Evidence through experiments questions the idea of trace decay. In an experiment by Waugh and Norman in 1965, participants were presented with a series of 16 numbers, e.g. 1, 3, 5, 6, 8, 3, etc. They were given a number from the series – this was known as the probe – and asked which number followed it. For example if the number was 6, the correct answer was 8. This procedure was known as the serial probe technique.
The numbers were presented at different speeds. If information fades away due to the passage of time, then numbers presented at a faster rate have less time to decay than numbers presented at a slower rate. If trace decay is occurring then memory should be better – more correct answers – when the information is presented fast. However, presentation rate appeared to make little difference. There was no significant relationship between the speed of presentation and the recall of correct numbers. These findings show extreme doubt of the trace decay theory of forgetting.
- Interference
This theory states that forgetting occurs because memories interfere with and disrupt each other. Old memories may disrupt new ones – this is called proactive interference, which means forward interference. New memories can also disrupt old ones, which is known as retroactive interference, meaning backwards interference.
Interference becomes more likely when memories are similar. For example, if a person changes their telephone number the old one can interfere with the new one. And consequently, this may result in the forgetting of the new number. This is an example of proactive interference; the old memory disrupts the new one. The similarity of the memories i.e. they are both telephone numbers, also makes interference more likely.
Loess conducted an experiment in 1968 where participants were presented with lists of 3 words from a particular category, e.g. animals. They were asked to count backwards for 15 seconds to prevent rehearsal, and then asked to recall the three animals. This was done 6 times with 6 different lists of animals, The first list of words was well recalled, the second was reduced to an even lower level. This is an example of proactive interference. Since all the words belong to the same semantic group they are similar and as a result interference was more likely.
The category was the changed to colours and the same procedure was followed. Recall improved immediately. Proactive interference ceased as the colours were profoundly different to the animals. However, after the first list of colours, proactive interference began again as the following lists of colours belonged to the same semantic field.
Although there are lots of experimental demonstrations of interference, real-life situations are quite rare. Support for the interference theory is based mainly on laboratory findings. Although, these experiments may have little relationship to what actually happens in everyday life. The experiments have low ecological validity.
Slamecka conducted an experiment in 1966 where participants were given a word and asked for a word they associated with it. They gave the first word which came into their minds which probably effects what would happen in an everyday situation. They were then asked to learn a new set of words which were linked to the first one. They were then asked to recall all the words they’d learnt. This should result in retroactive interference because the words belonged to the same semantic field. New learning should disrupt older memories and participants should’ve forgotten the first word they chose. They didn’t. There was no evidence of interference. This experiment suggests that when participants behave ‘normally’ and select their usual associations, interference may not occur.
Baddeley (1990) points out that it has been very difficult to demonstrate significant proactive interference outside the laboratory; one reason being that when the learning of potentially interfering material is spaced out over time, interference is greatly reduced. However in the laboratory the experime` `nt is extremely compressed in time (artificially) and so it increases the probability of interference. Experimental studies of interference have very low ecological validity.
