Chapter 3: Tools for Exploring the World

Test Yourself 3.3

• Left-handedness is influenced by both heredity and environment. Research indicates that cultures discouraging left-handedness have fewer left-handed children. (\text{MarCori & Okazaki 2020})

• Motor development involves distinct skills organized and reorganized over time, depending on task demands.

• Skills important for learning to walk include maintaining upright posture and balance, stepping, and coordination.

• At 1 year, most infants use their left hand to steady a toy and their right hand to manipulate it.

Key Questions

• How well do infants hear?

• Are infants able to smell, taste, and experience pain?

• How well can infants see? Can they see color and depth?

• How do infants coordinate information between different sensory modalities, such as between vision and hearing?

Coming to Know the World: Perception

• Humans have several kinds of sense organs, each receptive to a different kind of physical energy.

  • The eye is sensitive to electromagnetic energy, resulting in sight.

  • The eardrum detects changes in air pressure, resulting in hearing.

  • Cells in the nasal passage detect airborne molecules, resulting in smell.

• Perception: The process by which the brain receives, selects, modifies, and organizes nerve impulses that are the result of physical stimulation.

• Newborns have a keen sense of smell, responding positively to pleasant smells and negatively to unpleasant smells. (\text{Mennella & Beauchamp, 1997})

  • They recognize familiar odors, such as their own amniotic fluid and their mother's odor. $(\text{Schaal et al., 2020})$

• Newborns have a highly developed sense of taste, differentiating salty, sour, bitter, and sweet tastes. $(\text{Schwartz et al., 2009})$

  • Most infants prefer sweet and salty substances, reacting with smiles, sucking, and licking. (\text{Beauchamp & Mennella, 2011})

  • They grimace when fed bitter or sour substances. $(\text{Kaijura et al., 1992})$

• Newborns are sensitive to touch, with reflexive movements occurring when touched.

• Babies' behavior in response to pain-provoking stimuli suggests that they experience pain.

  • Pain Cry Characteristics: The pain cry begins suddenly, is high-pitched, and is not easily soothed.

  • Physiological Responses: Heart rate jumps; attempts to move hands, arms, and legs indicate pain.
    $(\text{Warnock et al., 2014})$

• Smell and touch help newborns recognize their mothers.

• Smell and taste make it easier for them to learn to eat.

• Early development of smell, taste, and touch prepares newborns and young babies to learn about the world.

Hearing

• Fetuses can hear at 7 or 8 months after conception.

• Newborns respond to sounds in their surroundings by startling, blinking, and moving their arms or legs.

• Adults hear better than infants, but infants eliminate much of the gap by 6 months, particularly for higher-pitched sounds.

• Infants can pick out a sound from background noise, though not as skillfully as adults. $(\text{Litovsky, 2015})$

• Infants best hear sounds that have pitches in the range of human speech.

• Infants can distinguish speech sounds and recognize their own names by 4 or 5 months. $(\text{Jusczyk, 1995; Mandel et al., 1995})$

• Infants can distinguish different musical sounds and melodies and are sensitive to the rhythmic structure of music. $(\text{Hannon et al., 2011})$

Seeing

• The visual system (eye, nerve, brain) is relatively well developed at birth.

• Newborns respond to light and can track moving objects with their eyes.

• Visual acuity is defined as the smallest pattern that one can distinguish reliably.

• Newborns and 1-month-olds see at 20/200 to 20/400; 1-year-olds have the acuity of an adult with normal vision. (\text{Kellman & Arterberry, 2006})

• This improvement reflects changes in the receptors, which move to the center of the eye and become longer, allowing them to gather more light. $(\text{Johnson, 2013})$

Color

• The wavelength of light is the basis of color perception.

• Cones: Specialized neurons in the back of the eye along the retina that sense color.

  • Some cones are sensitive to short-wavelength light (blues and violets).

  • Others are sensitive to medium-wavelength light (greens and yellows).

  • Still, others are sensitive to long-wavelength light (reds and oranges).

  • By 3 months, the three kinds of cones and their associated circuits are working, and infants can see the full range of colors. (\text{Kellman & Arterberry, 2006})

  • By 4 to 6 months, infants' color perception seems similar to that of adults: like adults, infants see categories of color. $(\text{Yang et al., 2016})$

Depth

• Depth perception tells us whether objects are near or far.

• Visual Cliff: A glass-covered platform used to study infants' depth perception.

  • Babies willingly crawled to their mothers when they stood on the shallow side but refused to cross the deep side.

  • Infants can perceive depth by the time they are old enough to crawl.

  • Babies as young as 6 weeks have a slower heart rate on the deep side of the visual cliff, indicating they notice a difference.

  • At 7 months, infants' heart rates accelerate on the deep side, a sign of fear. $(\text{Campos et al., 1978})$

Kinetic Cues

• Motion is used to estimate depth.

  • Visual Expansion: As an object moves closer, it fills an ever-greater proportion of the retina.

  • Motion Parallax: Nearby moving objects move across our visual field faster than those at a distance.

  • Babies use these cues in the first weeks after birth. (\text{Nánez & Yonas, 1994})

Binocular Disparity

• Based on the fact that the left and right eyes often see slightly different versions of the same scene.

• Greater disparity in retinal images signifies that an object is close.

• Infants use binocular disparity as a depth cue by about 4 months. (\text{Kavaek & Braun, 2016})

Pictorial Cues

• Depend on the arrangement of objects in the environment.

  • Linear Perspective: Parallel lines come together at a single point in the distance.

  • Texture Gradient: The texture of objects changes from distinct for nearby objects to finer and less distinct for distant objects.

Perceiving Objects

• Perception creates an object from sensory stimulation.

• Perception of objects is limited in newborns but develops rapidly in the first few months after birth. $(\text{Johnson, 2001})$

• By 4 months, infants use cues to determine which elements form objects.

  • Motion: Elements that move together are usually part of the same object. (\text{Kellman & Arterberry, 2006})

• Infants use common motion to identify objects. (\text{Valenza & Bulf, 2011})

• Infants group features together (i.e., believe they're part of the same object) when they are the same color, have the same texture, and their edges are aligned. $(\text{Bremner et al., 2013; Johnson, 2001})$

Perceiving Faces

• Young babies prefer faces with normal features over scrambled features. $(\text{Dalrymple et al., 2020})$

• They prefer upright faces over inverted faces. $(\text{Mondloch et al., 1999})$

• They prefer attractive faces over unattractive faces. $(\text{Damon et al., 2017})$

• Newborns' face perception may be reflexive, based on primitive circuits in the brain.

• At about 2 or 3 months of age, different circuits in the brain's cortex begin to control infants' looking at faces, allowing infants to learn about faces and distinguish between them. (\text{Morton & Johnson, 1991})

• Over the first year, infants fine-tune their prototype of a face so that it reflects faces that are familiar in their environments. $(\text{Pascalis et al., 2002})$

• Between 6 and 9 months of age, infants typically lose the ability to recognize faces from other races. $(\text{Pasclais et al., 2020})$

Integrating Sensory Information

• Infant experiences are often "multimedia events."

• Temporal information, such as duration or tempo, can be seen or heard.

• The texture of a surface can be detected by sight or feel.

• Infants can recognize visually an object they have only touched before. (\text{Bremner & Spence, 2017})

• Babies look longer when an object's motion matches its sound. $(\text{Walker et al., 2010})$

• They can link the temporal properties of visual and auditory stimulation. $(\text{Lewkowicz, 2000})$

• They move their body in time with the beat of music. $(\text{Hannon et al., 2018})$

• Cross-modal perception may be easier for infants because regions in the brain devoted to sensory processing are not yet specialized in infancy. (\text{Spector & Maurer, 2009})

• Infants' sensory systems are particularly attuned to intersensory redundancy, that is, to information that is presented simultaneously to different sensory modes. (\text{Bahrick & Lickliter, 2012})

Test Yourself 3.4

• Infants respond negatively to substances that taste sour.

• Infants respond with a high-pitched cry that is hard to soothe.

• Infants' hearing is best for sounds that have the pitch of speech.

• At age 4, infants' acuity is like that of an adult with normal vision.

• Cones are specialized neurons in the retina that are sensitive to color.

• Binocular disparity refers to the fact that images of an object in the left and right eyes differ for nearby objects.

• When elements consistently move together, infants decide that they are part of the same object.

• Infants readily integrate information from different senses, and their sensory systems seem to be particularly attuned to intersensory redundancy.

Becoming Self-Aware

• Not until 15 to 18 months of age do babies recognize themselves in the mirror, which is an important step in becoming self-aware.

• Between 18 and 24 months, toddlers look more at photographs of themselves, refer to themselves by name or with personal pronouns (I, me), and sometimes know their age and gender.

• Self-awareness is well established in most children by age 2, and it develops faster in cultures that encourage toddlers to be independent. $(\text{Lewis, 2011; Ross et al., 2017})$

• Children recognize continuity in the self over time. $(\text{Nelson, 2001})$

• Self-concepts emphasize physical characteristics, preferences, and competencies. $(\text{Harter, 2006})$

Theory of Mind

• Infants understand that people's behavior is often intentional—designed to achieve a goal.

• Between 2 and 5 years of age, children develop a theory of mind, a naive understanding of the relations between mind and behavior.

• Henry Wellman (2014) believes that children's theory of mind moves through several phases during the preschool years:

  • Preschoolers understand that people can have different desires.

  • Children know that people can have different beliefs.

  • Children understand that different experiences can lead to different states of knowledge.

  • Children understand that behavior is based on a person's beliefs about events and situations, even when those beliefs are wrong.

  • Children understand that people may feel one emotion but show another.

• In collectivist cultures, preschoolers typically understand differences in knowledge (phase 3) before differences in beliefs. $(\text{Wellman, 2018})$

Children with Autism

• Individuals with autism spectrum disorder (ASD) acquire language later than usual and sometimes become intensely interested in objects.

• They often seem uninterested in other people, and when they do interact, those exchanges are often awkward.

• Symptoms usually emerge early in life, typically by 2 years of age.

• About 2% of American children are diagnosed with ASD; about 75% of them are boys. $(\text{Hodges et al., 2020})$

• Children with ASD grasp false belief very slowly. (\text{Peterson & Wellman, 2019})

• ASD reflects problems in inhibiting irrelevant actions and shifting smoothly between actions. $(\text{Pellicano, 2013})$

• Another idea emphasizes a focused processing style common in ASD. $(\text{Chen et al., 2012})$

Test Yourself 3.5

• Apparently, children are first self-aware at age 2 because this is when they first recognize themselves in a mirror and in photographs and when they first use personal pronouns such as "I" and "me."

• During the preschool years, children's self-concepts emphasize physical characteristics, preferences, and competencies.

• Unlike 4-year-olds, most 3-year-olds don't understand that other people's behavior is sometimes based on false beliefs.