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Why can't we move our toes and some fingers separately?

Why can't we move our toes and some fingers separately?


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In our feet, other than the large toe, the other toes cannot be moved separately. If we try to move them, then all the four toes move together. We cannot move each toe by itself.

Same thing occurs in the hands of some of us, where we cannot move the little finger by itself. While folding the little finger, the ring finger before that also has to be folded to some extent, and vice-versa.

An explanation to the problem with the ring finger and the little finger can be found here.

The phalanges make the toes. Are the phalanges of the small toes connected, such that we cannot move them separately?


A relatively new area of the brain's cerebral cortex evolved to enable humans and other primates the necessary small motor skills to pick up small objects and deftly use tools, scientists now say. https://www.youtube.com/watch?v=zyl6eoU-3Rg

Primates can move their ears too, here's a theory of it. Other motor skills that are not often developed are individual eyebrow movement, pectoral flexing, ability to sneeze with your eyes open.

Hand movement is new and developing compared to chimps.

Toe movement is latent and receding.

The human hand is built up onto a squirrel/clawed paw, If you take a while to rotate your forearm and the flexors of the fingers, you will see that it's a mutated simple flexing mitt thing with with a new fine motor dexterity that you use all day, added on top of the vestigial clawing and grasping hand.

https://www.youtube.com/watch?v=vlwAoKpSI7s

This page says: Signals generated in the primary motor cortex travel down the corticospinal tract through the spinal white matter to synapse on interneurons and motor neurons in the spinal cords ventral horn. Ventral horn neurons in turn send their axons out through the ventral roots to innervate individual muscle fibers.

The motor cortex is subject to plasticity and remapping. To know this question is beyond my field of knowledge, someone else can go on from here :) you'd have to learn about the motor cortex, plasticity, vestigial nerves, nerve mappings, it's a fantastically complex topic.

What's interesting is the variety and quantity of different muscular abilities that are inherited by a population, it reflects an optimized level of evolutionary plasticity and specific types of variety of useful traits like muscle and joint proportions to ensure fast and flexible species development.


Why can't the human body multi-task?

Why can't the human body multi-task? If you turn your right foot and move it slowly in a clockwise circle. So you're going round in a circle with your foot. Then writing a number 6 with the same hand that you're moving your foot on a piece of paper. But the better way to show this actually is to take your hand on the same side of your body as you're moving your foot. Now, try and make that move in a circle in the opposite direction to your foot.The foot follows the hand. Why does that happen?


Finger Extension

Terms like straighten out, point, stretch out, and spread out are used to describe extension of the fingers.

Extensor tendons attach on the top, or back side of the fingers. As the extensor muscles fire, their tendons pull on the finger bones to straighten them out.

The muscles that make the fingers extend are on the back side of your forearm. A perfectly straight finger might be called a finger “in full extension”, but some finger joints extend past zero degrees – this is called hyperextension. Some degree of hyperextension can be normal, but it’s also a term that describes an injury, when the finger is “bent back” and dislocates or fractures.


Why Do You Exist?

For over 300,000 years we've looked to the sky and gods for answers. We invented fire, landed on the moon, and even flung a piece of metal outside the solar system. But despite the development of super-proton-antiproton-synchrotrons, and now, superconducting-supercolliders that contain enough niobium-titanium wire to circle the earth sixteen times, we have no more of an understanding of why we exist than the first thinkers of civilized consciousness. Where did it all come from? Why are we here?

We're like Dorothy in "The Wizard of Oz," who went on a long journey in search of the Wizard to get back home, only to find the answer was inside her all along. The farther we peer into space, the more we realize that the secret of life and existence can't be found by inspecting spiral galaxies or watching distant supernovas. It lies deeper. It involves our very selves.

We've looked at the world for so long that we no longer challenge its reality. Here is the Universe: our sense organs perceive atoms and galaxies to some 14 billion light-years, although we can't see with the eye of reason, that the world is for us merely a bundle of sensations unified by laws which exist in our understanding. We can't see the laws that uphold the world and that if they be removed, the trees and the mountains, indeed the whole Universe, would collapse to nothing.

"We are too content with our sense organs," Loren Eiseley once said. "It's no longer enough to see as a man sees — even to the ends of the universe." Our radiotelescopes and supercolliders merely extend the perceptions of our mind. We see the finished work only. In this world, only an act of observation can confer shape and form to reality — to a dandelion in a meadow, or a seed pod, or the sun or wind or rain. Anyway, it's impressive, and your cat or dog can do it, too. And perhaps even the spider, there on her web, moored outside my window.

We're more than we've been taught in biology class. We're not just a collection of atoms — proteins and molecules — spinning like planets around the sun. It's true that the laws of chemistry can tackle the rudimentary biology of living systems, and as a medical doctor I can recite in detail the chemical foundations and cellular organization of animal cells: oxidation, biophysical metabolism, all the carbohydrates, lipids and amino acid patterns. But there's more to us than the sum of our biochemical functions. A full understanding of life can't be found only by looking at cells and molecules. Conversely, physical existence can't be divorced from the animal life and structures that coordinate sense perception and experience (even if these, too, have a physical correlate in our consciousness).

It seems likely that we're the center of our own sphere of physical reality, connected to the rest of life not only by being alive at the same moment in the Earth's 4.5 billion year history, but by something suggestive — a pattern that's a template for existence itself.

Science has failed to recognize those properties of life that make it fundamental to our existence. This view of the world in which life and consciousness are bottom-line in understanding the larger universe — biocentrism — revolves around the way our consciousness relates to a physical process. It's a vast mystery that I've pursued my entire life with a lot of help along the way, standing on the shoulders of some of the most lauded minds of the modern age. I've also come to conclusions that would shock my predecessors, placing biology above the other sciences in an attempt to find the theory of everything that has evaded other disciplines.

We're taught since childhood that the universe can be fundamentally divided into two entities — ourselves, and that which is outside of us. This seems logical. "Self" is commonly defined by what we can control. We can move our fingers but I can't wiggle your toes. The dichotomy is based largely on manipulation, even if basic biology tells us we've no more control over most of the trillions of cells in our body than over a rock or a tree.

Consider everything that you see around you right now — this page, for example, or your hands and fingers. Language and custom say that it all lies outside us in the external world. Yet we can't see anything through the vault of bone that surrounds our brain. Everything you see and experience — your body, the trees and sky — are part of an active process occurring in your mind. You are this process, not just that tiny part you control with motor neurons.

According to biocentrism, you're not an object — you're your consciousness. You're a unified being, not just your wriggling arm or foot, but part of a larger equation that includes all the colors, sensations and objects you perceive. If you divorce one side of the equation from the other you cease to exist. Indeed, experiments confirm that particles only exist with real properties if they're observed. As the great physicist John Wheeler (who coined the word "black hole") said, "No phenomenon is a real phenomenon until it is an observed phenomenon." That's why in real experiments, the properties of matter - and space and time themselves — depend on the observer. Your consciousness isn't just part of the equation — the equation is you.

Even Steven Weinberg, who won the Nobel Prize in Physics in 1979, concedes in his book "Dreams of a Final Theory" that there's a problem with consciousness, and despite the power of physical theory, the existence of consciousness doesn't seem derivable from physical laws.

"It will remain remarkable," said Nobel physicist Eugene Wigner, who helped lay the foundations for the theory of symmetries in quantum mechanics "in whatever way our future concepts may develop, that the very study of the external world led to the conclusion that the content of the consciousness is an ultimate reality."

The answer to life and the universe can't be found by looking through a telescope or examining the finches of the Galapagos. It lies much deeper. Our consciousness is why they exist. It unifies the thinking and extended worlds into a coherent experience and animates the music that creates our emotions and purposes — the good and the bad, wars and love. It doesn't load the dice for you to play the game of life. True, there's pain and strife everywhere. But as Will Durant pointed out, we need to see "behind the strife, the friendly aid of neighbors, the rollicking joy of children and young men, the dances of vivacious girls, the willing sacrifices of parents and lovers, the patient bounty of the soil, and the renaissance of spring."

In whatever form it takes, life sings because it has a song. The meaning is in the lyrics.


How Did You Get Five Fingers?

Your arms and toes began as tiny buds that sprouted from your sides when you were just a four-week-old embryo. By six weeks, these limb buds had grown longer and five rods of cartilage had appeared in their flattened tips. By week seven, the cells between the rods had died away, sculpting five small fingers or toes from once-solid masses of flesh.

Now, a team of scientists led by James Sharpe from the Centre for Genomic Regulation in Barcelona has discovered that these events are orchestrated by three molecules. They mark out zones in the embryonic hand where fingers will grow, and the spaces in between that are destined to die. Without this trinity, pianos and keyboards wouldn’t exist, jazz hands would be jazz palms, and giving someone the finger would be impossible.

These three molecules work in a way first envisioned by legendary English mathematician and code-breaker Alan Turing. Back in 1952, Turing proposed a simple mathematical model in which two molecules could create patterns by spreading through tissues and interacting with each other. For example, the first molecule might activate the second, while the second blocks the first. Neither receives any guidance about where to go through their dance, they spontaneously organise themselves into spots or stripes.

Since then, many scientists have found that these Turing mechanisms actually exist. They’re responsible for a cheetah’s spots and an zebrafish’s stripes. For 30 years, people have also suggested that they could sculpt our hands and feet, but no one had found the exact molecules involved.

Sharpe knew that these molecules would need to show a striped pattern—they’d either be active in the bits that become the fingers or the areas in between. Sox9 seemed like the most promising candidate. It is activated in a striped pattern from a very early stage of development. It controls the activity of other genes and if you get rid of it, its underlings lose their neat periodic patterns.

By comparing cells where Sox9 is active or inactive, Jelena Raspopovic and Luciano Marcon found two other groups of genes—Bmp and Wnt—also formed striped patterns. Bmp rises and falls in step with Sox9 and both are active in the digits. Wnt is out of phase it’s active in the gaps. The three molecules also affect each other: Bmp activates Sox9 while Wnt blocks it and Sox9 blocks both of its partners.

It looked like these were the molecules the team was searching for—not a pair, as Turing suggested, but a trinity. To confirm this, they created a simulation of a growing limb bud and showed that Sox9, Bmp and Wnt can organise themselves into a pattern of five stripes, by activating and blocking each other.

The team also used their simulation to predict what would happen if they removed each of the partners from the dance. If they took out Bmp, Sox9 activity also died away and the fingers didn’t form at all instead, the virtual limb bud continued growing as a shapeless lump. If they took out Wnt, Sox9 became active everywhere and the spaces between the fingers disappeared. If they blocked Bmp and Wnt together, these effects partly cancelled each other out but the number of fingers decreased.

The team then checked these predictions by applying drugs that block Wnt and Bmp to isolated limb buds growing in Petri dishes. In every case, the reality matched the predictions.

There’s still a lot to discover, though. For example, I’ve used Bmp and Wnt as shorthands here—in reality, each represents a class of several molecules, and the team still needs to work out which specific member is part of the Turing trinity.

They also want to identify molecules that affect the trinity. One of these might be FGF, a protein that’s more concentrated at the fingertips than at the base of the hand. Sharpe thinks that it changes the relationships between the Turing trinity to widen the Wnt canyons between the Sox9/Bmp peaks. It effectively increases the wavelength of the fingers as you move to the tip of the hand. It might explain why your fingers are slightly splayed, rather than strictly parallel.

There’s also the most obvious question: why do we have five fingers and toes?

On one level, the answer depends on simple physical traits like how quickly the Turing molecules spread through the hand, how strongly the interact with each other, and how fast the limb bud grows. If the molecules diffuse more quickly, the gap between the fingers would be larger and you’d get fewer digits. If the limb bud grows 20 percent bigger and everything else stays the same, you suddenly have room for an extra digit—this is why around 1 in 500 people are born with an extra finger or toe.

These cases, known as polydactyly, show that there’s a lot of flexibility built into the Turing system. Change the parameters slightly, and you can change the numbers of fingers and toes. So why has evolution set these parameters so they almost always make five? It’s clearly possible to make more. Some people are born with more. Ernest Hemingway used to own a six-toed cat, whose descendants still live in the writer’s Florida home. And the first tetrapods (four-legged animals) to invade the land had anywhere up to eight toes per foot.

But the common ancestor of all mammals, birds, reptiles and amphibians had five, and we have stuck with that number. Many groups have lost digits, but five is still the basic number. A horse has a single toe on each foot but if you look at an early horse embryo, its limb buds have five little stripes of Sox9, just like ours.

Some might say that we never need more than five fingers, but that’s not true either. Pandas have adapted a wrist bone into a pseudo-thumb to help them grasp bamboo they effectively have six fingers. Others think that it’s too hard to change the number of digits because the pertinent genes (like Sox9) control the development of other body parts. Mutations that give you more fingers might also screw up your heart or spine. But Sharpe doesn’t like this answer either. “It implies that the animal body plan is fairly locked, and obviously evolution happens,” he says.

So, why five? No one really knows. “It’s the ultimate meta-problem on top of everything,” says Sharpe. “I often say that if we understood why five, we’d probably understand everything.”


Conclusion

Family studies clearly demonstrate that tongue rolling is not a simple genetic character, and twin studies demonstrate that it is influenced by both genetics and the environment. Despite this, tongue rolling is probably the most commonly used classroom example of a simple genetic trait in humans. Sturtevant (1965) said he was "embarrassed to see it listed in some current works as an established Mendelian case." You should not use tongue rolling to demonstrate basic genetics.


Movement at Synovial Joints

Synovial joints allow for many types of movement including gliding, angular, rotational, and special movements.

Learning Objectives

Differentiate among the types of movements possible at synovial joints

Key Takeaways

Key Points

  • Gliding movements occur as relatively flat bone surfaces move past each other, but they produce very little movement of the bones.
  • Angular movements are produced when the angle between the bones of a joint changes they include flexion, extension, hyperextension, abduction, adduction, and circumduction.
  • Rotational movement involves moving the bone around its longitudinal axis this can be movement toward the midline of the body (medial rotation) or away from the midline of the body (lateral rotation).
  • Special movements are all the other movements that cannot be classified as gliding, angular, or rotational these movements include inversion, eversion, protraction, and retraction.
  • Other special movements include elevation, depression, supination, and pronation.

Key Terms

  • adduction: the movement of a bone toward the midline of the body
  • abduction: moving a bone away from the midline of the body
  • supination: the action of rotating the forearm so that the palm of the hand is turned up or forward
  • pronation: the action of rotating the forearm so that the palm of the hand is turned down or back

Movement at Synovial Joints

The range of movement allowed by synovial joints is fairly wide. These movements can be classified as: gliding, angular, rotational, or special movement.

Gliding Movement

Gliding movements occur as relatively flat bone surfaces move past each other. They produce very little rotation or angular movement of the bones. The joints of the carpal and tarsal bones are examples of joints that produce gliding movements.

Angular Movement

Angular movements are produced by changing the angle between the bones of a joint. There are several different types of angular movements, including flexion, extension, hyperextension, abduction, adduction, and circumduction. Flexion, or bending, occurs when the angle between the bones decreases. Moving the forearm upward at the elbow or moving the wrist to move the hand toward the forearm are examples of flexion. In extension, the opposite of flexion, the angle between the bones of a joint increases. Straightening a limb after flexion is an example of extension. Extension past the normal anatomical position is referred to as hyperextension. This includes moving the neck back to look upward or bending the wrist so that the hand moves away from the forearm.

Abduction occurs when a bone moves away from the midline of the body. Examples of abduction include moving the arms or legs laterally to lift them straight out to the side. Adduction is the movement of a bone toward the midline of the body. Movement of the limbs inward after abduction is an example of adduction. Circumduction is the movement of a limb in a circular motion, as in swinging an arm around.

Angular and rotational movements: Synovial joints give the body many ways in which to move. (a)–(b) Flexion and extension motions are in the sagittal (anterior–posterior) plane of motion. These movements take place at the shoulder, hip, elbow, knee, wrist, metacarpophalangeal, metatarsophalangeal, and interphalangeal joints. (c)–(d) Anterior bending of the head or vertebral column is flexion, while any posterior movement of the head is extension. (e) Abduction and adduction are motions of the limbs, hand, fingers, or toes in the coronal (medial–lateral) plane of movement. Moving the limb or hand laterally away from the body, or spreading the fingers or toes, is abduction. Adduction brings the limb or hand toward or across the midline of the body or brings the fingers or toes together. Circumduction is the movement of the limb, hand, or fingers in a circular pattern, using the sequential combination of flexion, adduction, extension, and abduction motions. Adduction/abduction and circumduction take place at the shoulder, hip, wrist, metacarpophalangeal, and metatarsophalangeal joints. (f) Turning of the head side to side or twisting of the body is rotation. Medial and lateral rotation of the upper limb at the shoulder or lower limb at the hip involves turning the anterior surface of the limb toward the midline of the body (medial or internal rotation) or away from the midline (lateral or external rotation).

Rotational Movement

Rotational movement is the movement of a bone as it rotates around its longitudinal axis. Rotation can be toward the midline of the body, which is referred to as medial rotation, or away from the midline of the body, which is referred to as lateral rotation. Movement of the head from side to side is an example of rotation.

Special Movements

Some movements that cannot be classified as gliding, angular, or rotational are called special movements. Inversion involves moving the soles of the feet inward, toward the midline of the body. Eversion, the opposite of inversion, involves moving of the sole of the foot outward, away from the midline of the body. Protraction is the anterior movement of a bone in the horizontal plane. Retraction occurs as a joint moves back into position after protraction. Protraction and retraction can be seen in the movement of the mandible as the jaw is thrust outwards and then back inwards. Elevation is the movement of a bone upward, such as shrugging the shoulders, lifting the scapulae. Depression is the opposite of elevation and involves moving the bone downward, such as after the shoulders are shrugged and the scapulae return to their normal position from an elevated position. Dorsiflexion is a bending at the ankle such that the toes are lifted toward the knee. Plantarflexion is a bending at the ankle when the heel is lifted, such as when standing on the toes. Supination is the movement of the radius and ulna bones of the forearm so that the palm faces forward or up. Pronation is the opposite movement, in which the palm faces backward or down. Opposition is the movement of the thumb toward the fingers of the same hand, making it possible to grasp and hold objects.

Special movements: (g) Supination of the forearm turns the palm upward in which the radius and ulna are parallel, while forearm pronation turns the palm downward in which the radius crosses over the ulna to form an “X.” (h) Dorsiflexion of the foot at the ankle joint moves the top of the foot toward the leg, while plantar flexion lifts the heel and points the toes. (i) Eversion of the foot moves the bottom (sole) of the foot away from the midline of the body, while foot inversion faces the sole toward the midline. (j) Protraction of the mandible pushes the chin forward, while retraction pulls the chin back. (k) Depression of the mandible opens the mouth, while elevation closes it. (l) Opposition of the thumb brings the tip of the thumb into contact with the tip of the fingers of the same hand.


Sensing with Your Feet!

Introduction
How many objects do you think you touch with your hands every day? A lot! Every time you touch something your hands are able to feel how smooth, cold, warm or rough the object is. In fact, your hands and fingers are so good at sensing details of shapes and surface textures that you are able to identify an object just by touch and without seeing it. Here is the challenge though: Do you think your feet are sensitive enough to do the same? Are they able to identify objects just by touching them? Try this activity to find out!

Background
When we touch something, we get a lot of information about the object. This is possible because our skin contains an extensive network of nerve endings and touch receptors, which make it sensitive to many different kinds of stimuli. A stimulus can be anything that triggers the receptors in your skin to a response, such as pressure, temperature, vibrations or pain. Once the receptors are activated by the stimulus, a series of nerve impulses is triggered and transmitted to our brains, which then use this information to identify the object. Just passive contact of an object is not enough to identify it, however. To make out its shape and details, we have to actively explore its surfaces and the object as a whole by moving it in our hands. This is called haptic perception.

To be able to identify an object by just using haptic perception, we use different receptor types that are each responsible for sensing different stimuli. The mechanoreceptors, for example, perceive sensations such as vibrations, pressure or texture whereas the thermoreceptors respond to the temperature of an object. Special pain receptors are responsible for picking up anything that has the potential to damage the skin, and proprioceptors can sense the position of different parts of the body in relation to one another and the surrounding environment. These sensors in combination allow us to pick up an object&rsquos shape and temperature as well as its surface texture just by touching it. The gathered information then makes it possible for our brains to identify it.

But why are we able to identify an object just with our hands? Is it because we had a lifetime of experience seeing objects in front of us as we touched them? Did this combination of visual and haptic perception wire our brains in a way that it is able to combine these two sensory inputs? Are we evolutionary conditioned to &ldquosee&rdquo with our hands? There is an easy experiment to investigate these questions. What if we use another bodily part to identify a familiar object that has not been trained to do this kind of task: your feet! Do you think your feet can &ldquosee&rdquo?

  • Chair
  • Helper
  • Blindfold (such as a scarf)
  • About 20 familiar objects to identify, such as toys, foods, household items, clothes etcetera. (Make sure none of these objects have sharp ends or can break easily. They should be at least the size of your fist or as long as your fingers. Have your helper gather these, and make sure that you do not see them.)

Preparation

  • Sit on a chair. Your feet should still be able to comfortably reach the ground.
  • Let your helper blindfold you.
  • Have your helper bring over the 20 familiar objects from your environment.
  • You will only have 10 seconds to identify each object, so once you are handed an object, your helper has to slowly count to 10 and then take it away again.
  • While still blindfolded and sitting on the chair, ask you helper to place one of the objects in your hands. Move the object in both of your hands and explore its shape and texture. How big is the object? Does it feel warm or cold? Is its surface rough or smooth?
  • As soon as you think you have identified the object, tell your helper your guess and pass it back. Were you able to identify it within the given 10 seconds? Did you feel it was easy or hard to identify?
  • Once your helper gets the object back, without telling you, he or she will place the object in a &ldquoWrong&rdquo pile if you could not identify it and in a &ldquoRight&rdquo pile if you could. This way, you can keep track of your responses.
  • After finishing with the first object, repeat the steps with another nine objects, so you have explored a total of 10 objects with both of your hands. Was there any object that you could not guess in time? How easy or difficult did you find the task? Were there any stimuli that helped you more or less in identifying the object?
  • For the next 10 objects (they should not be the same as the previous ones), you will use your feet to identify them. Remove your shoes and socks so your feet are bare.
  • While still blindfolded and sitting, let your helper place one object close to your feet. Then explore the project with your feet and toes and again try to make a guess of the object&rsquos identity within the first 10 seconds. Do you find it easy to explore the object with your feet? Is it easier or harder than using your hands?
  • After 10 seconds make a guess and let your helper take the object away. Your helper should make two separate piles for the feet experiment depending on if you guessed the object right or wrong.
  • Follow the same procedure (just using your feet) to identify the remaining nine objects. Can you sense details of the object such as surface texture, shape or temperature with your feet? Were you able to identify all the objects within 10 seconds? Did you have difficulties identifying all of them?
  • Once you have completed identifying all 20 objects (10 with your hands and 10 with your feet), remove your blindfold and look at all the objects. First, let your helper explain to you which objects you guessed right and wrong with your hands. Did you guess all the objects right? Which ones were difficult or did you get wrong? Can you think of a reason why?
  • Next, let your helper show you which objects you guessed right and wrong with your feet. How many objects did you guess right, wrong or were unable to guess in time? Were you able to identify more objects with your hands or your feet within 10-second limit? Can you explain your results?
  • Extra: In addition to using both of your hands and feet, run the same experiment again (using different objects). But this time only use one hand or one foot to explore the objects. Is it easier or more difficult compared with using both hands and feet? Does it make a difference if you use your left or right foot or hand?
  • Extra: Instead of allowing only 10 seconds for each object, take your time until you can make a confident guess of the object&rsquos identity. Let your helper time how long you need to identify each object using your hands and feet, respectively. Do you see any trends in your results? Does it take longer using your hands or feet? Does it depend on the type of object?
  • Extra: Explore how the object size affects your results. Try the same test with different-size objects. Which are easier to identify&mdashbig objects or small?

Observations and results
Did you get all objects right when exploring them with your hands? You were probably able to identify most of the objects when using both of your hands to touch and feel the object. The receptors in your hands are trained and used to recognize various stimuli that come from the object, such as its surface texture, shape and temperature. In combination with the knowledge of how certain objects look and feel, your brain can make a positive identification of the object even though it does not really see it. Ten seconds was probably also long enough to make a good guess for each object&mdashand in case you did not get the object right, it was most likely due to the fact that it was an unfamiliar object that you have not seen or touched that often before.

With your feet, everything gets more complicated. One reason is that your feet have very different anatomy from your hands. Your toes are much shorter than your fingers and much less flexible, which makes it harder to grasp and enclose the object. The other reason is your feet are not used to using their touch receptors to feel and explore objects like your hands do. As a result, you should have noticed that you had more wrong guesses (or could not make a guess in time) when using your feet to identify the object&mdashalthough you might have been surprised by how many objects you guessed right!

If you measured your response time for each object, you should have found a slower recognition by feet than by hands. Recognition with your feet should have also improved with larger object sizes because small objects are difficult to grasp with your toes. Now that you know that not only your hands but also your feet are capable of identifying objects just by haptics, do you think you can &ldquotrain&rdquo your feet to get as good as your hands?

More to explore
Sense of Touch, from Home Science Tools
Super Powers for the Blind and Deaf, from Scientific American
Recognizing Familiar Objects by Hand and Foot: Haptic Shape Perception Generalizes to Inputs from Unusual Locations and Untrained Body Parts (pdf), from Attention, Perception & Psychophysics
The Touch Response, from Science Buddies
Science Activity for All Ages!, from Science Buddies


Exercises for Curled Toes

The best way to fix curled toes is to rewire the brain through specific toe exercises.

The following exercises for curled toes below will help — but they may feel weird at first. Some of them require you to curl your toes even more, which you might not want to do.

However, using those muscles is how you will regain control of them.

Here are some simple curled toes exercises to start with:

  • Toe Taps. Attempt to raise all your toes up off the ground and then place them back down. Repeat 10 times. It’s okay if you can’t move your toes very much yet. Attempting the movement will initiate important changes in the brain.
  • Floor Grips. With your feet flat on the floor, attempt to grip the floor by curling your toes, and then release as best you can. Repeat 10 times.
  • Finger Squeezes. Cross your foot over your knee and place a finger in between your big and second toes. Then, squeeze your toes together to pinch your finger as hard as you can. Release, and repeat 10 times.
  • Marble pickup. Place a dozen marbles on the floor and attempt to pick them up using your toes. This can be difficult at first, and it’s okay if you need a caregiver to assist you.
  • Towel curls. Place a towel on the floor and use your toes to pinch the towel and pick it up. Then, place it back down, flatten it out, and repeat. This is a difficult exercise, so it’s okay if you don’t get it at first. You will get better with practice.
  • Toe Extensor Strengthening. Cross your foot over your knee so that you’re sitting cross-legged. Then, place a resistance band around the top of your foot to pull your toes back toward your body, like so:

Then, use your foot to push the resistance band away from your body. Return to center and repeat 10 times.

This will be very difficult in the beginning, so remember: as long as you attempt to make the movement, you’re stimulating changes in the brain.

If you need to do these exercises passively with the help of a caregiver, that’s a great place to start.


Blind Spot

The eye’s retina receives and reacts to incoming light and sends signals to the brain, allowing you to see. One part of the retina, however, doesn't give you visual information—this is your eye’s “blind spot.”

Tools and Materials

  • A few 3 × 5 cards or other stiff paper
  • Black marking pen (felt tip works best)
  • Optional: yard stick or meter stick and a partner

Assembly

Mark a dot and a cross on a card as shown.

To Do and Notice

Hold the card at eye level about an arm’s length away. Make sure that the cross is on the right.

Close your right eye and look directly at the cross with your left eye. Notice that you can also see the dot.

Focus on the cross, but be aware of the dot as you slowly bring the card toward your face. The dot will disappear, and then reappear, as you bring the card toward your face. Try moving the card closer and farther to pinpoint exactly where this happens.

Now close your left eye and look directly at the dot with your right eye. This time the cross will disappear and reappear as you bring the card slowly toward your face.

Try the activity again, this time rotating the card so that the dot and cross are not directly across from each other. Are the results the same?

What’s Going On?

The optic nerve—a bundle of nerve fibers that carries messages from your eye to your brain—passes through one spot on the light-sensitive lining, or retina, of your eye (click to enlarge diagram below). In this spot, your eye’s retina has no light receptors. When you hold the card so the light from the dot falls on this spot, you cannot see the dot. The fovea is an area of the retina that is densely packed with light receptors, giving you the sharpest vision.

Going Further

Here are a few variations of this activity that you might try.

Fill in your blind spot:

Draw a straight line across the card, from one edge to the other, through the center of the cross and the dot, and try again. Notice that when the dot disappears, the line appears to be continuous, without a gap where the dot used to be.

Your brain automatically “fills in” the blind spot with a simple extrapolation of the image surrounding the blind spot. This is why you don’t notice the blind spot in your day-to-day observations of the world.

Measure the size of your blind spot without a partner: Take a new card and mark a cross near the left edge of a 3 × 5 card. Hold the card about 10 inches from your face. (It's helpful to use a meter stick or ruler to measure this distance you'll need it to calculate the size of your blind spot.)

Close your left eye and look directly at the cross with your right eye. Move a pen across the card until the point of the pen disappears in your blind spot. Mark the places where the pen point disappears. Use the pen to trace the shape and size of your blind spot on the card. Then you can measure the diameter of the blind spot on the card (see equation below).

Measure the size of your blind spot with a partner:

Hold your 3 x 5 card at arm's length. Have your partner measure the distance from the card to your eye.

Slowly move the card horizontally left and right, and note where the cross disappears and reappears. Have your partner measure the distance between the two places where the dot disappears and reappears.

In our simple model, we are assuming that the eye behaves like a pinhole camera, with the pupil as the pinhole. In such a model, the pupil is 0.78 in (2 cm) from the retina. Light travels in a straight line through the pupil to the retina. Similar triangles can then be used to calculate the size of the blind spot on your retina. The simple equation for this calculation is

where s is the size of the blind spot on your retina (in cm), d is the diameter of the blind spot on the card, and D is the distance from your eye to the card (in the examples above, 10 in [25 cm] or the length of your arm, roughly 2–2.5 feet (60–75 cm). Note that d and D must always be expressed in the same units, whether inches or centimeters.

This Science Snack is part of a collection that highlights Black artists, scientists, inventors, and thinkers whose work aids or expands our understanding of the phenomena explored in the Snack.

Dr. Patricia Bath (1942-2019), pictured above, was an ophthalmologist and laser scientist, and was the first woman chair of ophthalmology at a US university. She studied the causes of and cures for blindness, and invented a widely used method of using laser surgery to treat blindness caused by cataracts. Dr. Bath also co-founded the American Institute for the Prevention of Blindness. This Science Snack can help you investigate the structures in the eye that help you see, so you can understand the eye like Dr. Bath did.