Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 06 table of contents.
Ebbinghaus, it seems, did not believe some of his own data. His forgetting curve dropped off steadily except for one period of time: between 8 and 14 hours after learning. During those six hours the curve was completely flat, showing no forgetting. Ebbinghaus wrote, "Such a relation is not credible" and rejected the data, blaming it on accidental errors in his experiment.
Why did Ebbinghaus reject some of his own data? How did Jenkins and Dallenbach explain the Ebbinghaus observation?
Jenkins and Dallenbach (1924) thought Ebbinghaus made a mistake by rejecting the idea (which he briefly considered) that sleep reduced the amount of forgetting. There was no big drop-off in retention between 8 and 14 hours because Ebbinghaus was asleep then. Jenkins and Dallenbach tested this idea with students. They taught students nonsense syllables around midnight, right before bed, or early in the morning before their classes. The results were clear. Students remembered more if they slept during the retention interval instead of attending classes.
This finding probably led students of the 1920s to make jokes about the virtues of staying in bed and skipping classes. Jenkins and Dallenbach considered their finding to be evidence for an interference theory of forgetting. They assumed the brain was resting during the night, so there was less interference, and the memory persisted. However, we now know that the brain is very active during sleep. Something else was happening during sleep to improve memory.
Why might it be a good idea for students to study right before going to sleep?
Many students report that, after intense studying right before going to bed, they spend the night dreaming about bits and pieces of the material they studied. In one experiment, subjects played the computer game Tetris. The following night they were awakened during sleep, and most reported dreaming about the images of bricks falling into place. Such "bits and pieces going through the mind" may be the subjective accompaniment of important memory-enhancing brain processes. Rather than being a blank time, sleep may be a time of helpful information processing.
What evidence suggests that rats dream about succesful maze runs?
A Nova: Science Now documentary in 2007 rallied the evidence for learning improvement during sleep. One interesting experiment involved microelectrodes implanted into the brains of rats. Each microelectrode could record from a dozen nerve cells, and the tips of the electrodes were in regions of the rat's brain that processed movements during a run through a maze. As the rat successfully navigated the maze, the neurons fired in a distinctive pattern. Later, as the rats slept, the researchers observed those same neurons firing in the same distinctive pattern. This suggested that the rats were reliving the successful run through the maze, in their dreams. Other researchers showed that memory for experimental tasks improved for all sorts of animals, even fruitflies, if the animals were allowed to sleep or rest during the night instead of being kept up and active. (Nova Science Now, July 14, 2007)
When is this advice most likely to work?
The obvious conclusion is that students should study right before going to sleep...but there is one problem with putting that advice into action. Remember that adrenaline is supposed to aid memory formation. Many people are low in adrenaline before going to sleep. Perhaps the "study before you sleep" effect is best used during final exam times or before a big test, when all distractions are put aside-or should be-and there is adrenaline due to the stress. In these conditions, the material studied before bedtime is likely to circulate in the mind all night, perhaps growing stronger in the process.
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