Journal of Experimental Psychology: Copyright 1997 by the American Psychological Association, Inc. Human Perception and Performance 0096-1523/97/$3.00 1997, Vol. 23, No. 6, 1631-1643 Perception-Action Coupling in the Development of Visual Control of Posture Bennett I. Bertenthal, James L. Rose, and Dina L. Bai University of Virginia In this investigation of developmental changes in the coordination of perceived optical flow and postural responses, 4 age groups of infants (5-, 7-, 9-, and 13-month-olds) were tested while seated on a force plate in a "moving room." During each trial the walls oscillated in an anteroposterior direction for 12 s, and the postural sway of the infant was measured. The results revealed that infants perceived the frequency and amplitude of the optical flow and scaled their postural responses to the visual information. This scaling was present even before infants could sit without support, but it showed considerable improvement during the period when infants learn to sit. Taken together, these results suggest that the visuomotor coordination necessary for controlling sitting is functional prior to the onset of independent sitting but becomes more finely tuned with experience. An emerging theme in the developmental literature is that perception and action are dynamically coupled in the regulation of coordinated movements (Bertenthal, 1996; Thelen, 1990; von Hofsten, 1993). This coupling is neces- sary to ensure stable action patterns that are appropriate to the specific environmental demands of the situation. Con- sider the case of locomotion. It would be nearly impossible to move from one location to another if the motor response synergies necessary for this action were not modulated by perceptual information specifying the layout of surfaces and the spatial orientation of the organism. One of the most useful paradigms for studying the early development of this coupling involves the visual control of posture in a "moving room" (see Figure 1). In this paradigm, the infant sits or stands on a stationary floor while the surrounding walls and ceiling move forward and back- ward. This movement produces visual information congru- ent with movement of the head in the opposite direction. If the optical flow is perceived as specifying self-motion (as opposed to object motion), 1 then a compensatory response that varies with age and motor development will be produced. In the initial study with this paradigm, Lee and Aronson (1974) reported that infants who were just beginning to stand on their own would sway or stagger when the walls moved. This finding was subsequently replicated and ex- tended to show that optical flow restricted to the peripheral portions of the visual field was sufficient to induce postural Bennett I. Bertenthal, James L. Rose, and Dina L. Bai, Depart- ment of Psychology, University of Virginia. This research was supported by National Institutes of Health (NIH) Grants HD16196 and HD23144 and by a predoctoral fellowship from NIH Grant HD07323. We thank Dawn Chandler, Sharon Lambert, Leslie Ferree, and Stephen Garrison for their assistance in testing infants and scoring data. Correspondence concerning this article should be addressed to Bennett I. Bertenthal, Department of Psychology, Gilmer Hall, University of Virginia, Charlottesville, Virginia 22903. Electronic mail may be sent via Intemet to bib@virginia.edu. compensations (Bertenthal & Bai, 1989; Stoffregen, Schmuckler, & Gibson, 1987). Additional evidence for the coupling between vision and posture was reported by Butterworth and Hicks (1977) and Bertenthal and Bai (1989), who showed that infants who could sit indepen- dently would produce postural compensations with their trunks when tested in the moving room. Some of the most recent evidence (Jouen, 1990; Jouen, Lepecq, Gapenne, & Bertenthal, in press) suggests that even newborn infants show postural compensations with their heads when stimu- lated by an optical flow pattern. This last finding is especially provocative because it suggests that the rate-limiting factor in the visual control of posture is not the perception of optical flow. Even neonates detect optical flow information as specifying self-motion. Nevertheless, the detection of this visual information does not guarantee that the infant will produce the appropriate postural responses in all situations. Systematic postural compensations while sitting or standing occur later than compensations with the head because the necessary muscle strength and coordination develop at different rates for each posture (Woollacott & Sveistrup, 1994). Moreover, percep- tual sensitivity to visual information improves rapidly during the first few months after birth. In particular, thresh- olds for spatial and temporal frequencies improve, as do thresholds for detecting motion (Banks & Dannemiller, 1987; Bertenthal & Bradbury, 1992). As these thresholds improve, the minimal information for inducing a postural compensation will change. Thus, it is the development of both sensory and motor skills that are necessary for improvements in postural 1It is important to emphasize that the perception of self-motion from optical flow does not imply any awareness of the self. The perception of self-motion is based on infants' showing a direction- ally appropriate postural response to the optical flow information. It would be misleading and unnecessary to conclude any more about the perception of the self from this response. See Bertenthal and Rose (1995) for further discussion of this point. 1631