<unk>  (Greek: "difficult to measure") is a condition that describes a lack of coordination of movement typified by the undershoot and/or overshoot of intended position with the hand, arm, leg, or eye. It is sometimes described as an inability to judge distance or scale .
(From the Online Medical Dictionary) an aspect of ataxia, in which the ability to control the distance, power, and speed of an act is impaired. Usually used to describe abnormalities of movement caused by cerebellar disorders.
As<unk>  can refer to more than just a motor problem, an overlying definition that encompasses all forms of it is “the inability to receive and process information rapidly, to retrieve the relevant associated constructs, and to produce a well-modulated and fine-tuned response.”
Hypermetria describes undershooting intended position and hypometria describes overshooting intended position .
The cerebellum is the area of the brain that contributes to coordination and motor processes and is anatomically inferior to the cerebrum  .  Sensorimotor integration is the brain’s way of integrating the information received from the sensory (or proprioceptive) neurons from the body, including any visual information. To be more specific, information needed to perform a motor task comes from retinal information pertaining to the eyes’ position and has to be translated into spatial information . Sensorimotor integration is crucial for performing any motor task and takes place in the post parietal cortex  .  After the visual information has been translated into spatial information, the cerebellum must use this information to perform the motor task . If there is damage to any pathways that connect the pathways,<unk>  may result.
Motor<unk>  is the customary term used when a person refers to<unk> .<unk>  of the extremities caused by hemispheric syndromes is manifested in multiple ways: dysrhythmic tapping of hands and feet and dysdiadochokinesis, which is the impairment of alternating movements .. Damage to the cerebellum makes a person slow to orient their extremities in space .
Motor Control as a Learning Process
Recent research has also shed light upon a specific process that if interrupted, may be the cause of ataxia and<unk> . According to sources cited in this article, motor control is a learning process that occurs in the synapses of Purkinje dendrites . Research has shown that inhibitory synaptic connections are the primary way the learning occurs, as saturation would occur with excitatory synaptic transmission  . There have been varying theories as to the makeup of the cerebellum, which controls this process . Some predicted that the cerebellum was an array of adjustable pattern generators (APGs), each of which generate a “burst command” with varying intensity and duration . Other models, which apply mostly in robotic applications, propose that the cerebellum acquires an “inverse model of the motor apparatus .” More recent research in electrophysiology has shown modular structures in the spinal cord known as “motor primitives .”
Based on the APG model, modules of APG are the features that control motor learning .  The entire process is a positive feedback loop . Inhibitory input is transmitted and received from various components of the cortex, including the cerebellar nucleus, a motor cortical cell and Purkinje cells .  Purkinje cells send the inhibitive information by obtaining learning information from parallel fibers of granule cells .  This model of APGs is useful in that it effectively describes the motor learning process .
Motor primitives are another proposed module of motor learning . This information was found by electrical stimulation of the lumbar spinal cord in rats and frogs . Upon the stimulation, researchers found that motor primitives are found in the spinal cord and use patterns of muscle activation to generate a specific motor output . Different movements are learned from different levels of activation . These findings lead researchers to believe that these same motor primitives could be found in the cerebellum .
These two different models combined show that it is possible that motor primitives are in the cerebellum, because, “a set of parallel arrays of APG can drive each motor primitive module in the spinal cord .” The authors have generated a model of adjustable primitive pattern generator (APPG), which is basically a group of parallel APGs summed together .
The APPG model is a vector sum of all the inputs of the APG, which are units of position, velocity and time . Granule cells send information from the spinal cord and the motor cortex which in turn translates the information in a process called state mapping . The final model of the APPG becomes linear upon the vector summation of the information from the neurons and muscles .  This model is consistent with the “virtual trajectory hypothesis” which states that the desired trajectory is sent to the spinal cord as a motor command .
Saccadic eye movements are the very quick, simultaneous movements made by the eye to receive visual information and shift the line of vision from one position to another . A person depends profoundly on the ability of the accuracy of these movements .. The area of the brain that controls saccades is the superior colliculus, specifically the fastigial oculomotor region (FOR) .. The information is received from the retina, is translated into spatial information and is then transferred to motor centers for motor response. A person with saccadic<unk>  will constantly produce abnormal eye movements including microsaccades, ocular flutter, and square wave jerks even when the eye is at rest . During eye movements hypometric and hypermetric saccades will occur and interruption and slowing of normal saccadic movement is common .
There have been many studies concerning the cerebellum’s role in cognitive processes. The cerebellum is connected to other higher-order areas of the brain and is therefore thought to take part in many cognitive processes . Previously there has been evidence that the cerebellum contributed to cognitive processes but with the development of functional magnetic resonance imaging (fMRI), researchers have proved that the cerebellum is associated with higher-order functions including attention,  perception, and language  . Some clinical studies have revealed that there is an association between the cerebellum and personality . Researchers have also been able to find correlations between cerebellar disorders and psychosis, especially schizophrenia . In particular, cerebellar cognitive affective syndrome (CCAS) is a cerebellar disorder that exhibits both motor dysfunction (including<unk> : referred to as impaired spatial cognition), personality change, impairment of linguistic abilities, and disturbance of higher-order functions including reasoning and memory . It is believed that the there are specific pathways that link not only the prefrontal cortex, superior temporal regions, posterior parietal lobes, and hippocampus to the cerebellum, but there are also very specific pathways that link the cerebellum back to these areas of the brain . These loops may contribute to the cognitive properties of the cerebellum that have recently been discovered. A good definition of cognitive<unk> , also referred to as<unk>  of thought, is “a difficulty in coordinating and monitoring the process of receiving, processing, and expressing information” . Cognitive<unk>  manifests itself in association with other cerebellar disorders .
Dysmetria
Dysphonia
Dysphoria
Dysarthria
Dyslexia
Dysprosody
Dyspraxia
Agnosia