 1997 John Wiley & Sons, Inc. CCC 0012-1630/97/040287-11 Martha Ann Bell Virginia Polytechnic Institute and State University Department of Psychology Blacksburg, VA 24061–0436 Nathan A. Fox University of Maryland Institute for Child Study College Park, MD Individual Differences in O bject Permanence Performance at 8 M onths: Locomotor Experience and Brain Electrical Activity Received 16 January 1996; accepted 10 February 1997 Abstract: This work was designed to investigate individual differences in hands-and-knees crawling and frontal brain electrical activity with respect to object permanence performance in 76 eight-month-old infants. Four groups of infants (one prelocomotor and 3 with varying lengths of hands-and-knees crawling experience) were tested on an object permanence scale in a research design similar to that used by Kermoian and Campos (1988). In addition, baseline EEG was recorded and used as an indicator of brain development, as in the Bell and Fox (1992) longitudinal study. Individual differences in frontal and occipital EEG power and in locomotor experience were associated with performance on the object permanence task. Infants successful at A-not-B exhibited greater frontal EEG power and greater occipital EEG power than unsuccessful infants. In contrast to Kermoian and Campos (1988), who noted that long- term crawling experience was associated with higher performance on an object permanence scale, infants in this study with any amount of hands and knees crawling experience performed at a higher level on the object permanence scale than prelocomotor infants. There was no interaction among brain electrical activity, locomotor experience, and object permanence per- formance. These data highlight the value of electrophysiological research and the need for a brain-behavior model of object permanence performance that incorporates both electrophys- iological and behavioral factors.  1997 John Wiley & Sons, Inc. Dev Psychobiol 31: 287–297, 1997 Keywords: human infants; object permanence; EEG; frontal lobe; crawling; individual dif- ferences In the recent developmental literature there have been two separate lines of research emphasizing individual differences in object search performance among same- age infants. Researchers from these two perspectives Correspondence to: M. A. Bell Contract grant sponsor: NIH Contract grant number: HD 26728 have implicated self-produced locomotion (e.g., Ber- tenthal, Campos, & Kermoian, 1994) and dorsolateral prefrontal cortex (e.g., Diamond, 1990a, 1990b) as contributing either directly or indirectly to these in- dividual differences in search performance. While these two areas of work appear to be fuel for the classic maturation versus experience debate, it may be that