Academic journal article Attention, Perception and Psychophysics

Gut Estimates: Pregnant Women Adapt to Changing Possibilities for Squeezing through Doorways

Academic journal article Attention, Perception and Psychophysics

Gut Estimates: Pregnant Women Adapt to Changing Possibilities for Squeezing through Doorways

Article excerpt

Published online: 14 December 2013

# Psychonomic Society, Inc. 2013

Abstract Possibilities for action depend on the fit between the body and the environment. Perceiving what actions are possible is challenging, because the body and the environment are always changing. How do people adapt to changes in body size and compression? In Experiment 1, we tested pregnant women monthly over the course of pregnancy to determine whether they adapted to changing possibilities for squeezing through doorways. As women gained belly girth and weight, previously passable doorways were no longer passable, but women's decisions to attempt passage tracked their changing abilities. Moreover, their accuracy was equivalent to that of nonpregnant adults. In Experiment 2, nonpregnant adults wore a "pregnancy pack" that instantly increased the size of their bellies, and they judged whether doorways were passable. Accuracy in the "pregnant" participants was only marginally worse than that of actual pregnant women, suggesting that participants adapted to the prosthesis during the test session. In Experiment 3, participants wore the pregnancy pack and gauged passability before and after attempting passage. The judgments were grossly inaccurate prior to receiving feedback. These findings indicate that experience facilitates perceptual- motor recalibration for certain types of actions.

Keywords Perception and action . Locomotion . Navigation

Over the course of pregnancy, women's bodies undergo dramatic changes. These changes include the obvious gains in body mass: The typical weight gain during pregnancy is 12- 16 kg (US Institute of Medicine, 1990), and some women enlarge by 20 kg or more (Bracero & Byrne, 1998). Weight gain is slow in the first trimester, becomes rapid in the second trimester, and tapers off slightly in the third trimester (Carmichael, Abrams, & Selvin, 1997). Of course, the additional body mass is not evenly distributed: Women's abdomens increase by 31 % of their original size in order to accommodate the growing fetus (Jensen, Doucet, & Treitz, 1996). The change in body proportions causes an anterior shift in the center of mass, as women's large bellies pull them forward (Fries & Hellebrandt, 1943). But these changes are not permanent. During delivery, mothers immediately shed much of the acquired mass in the form of 3.4 kg of newborn infant and 0.6 kg of placenta, eventually losing a total of 10 kg of their pregnant body mass by 6 months postpartum (Soltani & Fraser, 2000).

Physical changes to the body have functional consequences for motor abilities. The forward shift of the center of mass destabilizes the body. While trying to stand still, pregnant women sway more than nonpregnant women (Butler, Colon, Druzin, & Rose, 2006). Moreover, pregnant women lean backward-by as much as 28o-to compensate for their large bellies (Whitcome, Shapiro, & Lieberman, 2007). Balance in pregnant women is precarious, and the risk of falling increases (Dunning et al., 2003). Changes in body size and proportions also affect gait. Some pregnant women adopt a "waddling gait" by widening their base of support to keep balance (Bird, Menz, &Hyde,1999). Most, however, maintain an outwardly normal gait pattern (Wu et al., 2004), but to do so places additional strain on their hip and ankle muscles (Foti, Davids, & Bagley, 2000). After delivery, balance and locomotion return to normal as women's bodies begin reverting to their original size and shape.

Perceiving changing possibilities for action

The relation between pregnant women's changing bodies and abilities typifies a general issue in perception and action: Possibilities for action reflect the fit between body and environment-what Gibson (1979) termed "affordances." When the body changes relative to the environment, affordances also change (Adolph, 2008). Affordances change across the lifespan. From infancy to old age, motor abilities depend on body size and morphology. …

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