Encoding refers to the process of transforming thoughts, feelings, or perceptions into enduring mental structures in long-term memory. Long-term memory stores information and experiences for periods ranging from minutes to a lifetime. It is divided into two broad subtypes: explicit memory and implicit memory. Explicit memory (also called declarative memory) is stored information that can be consciously retrieved. Explicit memory involves "knowing that." Explicit memory for facts is called semantic memory, in which a network of associated concepts makes up a person's knowledge of the world. Explicit memory for personal experiences is called episodic memory, which stores the collection of personal experiences. For example, remembering the results of a presidential election or the contents of last night's dinner would be semantic memory. Remembering how you felt about those events would be episodic memory.Implicit memory refers to memory for behaviors people learn and retrieve without conscious awareness. People do not need to intentionally recall these memories to perform the behaviors. For example, in one study, people were shown line drawings of everyday objects. A short time later, they were shown fragmented line drawings with pieces missing. Some were based on the original drawings, and others were of new objects. The missing pieces made it difficult to figure out what the objects were, but people were better at identifying fragmented drawings of the objects they'd seen before than of new objects. The same participants were shown the fragmented drawings 17 years later. These participants claimed no memory for the objects shown in the experiment. Some people didn't even remember participating in the experiment. However, people were still better at identifying fragmented drawings of objects they had originally studied. This demonstrates implicit memory. There are two categories of implicit memory: procedural memory and priming. Procedural memory involves the acquisition of skills, or "knowing how." Procedural memory includes knowing how to ride a bicycle, drive a car, or play piano. It is difficult to explain how to ride a bicycle because most of the skill takes place automatically outside of awareness. Well-practiced tasks such as these can be performed with relatively little conscious attention. Priming refers to a nonconscious memory effect in which exposure to a cue influences the activation or recall of words, objects, or ideas. For example, people exposed to the word yellow and then asked to name a fruit are more likely to say banana than orange or apple. This occurs because the word yellow activates the memory of words and objects associated with that color.
Long-Term and Short-Term Memory
Explicit memories, or stored facts and experiences, are remarkably fragile. Creating them typically requires effortful processing strategies. One strategy is maintenance rehearsal, the process of keeping information active in short-term memory through mental repetition. For example, most people can remember a seven-digit telephone number for a few seconds if they keep repeating it. However, they forget the number as soon as they stop repeating it to themselves. Elaborative rehearsal (sometimes called semantic encoding) is the process of actively enhancing stored information with related information. For example, people remember the name of a new acquaintance more easily if they relate the name to a physical or personality trait of the person. People asked to pay attention to word meanings memorize words more easily than people asked to pay attention to the type fonts of words. Deep understanding and a rich web of connections makes information easier to remember. Visual imagery encoding is the process of storing new information by converting it to mental images, such as remembering the word flower by visualizing a red rose.
Chunking involves combining small pieces of information to form larger units. Short-term memory can hold about five to nine units of information. Chunking stretches this limit to accommodate more information. For example, strings of numbers ("03251967") can be better remembered if they are interpreted as dates ("03-25-1967"). People use chunking to remember phone numbers, Social Security numbers, and combinations. It often occurs naturally and outside conscious awareness.A mnemonic is a technique that enhances learning and retrieval. One powerful mnemonic, called the method of loci, involves imagining items to remember as if they were in the rooms of a familiar building. People retrieve the items by mentally walking through the building and looking in each room. Chunking can also serve as a mnemonic. For example, it is difficult to simply memorize the correct order of operations for solving equations: parentheses, exponents, multiplication, division, addition, and subtraction. The order is easier to remember if the first letter of each operation (PEMDAS) is converted to a simple sentence, such as "Please Excuse My Dear Aunt Sally" or "Purple Elephants May Destroy A School." Memorizing material depends on more than just the total time spent studying that material. Distributed practice involves learning sessions spread out over time, usually with significant breaks between sessions. Massed practice involves continuous learning sessions with no rest breaks. Spreading study sessions over a semester is an example of distributed practice. Cramming for exams is an example of massed practice. Numerous studies show that distributed practice leads to longer-lasting memories than massed practice, even when students invest the same number of hours in each strategy. Distributed practice provides more opportunities for attempted memory retrieval. Multiple successful memory retrievals make people less likely to forget that memory. In addition, sleeping between study sessions helps with memory storage and studying in multiple settings makes memories easier to retrieve. Those events are more likely with distributed practice.