Serial memory processing

Serial memory processing is the act of attending to and processing one item at a time. This is usually contrasted against parallel memory processing, which is the act of attending to and processing all items simultaneously.

In short-term memory tasks, participants are given a set of items (e.g. letters, digits) one at a time and then, after varying periods of delay, are asked for recall of the items. As well, participants could be asked whether a specific target item was present in their original set. The serial order of items and the relationships between them can have varying effects on the item's speed and accuracy of recall.

Serial memory processing uses internal representations of the memory set in order to compare them to a target stimulus or item that is being presented. These internal representations are then compared to the target stimulus, one at a time. Reaction time increases linearly with the set size, where the more items in the memory set, the longer it will take to compare.

Serial memory processing can be either self-terminating or exhaustive. Self-terminating implies that comparisons stop abruptly as soon as the target is found, and then the response is generated. Evidence for this method is found in reaction time studies. If the reaction time slope for a positive trial (where the target was present in the memory set) is about half of the slope for a negative trial (where the target was not present in the memory set) this demonstrates self-terminating processing. This is because, on average, participants (on positive trials) will stop comparisons about halfway through when they find the target match but participants (on negative trials) will need to compare until the end when no target match is found. On the other hand, exhaustive implies that comparisons continue until the entire set is compared and then a response is generated. Evidence for this method is also found in reaction time studies. In this case, the reaction time slope is equal for both positive and negative trials, as comparisons are made to the end in both cases. Participants may process some serial memory sets using the self-terminating method and in other cases use the exhaustive method, there is no clear distinction between which method is better to use.

In serial memory processing, Primacy effect and Recency effect effects for accuracy of recall are commonly found. These effects are found for both visual and auditory stimuli in memory tasks. This means that of the many items in a memory set during serial memory processing, the first item and the last seem to be recalled faster and more accurately than the other items. These effects may exist if recall errors are due to serial position. It is theorized that items are mistaken for other items from a nearby position in the memory set (e.g. the 5th item is mistaken for the 4th item or the 6th item). Since there are more nearby serial positions to middle items in a set, there are therefore more opportunities for mixing-up items. On the other hand, there are very few serial positions nearby to the first and last position, and therefore these positions may be remembered more accurately (or mistaken less). The first and last position may be less error-prone positions and more easily recalled.

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