SENSATION AND PERCEPTION - PSY336 Flashcards
Sensation
Sensation is the process by which the sense organs gather information from the environment. This happens when sensory receptors of any if the sense organs are stimulated by stimuli gathered from the environment and is then transmitted to the central nervous system, the spinal cord and the brain.
E.g: Light to Images, Sound to voices, Gales to odor etc
Sensory Processing
The stimulation of the senses happens automatically. The first step of this process starts at the receptor cells. Stimulus (e.g., light) excites the receptor cells of the senses (e.g., rods and cones of the eye or taste buds of the tongue etc) and the energy is then transformed into neural impulses or action potential in a process called transduction, the second stage of sensation. These are them sent via neural pathways to the various parts of the brain that processes them into light, shapes, sound, smell, taste or touch. I summary, information captured by the sense organs (reception) in physical form is converted into electrical impulse by receptor cells which makes it possible for it to flow through the nerves to the brain.
Perception
While sensation takes in information from the physical environment, perception helps us make sense of the information received. It is a process of selecting, organizing, transmitting and interpreting sensory inputs.
Concepts and Terminologies
• Stimulus Coding: This refers to how the sense organs interpret different information. Environmental Stimuli come in several forms, e.g., light rays, loud noise, etc. Stimulus coding is the several ways the system detects and identifies each Stimuli from the other. Some ways Stimuli is decoded include;
- Intensity or Quality: This refers to the loudness, brightness or largness of the Stimulus. It is basically about the strength of the Stimulus. E.g., Bright light at night(car headlamp)
- Spatial Localization: This involves the direction or location of the Stimulus, where the Stimulus is perceived to be or coming from. E.g the bright light is coming from the main gate area
- Relative Temporal Order: The order in which the Stimulus arrives. E.g., Perceived bright light (car headlamp) then a loud hunk (car horn)
- Acuity: Sharpness of the Stimulus: you can tell its a car from the Sharpness of the light, and you can tell it’s a car horn from the Sharpness of the noise.
- Quality: the smoothness or fineness of the Stimulus: the ability to differentiate a car horn from any other sound
- Duration of the Stimulus…
Concepts and terminologies
• Transduction: This refers to the conversion of physical stimulus to neural impulses or action potentials.
• Sensory Reduction: This is the ability of the Sensory system to focus on some sensations while disregarding the others. It’s the process of filtering information before sending it to the brain.
• Absolute Threshold: The minimum amount of stimulation necessary to produce a sensation. It is the weakest amount of stimulus that can be distinguished from no Stimuli at all. It is also the physical or psychological limit below which an individual will not respond to stimulation.
• Difference Threshold: Referes to the minimum degree of Difference between two Stimuli before they are perceived as different.
• Perceptual Difference: This is the ability to resist or prevent unwanted Stimuli from taking our attention, that is, we pay attention or are sensitive to certain stimulation and disregard others. Perceptual Difference is the intensity or volume at which a particular sensation becomes perceivable.
Signal Detection Theory
Sensitively to Stimuli does not always rely on physical intensity of the Stimuli and the observers sensory ability, but also on factors such as individual differences and environmental Stimuli. For example, if you’re in a room with a cultists and a gunshot is heard nearby, you may be startled, but it may not affect the cultists (because of the kind of person they are) or you’re walking on a street you’re familiar with and there’s the sound of rustling of leaves. This sound will only register as background noise. But if you’re in an environment you’re not familiar with, same noise would catch your attention. The theory has to do with awareness. The detection of a stimulus depends on both the intensity of the stimulus and the physical/psychological state of the individual. Basically, we notice things based on how strong they are and on how much we’re paying attention.
The Chemical Senses
Olfactory and Gustatory: Both stimulated by chemicals and work simultaneously because of the closeness between the nasal cavity and the mouth. However, they travel through different pathways to the brain, one interpreting smell/odor (Olfactory) and the other interpreting taste (gustatory). Olfactory is a stronger sense than gustatory, hence Olfactory sensations can sometimes cloud gustatory sensations. For example, if we have stuffed nose or a cold, food can become tasteless in the mouth or may taste a bit different than usual.
Olfactory Stimuli
Olfaction is the sense of smell, the detection and recorgnition of chemicals that contact the membranes inside the nose. The assessory organ is the nose and the physical stimulu are volatile chemical substances that can evaporate and are in the air. When in contact with the nose, it is dissolved in the fluid - the mucous in the nose.
• Structure: The nasal cavity is divided into two by a cartilage called septum that separates the nostrils which is the major route for passage of air. The roof of the nose is formed by the cripriform plate and the Sphenoid bone, also the frontal bone and the nasal bone. The floor is formed by the roof of the mouth. The nose is lined by a ciliated mucous membrane called the epithelium which contains mucous secreting goblet cells.
• Neurons: Neurons responsible for smell are the olfactory cells lining the olfactory epithelium in the rare of the nasal passages.
• Receptors: The receptors of olfactory stimulations are found in the cilia (hair like structures) which contain olfactory cells that have specialized cilia extensions (thread-like dentrites) that extend from the cell body into the mucous surface of the nasal passage. They have a short lifespan of about 30-60 days, they die off and a constantly regenerated.
Stimulation: When stimulated, the receptor axons carry impulse to the olfactory bulb where the electrochemical energy is distributed to various olfactory areas of the cerebral cortex, where there are several clusters of Neurons responding to particular types of smell (the opitofrontal cortex - where olfactory impulse are interpreted, and odor/smell percieved.
• Sensory Adaptation: The perceived strength of an odor fades to less than half of its original strength within about 4 minutes. This is the time it takes for one to “get used to a smell” and be able to stay within it.
• Importance: The olfactory sense is important because it helps in differentiating good from bad smells, appetizing from repulsive smell (in terms of food). Its also an important sense for reproduction as it arouses sexual interest or repulses it, etc.
Summary of olfactory stimulation
Gas penitrates into the nostrils, it is then devolved by mucous that allow Stimuli to be picked up by the receptors. After stimulus coding and transduction, nerve impulse is generated and from the olfactory bulb, through the olfactory track which are connected to the amygdala and the pyrifiorm cortex of the medial temporal lobe, to the orpitofrontal cortex (olfactory cortex), the brain interpretes the Stimulus and sends feedback through motor Neurons to olfactory organs or other effectors that are required for necessary action.
Theories
• Lock and Key
This theory illustrates that there are holes of different shapes on the odor receptor, an odor will be produced once the molecules producing the odor match into a hole of similar shape, i.e., the molecules serve as key, and cell receptors serve as lock.
• Chemical Substance Theory
Simply proposes that the chemicals that producing any particular odor will determine the type of odor we perceive.
• Chemical Reaction Theory
Reaction between the nasal cavity and the chemical substance determine the smell produced.
• Enzyme Theory
The secretion of certain chemicals in the olfactory tissue is negatively influenced by some enzymes and so affects the odor produced.
• Stereo Chemical Theory
Similar to the lock and key, it illustrates that there are seven primary odors that excite different receptors in the olfactory cells, each having it’s own molecular shape that fits it’s own receptors. Our perception of smell is determined by the primary odor that excites the molecules and they will fit into their receptors.
Gustatory Sense
Gustatory sensation like olfactory also involves stimulation of chemo receptors by dissolved chemicals.
• Structure: The tongue is covered with tiny bumps (papillae) across it’s surface which contain cluster of taste buds arranged on either side. Each taste buds contain several receptor cells responsible for sensation of taste.
• Receptors: Taste receptors are found in taste buds on the papillae. A papillae may contain 0 - 10 or more taste buds and each taste buds contains about 50 receptors.
• Stimulation: When we eat or whenever substances come in contact with the tongue, saliva mixes with the substance to dissolve it, allowing the receptor cells absorb the chemicals and detect taste by triggering neural impulse. These impulses travel along the glossopharyngeal (facial) and vagus nerves and into the medulla and thalamus. The final destination is the taste area in the parietal lobe of the cerebral cortex where taste is perceived.
Cross Enhancement and Cross Adaptation
Cross Adaptation: This is the effect of one adapting stimulus on the sensitivity to another one. It is common with chemical stimulants. In taste, when we have become accustomed or adapted to the taste of one substance, we become less sensitive to the same taste in other foods.
Cross Enhancement is the opposite where tasting one food can intensify certain components of another, for example, when you’ve just taken some drugs and you eat food, sometimes the food kind of taste like the drug.
Theories of Taste
Doctrine of Specific Nerve Energy (Label Line Theory)
This their assumes that there are four primary taste qualities of which all other taste sensations are mixtured. Each taste quality has its own receptor cell and cranial nerve fiber, that is, each receptor has its own line to the taste centre in the brain and the brain can tell which chemical is stimulating the tongue by the line that is active.
Across Fibre Pattern Theory
There are no primaries in taste quality and that each separate chemical stimulus is coded into different patterns. This suggests that each chemical stimulus has its own coding pattern. For the brain to recognize any stimulus, there is a pattern of response that must follow from the fibres.
Dual Process Theory
Basically combines both labeled lines and Across Fibre theories. It assumes that certain parts of the brain response to stimuli according to the line theory and other parts of the brain according to the across Fibre theory.
Visual Organ
• The scleratic layer: this is the outermost part of the eye that firms the white of the eye
- Function: Gives shape and firmness, protects and supports the inner eyes.
• The Cornea: On the bulge of the scleratic layer is the transparent part of the eye Called cornea.
- Function: It admits light into the eye, bends the light rays to bring them to focus of the retina, protects the eye externally.
• Conjuctina; Associated with the scleratic layer, it is the transparent membrane which line the inside of the eyelids and covers the cornea protectively.
- Serves as protective shield, it is the part that gets inflamed when the eye is infected instead of the entire eye, it also allows the passage if light into the eye.
• The Optic Nerves: They are found at the back of the scleratic layer, penetrating the chloride and the retina at a spot called the blind spot.
- The optic nerve transmits sensory impulse to and from the brain.
• The Middle Layer choroid: The choroid is highly vascularized and it consists of the blood capillaries which gives it the brownish or redish appearance.
- It provides food and oxygen to the cells of the eye, the pigments in the layer helps to absorb light rays and prevent too much reflection onto the eye.
• The Iris: This is closely associated with the chloroid layer and it also controls the amount of light passing through the eye.
• The pupil: The opening through the iris where light enters through.
- When bright light shines on the eye, muscles of the pupil contrast to become smaller (constriction) or get bigger in order to accommodate more light in darker places (dilation)
