eye fixation position measurement have been used in recent years to assess such variables of visual behavior as duration of looking and the area(s) of the stimulus fixated. These techniques are especially useful when measuring visual regard in infants and young children as head restraints are not required. In an earlier article the present authors demonstrated, empirically, that the common assumption that the center of the pupil represents the line of sight is untenable. The present article considers the causes of the errors present in these techniques: it can be shown that theoretical calculations of these sources of error, calculations based both on the anatomy of the eye, and on the optics involved, produce good agreement with their empirically derived magnitudes.

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In adults, visual fixation is a foveal function in which a single retinal locus of regard (the fovea) is directed to a point of regard in the stimulus. Because of the immaturity of the infant fovea, the question arises as to whether or not infants use a consistent retinal locus of regard to direct fixations. Consistency of refixations of a small eccentric target was quantitatively examined in infants and adults using a television-based corneal reflection eye tracker. The scatter of refixations for most infants extended beyond the boundaries of the 1.5° square target but was not as large as the degree of central retinal immaturity that has been reported for infants. The mean standard deviation of scatter was about 0.8° [n = 73]. No trend in age (19–388 days) was found. This scatter was greater for infants than for adults instructed to fixate carefully (0.1°). However, uninstructed adults exhibited extensive scatter (0.4°, n = 25), and some showed more scatter than some infants. These results suggest that attentional factors limit the scatter in refixations more than sensory or oculomotor immaturity in the visual system. The implications of these findings for the measurement and calibration of infant looking behavior are discussed.
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We studied infants' scanning of two compound stimuli, in each case by presenting features inside a frame, the frame alone, and the features alone. One stimulus was composed of squares and was like that studied by P. Salapatek (in L. Cohen & P. Salapatek (Eds.), New York: Academic Press, 1975); the other was a schematic face. Newborns and 1-month-olds looked at the small square when it was presented alone, but rarely looked at it when it was framed by the larger square. In contrast, 2-month-olds looked at the small square for long periods whether or not it was framed. However, when newborns and 1-month-olds were shown a schematic face, they looked at its internal features at least half the time. Thus, young infants show no external bias when scanning a schematic face.

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The corneal reflection technique and the visual preference method: Sources of error

Abstract

Journal of Experimental Child Psychology

Journal of Experimental Child Psychology

Journal of Experimental Child Psychology

Journal of Experimental Child Psychology

Journal of Experimental Child Psychology

The eye as an optical system

The physiology of the eye

A method for studying early visual development

Perceptual and Motor Skills