Biology 202

2006 Book Commentaries

On Serendip

The most interesting points raised by the author are similar to many of those that were raised in class. One of his first experiments deals with eye movements and perception of direction. The experimental results describe the differences seen when the eyes are moved from side to side and when they are moved manually (by pushing the eyeball with a finger). These experiments are similar to those that were done in class, and our conclusions were the same: the brain/CNS is receiving many signals from the outside world, and it is by sorting through these signals that we perceive what we do. In the first experiment (where the eyes are moved on their own), the picture does not seem to move with them-that is to say, the objects in the image that we see do not seem to change position relative to ourselves when our eyes move. When moving the eyes manually (by poking them with a finger) as in the second experiment, the picture that we perceive does seem to shift, with objects moving even though we have not moved. This is due to the fact that by moving themselves, the eyes are using muscles in the head that send signals to the brain, letting it know that even though they are moving, the rest of the body is not. This allows the picture to be seen as constant rather than shifting with our gaze. When the eyes are moved manually, the same muscles are not being employed and so no signal is being sent, meaning that the only signal the brain is receiving is that both the body and the eyes are still, leaving no way for it to compensate and correct for the manual movement of the eyes. Because of this lack of ability to correct the issue, the picture will continue to move even when we realise it to be an illusion.

This lack of control is another very interesting point the author makes over and over again with his experiments. The body is very good at interpreting signals and compensating for various movements in the body which allow us to see constant images and realise when our world is moving and when we are, but it can be easily fooled. Even worse, it often cannot remedy the situation and correct for the illusion even when it realises that it is being tricked and what it sees is not real!

The author also did many experiments with pupil contraction and dilation, leading to interesting observations that we did not cover in class. For example, when a bright light is introduced into the visual field of vision of one eye, the pupil will dilate as expected. However, the pupil of the other eye will also dilate together with the eye that was stimulated. This shows that the body is often programmed to do the fewest tasks necessary to survive. The contractions/dilations of the pupils are synchronized on the assumption that when one eye is experiencing a bring light or a dark space, the other eye is as well. This halves the amount of work the CNS/brain must do in regulating two potentially different signals.

Potentially what interested me most about the book were all of the different ways that the brain could be tricked into continuing to perpetuate illusions or being rendered unable to solve its issues with perception even when it realised that something was amiss. My favourite experiment involved using small black dots on glass slides to cover the pupil. When a size of dot comparable to the size of pupil dilation in the current light was found and placed in such a position that it covered the eye/pupil, the individual would observe a slight pulsation of the dot. This pulsation was due to the contraction and dilation of the pupil attempting to recover the balance between too much and too little light that it was used to. We didn't cover much about system confusions in class, but I think we might have come to a similar conclusion: that the brain tries in vain to return to what is "normal" under abnormal conditions, and no amount of realisation that what it sees is an illusion and there is no way to return to "normal" as long as the abnormal conditions persist will stop the brain from trying.

Overall, the ideas present by the author in this book seemed to correlate very well with the ideas that were present in class. Some areas are a bit more in-depth in the book, and they help to make more sense out of some ideas covered in the course. For example, the reason behind choosing electrical impulses as the signals for transmitting information between sensory neurons and the brain: in class, we talked briefly about how all of the signals were the same (all electrical impulses) and it was up to their destinations to determine what they actually meant. If the signals were crossed we would "see thunder and hear lightning". We also said that while the system was not perfect, it seemed to work well and quickly, and nature only goes for "good enough" not perfect. Hassenstein adds that perhaps this system for transporting information was chosen because it reduces the amount of "noise" in transmission. Because all of the signals are standardized in their value and duration, every active section returns the signal to its standard state before amplifying it and sending it off to the next active section. This return to the standardized state allows for any "noise", or misreading, of the information that occurred at the previous active section to be nullified at the following active section and so prevent the "noise" from accumulating at the end of the pathway. This elimination of "noise" allows for a cleaner, clearer signal, which may help explain why biological systems use this mode for transmitting messages rather than any other.


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