Exam 5: Sensation and Perception

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Difference thresholds, also known as just noticeable differences (JND), are determined through psychophysical experiments that measure the smallest detectable difference between two stimuli. These experiments involve presenting participants with two stimuli and asking them to indicate whether they perceive a difference between the two. By systematically varying the difference between the stimuli, researchers can determine the threshold at which participants can reliably detect a change.

Weber's law is a fundamental principle in psychophysics that describes the relationship between the magnitude of a physical stimulus and the perception of change in that stimulus. According to Weber's law, the just noticeable difference between two stimuli is a constant proportion of the original stimulus magnitude. In other words, the JND is not a fixed amount, but rather a constant fraction or percentage of the original stimulus.

For example, if you have a 10-pound weight and you can reliably detect a difference when an additional 1 pound is added, according to Weber's law, you should also be able to detect a difference when an additional 2 pounds is added to a 20-pound weight. This is because the ratio of the added weight to the original weight is the same in both cases.

Another example is in the perception of brightness. If you are in a dimly lit room and someone turns on a 100-watt light bulb, you will perceive a significant increase in brightness. However, if you are in a brightly lit room and the same 100-watt light bulb is turned on, you may not perceive as much of a difference in brightness. This is because the increase in brightness is a smaller proportion of the overall brightness in the second scenario, in line with Weber's law.

Overall, Weber's law provides a framework for understanding how our perception of differences in stimuli is related to the magnitude of those stimuli. It has important implications for fields such as marketing, where understanding how consumers perceive differences in product attributes can inform product design and pricing strategies.

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The trichromatic theory of color vision, also known as the Young-Helmholtz theory, suggests that there are three types of cones in the retina, each sensitive to a different range of wavelengths. These cones are sensitive to short (blue), medium (green), and long (red) wavelengths of light. According to this theory, all colors can be created by combining different levels of stimulation of these three types of cones.

On the other hand, the opponent-process theory of color vision proposes that there are three pairs of color receptors: red-green, blue-yellow, and black-white. This theory suggests that the perception of color is based on the output of these opponent processes, where the perception of one color inhibits the perception of its opponent color. For example, if the red receptors are stimulated, the green receptors are inhibited, and vice versa.

There is evidence to support both of these theories. The trichromatic theory is supported by the discovery of the three types of cones in the retina, as well as the ability to create all colors by combining different levels of stimulation of these cones. Additionally, color blindness, which is the inability to perceive certain colors, can be explained by deficiencies in one or more types of cones.

The opponent-process theory is supported by the observation of afterimages, where staring at a color for an extended period of time can result in the perception of its opponent color when looking away. Additionally, the existence of color constancy, where an object appears to be the same color under different lighting conditions, can be explained by the opponent-process theory.

In conclusion, both the trichromatic and opponent-process theories of color vision have evidence to support their key elements. The trichromatic theory is supported by the existence of three types of cones in the retina and the ability to create all colors by combining their stimulation, while the opponent-process theory is supported by the observation of afterimages and color constancy. These theories provide valuable insights into how we perceive and process color.