Sensory Perception
The Nervous system plays an important role in many mammals including man. The nervous system is responsible for the coordination of different stimuli in the body. Environmental changes can be felt in the body due to the nervous system present. The sense of touch, vision, audition and taste can be understood solely due to the nervous system.
A minute change or deficiency in these senses could lead to fatality. A failure in perception of any of the senses makes an individual dependent. Sensory perception is essential for all living organisms and forms the basis for homeostasis.
A series of experiments were conducted evaluating the different sensory organs of the human body. The experiments evaluated Olfactory, Visual and Auditory senses in different individuals. Simple experiments were conducted in groups using standard equipment and materials. The observations of each experiment were noted down without bias or partiality. The results were thoroughly evaluated and discussed among different groups.
The experiments enlightened students about different sensory receptors and their role in the human body. Impairment in any of the sensory organs could be fatal. Preventive methods should be applied to avoid impairment of sensory organs.
(Hudspeth AJ and Logothetis NK, 2000)
Investigating the sense of Smell and Taste
The sense of smell (olfactory) plays the most crucial role in the entire body. The sense of smell is located in the nasal cavity. Most vertebrates have their olfactory sense located in the nasal cavity. (Rabinerson D, Horovitz E and Beloosesky Y, 2006)
Olfaction in humans takes place only after molecules (odorant) bind to specific receptors in the nasal cavity. These receptors are termed as olfactory receptors and play specific roles in detection of smell. These receptors combine and meet at the glomerulus. The glomerulus is responsible for the transmission of signals to the olfactory bulb. The olfactory bulb is part of the brain and is located below the frontal lobe. In most vertebrates. Two types of olfactory systems are observed. The main olfactory system is used to detect volatile chemicals in the environment. The second, accessory olfaction (smell) along with sense of taste is known as chemoreception. Odorants are chemicals that activate the olfactory system. Hydrocarbons, proteins mainly non-volatile, and odorants primarily activate the olfactory system. (Breer H, Fleischer J and Strotmann J, 2006)
The sense of taste in humans are due to the presence of taste receptors. The sense of taste is humans is due to the presence of the gustatory system. There are 3 main taste buds involved. They are named as fungiform papillae, foliate papillae, and circumvallate papillae. Studies have revealed the presence of taste buds in the larynx and esophagus. The tongue itself consist of different nerves that help in the sense of taste. They are primarily known as vagus nerve, glossopharyngeal nerve, and the facial nerve. These play an important role in chemoreception. (Kapsimali M and Barlow LA. 2013)
Experiment
The aim of the experiment will be to detect a sense of smell and taste in an individual. The experiment will also enable to detect the phenomenon of chemoreception, i.e the sense of smell along with the sense of taste.
Raw onion, apple and potato was used for experimenting the sense of olfaction in an individual. During the experimentation, the eyes and nostrils of the subject are closed. Samples of cut pieces of apple, potato and onion are given. The subject is requested to rinse his/her mouth after tasting each sample. Onion was given last in order to avoid confusion. These food samples were not allowed to be swallowed. The food sample is to be placed on the tongue and made to identify. The next step is to conduct the same steps, although at this time nostrils are to be kept open. This step will enable to detect the phenomenon of chemoreception. It means detecting an individual’s sense of smell with taste.
Observation and Results
It was observed that the sense of smell and taste was the highest for onion, followed by potato and then apple. A rating chart (score 1 to 10) was used for sense of smell and sense of taste. A score of 4 was observed in the case of apple. An intermediate score of 6 was observed for sense of olfaction and taste for potato. The highest score was observed for onion.
Investigating Visual Activity
Visual function is important for daily activity and is explained on the basis of visual activity and visual field. In 1862, Herman Snellen, invented a chart to measure visual activity in an individual. The chart consisted of shapes and letters. The distance read by the patient is compared to the distance read by a normal individual. This comparison would determine the visual function of the patient. Visual field enables each eye to perceive objects at the side to the central area of vision. Normal vision field is said to be 180 degrees. An individual with a vision of 20 degrees or fewer is considered to be partially blind.
Peripheral Vision
The main parts in the eye responsible for vision are cones and rods. Cones are present in the central cornea and are responsible for perceiving colors and bright light. Rods on the other hand, help in perceiving dim or dull light. Rods are considered to be dominant in peripheral vision of the eye. (Earl L. Smith, Chea-su Kee, Ramkumar Ramamirtham,Ying Qiao-Grider, and Li-Fang Hung, 2005)
Color Blindness
Color blindness is associated with deformity in the color-sensing pigments in the eye. Cones are primarily found in the retina of the eye and are responsible for color perception in the eye. Malfunctioning of a single pigment can cause color-blindness, and this is namely with red and green colors. An individual without a single pigment would have color-blindness and have difficulty in perceiving green and red colors. If there is more than 1 pigment missing in the eye, it can lead to color-blindness. In this case, however, difficulty in perception of yellow and blue colors along with red and green is observed. A severe form of color-blindness in individuals with least color perception is observed and is termed as achromatopsia. (Gordon N. 1998)
Near Point
Near point in visual analysis is to check the shortest distance at which at object is clearly focused. It is considered that lesser the distance in object clarity, greater would be an individual’s visual perception in distance changes. As age increases, the near point distance increases. In severe cases, where the near distance point is higher than 100, it is termed as presbyopia. The normal range for a distance to a near point for a 20 year old individual is 10cm. This eventually increases as age increases. After age of 75, it is most like to develop presbyopia, where the distance for near point is over 100cm.
Eye Dominance
Eye dominance can detect visual perception of an individual. It is also termed as ocular dominance. It helps in determining if an individual is right or left handed. In daily activities like writing, batting and throwing, preference of right or left hand use is considered. Similarly, eye dominance in visual perception is considered. Around 65% of the population is right-eye dominant while nearly 25% of them are left eye-dominant. Only a small portion of the population, nearly 10% of them show no eye-dominance. It is considered that the best bowlers and batters in cricket lack eye dominance.
After Images
After image is a phenomenon where an object appears to be present in an individual’s visual field even after the object has been removed from sight. After image is also termed as a ghost-image and is an optical illusion. There are two kinds of afterimages, Positive and negative respectively. The occurrence of Positive after images have not been widely studied. Negative afterimages are caused due to overstimulation of cone cells. Some studies also reveal a link between rod cells and after images.
Experiment in assessing Visual activity and Function
Peripheral vision can be observed using a 3 step procedure. Firstly, a colored paper is drawn from behind the subject’s head. The colored paper is kept in the visual field of the subject. The subject should notify the instructor when the paper appears in his/her visual field. The subject would then determine the color of the paper. The instructor would note down the color mentioned by the subject. In the majority of the cases, the subject would be unable to determine the color.
In the case of Colorblindness, assessing a color blind individual was possible by suing Ishiara chart. The chart is used for detecting color blindness. It was devised by Dr. Shinobu Ishiara. The test was published in the year 1917, when Dr. Ishiara served as a professor at the University of Tokyo. The test consists of a series of images, in which numerals are put within spots of different colors. An individual with normal vision will be able to detect the numeral within the differently colored spots. On the other hand, a color blind individual may not be able to detect any such numeral. Tests are normally done to detect red and green color blindness followed by yellow-blue. In a rare case, where complete color blindness has to be detected, a series of tests using Ishiara charts and images are used.
Detecting near point of an individual is simple. A newspaper article is kept in front of the individual at arm’s length. One eye of the individual is closed, and he/she is made to focus on the article. The paper is moved closer to the face, until the word is blurred. Now the paper is slowly drawn away from the face. It is drawn away until the word or image is sharp. The distance between the paper and the eye is noted down. The distance noted down is the normal point distance. Higher the distance of near point, older should the individual be. If there is a visual problem, abnormal near pint distance is recorded.
Analysis of eye dominance is the simplest of all analysis. Both eyes are to be kept open. The subject would then observe an object kept at a near distance. The subject is then instructed to close one eye and made to observe the object. The same step was followed by for the other eye. The eye that is aligned into a straight line with the object is said to be the dominant eye.
After images can be detected by a series of steps. Two paper, black and whiter are taken and kept at a near distance. A blue colored paper is placed over the black paper. The subject is instructed to stare at the blue card for about 30 seconds. This is followed by a quick glance on the white paper. The same step is repeated, however. This time a yellow card is placed over the black paper. Observation by the subject is recorded after each step. The third step involved placement of the card on the white paper and observations by the subject was noted down.
Eye and Hand coordination was also carried out in the lab. The experiment tested the ability of the eye to coordinate with the right hand and consequently the left hand. The results showed that the right hand with continued repetition showed that the left had reduced time significantly than the right hand.
Auditory Senses
The human ear is complex compared to other vertebrates and mammals. The human ear consists of 3 main parts, the Outer, middle and inner ear respectively. The outer ear is different among different species. The inner ear is similar in function and structure in different species. Sound travels to the outer ear. It is then transmitted or modulated to the middle ear. After modulation, it is then received by the inner ear. The inner ear is also called as the vestibulocochlear nerve. The inner ear is responsible for transmission of signals to the temporal lobe of the brain.
The ear is responsible for auditory senses in the human body. The human ear can perceive sounds to a certain wavelength. The range at which the human ear can perceive sound is called the audible range. The range is calculated in terms of frequency. The audible range for the human ear is 20Hz to 20,000Hz. The audible range varies from health and age of an individual. Exposure to sound over the years will also determine the audible range. The middle ear is responsible for sound modulation and transmits select signals to the inner ear. The optimum frequency the human ear is most sensitive would be in the range of 1,000 Hz to 1,500 Hz. Studies have also revealed that human auditory perception is optimum at a frequency of 4,000 Hz.
Sound is measured in decibels (dB). The frequency at which hearing damage or permanent hearing loss is observed is termed as ‘Noise induced hearing loss.’ A frequency of over 100dB can cause auditory damage during a frequency of more than 120 dB can cause permanent hearing loss.
The device used in the evaluation of hearing loss in humans is termed as audiometer. It is mainly computerized, and patient friendly found in most ENT clinics. An audiogram is a graph upon analysis of the hearing frequencies of an individual. (National Institutes of Health, NIH Curriculum series)
References
Hudspeth AJ and Logothetis NK. Sensory systems. Curr Opin Neurobiol. 2000 Oct;10(5):631-41. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/11084326
Breer H, Fleischer J and Strotmann J. The sense of smell: multiple olfactory subsystems. Cell Mol Life Sci. 2006 Jul;63(13):1465-75. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/16732429
Rabinerson D, Horovitz E and Beloosesky Y. [The sense of taste]. Harefuah. 2006 Aug;145(8):601-5, 629. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/16983846
Gordon N. Color blindness. Public Health. 1998 Mar; 112(2):81-4. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/9581449
Earl L. Smith, Chea-su Kee, Ramkumar Ramamirtham,Ying Qiao-Grider, and Li-Fang Hung. Peripheral Vision Can Influence Eye Growth and Refractive Development in Infant Monkeys. Invest Ophthalmol Vis Sci. 2005 November; 46(11): 3965–3972. Retrieved from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1762100/#__ffn_sectitle
Information about Hearing, Communication, and Understanding. National Institutes of Health (US); Biological Sciences Curriculum Study. Bethesda (MD): National Institutes of Health (US); 2007. Retrieved from: http://www.ncbi.nlm.nih.gov/books/NBK20366/
