Vision, Senses, and Motor Control Worksheet

Using the text for this course, the University Library, the Internet, and/or other resources answer the following questions. Your response to each question should be at least 250 words in length.

1. What role does experience play in object recognition and visual perception? Be sure to include a specific example from your experience.

I would say that experience is the filter through which we accomplish object recognition and visual perception, but I am afraid that would be an understatement. In many cases, the experience is the tyrannical dictator or manipulator of our perceptions. Three key elements of experience are context, schemas, and motivation (Pinel, 2007). Context gives us the ability to interpret sensory information as an integrated whole, rather than a single unit. Schemas are sequences of thinking that we use for the future prediction of the environment. Schemas are very useful to our abilities of perception. Schemas allow us to perceive and anticipate our environment in a more efficient manner. Motivation has the ability to exert a top-down influence on perception; in that motivation can lead us to perceive what we would expect to perceive, rather than what objectively exists. I have experienced the effects of motivation on visual perception many times. One time, in particular, I could have sworn that I saw a ghost in a graveyard. I was a teenager and my friends and I decided to go walking in the graveyard at night. There was a tattered shirt hanging from a cross about 30 feet away. Anyway, it looked like a ghost to us. We thought it was until we went back the next day in daylight and saw that it was just a shirt. In that case, we had expected to see a ghost in the graveyard; therefore, when we saw the shirt our perception overrode what was actually there.   

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2. How does sensation and perception affect the five senses?

Transduction is, “[t]he process of converting physical energy or stimulus information into neural impulses…” (Pinel, 2007, p.105). It is through the action of transduction that sensory receptors transform the sensation of external stimulations into neural impulses. Perception is mainly concerned with the organization and interpretation of these neural impulses. Irving Biederman’s theory of perception explains that we perceive our surroundings by breaking down objects into their subsidiary parts and then comparing those parts and context of the object to sketches stored in memory. He was, of course, applying this theory to visual perception, but it could be adapted to all five senses. We might smell a whole array of smells, hear a swarm of noises, feel a whole set of tactile sensations, but we still have the ability to differential the whole of perception into its subsidiary parts. In this way, the never-ending flow of sensational information can be organized and categorized. Beyond this, we must also interpret the organized information. Object identification entails matching a current stimulus array to past memories in order to bring meaning to the stimulus. The meaning that we place on sensations can have a manipulating effect on the sensation itself. Meaning is all of the memories, contexts, and schemas that we attach to current stimuli. It is through meaning and organization that sensations become perceptions. It is also important to note that an absolute threshold of perception does exist, below which a stimulus cannot be perceived. Below the absolute threshold, a stimulus might exist, but it cannot be perceived by our senses. An example might be a dog whistle.      

3. What are the neurological foundations of taste, touch, and smell?

The sense of taste is based on the sensations produced from molecules of soluble substances in the saliva of the mouth (Pinel, 2007). The sense of smell is also highly implicated in the sense of taste. However, in the mouth, these soluble substances penetrate taste receptions, mainly on the tongue, and stimulate neural activity. There are two neural pathways that are activated as a result of taste sensation. The first leads to the medulla, pons, and primary gustatory cortex; and results in the perception of taste. The second leads to the limbic system and produced automatic responses, such as nausea.

The sense of touch is actually a tri-layered sensation of pressure, temperature, and pain. The sense of touch acts to maintain body temperature, help in identifying objects, and to protect the body from injury. As with the perception of vision, the touch sense is organized into receptive fields. Sensory neurons of the touch sense synapse with the spinal cord, resulting in reflexive actions when stimulated. The sensation of touch is also carried up the spinal cord to the medulla and thalamus; eventually terminating in the somatosensory cortex.

The sense of smell relies on small molecules of substances suspended in the air. We use the sense of smell to detect danger, identify spoiled food, and recognize familiar odors. The absolute threshold of the olfactory sense is surprisingly low—one molecule in 50 trillion for some odors. The actual place of sensation for the olfactory sense is the olfactory epithelium, which is located in the nasal passages. From there the sensational information is transmitted through the olfactory nerve to the olfactory bulb and finally terminates in the primary olfactory cortex. It is important to note that the sense of smell is the only sense not to pass through the thalamus before the cortex.

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4. How is the human motor system organized?

The primary organ of the body implicated in the control of the human motor system is the brain (Wickens, 2005). The sections of the brain most involved with movement are the brainstem, cerebellum, basal ganglia, and the motor cortex. It is also important to note that “higher” regions of the brain control more complex behaviors; whereas, less complicated behaviors are accomplished in “lower” regions of the brain. There are two main pathways by which the motor system is controlled: the pyramidal system and the extrapyramidal system. The pyramidal system is mostly contralateral, meaning that the nerve fibers pass over to the opposite side of the body in the pyramidal decussation, and forms the corticospinal tract. The other system is the extrapyramidal system and is comprised of the reticulospinal tract, the rubrospinal tract, and the vestibulospinal tract. This system is the means by which the brainstem, basal ganglia, and cerebellum exert control over the motor system. However, the basal ganglia and cerebellum have no direct link to the spinal cord but only integrate with other areas of the motor system. It is important to note that the extrapyramidal system is entirely lateral, meaning that the nerve fibers do not pass over to the other side of the body. Also, parts of the extrapyramidal system are influenced by axons from the cerebral cortex, implying some manipulation of basic reflexes by conscious information. Additionally, some of the reflex action of the motor system is controlled entirely by the spinal cord and adjacent nuclei. For instance, the knee-jerk action is accomplished without the benefit of the corticospinal tract or the extrapyramidal system.    

References

Pinel, J.J. (2007). Basics of biopsychology. Boston, MA: Allyn & Bacon. 

Wickens, A. (2005). Foundations of biopsychology, 2e. Upper Saddle River, N.J.: Pearson Hall. 

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