Unlike a digital recorder or video camera, human memory is highly selective and is reconstructive: People add, delete, and change elements in ways that help them make sense of information and events. They often experience source misattribution, the inability to distinguish information stored during an event from information added later. Even vivid flashbulb memories tend to become less accurate or complete over time.

Because memory is so often reconstructive, it is subject to confabulation, the confusion of imagined events with actual ones. Confabulation is especially likely when people have thought, heard, or told others about the imagined event many times and thus experience imagination inflation, the image of the event contains many details, or the event is easy to imagine.

The reconstructive nature of memory also makes memory vulnerable to suggestion. Eyewitness testimony is especially vulnerable to error when the suspect's ethnicity differs from that of the witness, when leading questions are put to witnesses, or when witnesses are given misleading information.

Like adults, children often remember the essential aspects of an event accurately but can also be suggestible, especially when responding to biased interviewing by adults—when they are asked questions that blur the line between fantasy and reality, are asked leading questions, are told what “other kids” had supposedly said, and are praised for making false allegations.

The ability to remember depends in part on the type of performance called for. In tests of explicit memory (conscious recollection), recognition is usually better than recall. In tests of implicit memory, which is measured by indirect methods such as priming and the relearning method, past experiences may affect current thoughts or actions even when these experiences are not consciously remembered.

In information-processing models, memory involves the encoding, storage, and retrieval of information. The three-box model proposes three interacting systems: the sensory register, short-term memory, and long-term memory. Some cognitive scientists prefer a parallel distributed processing (PDP) or connectionist model, which represents knowledge as connections among numerous interacting processing units, distributed in a vast network and all operating in parallel.

In the three-box model, incoming sensory information makes a brief stop in the sensory register, which momentarily retains it in the form of sensory images.

Short-term memory (STM) retains new information for up to 30 seconds (unless rehearsal takes place). The capacity of STM is extremely limited but can be extended if information is organized into larger units by chunking. Early models of STM portrayed it mainly as a bin for the temporary storage of information, but many models now envision it as a part of a more general working-memory system. Working memory permits us to control attention, resist distraction, and therefore maintain information in an active, accessible state.

Long-term memory (LTM) contains an enormous amount of information that must be organized to make it manageable. Words (or the concepts they represent) are often organized by semantic categories. Research on tip-of-the-tongue (TOT) states shows that words are also indexed in terms of sound and form. Memories can take different forms, such as procedural or declarative, and within declarative memories, either semantic or episodic. The three-box model is often invoked to explain the serial-position effect in memory, but although it can explain the primacy effect, it cannot explain why a recency effect sometimes occurs after a considerable delay.

Short-term memory involves temporary changes within neurons that alter their ability to release neurotransmitters, whereas long-term memory involves lasting structural changes in neurons and synapses. Long-term potentiation, an increase in the strength of synaptic responsiveness, seems to be an important mechanism of long-term memory. Neural changes associated with long-term potentiation take time to develop, which helps explain why long-term memories require a period of consolidation.

The amygdala is involved in the formation, consolidation, and retrieval of emotional memories. Areas of the frontal lobes are especially active during short-term and working-memory tasks. The prefrontal cortex and parts of the temporal lobes are involved in the efficient encoding of words and pictures. The hippocampus plays a critical role in the formation and retrieval of long-term declarative memories. Other areas, such as the cerebellum, are crucial for the formation of procedural memories. Studies of patients with amnesia suggest that different brain systems are active during explicit and implicit memory tasks. The long-term storage of declarative memories possibly takes place in cortical areas that were active during the original perception of the information or event. The various components of a memory are probably stored at different sites, with all of these sites participating in the representation of the event as a whole.

Hormones released by the adrenal glands during stress or emotional arousal, including epinephrine and norepinephrine, enhance memory. These adrenal hormones cause the level of glucose to rise in the bloodstream, and glucose may enhance memory directly or by altering the effects of neurotransmitters.

Some kinds of information, such as material in a college course, require effortful, as opposed to automatic, encoding. Rehearsal of information keeps it in short-term memory and increases the chances of long-term retention. Elaborative rehearsal is more likely to result in transfer to long-term memory than is maintenance rehearsal, and deep processing is usually a more effective retention strategy than shallow processing. Retrieval practice is necessary if a memory is going to be consolidated, and therefore last and be available for a long time.

Forgetting can occur for several reasons. Information in sensory and short-term memory appears to decay if it does not receive further processing. New information may erase and replace old information in long-term memory. Proactive and retroactive interference may take place. Cue-dependent forgetting may occur when retrieval cues are inadequate. The most effective retrieval cues are those that were present at the time of the initial experience. A person's mental or physical state may act as a retrieval cue, evoking a state-dependent memory. We tend to remember best those events that are congruent with our current mood (mood-congruent memory).

Amnesia, the forgetting of important personal information, usually occurs because of disease or injury to the brain. Psychogenic amnesia, which involves a loss of personal identity and has psychological causes, is rare. Traumatic amnesia, which allegedly involves the forgetting of specific traumatic events for long periods of time, is highly controversial, as is repression, the psychodynamic explanation of traumatic amnesia. Because these concepts lack good empirical support, psychological scientists are skeptical about their validity and about the accuracy of “recovered memories.”

Most people cannot recall any events from earlier than the age of 2. The reasons for such childhood amnesia include the immaturity of certain brain structures, making it difficult for very young children to focus attention, encode, and remember; cognitive factors such as immature cognitive schemas, lack of linguistic skills, and lack of a self-concept; and lack of knowledge of social conventions for encoding and reporting events.