Author Archives: Taryn Dawn Codner

Apparent Motion

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I decided to write my blog on the concept of apparent motion. Apparent motion is when we perceive motion even though there is no real motion. This was illustrated by a scientist by the name of Sigmund Exner who conducted an experiment where the participants perceived that the two sparks presented to them were actually one spark moving back and forth (Wolfe et al., 2012). However, it was actually two sparks that were just very close together and presented in rapid succession (Wolfe et al., 2012). The neurons in our motion detector system do not need actual motion to fire as evidenced by the perception of the participants in the experiment. Several things in everyday life make use of this concept. One example is TV. I watch TV every day and perceive movement on the television screen even though nothing is actually moving. To make it look like the figures on the screen are moving, there are many frames presented in a very short amount of time. As long as these images are presented at a fast enough pace, the viewer will perceive the illusion of continuous movement (Wolfe et al., 2012). For example, when I was younger I watched Bugs Bunny and he would run away from Elmer. This apparent movement was created with many (an example would be 100 frames a second) drawings presented very very quickly (Wolfe et al., 2012).This is very similar to other things that we see on everyday basis. Another example would be when I went to the movies to the Avengers. When people go to see movies and perceive movement it is very similar to the Bugs Bunny example. The only difference is that still photographs are used instead of drawings (Wolfe et al., 2012). This also the same process used for computers (Wolfe et al., 2012). Overall, apparent motion is a concept that surrounds us everywhere we look even though we may not be aware of it.

Light And Dark Adaptation

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Once when I was younger, I went to see a movie that was 4 hours long. When I was came out my eyes had to readjust just as they had to adjust when I first entered the dark theater. It took longer for my eyes to adjust to the darkness than to the light. This is a perfect example of the concept of dark and light adaptation. When I went into the movie theater my pupils dilated due to the decrease in light intensity. When I left the theater they constricted because of the increase in light intensity. In other words, the eye constricts and dilates to control the amount of light that enters the eye.

Another way the eyes adapt is that the amount of photopigments available in photoreceptors changes with the amount of light intensity.  When I left the theater, more light was entering my eye. In this situation, more photopigments are used up and fewer photopigments are available to process all of the light photons it is exposed to (Wede, 2014). When I was in the theater a smaller amount of photopigments were being used. There were more photopigments that were able to process the low intensity of light that was in the theater (Wede, 2014). When photopigments are used to process a photon, they have to regenerate before they can process more photons (Wolfe et al., 2012). As the level of light intensity increases, there are too many photons for the photopigments to handle because they are not regenerating at a pace where they can keep up with demand (Wolfe et al., 2012). However, the fact that it takes some time for the rods to regenerate actually increases how sensitive we are to situations with varying light conditions (Wolfe et al., 2012). To sum this mechanism up, when there is not much light we need all of our photoreceptors to sense the little light that is there (Wolfe et al., 2012). When there is sufficient light, we do not need all of the photoreceptors that we have so we can get rid of the ones that we do not need (Wolfe et al., 2012).

Another adaptation mechanism is the rods and cones. Rods are what allow us to see in situations where there is a low intensity of light such as in a movie theater (Wolfe et al., 2012). However, when there is a decent amount of light the level of cues the rods can pick up decreases. Cones do not perform well in situations where there is little light but they have a much broader range to process light than rods do (Wolfe et al., 2012). Cones also regenerate much quicker than rods do which is why my eyesight did not take nearly as long to recover when I left the theater than when I went in (Wolfe et al., 2012). In other words, rods and cones are in place to help us see in both dim and well lit situations.

Lastly, how the neural circuitry of the retina is wired plays a role as well. The receptive field of a ganglion cell will fire more than average as long as light on the ON center is more than the light on the OFF surround or vice versa (Wolfe et al., 2012). This helped my visual system to focus on the light and dark spots within and outside the theater that the retina sensed and not how much light was in the overall situation (Wolfe et al., 2012). This is relevant as long as the ganglion cells are completely covered with light or darkness (Wolfe et al., 2012).