To maintain balance and navigate space in our physical world, we must organize and integrate information from the visual eyes , proprioceptive information perceived through our muscles and joints to tell us where we are in space and vestibular inner ears sensing motion, equilibrium and spatial awareness systems.
For patients who may be suffering from balance issues, knowing that there is a strong, influential visual component may be the key to getting the help they need. For most of us, vision is a term used to describe how clear things are. In reality, the impact of vision on our lives is much more profound than just the clarity of the images being perceived. Vision is also connected to our balance system. It is this system that guides our balance, which in turn guides the development of our vision during our first years.
When we are young, movement guides vision. However, as soon as we develop the necessary visual skills, vision begins to guide balance. It is generally thought that between half and two-thirds of the brain is used for visual processing. When our eyes are open, two-thirds of the electrical activity of the brain is devoted to vision Fixot.
Our vision is such a powerful sense that it can override information from the other senses, which is sometimes beneficial and other times detrimental. When the visual system is not working properly, providing incorrect information to other somatosensory systems, it can dramatically interfere with our quality of life. Fortunately, the human brain is able to continuously create new pathways and neurological connections synapses throughout our lives, referred to as neuroplasticity.
This concept of neuroplasticity is what allows us to develop the necessary control over different sensory systems, so that we may be able to enhance our ability to interact with the physical world, and thus our overall quality of life.
Dizziness and disequilibrium are often the result of a vestibulo-ocular reflex VOR dysfunction a reflex which coordinates eye and head movement and an unstable binocular how well the eyes work together system Cohen. A disruption of balance, or just generally feeling off in our movements, is very common after an acquired brain injury.
This is due to a disruption in the integration of the vestibular and visual systems. This sensory incoherence is similar to the situation where the sound and the picture on the TV are out of sync. Both the sound and the picture work, and when isolated may even be pleasant to attend to.
However, when those systems are used together, with the timing off, there is a dramatically negative response. Fortunately, using the concept of neuroplasticity, the systems can be synced back together!
The proper source of this mismatch must be identified first in order to receive proper treatment. Through proper evaluation and skilled vision therapy, we can improve visual deficiencies.
One must take particular care in choosing an Optometrist that specializes in therapeutic vision treatment. Some common titles that we use to describe our specialties can include Developmental Optometrist, Vision Therapist or Neuro-Rehabilitative Specialist.
These are two of the leading communities with respect to the field of visual therapy. A functional vision exam from a Neuro-Rehabilitative, or Developmental, Optometrist is far different than routine eye exams. Additionally, we note the ocular alignment at different positions of gaze, including distance and near, as well as under different stressful situations such as cognitive loading.
Flexibility is another key component of our vision assessment, as patients should be able to efficiently move their fixation from one target to another such as a near to far target, and back. It is important to note how the visual system performs as the vestibular system is activated, as this may give the provider a clue where the disconnect in the sensory integration lies.
It is unknown whether the laterality of tinnitus would lead to impairment of visual processing in corresponding orientation, regarding that the allocation of attentional resources would be affected Chica et al. To our knowledge, previous studies focusing on visual processing in tinnitus patients presented the target stimuli in the center of the screen, while the spatial factor was neglected.
In contrast, the current study investigated the potential attentional bias of tinnitus patients associated with the laterality of their symptoms. This study used letter symbols Experiment 1 and emotional faces Experiment 2 as the target stimuli to explore the processing of visual stimuli in tinnitus patients. Signal detection and signal recognition were disassociated by manipulating the task instructions.
Specifically, in Condition 1, the subjects were asked to respond to the position perceptual feature of the target stimulus as soon as possible; however, they were not required to identify the content of the target. Thus, only signal detection was required in this condition. In Condition 2, the subjects were asked to judge the content conceptual feature of the target stimulus immediately, thus signal recognition was needed. Therefore, the RT in Condition 1 would reflect the time needed for signal detection, while Condition 2 would reflect the time needed for signal recognition.
Moreover, the RT in Condition 2 subtracted from that of Condition 1 defining the time needed for signal encoding i. However, whether tinnitus would selectively modulate signal detection or signal encoding is yet to be elucidated. In addition, seeing that tinnitus might affect attentional allocation, we investigated whether the visual processing of tinnitus group would show a spatial bias; that is, the response speed of tinnitus patients to target presentation on the tinnitus side would be significantly different from that on the non-tinnitus side.
Patients admitted to the Outpatient Department of Otorhinolaryngology, the Third Affiliated Hospital of Sun Yat-sen University, due to tinnitus as the first complaint, were selected. The exclusion criteria were as follows: 1 encountered significant life events promotion, divorce, unemployment within 2 weeks before the experiment; 2 administered sedative or psychotropic drugs within 24 h before the experiment.
All participants signed the informed consent before the experiment. Normal controls were recruited from the Internet and poster adverts at the Sun Yat-sen University. The inclusion criteria were as follows: 1 had no history of tinnitus, dizziness, hearing loss, and other ear diseases; 2 had no history of neurological and psychiatric diseases; 3 had normal vision or corrected vision; 4 had an education level of high school or above and could understand the operational instructions; 5 age 18—40 years; 6 right-handedness.
The exclusion criteria were the same as that for the tinnitus group. THI was used to measure the distress of tinnitus in the daily life of the patients. In Experiment 1, two composite figures consisting of the black letter E or F inside white circles, Figure 1A were used as target stimuli.
In Experiment 2, two facial expressions were used as the target stimuli: happiness and sadness, wherein the difference was the direction of the mouth upward vs. Prior to the experiment, 39 normal volunteers aged 20—40 years were recruited to assess the valence from 1: very negative to 7: very positive and arousal from 1: very low to 7: very high of the two facial expressions using two 7-point scales.
The results showed that the valence and arousal ratings of the happy face were 5. Subsequently, a target stimulus was displayed for ms at either side of the screen. The current trial would finish immediately after the subjects made a selection or 1, ms had passed Figure 2. A total of 40 trials were conducted. In both Experiment 1 and 2, each subject was required to complete the two conditions of tasks Conditions 1 and 2 in two independent blocks, at an interval of 10 min.
In Condition 1, the subjects responded to the position of the target stimulus. In Condition 2, the subjects responded to the content of the target stimulus. The order of the two conditions in the whole sample was balanced between the subjects, and approximately 15 min were required to complete the entire experimental procedure. Data analyses were performed using SPSS Omissions, incorrect responses, trials with RTs three standard deviations SDs away from the mean RT were excluded from further analysis.
Then, the mean RTs of the remaining trials were calculated. Normal distributed data were reported with mean and standard deviation. Inter-group difference and intra-group difference were evaluated by independent sample t -test and paired sample t -test, respectively. Otherwise, median and quartile range were presented, and difference was tested by Mann—Whitney Test or Wilcoxon Signed Ranks Test normal approximation test results were reported.
Omissions, incorrect responses, and trials with RTs that were 3 SDs away from the mean were defined as abnormal data and excluded from further analysis. The proportion of the abnormal data in each group were shown in Table 2. The independent samples rank-test showed that the tinnitus group was significantly slower than the control group in detecting and recognizing the target stimuli, while no significant differences were observed in encoding the target stimuli the recognition speed minus the detection speed between the two groups Table 3.
Meanwhile, paired sample t -test or rank-test showed that significantly lateral dominances were not observed in the left tinnitus group, right tinnitus group and the normal group in detecting, encoding and recognizing the target stimuli Table 4. Finally, the independent samples rank-test showed that neither gender nor tinnitus distress affected the speed in detecting, encoding and recognizing the target stimuli Tables 5 , 6. The independent samples rank-test showed that the tinnitus group was significantly slower than the control group in detecting and recognizing the target stimuli, while no significant differences were observed in encoding the target stimuli the recognition speed minus the detection speed between the two groups, regardless of whether the face was happy or sad Table 7.
Meanwhile, paired sample t -test or rank-test showed that there was no significant lateral effect in the left tinnitus group, right tinnitus group, or normal group in detecting, encoding, and recognizing the target stimuli, regardless of whether the face was happy or sad Table 8. Finally, the independent samples rank-test showed that neither gender nor tinnitus distress affected the speed in detecting, encoding, or recognizing target stimuli, regardless of whether the face was happy or sad Tables 9 , The paired sample t -test revealed that the difference between the RTs of happy and sad faces in the control group was insignificant, while the RTs of the happy face was significantly higher than that of the sad face in the tinnitus group in the left side, but not the right side Table In this study, two behavioral experiments were conducted to explore the cross-modal inference of tinnitus on visual processing.
The preliminary results of this study indicated that the signal detection and signal recognition were significantly declined in the tinnitus patients, irrespective of the stimulus type, which supports the first hypothesis of this study.
Meanwhile, an insignificant difference was noted in the encoding speed of the target stimuli between the two groups; thus, the decrease in signal detection might be a vital factor causing the decrease in signal recognition in tinnitus patients. Finally, the lack of significant difference in the influence of gender and tinnitus distress on both types of visual processing including detection, encoding, and recognition indicated that the decrease in the visual processing capacity is prevalent in the chronic tinnitus population.
Meanwhile, the results of this study showed that there was no significant lateral effect in visual processing in either the tinnitus group or the normal group, and therefore can not support the second hypothesis that tinnitus might affect spatial attentional allocation in visual processing.
In a previous research based on cue-target paradigm, there had the interstimulus interval ISI between the cue and the target Chica et al. However, the attention resources occupied by tinnitus were difficult to separate from the tinnitus signal Li et al.
Consistent with our expectation, the present study provided preliminary behavioral evidence for the cross-modal interference of tinnitus on visual processing. Specifically, the visual detection and recognition speeds of the tinnitus group to letter symbols and emotional faces were significantly slower than that of the control group, indicating that the effect of tinnitus may occur at both the perceptual and conceptual level in visual processing.
Therefore, the tinnitus signal might affect the allocation of attention resources in patients, thereby interfering with the processing in the visual channel. Concurrently, the findings also revealed that the decline in the visual processing speed in tinnitus subjects was primarily due to the decline in the detection speed of the target stimuli. This phenomenon suggested the presence of the cross-modal interference of tinnitus in the early stage of visual cognitive processing. Moreover, in the late stage of cognitive processing — ms , spatial tasks based on different channels activate different brain areas, which indicate that the visual and auditory channels have their independent attention regulation systems at this stage sensory-specific Banerjee et al.
It senses sound vibrations and transfers them onto the incus. Through these steps, the middle ear acts as a gatekeeper to the inner ear, protecting it from damage by loud sounds. Unlike the middle ear, the inner ear is filled with fluid. When the stapes footplate pushes down on the oval window in the inner ear, it causes movement in the fluid within the cochlea. The function of the cochlea is to transform mechanical sound waves into electrical or neural signals for use in the brain.
Within the cochlea there are three fluid-filled spaces: the tympanic canal, the vestibular canal, and the middle canal. Fluid movement within these canals stimulates hair cells of the organ of Corti, a ribbon of sensory cells along the cochlea.
These hair cells transform the fluid waves into electrical impulses using cilia, a specialized type of mechanosensor.
The cochlea : A cross-section of the cochlea, the main sensory organ of hearing, located in the inner ear. Hearing begins with pressure waves hitting the auditory canal and ends when the brain perceives sounds.
Sound reception occurs at the ears, where the pinna collects, reflects, attenuates, or amplifies sound waves. These waves travel along the auditory canal until they reach the ear drum, which vibrates in response to the change in pressure caused by the waves. The vibrations of the ear drum cause oscillations in the three bones in the middle ear, the last of which sets the fluid in the cochlea in motion. The cochlea separates sounds according to their place on the frequency spectrum.
Hair cells in the cochlea perform the transduction of these sound waves into afferent electrical impulses. Auditory nerve fibers connected to the hair cells form the spiral ganglion, which transmits the electrical signals along the auditory nerve and eventually on to the brain stem. The brain responds to these separate frequencies and composes a complete sound from them.
Structural diagram of the cochlea : The cochlea is the snail-shaped portion of the inner ear responsible for sound wave transduction. Humans are able to hear a wide variety of sound frequencies, from approximately 20 to 20, Hz. Our ability to judge or estimate where a sound originates, called sound localization, is dependent on the hearing ability of each ear and the exact quality of the sound.
Bushy neurons can resolve time differences as small as ten milliseconds, or approximately the time it takes for sound to pass one ear and reach the other. The gustatory system, including the mouth, tongue, and taste buds, allows us to transduce chemical molecules into specific taste sensations. The gustatory system creates the human sense of taste, allowing us to perceive different flavors from substances that we consume as food and drink.
Gustation, along with olfaction the sense of smell , is classified as chemoreception because it functions by reacting with molecular chemical compounds in a given substance. Specialized cells in the gustatory system that are located on the tongue are called taste buds, and they sense tastants taste molecules. The taste buds send the information from the tastants to the brain, where a molecule is processed as a certain taste. There are five main tastes: bitter, salty, sweet, sour, and umami savory.
All the varieties of flavor we experience are a combination of some or all of these tastes. The Mouth : A cross-section of the human head, which displays the location of the mouth, tongue, pharynx, epiglottis, and throat. The sense of taste is transduced by taste buds, which are clusters of taste receptor cells located in the tongue, soft palate, epiglottis, pharynx, and esophagus.
The tongue is the main sensory organ of the gustatory system. The tongue contains papillae, or specialized epithelial cells, which have taste buds on their surface. There are three types of papillae with taste buds in the human gustatory system:. Each taste bud is flask-like in shape and formed by two types of cells: supporting cells and gustatory cells. Gustatory cells are short-lived and are continuously regenerating. They each contain a taste pore at the surface of the tongue which is the site of sensory transduction.
Though there are small differences in sensation, all taste buds, no matter their location, can respond to all types of taste. Taste Buds : A schematic drawing of a taste bud and its component pieces. Traditionally, humans were thought to have just four main tastes: bitter, salty, sweet, and sour.
Spicy is not a basic taste because the sensation of spicy foods does not come from taste buds but rather from heat and pain receptors. In general, tastes can be appetitive pleasant or aversive unpleasant , depending on the unique makeup of the material being tasted.
There is one type of taste receptor for each flavor, and each type of taste stimulus is transduced by a different mechanism. Bitter, sweet, and umami tastes use similar mechanisms based on a G protein-coupled receptor, or GPCR. There are several classes of bitter compounds which vary in chemical makeup. The human body has evolved a particularly sophisticated sense for bitter substances and can distinguish between the many radically different compounds that produce a bitter response.
Evolutionary psychologists believe this to be a result of the role of bitterness in human survival: some bitter-tasting compounds can be hazardous to our health, so we learned to recognize and avoid bitter substances in general. The salt receptor, NaCl, is arguable the simplest of all the receptors found in the mouth. This depolarizes the cell and floods it with ions, leading to a neurotransmitter release. Like bitter tastes, sweet taste transduction involves GPCRs binding.
The specific mechanism depends on the specific molecule flavor. Natural sweeteners such as saccharides activate the GPCRs to release gustducin. Synthetic sweeteners such as saccharin activate a separate set of GPCRs, initiating a similar but different process of protein transitions.
Sour tastes signal the presence of acidic compounds in substances. There are three different receptor proteins at work in a sour taste. The first is a simple ion channel which allows hydrogen ions to flow directly into the cell.
The third allows sodium ions to flow down the concentration gradient into the cell. This involvement with sodium ions implies a relationship between salty and sour tastes receptors. Umami is the newest receptor to be recognized by western scientists in the family of basic tastes. We do know that umami detects glutamates that are common in meats, cheese, and other protein-heavy foods and reacts specifically to foods treated with MSG.
The olfactory system gives humans their sense of smell by collecting odorants from the environment and transducing them into neural signals. The olfactory system gives humans their sense of smell by inhaling and detecting odorants in the environment. Olfaction is physiologically related to gustation, the sense of taste, because of its use of chemoreceptors to discern information about substances.
Perceiving complex flavors requires recognizing taste and smell sensations at the same time, an interaction known as chemoreceptive sensory interaction. This causes foods to taste different if the olfactory system is compromised. However, olfaction is anatomically different from gustation because it uses the sensory organs of the nose and nasal cavity to capture smells. Humans can identify a large number of odors and use this information to interact successfully with their environment.
Olfactory sensitivity is directly proportional to spatial area in the nose—specifically the olfactory epithelium, which is where odorant reception occurs. The area in the nasal cavity near the septum is reserved for the olfactory mucous membrane, where olfactory receptor cells are located.
This area is a dime-sized region called the olfactory mucosa. In humans, there are about 10 million olfactory cells, each of which has different receptor types composing the mucous membrane.
Each of the receptor types is characteristic of only one odorant type. Each functions using cilia, small hair-like projections that contain olfactory receptor proteins.
These proteins carry out the transduction of odorants into electrical signals for neural processing. The Olfactory System : A cross-section of the olfactory system that labels all of the structures necessary to process odor information. Olfactory transduction is a series of events in which odor molecules are detected by olfactory receptors.
These chemical signals are transformed into electrical signals and sent to the brain, where they are perceived as smells. Once ligands odorant particles bind to specific receptors on the external surface of cilia, olfactory transduction is initiated.
In mammals, olfactory receptors have been shown to signal via G protein. Olfactory Nerve : The olfactory nerve connects the olfactory system to the central nervous system to allow processing of odor information. Individual features of odor molecules descend on various parts of the olfactory system in the brain and combine to form a representation of odor. Since most odor molecules have several individual features, the number of possible combinations allows the olfactory system to detect an impressively broad range of smells.
A group of odorants that shares some chemical feature and causes similar patterns of neural firing is called an odotope. Humans can differentiate between 10, different odors. People wine or perfume experts, for example can train their sense of smell to become expert in detecting subtle odors by practicing retrieving smells from memory. Odor information is easily stored in long-term memory and has strong connections to emotional memory. Human and animal brains have this in common: the amygdala, which is involved in the processing of fear, causes olfactory memories of threats to lead animals to avoid dangerous situations.
Pheromones are airborne, often odorless molecules that are crucial to the behavior of many animals. They are processed by an accessory of the olfactory system. Recent research shows that pheromones play a role in human attraction to potential mates, the synchronization of menstrual cycles among women, and the detection of moods and fear in others.
Thanks in large part to the olfactory system, this information can be used to navigate the physical world and collect data about the people around us. The somatosensory system allows the human body to perceive the physical sensations of pressure, temperature, and pain.
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