A physiological explanation of infant's early visual development.

Abstract

We propose a physiological explanation of infants' early visual development based on recent evidence that the cat's visual system contains at least three separate pathways — pathways which subserve different functions and develop at different rates. Several lines of evidence suggest the same is true in humans. Data from human newborns suggest that at birth two of these pathways (the X-pathway to the cortex and the Ypathways directly to the superior colliculus and pretectum) are functional, but that the third, the Y-pathway to the cortex, is not. Striking changes at 2 months appear to reflect the dawning influence of that Y-pathway to the cortex. Infants less than 2 months old can make a variety of visual discriminations (see Table 1). They can discriminate between moving and stationary stimuli (cf. Fantz, 1967); between flickering and non-flickering stimuli (Regal, Note 1); and between stimuli which differ in intensity (cf. Hershenson, 1964), in amount of contour (reviewed in Fantz, Fagan, & Miranda, 1975), in orientation (Maurer & Martello, in press; Slater & Sykes, 1977), in shape (Fantz & Miranda, 1975; Milewski, 1976), and in the arrangement of the figure's features (Maurer & Barrera, Note 2). Yet there is an interesting limitation on some of these discriminations. Infants less than 2 months old have difficulty in discriminating between shapes or between arrangements if the elements are surrounded by identical frames (Fantz & Miranda, 1975; Milewski, 1976; Maurer & Barrera, Note 2). In fact, if a circle is added inside a square they have been viewing, they seem not even to notice the change (Milewski, 1976). Infants less than 2 months old also can make a variety of eye movements (see Table 1). They can fixate a stationary stimulus (cf. Lewis & Maurer, in press; Salapatek & Kessen, 1966) and track it if it moves (cf. White, Castle, & Held, 1964). They can localize stimuli in the periphery (cf. Harris & MacFarlane, 1974; Lewis, Maurer, & Kay, 1978). And they demonstrate optokinetic nystagmus (OKN) to a repetitive moving pattern (cf. Brazelton, Scholl, & Robey, 1966). Yet there are important limitations on each type of eye movement (see Table 1). Infants less than 2 months old typically fixate only a very limited region of a stimulus, usually a part of the border (Hainline, 1978; Haith, Bergman, & Moore, 1977; Leahy, 1976; Maurer & Salapatek, 1976; Salapatek, 1968, 1975; Salapatek & Kessen, 1966, 1973; Maurer, Note 3). Their tracking is jerky. They constantly lose the stimulus, saccade to catch up with it, overshoot the stimulus, and backtrack to it (Barten, Birns, 8c Ronch, 1971; Dayton & Jones, 1964; Dayton, Jones, Steele, & Rose, 1964; Kremenitzer, Vaughn, Kurtzberg, & Dowling, 1979; White et al., 1964). Although they can move their eyes both to the left and to the right, they localize a stimulus in the temporal visual field (e.g., a line to the left viewed by the left eye) even when it is 30° off to the side, but do not localize a stimulus in the nasal visual field (e.g., a line to the right viewed by the left eye) if it is more than io° *We thank Myrna Martello for her many contributions to the thinking which preceded this paper. We also thank Murray Sherman, Michael Loop, Dick Aslin, Mort Mendelson, and Jerry Kagan for their helpful comments on a preliminary draft. This work was supported by Canadian National Sciences and Engineering Research Council grant A9797. Requests for reprints should be sent to Dr Daphne Maurer, Department of Psychology, McMaster University, Hamilton, Ontario, Canada L8S 4K1. 232 Canad. J. PsychoL/Rev. canad. Psychol., 1979,33 (4)