Storage is the process of retaining information in a memory system. There are three types of processes involved in storage: encoding, retrieval, and consolidation. Encoding is the first step and involves transforming incoming information into a form that can be stored in memory. Retrieval is the second step and involves accessing stored information and bringing it into working memory. Consolidation is the third step and involves strengthening the neural connections associated with a particular memory trace so that it can be accessed at a later time.
The capacity of human memory is believed to be virtually limitless; however, there are constraints on both the accuracy and recall of memories. The forgetting curve illustrates how quickly we forget new information if we do not consolidate it shortly after encoding. The size principle states that larger items are easier to remember than smaller items, while the spacing effect demonstrates that distributed practice leads to better retention than massed practice. Finally, level-of-processing theory suggests that deeper levels of processing lead to better retention than shallower levels of processing.
There are many different types of memory storage systems, each with its own strengths and weaknesses. Sensory Memory stores sensory input for a very short period of time (usually less than one second) before it decays or is replaced by newer input; echoic memory retains auditory input for slightly longer periods of time (up to several seconds), while iconic memory allows us to retain visual input for even longer periods (up to several minutes). Short-Term Memory (STM) has a limited capacity ( usually between 5 and 9 items) but can hold information “online” for relatively long periods of time (up to several minutes) if rehearsal occurs; working memory refers to our ability to keep track of multiple pieces of information at once and manipulate them mentally. Long-Term Memory (LTM) has an essentially unlimited capacity and can store information for years or even decades; declarative memories are facts or events that can be consciously recalled, while procedural memories refer to skills or habits that are acquired through repetition and practice but cannot be consciously recalled .
There are two main theories concerning how memories are encoded into LTM: connectionism and dual code theory . Connectionism posits that memories are encoded as patterns of interconnected neurons, while dual code theory suggests that there are separate verbaland nonverbal codes for storing memories . Research has shown support for both theories , although it is likely that both play a role in LTM encoding . The hippocampus plays an important role in consolidation , especially for declarative memories ; however , recent research has demonstratedthat some forms of learning can occur in the absenceof this structure .