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Chapter 5

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PSYC 251
Elizabeth Kelley

Page 156-180, 25 pages Page 1 of7 Chapter 5: Perceptual & Motor Development BASIC SENSORY & PERCEPTUAL PROCESSES • Sensory and perceptual processes are the means by which people receive, select, modify, and organize stimulation from the world. Each sense organ translates physical stimulation into nerve impulses. • Perceptual processes are closely linked to motor skills with coordinated movements of the muscles and limbs. Perception often guides a child’s movement, and movement provides variety in perceptual stimulation. • Researchers determine that a baby can distinguish between two stimuli by seeing if their responses are consistently different to the two, with heart rate, facial expression, head movement, etc. • Habituation is paying more attention to novel stimuli than familiar stimuli. By presenting the same stimulus repeatedly and then a novel stimulus, researchers see if the infant responds with habituation or with new behaviour that demonstrates ability to distinguish the two. • Faster habituation predicts later intelligence scores Smell, Taste, and Touch • Infants have a keen sense of smell, responding with the appropriate facial expressions to pleasant and unpleasant smells. They can also recognize familiar odours, such as their own amniotic fluid, or their mother’s breast. • Infants differentiate readily between tastes, particularly reacting to sweet substances favourably. They are sensitive to changes in breast milk that reflect a mother’s diet. • Pain is subjective, with individuals differing in response to the same stimulus. The infant has developed pain receptors and nerves capable of transmitting pain. Their behaviour to pain-provoking stimuli, such as the pain cry (sudden, high-pitched, not easily soothed), increased heart rate, and facial expressions strongly suggest babies experience pain. • Contact and sweet tastes with giving sucrose during the painful procedure both sooth and reduce pain experience Hearing • A fetus can hear at 7-8 months; however, infants do not hear as well as adults. The auditory threshold is the quietest sound a person can hear, measured in infants by presenting a tone and looking at reactions such as turning the head or changing facial expressions or activity level. • Infants hear best in pitches the range of human speech. They can differentiate vowels from consonants, and recognize their own names by 4.5 months. • Infants can also distinguish musical sounds and different melodies and rhythms. They can differentiate from a sequence of notes that they have heard before, from a new one. • Infants use sound to locating objects in terms of direction and distance. Infants hearing the sound of a rattle in the dark at 15cm away will reach for it, but not at 60cm away. Using sound to estimate distance, they change their behaviour. • Heredity is the leading cause of hearing impairments in newborns; after birth, meningitis, the inflammation of membranes around the CNS, is. Startle responses to sudden, loud sounds, turning the head to follow sounds, and imitation of sounds and simple words by 12 months are items to check on if concerned about hearing problems. • Children may benefit from mechanical devices such as cochlear implants, lip-reading, and learning sign language. Seeing Page 156-180, 25 pages Page 2 of7 • Newborns scan their environment by 2-3 months, though not coordinated since eye muscles not fully developed for synchronous movement. Newborns only catch 2% of light striking fovea due to shape of eyes, vs. adult 65% • Visual acuity is the smallest pattern that can be distinguished dependably, as tested by reading rows of progressively smaller letters. Infants prefer patterned stimuli over plain stimuli, and with progressively narrow lines at a certain point they will blend together to appear grey like the plain stimuli. • To estimate an infant’s acuity, a grey square is paired with a square with different stripe widths. When infants look at the two equally, it indicates they can no longer distinguish the stripes and have reached the limit of their visual acuity. • Newborns and 1-month-olds see at 6m what adults see at 60-120m, but improve to achieve equal acuity at 8mo. Newborns good at seeing 8-10 inches, optimal distance from mother’s face during feeding • Contrast sensitivity measures responses to stimuli which vary both in size and contrast. It may be a better measure of the development of the visual system. Development in this area is more gradual, equalizing with adults at age 9. • Colour is detected with cones in the retina, which have varying sensitivities to short-wavelength light (blue, violet), medium-wavelength light (green, yellow), and long-wavelength light (red, orange). • Neural circuits for colour perception come online after birth, able to see full range of colours by 3 months. This includes perceiving colours as categories. Integrating Sensory Information • Most infant experiences are multimedia events, with much stimulation spanning multiple senses. Infants can visually recognized an object that they only touched previously, detecting relations between information presented visually and tactily. • Infants look longer at novel experiences of video not synchronized with own movements, speech not synchronized with facial movements, or speech facial movements not synchronized with gender expectation • It was originally thought that infants must first master perceptual processes in each sense separately before coordinating and integrating across senses. • Bahrick & Lickliter: Intensensory Redundancy Theory where infant’s perceptual system is particularly attuned to amodal information (duration, rate, intensity) present in multiple sensory modes. Perception is best when information is presented redundantly to multiple senses. • When infant sees and hears mother clapping, he focuses on information conveyed to both senses over information only available in one sense. • Tested with hypothesis that infants will notice changes in amodal information more often when it is presented in multiple than a single sense. They should detect change more readily from clapping slowly to quickly if they both see and hear it, than if they only see it or only hear it. o Only infants who had information in both senses detected the change COMPLEX PERCEPTUAL & ATTENTIONAL PROCESSES Perceiving Objects • By 4 months, infants use cues to determine which elements go together to form objects. One important cue is motion: elements that move together are usually part of the same object. One would be surprised if elements moving together are revealed to be separate objects behind a mask. • Infants demonstrate this surprise: if revealed to be two pencils, they will look much longer as if trying to figure out what happened. If one pencil, they look briefly having expected it. Page 156-180, 25 pages Page 3 of 7 • Infants group features together as one object if they have the same colour, texture, and aligned edges. Perceptual Constancies • Infants master size constancy by 4-5 months, realizing that an object’s actual size remains the same despite changes in the size of its retinal image as a function of distance • Infants recognize a bear as familiar when it is seen as smaller at a farther distance, and a larger replica of the bear that casts the same retinal image size as novel – they respond more to the novel bear. • Brightness, colour, and shape constancy also exist. They are also achieved in rudimentary form by 4 months. Depth • Infants also need to know where objects are; left/right and up/down are easily represented on the retinal surface, but distance is not. • Visual Cliff: A glass-covered platform, with pattern appearing directly under the glass on one side, but several feet below glass on the other. Thus one side looks shallow, and the other has a steep drop-off. • Infants are placed on the platform, and their mother coaxes the infant to crawl towards her across the deep side; virtually all refuse to cross the deep side – this demonstrates depth perception. • Babies as young as 1.5 months who cannot crawl experience decrease in heartrate when placed on the deep side, a sign of interest in a novel stimulus; this demonstrates their ability to discriminate between the shallow and deep sides. • At 7 months, the infant’s heartrate would accelerate, as a sign of fear. This is informed by experience with crawling. • Kinetic cues is using motion to estimate depth. Visual expansion is when an object moves closer, it fills a greater proportion of the retina. • Motion parallax is that nearby moving objects move across the visual field faster than those at a distance – trees next to the road move rapidly, while mountains in the distance move slowly. • Retinal disparity from fact that left and right eyes often see slightly different versions of the same thing. When objects are distant, images appear similar for both eyes; when objects are close, there is greater disparity. • Pictorial cues include use of linear perspective (lines converge to appoint in the distance, can use distance between lines as cue), texture gradient (from coarse to finer/less distinct in the distance), interposition (nearby objects obscure distant objects), and relative size. Perceiving Faces • 1 month olds look at the outer edges of the face with highest contrast (chin, top of hair), but 3 month olds focus on the eyes and lips, which are essential for facial expression. • Newborns tend to prefer face-like stimuli (arrangement of two eyes and a mouth) over non-face-like stimuli, and faces over face-like stimuli. However, preference for tracking a moving face changes at 4 weeks, when infants start tracking all moving stimuli. Face-tracking may thus be a reflex for newborns, adaptive to enhance social connection, but taken over by the cortex after 4 weeks. Page 156-180, 25 pages Page 4 of7 • Newborns also prefer attractive over unattractive faces, e
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