Laboratory Report on 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, hearing, smell and taste is controlled by the nervous system Colborn, M. (2004).

This lab exercise is designed to illustrate some of the senses that humans use to respond to their environment. Sensory receptors range from simple free nerve endings (such as those that detect pain) to the vastly complex receptors like the eye and ear. An animal’s survival relies on its ability to detect and respond to stimuli in their environment. Vertebrates such as mammals possess a highly developed and specialized set of sense organs to detect changes in light, sound, temperature, pressure and an assortment of chemical stimuli Rhine, J. B. (1934).

This sensory and perception process begins when the presence of a stimulus activates sensory receptors. The sensory receptors transform the stimulus to a nerve impulse which is transmitted to the central nervous system, then to effectors and concludes with an appropriate response. It is important to note the difference between sensors and sensations. A sensor is a receptor that changes the form of the stimulus energy into the energy of a nerve impulse. A sensation is being consciously aware (e.g. pain) that receptor(s) have been stimulated Rhine, J. B. (1934).

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)


Taste and Smell Sensitivity

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)

Foods and substances in the environment are viewed as good to eat (pleasant taste or smell) or unpalatable (bad tasting) depending upon how taste receptors on the tongue and olfactory (smell/scent) receptors in the nasal passages respond. Only molecules and ions which dissolve in mucus or salivary secretions are capable of stimulating taste and odor receptors. Certain regions of the tongue are more or less sensitive to different flavors.

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 oftaste 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 senses of taste in humans are due to the presence of taste receptors. The sense of taste in 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 oesophagus. The tongue itself consists of different nerves that help in the sense of taste. They are primarily known asvagus nerve, glossopharyngeal nerve, and the facial nerve. These play an important role in chemoreception. (Kapsimali M and Barlow LA. 2013)

Purpose of the Experiment

The aim of the experiment was aimed at testing the levels of smell and taste sensitivity in an individual. The experiment would also enable one to detect the phenomenon of chemoreception, i.e. the sense of smell along with the sense of taste.

Procedure, Materials and Experiment

Taste or ‘gustatory’ receptors are a special type of chemoreceptor distributed over the surface of the tongue and adjacent portions of the larynx and pharynx. The receptors reside in structures called taste buds which are located in the epithelium along the sides of the papillae or bumps on the tongue. Taste sensitivity differs significantly among individuals; individuals vary in the number of taste receptors they have and in the sensitivity of these receptors to certain chemicals. Taste sensitivity has a hereditary component.


Raw onion, apple and potato


Raw onion, apple and potato were used to carry out the experiment of 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 was to be placed on the tongue and made to identify. The next step was to conduct the same steps, although at this time nostrils were to be kept open. This step would enable to detect the phenomenon of chemoreception. It meant detecting an individual’s sense of smell with taste.

Observation and Results

Table 1: Results showing fruits and vegetables that could be detected with eyes and nostrils closed or opened

Fruit or VegetableEyes and nostrils closedEyes closed and nostrils opened

It was observed that he sense of smell and taste of the onion was easily detected because of the gases it releases, therefore sending the messages to the brain, and because onions as well as other foods are common to us since we consume them all the time, it is possible for the brain receptors o identify the smell and taste before or after we have put the foods in our mouths. The sweetness and crunchiness of the apple could be detected

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.

As one ages, the elasticity of the lens decreases as a result of protein denaturation in the lens. This condition is called presbyopia. This is the reason why most people over the age of 45-50 require reading glasses. A measure of elasticity can be made by determining the closest distance you can focus on a printed letter with each eye (Wolfe et al 1995)

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.

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 colours 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. et al, 2005)

Color Blindness

The perception of color is a sensation achieved partly by the retina and partly by the brain. The receptors of the retina that are sensitive to color are the cones. According to the Young-Helmholtz theory of color perception, there are three different types of cones, each of which responds maximally, to a different color.

The three colors that trigger maximum stimulation of these cones are red, blue, and green. The degree of stimulation that each type of cone gets from a particular wavelength of light determines what color is perceived by the brain. For example, when the retina is exposed to red monochromatic light (wavelength of 610 nanometers), the red cones are stimulated at 75%, the green cones at 13%, and the blue cones, not at all.

The ratio of stimulation for red is thus 75:13:0. When the brain receives this ratio of stimulation from the three types of cones, the interpretation is for red color. When exposed to white light, which is a mixture of all colors of the spectrum, the three types of cones are stimulated equally.

Color blindness is a sex-linked hereditary condition which affects 8% of the male population and 0.5% of females. The most common type is red-green colour blindness, in which either the red or green cones are lacking. If red cones are lacking, a condition called protanopia exists. Individuals that have this condition see blue-greens and purplish-tinted reds as gray.

A lack of green cones is designated as deuteranopia. Although both protanopes and deuteranopes have difficulty differentiating reds and greens, their visual spectrums differ enough so that they can be diagnosed with color test charts. (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 refers to a phenomenon when 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 appearance of Positive after images has 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 and Procedure

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 using Ishiara chart. The chart is used for detecting color blindness. It was devised by Dr. ShinobuIshiara. 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.


Ishihara’s book of plates (Ishihara’s Tests for Colour Blindness, Concise Edition)


  • Have your partner hold the test plates about 1 meter from you. Start with plate #1 and proceed consecutively through plates 1 – 17.
  • You should respond within 3 seconds as to what you see on each plate.
  • Record your responses
  • After all plates have been observed and recorded; compare your responses with the correct answers on the separate documents associated with each set of plates.
  • Determine your color vision status


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.

A newspaper article is kept in front of the individual at arm’s length. With 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.

Two papers, black and white 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 were 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.

Table 2 Eye and Right Hand Coordination

Eye and Left Hand Coordination
Time StartTime endAgeGender


Table 3 Eye and Left Hand Coordination

Eye and Left Hand Coordination
Time StartTime endAgeGender



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 vestibule cochlear 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 to1, 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)


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