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How infants explore visual stimuli changes with age (Colombo, Brez, & Curtindale, 2015). Until about 1 month of age, infants tend to scan along the outer perimeter of stimuli. For example, when presented with a face, the infant’s gaze will scan along the hairline and not move to the eyes and mouth. This is known as the externality effect because infants scan along the outer contours of complex visual stimuli. By 6 to 7 weeks of age, infants study the eyes and mouth, which hold more information than the hairline, as shown in Figure 4.13 (Hunnius & Geuze, 2004). Similarly, the ability to follow an object’s movement with the eyes, known as visual tracking, is very limited at birth but improves quickly. By 2 months of age, infants can follow a slow-moving object smoothly, and by 3 to 5 months, their eyes can dart ahead to keep pace with a fast-moving object (Agyei, van der Weel, & van der Meer, 2016; Richards & Holley, 1999). The parts of the brain that process motion in adults are operative in infants by 7 months of age (Weaver, Crespi, Tosetti, & Morrone, 2015).

Description

Figure 4.13 Externality Effect and Face Perception

The externality effect refers to a particular pattern of infant visual processing. When presented with a complex stimulus, such as a face, infants under 2 months of age tend to scan along the outer contours, such as along the hairline. Older infants scan the internal features of complex images and faces, thereby processing the entire stimulus.

Source: Shaffer (2002, p. 190); adapted from Salapatek (1975).