This experiment didn’t really prove that trace decay existed. Participants might of guessed what they had to do or thought they knew what they had to do and therefore this would cause them to focus on what they think is the correct answer and not paying attention to everything else. In the trace decay theory you have to go on the assumption that it is a psychical basis, the trace which will decay if not rehearsed.
Peterson and Peterson did research and found that 10% of memories were lost after 18 seconds so this suggests that trace decay occurs within about 18 seconds. Reitman said that trace decay occurs when rehearsal is prevented, so the information is no longer available in the memory. These experiments supported the trace decay theory.
Decay is difficult to measure and there will always be other factors influencing forgetting and it would be impossible to isolate the traces from these factors. For example in Peterson and Peterson study where they had to recall trigrams it isn’t clear whether the trigrams have been decayed or if the numbers from the interference task have displaced the trigrams.
Displacement is another theory which try’ to explain memory in the STM. It says that you are replacing the information with newer information because the STM has a limited capacity. This theory does focus on capacity. This theory uses George Millers theory with 7 is the magic number +/- 2. So you can hold 5-9 items in your STM.
The serial probe technique could support this theory because it was found out that the participants remembered what came after the later numbers rather than the earlier numbers. This could be because the numbers came later in the sequence they had displaced the earlier numbers in the sequence. This is quite low on ecological validly though.
Shallice did an experiment which supported this theory. Participants were presented with a list of numbers and the more numbers that came after the probe number the less likely the participants would remember the probe number.
Once again like other experiments other factors may be influencing this experiment such as order effect
It was suggested that the later number displaced the earlier numbers including the probe number but it can also be because of trace decay because the earlier numbers were presented earlier in time and so this could be because they were forgotten as a result of trace decay.
Shallice recognized this and looked deeper into this. He said that although time did affect recall, the number of items following the probe number seemed to have a much greater effect so this suggests that the displacement theory provides a better explanation in forgetting in the STM.
So although these researchers have tried to prove their theories the evidence is inconclusive but the experiments suggest that these theories are possible. More research and evidence is needed. Measuring and trying to prove forgetting is hard to measure and control and many factors will influence forgetting which would be out of the experimenter’s control.
