What can I learn about sensation, perception, and action throughout the life span? - Chapter 6

Sensation stands for the process by which sensory receptor neurons find information and transmit it to the brain. An infant can sense light or sound. Perception then is the process of interpreting sensory input, like recognizing what you see or understanding what is said. The sense organs are active things and sensing and perceiving are at the heart of human functioning. 

What are some perspectives on perception?

Constructivists like Jean Piaget claimed nurture was responsible for the development of perception, through learning and experiencing things. However, new findings show object understanding at a very young age, which is why some researchers now believe in a more nativist and nature-emphasizing approach. This states that innate capabilities and maturational programs are responsible for perceptual development. According to them perception is direct and does not require interpretation based on earlier experience. In between those two perspectives is Gibson's ecologial theory of perception, which proposes that information essential for perception is stored in the objects that are to be perceived. Features of the object reveal its affordances (what it has to offer, how it should be used).So differing from the constructivist view, past experience is not needed: everything important is stored in the current situation. And the affordances are influenced by the individual's capabilities and motivations, so nature and nurture are inseparable. 

What does perception mean to the infant?

Through smarter research methods, researchers have found that infants have greater perceptual abilities than was initially believed. Methods to study infant perception are: 

• habituation: the same stimulus is presented until the infant grows bored with it. Shows how long it takes for an infant to get bored and how distinct another stimulus should be to regather attention.
• preferential looking: two stimuli are shown at the same time to determine which one the infant prefers (by looking at it longer). 
• evoked potentials: while exposed to a certain stimuli, electrical activity in the brain is measured. 
• operant conditioning: a response is learned and the researcher can examine the conditions under which the infants will continue that behavior. Do they react the same to different stimuli or can they distinguish those? 

The sense of vision works by the eye taking in stimulation in the form of light, and converting this to elektrochemical signals to the brain. Before birth a fetus can already detect bright light, and after birth a newborn can track a slow-moving thing. However, the visual capabilities are not equal to a child's or adult's, this takes around 6 months to a year. The visual acuity (ability to perceive detail) of a newborn is not developed enough yet, so objects have to be very close or have light-dark contrasts for the newborn to see it well. There are also limitations in visual accomodation (lenses ability to change shape to bring objects at different distances into focus). Color vision is present at birth but does still need development until around 3 months. 

The organization of their perceptions might be challenging to the infant, e.g. by seeing when one object ends and another one begins. How do they see this? Infants use the cue of common motion to distinguish objects (do they move the same way?), so stationary objects are harder to distinguish from others. An important breakthrough in form perception starts around 3 months. At 1 month infants focus on the outer lines of forms, at 2 months they look more at the inner qualities. 

In sum, newborns are best at attenting to stimuli with a light-dark transition (contour), moving things, and moderately complex patterns (not too simple, not too complex). 

Faces are important as well, and babies seem to have an innate tendency to discriminate faces from non-faces, but environment adds to this as well. However they focus more on action than on faces, they can't focus on both simultaneously yet.

Infants seem to have some innate abilities to see depth (they will blink if something moves toward their faces). 4 months old, they seem to understand size constancy (recognizing that an object is the same size whether it's near or far from their eyes). By using the visual cliff experiment (using a visual, but not real cliff to fall off) it was shown infants of crawling age perceived depth and did not dare to crawl over the fake cliff.  Very young infants can sense a difference between a cliff and non-cliff, but they do not fear it yet. It may be because of learning - e.g. by having fallen before an infant is cautious of a cliff. Another interesting thing is that infants seem to have knowledge of the laws of gravity and other physics principles. This leads researchers to think that young infants have intuitive theories which are innate organized systems of knowledge and allow them to make sense of the world. 

The process of hearing begins with air molecules entering the ear and vibrating the eardrum. The vibrations are then transmitted to the cochlea in the inner ear, and converted to signals that the brain can interpret as sound.

Infants can hear well, even as fetuses they can hear the outside of the womb! Prenatal auditory experiences, like hearing music, can even shape the neural system of the brain. After birth, infants respond more to human speech than to nonspeech sound. Their mom's voice is most preferred. Even unborn fetuses can distinguish their mom's voice from a stranger's voice. Phonemes (basic speech sounds) can be distinguished very early. Native and nonnative sounds can be discriminated very early as well, showing they have been hearing in their prenatal environment. They can learn every language though - but as they mature they become sensitive to the sounds in their own language and less sensitive to other language sounds. 

The chemical senses are taste and smell, since both of these rely on the detection of chemical molecules. The sensory receptors for taste (taste buds) are mainly on the tongue. Babies can distinguish taste from birth and sweets are preferred, even pre-birth. However flavor preferences are also responsive to learning, especially more sophisticated perception of flavors. Our perception of flavor is dependent on how our brains assign meaning to the signals received from the senses. There is a sensitive period, during the first 4-6 months post-birth, when long exposure to certain tastes influences later acceptance of these flavors. So early experiences with flavors have their influence on us, however, there are also "taste genes". 

The sense of smell (olfaction) works good at birth too. Premature babies can already detect various odors. Exposure to a familiar odor (breast milk, amniotic fluid) can calm the baby, whereas unpleasant smells can get a response too. Smell can also cause recognition of each other. 

The somaesthetic senses are the body senses, like touch, temperature and pain, and also the kinesthetic sense (knowing where your body is in relation to other body parts and the environment). Touch operates before birth already, and the sensitivity to touch stimulation goes in the cephalocaudal (head-to-toe) direction, so the face and mouth are most sensitive first. Touch can calm babies. Babies are also sensitive to warmth and cold and painful stimuli. And previous experiences have their influence in this as well (babies can "learn" a painful moment is coming). 

Many of the perceptual capacities seem innate (most are present at birth) or develop rapidly in normal infants (by 2 years, perceptual development is globally complete), so what is the role of nurture? When it comes to vision, there are sensitive periods (periods during which an individual is more affected by experience and thus has a higher level of plasticity than in other periods). For vision there are multiple sensitive periods. Firstly, the period called visually driven normal development, when expected developmental changes in vision will occur only with exposure to normal visual input. Secondly, the period sensitive for damage: when abnormal visual input can lead to permanent deficits. And thirdly, a sensitive period for recovery: when there is a potential to recover from damage. 

Congenital cataracts is a condition where there's a clouding of the lens, leaving infants nearly blind from birth. This could be fixed with surgery but this should be done asap, because when visual input is lacked for a long period, normal vision may never occur. The first 3 months are viewed as critical. Sensory experience is essential in organizing the developing brain. However, years after surgery vision grows seemingly normal, except in some areas. This could be due to sleeper effects (delayed outcomes of early visual deficits). Even if a certain ability actually develops later in life (after surgery), missed visual input at infancy can still alter the brain so that these abilities do not develop as good. The same thing goes for hearing.

Infants are active explorers who seek their own stimulation and thus cause development. Perception goes with action. According to Gibson's ecological perspective, there are three phases of exploratory behavior:

1. From birth to 4 months, infants explore their immediate surroundings, e.g. their caregivers, mostly by looking and listening. They can can learn about objects by mouthing them and watching them move.
2. From 5 to 7 months, babies pay closer attention to objects, now exploring with their hands (grasping) as well. 
3. By 8 or 9 months, most have begun to crawl and infants can explore a larger environment and explore all objects they meet. 

What does perception mean to the child?

Sensory and perceptual development is largely complete by the end of infancy, but the sensory systems and perceival abilities keep refining and improving during childhood. 2 important things happen with the transition from infancy to childhood, namely (1) the coupling of perception and action leading to purposeful movement, and (2) the integration of multiple sources of sensory information. 

Locomotion is movement from one place to another and is vital for development. Young kids start walking which gives them many more possibilities. During infancy they gathered gross motor skills and slowly start mastering fine motor skills. They learn through taking one step forward and two steps back. The cephalocaudal (head-to-toe) and proximodistal (arms and legs before hands and toes) principles of development are at work again. 

The emerging of motor skills has to do with rhythmic stereotypies, which is body movement in repetitive ways, which occurs just before learning a new skill. The dynamic systems theory tried to explain motor development like this, and states that development takes place over time during a process in which children use the sensory feedback they get when they try different movements, to modify their motor behavior in adaptive ways. So motor decisions over a longer period influence new skills. A quote by Spencer says: "Infants must explore a wide range of behaviors to discover and select their own solutions in the context of their intrinsic dynamics and movement history." Characteristics of the child interact with environment characteristics to create an unique process, and toddlers can adjust their motor skills to change in their bodies or the environment. In the dynamics system approach, nature and nurture are inseparable. Important is that different motor skills bring about different challenges, children need feedback with every motor activity. And for motor development, thought and its integration with action is needed.  

An example: infants start with the ulnar grasp (clumsily pressing the palm and outer fingers together). Eventually and with the proximodistal principle they can use the pincer grasp (using the thumb and the forefinger), which is more useful. Improving more and more, they can control differentiated movements and later integrate those movements into coordinated actions. 

The integration of sensory information is also a very important development. In some way, the senses are integrated at birth already: babies looking in the direction of a heard sound, or feeling objects they can see. However, full multisensory integration develops later, when the brain develops. A type of multisensory integration is cross-modal perception, which is required in games that involve feeling objects hidden in a bag and telling what they are by touch alone. 

Attention develops in childhood and adolescence as well. While an infant's attention is "captured" by something, an older child "directs" its attention to something. This difference is the difference between having an orienting system (reacting to the environment, like babies) and a focusing system (choosing and maintaining attention to something). As children get older, their attention spans become longer, they become more selective in what they attend to and they can plan and carry out strategies for using their senses to achieve goals better. So for really young children distraction should be avoided to enhance performance.

What does perception mean to the adolescent?

Adolescents have longer attention spans and can shift their attention better, but they also face the challenge of being flooded with information from multiple sources nowadays and they"multitask" a lot. However this multitasking decreases performances on tasks. 

For adolescents, their hearing may be impaired due to loud noise exposure (concerts, headphones etc) without ear protection. This may result in tinnitus (ringing sounds in one or both ears lasting days, weeks or indefinitely).

During adolescence the preference for sweets decreases slightly and sour tastes are liked more. As an adolescent you might now like food you didn't like before, as the taste buds mature. Research has found out too that taste is mediated by more than smell and taste buds alone. It is also mediated by chemosensory irritation (reaction of the skin in mouth and nose to chemical compounds in foods), like the burn of hot pepper. It's personal if you enjoy this or not. Taste is also influenced by cognition: you will taste what you expect to taste. 

In adolescence and adulthood women have greater sensitivity to smelling certain odors than men, which may reflect hormonal differences. Smell is important for men and women to pick someone as a romantic mate. 

Culture affects perceptions, like some cultures finding slim women more attractive and others finding bigger women more attractive. Furthermore, culture seems to influence how well you can detect and describe an odor. And as you grow older and certain things (like music from you country) become more familiar, this affects your perceptions as well (you may perceive music from other countries in a different manner). So the sensory system is overall similar across cultures, but perception can differ.

What does perception mean to the adult?

Sensory and perceptual capacities gradually decline with age. This begins usually in early adulthood, becomes noticeable in the 40s, and is even more noticeable with elderly age. However the changes are gradual and minor, so we can usually adjust: just turning up the volume of the TV for instance. The losses experienced take two forms. First, sensation is affected. This is indicated by raised sensory thresholds (so, the points at which levels of stimulation can be detected get higher). Second, perceptual abilities decline in some aging adult, for instance having a harder time understanding speech in a noisy room or more difficulty recognizing what they are tasting. 

To understand why many adults face vision problems as they age, we need to understand the workings of the visual system: light enters the eye through the cornea, passing through the pupil and lens before being projected (upside down) on the retina. Frorm there, images are sent through the brain by the optic nerve at the back of each eye. The pupil changes size depending on the lighting, and the lens accomodates to keep images focused on the retina. Visual acuity (sharpness of vision) decreases with older age and there are many other age-related changes that occur in different parts of the visual system:

• The pupil becomes less responsive to changes in lighting and to dim light, resulting in problems with e.g. night driving. 
• In the lens, cataracts (cloudiness of the lens) can come up resulting in blurred vision, or presbyopia (thickening/hardening of the lens), resulting in decreased ability to see close objects.
• In the retina, age-related macular degeneration (AMD) can occur, meaning photoreceptors in the middle of the retina (the macula) deteriorate. Also, retinitis pigmentosa (RP) can occur: deterioration of light-sensitive cells outside of the macula. The first can result in loss of central vision and RP in loss of peripheral (side) vision.
• In the eyeball, glaucoma can occur (increased fluid pressure in the eyeball), resulting in the loss of peripheral vision and eventually of all vision.

Sustained, divided and selective attention all generally decline when people face old age.  They seem to have difficulty inhibiting responses to irrelevant stimuli, and reaction time increases. Greatest difficulty comes when a situation is novel or complex. 

Hearing problems are approx. three times as common as visual problems in elderly. Hearing problems can have different causes, like excess wax buildup, infenctions, or a problematic nervous system. Most problems seem to come from the inner ear. The cochlear hair cells, serving as auditory receptors, their surrounding structures and the neurons leading from them to the brain gradually degenerate in the adult years. This can cause presbycusis, which most common symptom is loss of sensitivity to high-frequency or high-pitched sounds. After age 50 lower-frequency sounds also become more difficult. So the auditory threshold rises. While visual problems are more noticeable among women, hearing problems are more noticeable among men. Experience can also have an influence, like having worked in a loud environment. Cochlear implants can work well for elderly, however it can take a while to adjust to them.

Older adults generally also have more difficulty with the perception of speech, thus understanding conversation. Of course hearing problems contribute, but there's also a role for cognitive decline and attention problems. Again, greatest difficulty arises with a novel or complex situation. 

There is also a general decline in taste sensitivity, men more than women, but it's very variable among people. Older adults can produce less saliva, and this saliva facilitates the distribution of chemical molecules with information about taste. Sweet taste sensitivity seems to stay the same. The ability to smell also declines over age. However, again it's very different from person to person due to environmental factors, and it also depends on the type of odor: sensitivity to unpleasant odors seems to stay the same. 

The threshold for experiencing touch increases slightly as well, but it's not sure if this really affects daily life. Elderly may also be less sensitive to temperature. An even temperature is harder to maintain, so there's an increased risk of death in heat waves or cold spells for elderly. 

People limited by sensory impairments usually face physical or intellectual impairments as well, probably because of the general declines in neural functioning that affecet both perception and cognition. In sum, most elderly experience declines in abilities with age, but these changes do not necessarily have to weaken their quality of life.