Prenatal and Perceptual Development

Prenatal Development

• Definition and Duration: Prenatal development refers to the process that occurs between the time of conception and the moment of birth.

• Commencement: The process begins in the fallopian tube at the moment a sperm cell penetrates an egg cell.

• Stages of Development: Prenatal development is categorized into three distinct periods:

• Germinal Period: This occurs during the first $14$ days after conception.     

• Embryonic Period: This occurs from week $3$ through week $8$.

• Fetal Period: This occurs from week $9$ until the time of birth.

The Germinal Period: First 14 Days

• Zygote Activity: During the first $14$ days, the zygote undergoes cell division while travelling toward the uterus.

• Developmental Milestones

  • 3 Days: The zygote consists of approximately:$6-10$ cells.

  • 5-6 Days: The organism becomes a blastocyst, described as a cluster of rapidly dividing cells.

• Survival Risk: If an interruption occurs during this specific stage, it is highly likely that nothing will develop further, and the woman will not become pregnant.

The Embryonic Period: 3rd to 8th Week Most Vulnerable Stage

• Implantation: During this timeframe, the blastocyst implants itself into the uterine wall.

• Critical Vulnerability: This is the phase where most vital functions and features form. Consequently, this period is the most prone to damage.

• Cell Differentiation: Layers of cells begin to differentiate to eventually become specific parts of the body.

• Organogenesis and Milestones:     * 3 Weeks: The neural tube closes. The top portion is destined to become the brain, while the bottom portion becomes the spinal cord.     * 24 Days: The heart begins to beat.     * Limbs and Organs: Major organs and limbs begin to form, though they are not yet functional.     * Facial Architecture: This period involves the fusion of facial structures.

• Developmental Disruptions: If the neural tube does not close properly, severe conditions occur:     * If the bottom of the neural queue does not close, conditions such as spina bifida result.     * If the top of the neural tube fails to close, the baby will not develop a brain.

The Fetal Period: The Final Seven Months

• Growth and Refinement: This period is characterized by rapid growth and the refinement of brain systems and internal organs.

• System Integration: The fetus becomes increasingly responsive, and its behavior becomes more regular and integrated.

• Chronological Development:

  • 12 Weeks: Sex differentiation occurs.  

  • 6 Months: The fetus is capable of responding to light and can hear sounds.

• Limit of Viability: At weeks, the fetus reaches the limit of viability. A baby born at current weeks has a chance of survival.

Teratogens

• Definition: A teratogen is any disease, drug, or other environmental agent capable of causing harm to a developing embryo or fetus.

• eg. alcohol, thalidomide, zika virus

• Factors Influencing Impact:

  • Timing: The brain and organ systems are particularly susceptible during periods of rapid development.

  • Dose: The amount of exposure affects the outcome.

  • Duration: The length of time exposure lasts affects the outcome.

• Vulnerability Phase: The embryonic period is designated as the stage when the organism is most vulnerable to abnormalities caused by teratogen exposure.

• Example (Brazil):

• Microcephaly in Brazil is cited as a real-world example of teratogenic effects caused from zika virus

Specific Teratogens: Thalidomide and Alcohol

• Thalidomide:     * Context: A drug developed in the late $1950s$ and prescribed to pregnant women to treat morning sickness.     * Consequences: Babies were born with significant limb and facial abnormalities.     * Findings: The specific parts of the body or specific limbs affected were correlated directly to the specific day the woman ingested thalidomide. There was a direct relationship between frequency of use and the severity of abnormalities.     * Withdrawal: The drug was withdrawn from the market by $1961$.

• Alcohol - Fetal Alcohol Syndrome (FAS):     * Definition: A cluster of abnormalities appearing in the offspring of mothers who consume alcohol heavily during pregnancy.     * Associated Symptoms:

  • Malformations of the face, underdeveloped ears, smooth philtrum

  • congenital heart disease,

  • microcephaly, and behavioural or cognitive issues/learning delays, deformed brain

• * Observation: This is typically seen in women who abuse alcohol. Brain comparisons show marked differences between brains with and without FAS.

Perceptual Development: Visual Foundations

• Focus: Visual development and how it influences overall perceptual development.

• The Developmental Question: Is early visual experience necessary, or can deficiencies be corrected later?

• Critical Period: A specific timeframe in development when certain experiences are absolutely crucial for a particular feature of development to emerge. Developments missed during this period cannot be recovered later (e.g., imprinting in birds).

• Sensitive Period: A timeframe where experience is considered optimal for the development of a function, but it is not strictly critical for basic emergence.

Measuring Infant Visual Behavior

• 1. Visual Scanning: Analysts use eye trackers to determine what infants look at, providing insight into what they can see.

  • 1-month-olds are not able to discriminate faces as they have poor visual acuity

• 2. Habituation:

  •  * Measures: Researchers track heart rate, looking time (length of observation), and sucking rate.  

  •  * Interest Correlates from novelty preference: the longer they look at somethig, A faster sucking rate indicates higher interest, heart rate   

  • * The Habituation Process: When an infant is first shown a picture, interest measures are high. Repeated exposure leads to a drop in interest, known as habituation.

  • * Dishabituation: If the stimulus is changed and the infant detects the difference, interest levels will increase again. This allows researchers to determine if infants can visually discriminate between two images.

• 3. Visual Preferences: Using eye trackers to see what babies look at longer.     * Findings: Infants prefer faces over other objects, textures and patterns over plain objects, high contrast stimuli, and the color red over other colors.

• 4. Teller Acuity Test:     * Infants are presented with two side-by-side images (e.g., stripes vs. a blank grey side).     * Because infants prefer high contrast, they will look at the stripes.     * Calibrated trials make the stripes increasingly narrow until they are indistinguishable from the grey background. At the point where preference becomes null, researchers can determine the limits of the infant's eyesight.

Experience and Perception: Expertise and Face Processing

• Other-Species Effect (Pascalis et al., 2005):     * Infants at $6$ months can discriminate between different monkey faces.     * By $9$ months, they lose this ability unless they have been given specific experience (e.g., looking at a monkey face storybook).

• Other-Race Effect:     * Humans find it more difficult to distinguish faces from races other than their own. This effect emerges early in life.     * Caucasian Study: A cross-sectional design involving $3-, 6-,$ and $9$-month-old Caucasian infants showed early emergence when presented with Middle Eastern, Chinese, and Caucasian faces.     * Chinese Study: A cross-sectional design involving $3-, 6-,$ and $9$-month-old Chinese infants presented with African, Caucasian, and Chinese faces showed similar narrowing results.

Perceptual Narrowing and Synaptic Pruning

• Perceptual Narrowing: This process reflects typical everyday experience and indicates the development of expertise. The brain becomes more efficient at processing familiar things seen often.

• Mechanism: Synaptic pruning involves the brain strengthening synapses it uses regularly while pruning away those that are not typically used.

Effects of Atypical Experience: Animal Models and Clinical Studies

• Animal Model (Hubel and Weisel):     * Conducted monocular deprivation experiments on kittens by sewing one eye shut.     * Result: Even after the eye was unsewn, vision remained impaired because the visual system did not develop during the critical early stages.

• Congenital Cataracts:     * Clouding of the lens in young infants requires early removal to allow visual input.     * Failure to remove cataracts early results in permanent vision impairment.

• Case Study (Baby Holly):     * Clinical observation showed that after cataract removal, Holly was initially seeing as well as a newborn.     * Her vision improved rapidly; after only one hour of visual input, there were significant improvements.     * This demonstrates that the brain is ready for visual input, though the newborn visual system is immature and relies on experience to develop expertise in processing the world.