Speech Perception Worksheet
Complete the following table.
|Dual-stream model of speech perception|
|Motor theory of speech perception
The Embryonic Period The embryonic period is the period of prenatal development that occurs from two to eight weeks after conception. During the embryonic period, the rate of cell differentiation intensifies, support systems for cells form, and organs develop. The mass of cells is now called an embryo, and three layers of cells form. The embryo’s endoderm is the inner layer of cells, which will develop into the digestive and respiratory systems. The ectoderm is the outermost layer, which will become the nervous system, sensory receptors (ears, nose, and eyes, for example), and skin parts (hair and nails, for example). The mesoderm is the middle layer, which will become the circulatory system, bones, muscles, excretory system, and reproductive system. Every body part eventually develops from these three layers. The endoderm primarily produces internal body parts, the mesoderm primarily produces parts that surround the internal areas, and the ectoderm primarily produces surface parts. Organogenesis is the name given to the process of organ formation during the first two months of prenatal development. While they are being formed, the organs are especially vulnerable to environmental influences.
How Would You…?
As a human development and family studies professional, how would you characterize the
greatest risks at each period of prenatal development? As the embryo’s three layers form, life-support systems for the embryo develop rapidly. These systems include the amnion, the umbilical cord (both of which develop from the fertilized egg, not the mother’s body), and the placenta. The amnion is like a bag or an envelope; it contains a clear fluid in which the developing embryo floats. The amniotic fluid provides an environment that is temperature- and humidity-controlled, as well as shockproof. The umbilical cord, which typically contains two arteries and one vein, connects the baby to the placenta. The placenta consists of a disk-shaped group of tissues in which small blood vessels from the mother and the offspring intertwine but do not join. Page 51
Very small molecules—oxygen, water, salt, and nutrients from the mother’s blood, as well as carbon dioxide and digestive wastes from the baby’s blood—pass back and forth between the mother and the embryo or fetus. Large molecules cannot pass through the placental wall; these include red blood cells and some harmful substances, such as most bacteria, maternal wastes, and hormones (Holme & others, 2015; Pfeifer & Bunders, 2016). Virtually any drug or chemical substance a pregnant woman ingests can cross the placenta to some degree, unless it is metabolized or altered during passage, or is too large (Burton & Jauniaux, 2015).
A recent study confirmed that ethanol crosses the human placenta and primarily reflects maternal alcohol use (Matlow & others, 2013). Another study revealed that cigarette smoke weakened and increased the oxidative stress of fetal membranes from which the placenta develops (Menon & others, 2011). The stress hormone cortisol also can cross the placenta (Parrott & others, 2014). The mechanisms that govern the transfer of substances across the placental barrier are complex and not yet entirely understood (Kohan-Ghadr & others, 2016; Lecarpentier & others, 2016; Mandelbrot & others, 2015).
The Fetal Period The fetal period, which lasts about seven months, is the prenatal period that extends from two months after conception until birth in typical pregnancies. Growth and development continue their dramatic course during this time. Three months after conception, the fetus is about 3 inches long and weighs about 1 ounce. It has become active, moving its arms and legs, opening and closing its mouth, and moving its head. The face, forehead, eyelids, nose, and chin are distinguishable, as are the upper arms, lower arms, hands, and lower limbs. In most cases, the genitals can be identified as male or female. By the end of the fourth month of pregnancy, the fetus has grown to 6 inches in length and weighs 4 to 7 ounces. At this time, a growth spurt occurs in the body’s lower parts. For the first time, the mother can feel arm and leg movements. By the end of the fifth month, the fetus is about 12 inches long and weighs close to a pound. Structures of the skin have formed—including toenails and fingernails. The fetus is more active, showing a preference for a particular position in the womb. By the end of the sixth month, the fetus is about 14 inches long and has gained another 6 to 12 ounces.