Academic journal article The Psychological Record

The Development of Postnatal Turning Bias Is Influenced by Prenatal Visual Experience in Domestic Chicks (Gallus Gallus)

Academic journal article The Psychological Record

The Development of Postnatal Turning Bias Is Influenced by Prenatal Visual Experience in Domestic Chicks (Gallus Gallus)

Article excerpt

It has long been recognized that the avian brain is structurally and functionally lateralized (Bradshaw & Rogers, 1993). Additionally, the avian nervous system has anatomical and developmental features that make it an excellent model for studying laterality. For example, in the avian brain the optic nerves are completely decussated. This neuro-anatomical feature allows unilateral visual experience to the bird's contralateral hemisphere without the need for invasive surgical procedures (Cowen, Adamson, & Powell, 1961). In terms of the developmental process, the embryonic bird develops entirely within the amniotic egg, providing a useful "laboratory" for introducing experimental manipulations into the prenatal environment.

Rogers and her colleagues (Rogers, 1982; Rogers & Bolden, 1991; Rogers & Workman, 1989) have demonstrated that the direction of lateralization in the domestic chick forebrain is determined, at least in part, by the asymmetrical prenatal visual experience of the developing embryo (see Rogers, 1991, for review). At the onset of the lengthy hatching process, the chick embryo is oriented in the egg such that its left eye is blocked by the body and yolk sac, while the right eye is exposed to light entering through the shell. Furthermore, this embryonic orientation occurs at a developmental stage in which the central visual connections are becoming functional and when light stimulation can elicit motor responses (Rogers, 1991). Rogers has argued that the differential prenatal visual experience that results from the asymmetrical orientation of the embryo just prior to hatching serves to facilitate the development of the left hemisphere in advance of the right.

Turning Biases and Spatial Orientation

Rotatory or turning biases are a variety of motor asymmetry in which an animal turns all or part of its body toward one side (left or right) in responding to sensory stimuli. Such biases have been studied in several species, rats (Denenberg, Garbanati, Sherman, Yutzey, & Kaplan, 1978; Glick, 1985), primates (Warren, 1977; Westergaard & Suomi, 1996), and humans (Bradshaw & Bradshaw, 1988; Melekian, 1981). Turning biases are significant because they appear to be evolutionarily old and many motor behaviors have become associated with such behavioral asymmetries (Gospe, Mora, & Glick, 1990; Schone, 1984). For example, lateralized nervous system activity may trigger turning, and conversely, turning may induce other asymmetric activities.

Although extensively studied in mammalian species, turning and rotational biases have been given less of an empirical focus in birds. In the following experiment, we examined the role that prenatal sensory experience plays in the development of turning bias in domestic chicks. Because visual experience has been demonstrated as a powerful prenatal lateralizing influence in other studies of precocial birds, we hypothesized that prenatal visual experience would also prove to be a significant influence on postnatal motor asymmetry in domestic chicks.

General Method

Subjects

Maternally naive, incubator-reared domestic chicks (Gallus gallus) served as subjects. Fertile, unincubated eggs were received weekly from a commercial supplier and set in a Hovi-bator portable incubator, maintained at 37.5 [degrees] C and 80-85% humidity. Eggs were incubated until Day 20 in relative darkness. Incidental exposure to light may have occurred when water was added to the incubator, but for a very brief period. Plastic viewing holes were blocked by thick black cardboard. After 20 days of incubation, the eggs were transferred to a hatching incubator. The possible influence of between-hatch variation in behavior was controlled by drawing subjects for each experiment from at least two different egg batches.

Following hatching, each chick was labeled with a small, water-soluble colored dot on the top of its head. …

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