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[1] Research suggests that humans aren’t the only members of several species in the animal kingdom which exhibit handedness, meaning the preference for one hand over the other. Handedness is related to lateral asymmetry, which refers to physical and functional aspects between sides of the brain. It appears that nine out of ten humans throughout history have preferred to use their right hand, and that eight of ten were right foot dominant. A genetic link, or some kind of inherited trait, has been attributed to hand preference, though there is no guarantee that a right or left handed person’s child will have the same hand preference. On the other hand, left-handedness does tend to run in families. In fact, around 6 percent of children whose parents are both right hand dominant will end up left-handed. Meanwhile, among children with two left-handed parents, up to 40 percent grow up left-handed, too. The occurrence of left-handed children with one left-handed and one right-handed parent typically ranges from about 15 to 20 percent. Amazingly enough,one in six pairs of identical twins will differ in their handed preference in spite of having the same genes.

[2] If hand preference goes beyond genetics alone, there must be other unknown variables at play. To learn more, researchers have closely studied the brain in regards to this subject. French anthropologist, Dr. Paul Broca, found that patients who had lost the ability to speak due to a stroke would also become paralyzed on the right side of their body. From this, Broca realized that because the left hemisphere of the brain controls the right half of the body and vice versa, the brain damage must have been in the brain’s left hemisphere. Psychologists have theorized that 95 percent of right-handed people’s language centers are in the left hemisphere of their brains, while 5 percent have language centers on the right side. Surprisingly enough, left-handed people do not show the exact reverse of this, and instead, a majority have their language center located in the left hemisphere, with some 30 percent in the right hemisphere.

[3] At the Australian National University in Canberra, Dr. Brinkman has suggested that human speech evolved alongside a preference for the right hand. From her research, Brinkman believes that one side of the brain became specialized for fine motor skills, which are necessary for speech and as the brain continued to evolve for speech, the right-hand preference emerged. According to Brinkman, the majority of left-handed people exhibit left hemisphere dominance with some capacity in the right hemisphere as well. Dr. Brinkman has observed that a left-handed person with brain-damage to the left hemisphere is often able to recover speech ability more effectively. She thinks this phenomenon can be explained by left-handed people’s tendency towards bilateral speech function.

[4] Dr. Brinkman research has expanded her research into primates as well. In her studies of macaque monkeys, she found that the year-old babies appeared to learn either hand preference from their mothers. In humans, on the other hand, specialization of the two hemispheres’ functions actually creates physical differences in the anatomy of the brain, with areas associated with speech production often being larger on the left side than on the right. Because monkeys and apes do not have the ability of speech, one would not expect to see such a variation in these animals. However, Brinkman believes that she has discovered a trend in monkeys’ brains which suggests the same asymmetry seen in human brains.

[5] Recent research on human embryos led to the discovery that a left-right asymmetry is evident before birth. However, there are many other variables which can affect brain development along the way. Initially, all brains begin as female, becoming male brains if the male fetus secretes hormones. The sides of the brain mature at different rates; the right hemisphere develops first, then the left. Moreover, a female brain develops slightly more quickly than a male brain. During a fetal brain’s development, a male brain is more likely to be affected, and the left hemisphere is also more likely to be affected. The brain may lose some lateralization, resulting in left-handedness as well as a tendency towards skills which are typically associated with the left brain hemisphere, such as logic, rationality, and abstraction. It is possible that this explanation captures why professionals such as mathematicians and architects tend to be left-handed more often, as well as a higher occurrence of left-handed males than females.

[6] Throughout our history, our language subliminally reinforces the notion that the right side is good, while the left is potentially dangerous. In fact, the Latin word “sinister” actually means “left.” It is no coincidence that left-handed children, forced to use their right hand, often develop a stammer as they are robbed of their freedom of speech.” However, as more research is undertaken on the causes of left-handedness, attitudes towards left-handed people are gradually changing for the better.

[1] In studies of the perceptual abilities of human adults, researchers are able to ask the subjects about what they have perceived. For example, subjects can fill out questionnaires, respond to questions verbally, and provide descriptions of their perceptions. Subjects may also simply press a button to indicate that they have perceived a stimulus. These types of feedback mechanisms work for adults, who have language and motor skills, but in the past researchers have had much more difficulty studying perception in infants. Babies simply aren’t able to give us direct feedback.

[2] Instead, researchers learned to use indirect methods of determining infant responses based on naturalistic observation. In these ways, they could understand firstly whether infants perceived a stimulus, and secondly to what degree they were interested in it. To do this, they would often compare an infant’s state before and after a stimulus was introduced. For example, a researcher might show an infant a repetitive pattern of visual objects. If the baby’s eyes followed the movement of the objects, then the researcher could surmise that the baby perceived it, at some level. Researchers also looked at other responses, such as head-turning and crying.

[3] However, these techniques based on a researcher’s observation of response to stimulus are not always reliable. For one thing, the observation itself involves some subjective judgment; that is, two observers may not agree on the type of response that they have just witnessed. Another limitation is that observations of responses such as these may be difficult to quantify. And finally, there is no guarantee that the infant is actually responding to the aspect of the stimulus that the researcher is attempting to study. A subject’s response might arise from other aspects of the stimulus, or for internal reasons (pain, hunger, etc.). For these reasons, observations of infant responses may not be the most trustworthy measures of perception.

[4] Fortunately, we now have ways of overcoming many of these limitations. We have the ability to record infants’ responses so that we may repeat our observation and discuss with other observers. Recordings also allow researchers to make measurements of the duration and frequency of responses. We can also use technology to monitor heart rate and respiration. Increased heartrate and respiration can be indications of infant perception. And, since the late 1960s, researchers commonly use sucking devices to measure the intensity of sucking action as infants respond to stimuli. We even have technology that connects a sucking device to a computer that counts the number of sucks in response to different stimuli.

[5] Studies of infant perception now rely on other methods, such as “habituation-dishabituation.” With this method, researchers present a stimulus repeatedly or continuously to an infant. Eventually, the infant will become habituated to, or bored with, the stimulus. At this point, the infant will tend to look at a new, novel stimulus. If the infant does not, in fact, show attention to the new stimulus, then it may be that the infant perceives no difference between the two stimuli. By determining whether an infant can distinguish between two stimuli, researchers can determine which stage of perceptual development the infant has reached.

[6] One other method relies on electrodes located around a subject’s head. Referred to as electroencephalography, or EEG, this technique allows researchers to study how brain activity in the infant changes in response to different stimuli. The responses themselves are called “event-related potential,” or ERP. With EEG, researchers are able to make very specific measurements of response activity. It is an excellent way to study brain activity more generally, and is a non-invasive way of evaluating brain activity in people with cognitive disorders.