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Lecture to 2nd year medical students, Kulliyah of Medicine, International Islamic University, Kuantan Malaysia by Prof Omar Hasan Kasule, Sr. 23rd January 1999
OUTLINE
GENERAL CONCEPTS
Types of sensory modalities
Senses as a gift:
Senses and appreciation of Allah's signs
Senses and the environment
Relativity of sensory acuity:
Limitations of human senses:
Sensory adaptation:
VISION
Looking and seeing
Qur'anic terminology for vision
Physical and moral sight
Light as the basis for vision
Types and sources of light
Vision and beauty of the environment
Functions of the visual sense
Limitations/ deception of human vision
Blindness (‘ama)
Congenital blindness (akmah)
HEARING
Types and sources of sounds
Human hearing
Functions of hearing
Misuse of the hearing function
Limitations of human hearing
Deafness
SMELL
TASTE
PRESSURE and TOUCH (LAMS)
PAIN (ALAM):
HEAT (HAMAM)
COLD (BARD)
HUNGER (JUU)
THIRST (‘ATASH)
1.0 GENERAL CONCEPTS
TYPES OF SENSORY MODALITIES
The primary sensory modalities are: vision, hearing, balance, touch, cold, warmth, and pain. The secondary modalities are a combination of the primary ones: vibration, itching, tickling, roughness, smoothness, and wetness. There may exist other sensory modalities not yet described. The most likely candidates are in the electro-magnetic spectrum.
There is a hierarchy among senses. Sight is the most important sense. This is indicated by the finding that the optic nerve has 35% of all fibers entering or leaving the CNS. Hearing and touch come next to sight in importance. The senses of smell and taste are poorly developed in humans.
SENSES AS A GIFT:
The senses are a gift from Allah for which humans must be grateful (16:78). Humans take them for granted. It is only when the senses are impaired or absent that their importance is appreciated. The life of those with a full complement of their senses is better and more satisfying than those with impaired senses (13:16). Human life and civilization as we know them today could not have developed in the absence of a sophisticated sensory system. Humans would have no means of communication and receiving information from one another. They would not be able to receive and act on environmental stimuli. Life would be very monotonous and most boring.
Combination of senses: The Qur'an normally mentions 2 or 3 sensory modalities together, a suggestion that sensation is full experience of the environment through various sensory inputs. Perceptions by one sensory modality are affected by those of another. Hearing and balance operate together. Taste and smell also work together. In a similar way the Qur'an mentions absence of sensory modalities together for example deafness, muteness, and blindness were mentioned together (2:171). Blindness and deafness were also mentioned together (5:71, 11:24). The packaging of several sensory modalities together is understandable since the cerebral cortex will appreciate the environmental stimulus better if it receives input from more than one sensory modality.
SENSES AND APPRECIATION OF ALLAH'S SIGNS:
The universe is full of Allah's signs for humans to study and understand, ayat al llaahi fi al afaaq (2:164). The senses help humans appreciate the signs by sight (2:73, 17:1) and hearing (10:67, 16:65).
SENSES AND THE ENVIRONMENT:
Environmental sensory input: Sensation has been approached in this presentation as information input from the environment. Senses are a window to the external environment. Allah gave humans senses to be able to interact intelligently with their environment. This partly explains the long period of human growth and development. Relative to life-span, humans have the longest period of dependence on parents before reaching independent adulthood. This long period gives them an opportunity to interact with the environment through their senses, internalize, and understand its stimuli. The human brain in the first years of life requires constant environmental stimulation to develop well. The environment becomes incorporated into the human development process. A good environment will lead to a good human both in the physical and moral sense. A bad one will lead to a bad one.
Intra-uterine and childhood periods: The process of interaction with the environment starts from the intra-uterine period. Fetuses interact with the external physical environment through the maternal circulatory system. They feel and may be hear movements of their mother's body. They are soothed by the maternal heart-beat. It is possible that they may react to sounds of reciting Qur'an or the sounds of soothing music. After birth, infants receive a lot of environmental stimulation that is a necessity for their proper and full development. Children deprived of intense and early environmental stimulation have defective cognitive development.
RELATIVITY OF SENSORY ACUITY:
Allah deliberately created the senses with varying acuity in different situations. Each variation has a reason behind it. Infants can not distinguish colors very well; they live in a grayish world. At that early age they have no need to define objects clearly and often recognition of parents is based more on voice than sight. Children hear a wider range of human sounds than adults. This enables children to learn many languages fluently. As they grow the acuity for sounds outside their native language decreases with the result that adults find it difficult to learn and pronounce a new language accurately. Infants have a dull taste sensation which enables them to eat a range of nutritious food that is not tasty to adults. In adults sensory perception can be affected by their psychological and emotional state. Competing sensory inputs also affect acuity.
LIMITATIONS OF HUMAN SENSES:
Limitation to empirical world: Human senses are limited to the empirical world, alam al shahadat. Their senses can not go beyond this to the world of the unseen, alam al ghaib.
Human vs animals: Humans can not boast of having the best developed senses. Other animals are superior to humans in specific sensory modalities. Dogs hear and smell better than humans. Cats have better night vision. Snakes have a better developed vibration sensation. What distinguishes humans is their ability to process the sensory input to a very high level of sophistication and to use that sensory input in their intellectual functioning.
Environmental noise: Human senses are limited and can be deceived. The limitations are innate in humans since only Allah is perfect. However there is an additional practical reason for this. If human senses were more sensitive than they are, human social and intellectual life would be different. There would be so much sensory input and from many sources that it would be impossible for humans to process the information and take meaningful action on it. There is also so much extraneous information 'noise' in the environment that the human would be overwhelmed. Sleep will for example be impossible if a human heard all the noises by small insects around the house, the sound of moving muscles in his body, and the movement of blood in his arteries. Thus to achieve a balance the senses have innate limitations. The limitations further protect the human from unpleasant sensory input. A more acute sense of smell would pick up so many odors that life would be unpleasant.
SENSORY ADAPTATION:
It is also part of Allah's mercy that senses can be 'dulled' ie their sensitivity to a stimulus decreases if the exposure is continuous; for example a bad smell is obnoxious at the start but with time the human gets used to it and may not even be aware of its continued existence. Similarly continuous annoying sounds may become accepted as part of the background.
2.0 VISION
CONCEPTS
Looking and seeing: A distinction must be made between looking and seeing. The former is the attempt to see whereas the latter is internalizing and understanding the image looked at. Sight is involves not only the physical optical processes but also intellectual processing. Looking is a physical process involving eye muscles and the optical pathway that results in the projection of an image onto the visual cortex. Sight involves the process of perception, understanding and appreciating the image based on the physical image and previous knowledge. We learn from the Qur'an that a moral dimension is also involved in sight since different people can get different perceptions of the same visual reality depending on their moral insight. It is possible to look without seeing. The Qur'an has described this as a form of blindness which is an internal blindness, 'amy al quluub, and not that of the external eyes, amy al absaar (22:46). In most normal situations sight is preceded by looking except in situations of visual perceptions during dream, ru'uyat manamiyat (p 516 8:43, 12:4-6, 12:36, 12:43-44, 12:100, 21:5, 37:102, 37:105, 48:27, 52:32). Human imagination can form vivid images in the mind that are not due to any physical visual process.
Qur'anic terminology for vision: The Qur'an uses three terms for vision: nadhar, ru'uyat, and basar. They are used in the noun, verb, and adjective forms. They are also used interchangeably; the exact meaning can be worked out from the context. The term nadhar is used in the following verses (2:50, 2:69). The term ru'uyat is used in the following verses (2:73, 2:128). The term basar has been used in the verses: (6:46, 6:50). The term basirat refers to insight, guidance with a moral or ethical connotation and was mentioned in the following verses (6:104, 12:108).
Physical and moral sight: Seeing can be physical (basar hissi) or moral (basar ma'nawi). The Qur;'an always makes it clear what type of sight is intended. Physical seeing (6:46, 6:50) is just the projection of the image onto the visual cortex. Moral insight is perception that is superior to physical sight. It seems that moral sight helps the physical ones. A person who is rightly guided may see and internalize physical phenomena that others look at without registering.
Sight on earth and in the hereafter: Human sight on earth is limited to some physical realities. Humans can not see the angels, malaika, or the jinn. The jinn have sight on earth p 524 7:27, 8:48. Allah can not be seen on earth (2:55, 4:153). He is however omnipresent and sees everybody and everything (2:144, 9:94). Sight in the hereafter according to the Qur'an will be physical sight, ru'uyat ukhrawiyyat (2:165-167). The believers will see Allah in the hereafter (75:22-23). The unbelievers will not be allowed to see Allah (3:77, 68:42-43). The Prophet Musa (PBUH) requested to see Allah and was overwhelmed by the experience (7:143). Sight in dreams has been described in the Qur'an. This is review of images stored in the brain rather than a new physical visual experience.
Light as the basis for vision: Light is involved in the visual process (3:13, 2:17). Light is a condition for sight (2:17, 2:20).
Types and sources of light: The Qur'an has described light using the terms nur, dhaw'u, and barq. It has also described various sources of light as the sun, shams, the moon, qamar, and the stars, nujuum. Sources of light have also been described as lamps, misbah and siraaj. Light, nur, guides those who walk in the dark (6:122, 57:27). Sight in the dark is not possible in the absence of light (2:17). Light, described as dhaw'u, lights the dark leading to clarity (2:17, 2:20). Lightning, barq, is a sudden burst of light energy (2:19-20, 13:12). Lightning was described as both a source of light and also a cause of temporary blindness when too much sudden light overwhelms the visual system. The sky is decorated with lamps described as misbah (41:12, 67:5) and siraaj (25:61, 71:16). The sun is the major source of light energy (78:13, 91:1). The sun's light reflected off the moon reaches the earth as moon light, nur al qamar (10:5, 25:61). The light of the stars guides travelers (6:97, 16:16).
The eye: The Qur'an has described the eye, 'ayn, as the organ of vision (3:13, 7:116). It also has other functions such as communication and expression of emotions. The human eye is unique in having a well developed binocular vision. The visual field is the projection of the external world that is visible by the eye. Other animals may have a wider angle of vision but they can not get the richness of all they can see because of limited cerebral processing of visual information. Binocular vision is important for judging distance by detecting differences in the images from both eyes. There is fusion of images from both retinas enabling 3-dimensional observation. Eye muscles ensure co-ordination of movements of the two eye balls to ensure binocular vision.
Vision and beauty of the environment: In several verses Allah calls upon humans to use their sense of vision and their intellectual insight to see the signs of Allah in the universe. There is a diversity of shapes, colors, and movements that all testify to the power and majesty of the creator. The human body itself is a work of beauty whose marvels medical science in unraveling every day.
Functions of the visual sense: As mentioned before sight is the most important sensory input. It enables a human look for food, identify enemies, avoid obstacles on the way, and carry out the multitude of activities of daily living (ADL).
LIMITATIONS AND DECEPTION OF HUMAN VISION
Human vision is limited: (2:7, 2:17). Humans unlike other animals can not see well in the dark (2:17). Human vision can be deceived for example it can see a mirage, sarab, where no water exists (24:39, 78:20). Professional magicians can play 'visual tricks' that deceive ordinary humans (7:116). The modern cinematography industry relies on optical tricks and special effects to create visions that look very real to the untrained eye. Humans can not visually appreciate very slow or very rapid movements. The discrimination of human vision is limited. Small objects can not be seen. Very large objects can not be appreciated if there is no background against which to compare. For example a human is lost in the middle of an empty desert or in the middle of the ocean. Sight in darkness or in very bright light is difficult.
THE EYE AS A SEAT OF EMOTIONAL EXPRESSION
Sadness (huzn): Sadness is a normal human emotional state (2:139, 9:92). The eye is often the first indicator of sadness.
Crying and tears: The Qur'an has described the shedding of tears (9:82, 12:16). Tears are also an expression of emotions. They may be emotions of sadness, fear, or remembrance of Allah. The Prophet shed tears when his son Ibrahim died (KS 186). Also described are tears in salat (KS 121), when reciting Qur'an (KS 121), when remembering Allah (KS 122), and for fear of Allah (5:83, KS 122). It is also possible to pretend to cry, al tabaaki (KS 121).
Pleasure: Eyes are also described as the seat of pleasure and happiness, qurrat 'ayn (20:40, 28:13).
Eyes and expression of beauty: The Qur'an has described beauty in heaven as beauty of the eyes (37:48, 38:25).
PATHOLOGY
Blindness (‘ama): The Qur'an has discussed blindness in both its physical and moral perspectives (2:17-18, 2:171, 5:71, 6:50, 6:104, 7:64, 10:43, 11:24, 11:28, 12:84, 13:16, 17:72, 17:9, 20:102, 20:124-125, 22:46, 24:61, 25:73, 27:66, 27:81, 28:66, 30:53, 35:19, 36:66, 40:58, 41:17, 41:44, 43:40, 47:23, 48:17, 54:37, 80:2). Physical sight is not much use in the presence of moral blindness that prevents correct perception of the visual impulses. Moral blindness is clearly worse than physical blindness. Loss of sight is a great human tragedy. The eyes are referred to by the Prophet as the 2 dear ones and who loses sight and is patient will get great reward (KS 405).
Congenital blindness (akmah): p 851 3:49, 5:110
3.0 HEARING
CONCEPTS
The ear in the Qur'an (udhn): The Qur'an mentioned the ear as an organ of hearing (2:19, 5:45). Most verses about hearing are about deliberate human refusal to use the ears to hear words of wisdom.
Types and sources of sounds: Some sounds are pleasant to the ears such as singing, ghina, and recitation of the Qur'an in a good voice. The Prophet (PBUH) used to like listening to the Qur'an (KS 439). He ordered his companions to decorate the Qur'an using the voice, tazyiin al Qur'an bi al saut (KS 444). Some sounds are unpleasant such as shouting, and the sound of the donkey (31:19). It is sometimes desirable to hear loud sounds such as in adhan (KS 70) and sometimes more desirable to listen to soft sounds such as the response to the adhan (KS 71). The recitation of Qur'an in some types of salat is aloud and is soft in others. There are several sources of sound in the environment: thunder, rain, wind, sea waves, waterfalls, movements of plants and animals, human activity, human voice, and man-made sounds. It is a sign of Allah's power that a human sound in whatever language it may be, will be recognized as human by all other humans.
Human hearing: The Qur'an has used the word sam'u in the verb and noun forms to refer to human hearing (2:93, 2:104). In Qur'anic terminology listening or hearing are very akin to obedience. Refusal to hear is associated with disobedience. Humans start hearing even in the uterus. It is recommended to make adhan into the ear of the new born because they hear and retain it (KS 71).
Functions of hearing: The sense of hearing is related to the intellect, communication, and self-protection. The Qur'an in many verses has mentioned hearing with intellect at the same time (2:7, 2:171). The relation between hearing and intellect should not be difficult to appreciate. Humans have the most developed intellectual and communication functions. Human communication uses words to describe very complex and sophisticated sometimes abstract concepts. Thus humans must hear words to be able to communicate ideas and concepts. This is in addition to hearing other aural sensory inputs from the environment. In comparison to vision, the sensory input from hearing is of a higher quality because it is human language. Ability to hear and process language places humans far and above other animals and enables them to build social relations and a civilization in which there is inter-generation transmission of knowledge and experiences.
Other types of hearing: Hearing is not confined to humans. Allah hears (3:181, 20:46). The jinn can hear (15:18, 26:212). Other members of the animal and plant kingdoms also have varying abilities to hear and react to sound. Inanimate objects do not hear. Idols that have been worshipped by humans in many societies and in all ages are not living and can not hear (19:42, 26:72). The dead do not hear (27:80, 30:52) except in special circumstances for example the Prophet addressed the dead at Badr (KS p. 114) and said that they heard him. Ordinary humans can not hear the dead but the Prophet is reported to have heard noises from the grave.
Misuse of the hearing function (ta'atil al samau): The Qur'an has dealt at length with metaphorical deafness (6:25, 17:46). Humans can deliberately refuse to listen to the truth or Allah may close their ears to the truth because of the evil in their hearts (2:7, 6:36, 7:100). Deliberate refusal to listen has been likened to the Qur'an to putting wax in the ears (17:46). The Qur'an describes the people of Nuh as putting their fingures to block their ears from hearing the truth.
LIMITATIONS OF HUMAN HEARING
Limitation of human hearing: Human hearing is not the most sensitive in the animal kingdom. Humans have a narrow range of frequencies that they can hear. Very loud or very soft sounds can not be heard.
PATHOLOGY
Deafness: The Qur'an has described both physical deafness, samam, and metaphorical deafness, ta’atil al sam’u (2:7, 2:18). The distinction between the two forms is not major because the end-result is the same, non-communication of vital messages of truth.
4.0 CHEMICAL SENSATION
THE NOSE AND SMELLING (olfaction)
The nose in the Qur'an: The Qur'an mentioned the nose but did not refer to its olfactory function (5:45, 68:16).
Types and sources of odors. The Qur'anic term for odour is raihat. The Qur'an reports the prophet Yaqub smelling the odor of his approaching son, Yusuf (12:94). Odors may be pleasant or unpleasant. Musk, misk, has been mentioned in the Qur'an (83:26) and hadith (Muslim #5578) as a pleasant odor. The Prophet enjoyed the smell of perfumes (KS 479). The odor of raw garlic, thum, is unpleasant and the Prophet forbade those who had eaten it from the mosque (KS 119). The oral odor of the fasting person is unpleasant to humans but is most pleasant to Allah (KS p. 325). Perfumes were used and were recommended by the Prophet. They suppress unpleasant odors. Perfume was recommended for pubic places (MB# 493) because they are likely to be a source of obnoxious odors. Perfumes also make the atmosphere smell well thus creating a feeling of pleasure. This facilitates social intercourse.
Smell and gender: There is a relation between smell and sex in animals. Pheromones act chemical sexual attractants in animals. Animals can smell out their mates. Existence of pheromones in humans has not been proved. Human females have better smell than males. This smell is more acute during ovulation.
Human vs animal smell: Humans are micro-osmic with small olfactory lobes. Animals are macro-osmic with relatively large olfactory lobes. Humans can distinguish among 2000-4000 different odors; however they have poor ability to distinguish intensity of smells. Dogs have better developed smell that is used by the police and hunters.
Functions of smell: The smell of food raises appetite. It also stimulates salivary and stomach secretion in preparation for digestion of food. The sense of smell as a means of self-protection is limited in humans because they generally can not smell out enemies. Humans have learned to associate some smells with dangerous substances that have to be avoided. For example the smell of rotten food warns humans not to eat it.
TASTE
Taste in the Qur'an: The Qur'an concentrates on the tongue, lisaan, as an organ of talking and not tasting. The term taste, dhawq, has been used to refer to Adam tasting the forbidden tree (7:22) or the tasting of punishment by those condemned to hell (38:57, 78:24).
Functions of taste: The sense of taste like that of smell helps in provoking appetite and preparation for digestion. Dangerous substances can be smelled out and can be avoided.
5.0 SURFACE SENSORY SYSTEM
PRESSURE and TOUCH (LAMS)
Touch in the Qur'an: The Qur'an has mentioned touch in some verses using the words lams or mass (p 382 4:34, 5:6). The mushaf for example should not be touched by those who are ritually impure (56:79). In all these verses touch is understood to mean handling things and not as a sensory modality.
The human hand: The hand is a sense organ. It can help explore and define size, shape, and texture of many objects. The hand can be said to be the basis of human civilization. The human hand is able to manipulate objects and make tools. Its fine movements are helped by its great tactile sensitivity. The Qur'an dealt with the hand not as a sense organ but as an organ of actions that may be good of bad (2:79, 5:28, 7;195).
Functions of the touch sensation: Touch provides humans with the ability to appreciate physical properties of solid materials. It can also help in avoiding obstacles for those not able to see them.
PAIN (ALAM):
Pain, alam or wajau, in the Qur'an: The Qur'an describes the sensation of pain in the context of the suffering of those being punished on earth (4:104, 8:32) and in the hereafter.
Types and sources of pain: Pain is a response to some insult to the body. The insult may be mechanical, chemical, thermal, or inflammatory injury. Some types of headache are pain with a psycho-genic basis. Pain can be described as different qualities and intensities.
Functions of the pain sensation: Pain is protective. The feeling of pain warns the person of an injury so that measures can be taken to prevent further injury or mitigate the effects of the injury.
HEAT (HAMAM)
Heat in the Qur'an: The Qur'an discusses heat mostly in the context of punishment in hell (6:70, 9:35, 9:81). Heat is also discussed in the context of the discomfort of hot days (15:2, 15:28, 15:33) or protection from the hot sun (16:81). The heat of the day and fever are considered as blows from the heat of hell indicating that heat energy on earth is the same type of heat that will be in hell but in a milder form.
COLD (BARD)
Cold in the Qur'an: The Qur'an treats cold as the opposite of hot. In an example of direct divine intervention to change the causal relations, sunan al llaah fi al kawn, Allah made the fire cold for Ibrahim (21:69). The Qur'an describes rain as cold showers from clouds (24:43). The Qur'an also describes cold drinking water ( 38:42, 76:13). The drink of those punished in hell will not be cold (56:44, 78:24).
6.0 OTHER SENSORY MODALITIES
HUNGER (JUU)
Physiological hunger: Hunger can be defined physiologically, psychologically, and morally. Physiological hunger occurs when the level of glucose and other essential metabolites in he serum are low triggering a response by the hunger center. The sensation of hunger occurs a long time before the level of nutrients reaches danger levels. Thus hunger is a warning mechanism that Allah gave humans and other animals to start looking for food before all nutrients are exhausted. Hunger is associated with stomach and abdominal discomfort or pain. The Prophet experienced pangs of hunger. Abu Hurairah did also agonize with hunger (MB # 1887). Hunger may be quantitative due to absolute inadequate dietary intake or may be qualitative due to missing essential nutrients.
Psychological hunger: The psychological feeling of hunger has no direct relationship with the actual state of nutrients in the body. People used to taking meals at a certain time of the day may start feeling hungry when that time approaches.
Moral hunger: When a human is so consumed with pursuit of material pleasures and food, they will always feel in need of food irrespective of their physiological state. There is loss of control over appetite that results in over nutrition and the attendant diseases of obesity, coronary heart disease, and cancer.
General hunger & Specific hunger: a person may feel hungry overall or they may have hunger for a specific food item.
Qur’anic description of hunger: Hunger is a test for humans (2:155). Hunger can be a punishment from Allah (16:11). There will be no hunger in jannat (20:118). The food of the dwellers of hell does not cure or satisfy hunger (88:7). Feeding the hungry is a noble act (90:14). It is Allah who feeds the hungry (106:4).
Functions of hunger sensation: The sensation of hunger is essentially a warning to the person to replenish food stocks. It does not indicate immediate danger or pathology.
Control of appetite: The Prophet recommended eating little food (MB # 1893 p 915). A person should not eat to fill the stomach/complete satisfaction (MB # 1889 p 915).
THIRST (‘ATASH)
Definition of thirst: The various definitions of hunger mentioned above also apply to thirst.
Qur’anic description of thirst: The Qur'an uses the term dhama'u to refer to thirst (9:120, 20:119, 24:39). Water is an essential for life. The Qur'an described the drink of the dwellers of jannat as good (p 619-620 2:60, 2:249, 2:259,).
Functions of thirst sensation: Thirst is a warning to start looking for water. It does not indicate immediate danger.