Memory allows us to encode, store and retrieve information. Encoding is the function by which information is coded in a form that allows it to be stored in memory. Storage is the function by which information is retained in memory. Retrieval is the function by which information is recollected as needed. There are several types of memory:

1. Short-term memory
   This is where accessible information is held for a short period of time.
2. Long-term memory
   This is the system where information is held for longer periods and can be accessed when needed.
3. Working memory
   This is the system in which information is held and manipulated in order to perform a task. There is overlap between short-term memory and working memory.
4. Sensory memory
   This is the temporary sensory register that allows input from the sensory modalities to be prolonged.

Sensory memory can be easily disrupted. Masking refers to reduced perception of a visual stimulus when another stimulus is presented in spatial or temporal proximity to it. The stimulus onset asynchrony refers to the time between the onset of a stimulus and the presentation of a mask. Recognition of visual stimuli increases as the time of the mask is later after the original visual stimuli. There are several modality-specific sub-stores in the sensory memory:

1. Iconic memory
   This is called the iconic store, the sensory memory store for visual stimuli. It allows visual input to be prolonged. Evidence for this store comes from Sperling’s experiment. People can, for a short time, register a large amount of information. The iconic memory rapidly fades away.
2. Echoic memory
   This is called the echoic store, the sensory memory store for auditory stimuli. It allows auditory input to be prolonged. Evidence for this comes from Darwin’s experiments and from the shadowing technique, in which people have to repeat an auditorily presented message.
3. Haptic memory
   This is the sensory memory store for stimuli sensed through touch.

Holcombe states that visual processes can be categorized into two groups:

1. Fast group
   This involves processes relating to detection of motion, depth and edges
2. Slow group
   This involves less sensitive temporal limits involved in higher-level perception, including high-level motion processing and the integration of colour. (e.g: words take longer to be perceived than motion).

Short-term memory holds information in consciousness, It provides temporary storage of active information and has a limited capacity. Atkinson introduced the modal model. It proposes that there are three memory stores, the sensory register, the short-term store and the long-term store. According to the modal model, information is first registered in the sensory store and salient information is transferred to the short-term memory store. The type of processing carried out will determine whether information will be stored in the long term memory store. There are several ways of information processing:

1. Rehearsal
   These are processes by which we can act on currently active information (e.g: repeating the item of thought to yourself).
2. Maintenance rehearsal
   Retains information in short-term memory.
3. Elaborative rehearsal
   Organizes the information so that is can be integrated into the long term memory.
4. Decay
   A process by which information is lost from the short-term memory over time.
5. Displacement
   A process by which information coming into the short term memory causes information already held there to be lost.

The assumptions of the modal model were that there are separate memory stores, processing in the short-term memory store determines the memory storage in the long-term memory and that short-term memory is a limited capacity. The digit span task is a measure of the short-term memory and tests the number of digits a person can recall. Chunking increases the capacity of short-term memory. Chunking refers to a strategy to improve memory by grouping smaller units together into a larger unit or chunk.

The recency effect refers to the tendency to recall the things of the end of a list more readily than items from the middle. Performance is also relatively good for items at the start of the list. This is called the primacy effect. The negative recency effect is the tendency to recall items at the end of a list poorer than items at the beginning of a list. The double dissociation of function refers to the contrasting patterns of deficit in two patients or patient groups which provides evidence for functionally independent systems.

Working memory is the workbench of human cognition. It is the collection of mental processes that permit information to be held temporarily in an accessible state, in service of some mental task. Working memory may have three definitions:

1. Focus of attention
2. Information that is temporarily activated in the system
   This includes information about our current goals and plans.
3. Sensory-specific multi-component storage system
   This is for short-term storage and processing of information.

In Cowan’s embedded processes model, memory within the focus of attention, the time-limited active memory (no conscious awareness) and the long-term memory form the working memory. Baddeley’s working memory model proposes three main components to working memory:

1. Central executive
   This controls and coordinates the activity of the other components.
2. Visuospatial sketchpad
   This is the temporary storage and manipulation of visual and spatial information
3. Phonological loop
   This is the temporary storage and manipulation of sound or phonological information.
4. Episodic buffer
   This is the temporary storage of information integrated from the phonological loop, the visuospatial sketchpad and long-term memory into single structures or episodes.

The phonological loop is specialized for speech-based information. It holds as many verbal items as a person can say in about two seconds. It uses an articulatory control process, which allows the maintenance of information in the store and converts visual information (e.g: written text) to a speech-based form. There is plenty of evidence for the phonological loop:

1. Word length effect
   People can store more words in the phonological loop if the words take less time to speak. This is also shown in the differences between total words in the phonological loop between languages.
2. Effects of articulatory suppression
   The ability to sub-vocally rehearse the words can be disrupted if the participant is required to do a task while learning a string of words. This is called articulatory suppression. It reduces the memory span of the phonological loop and eliminates the word length effect. It also disrupts transfer of visually presented material to the phonological loop.
3. Irrelevant speech effect
   Recall of visually presented verbal material is poorer when irrelevant speech is presented during learning because this takes up some of the memory of the phonological loop.
4. The phonological similarity effect
   The recall is poorer for an ordered list of verbal items when the items sound alike. An explanation for this is that the phonological loop uses phonological fragments within the items and confusion arises as the number of shared fragments increase.

The visuospatial sketchpad is specialized for dealing with visual and spatial information. It has the capacity of about three to four objects. A visual cache stores information relating to visual form and an inner scribe allows spatial processing. There is selective interference of visual and spatial working memory tasks.

The central executive is the workhorse and mastermind of human cognition. It is active in controlling active information. There are two types of cognitive control:

1. Automatic system of control
   This system allows us to perform routine and well-practised actions through the selection of learning habits and schemas without the need for deliberate cognitive control.
2. Attentional control system
   This can interrupt automatic processing, select an alternative schema and allow attention directed toward a goal. This is used for tasks that are not routine (e.g: driving at the opposite side of the road).

These control systems allow three levels of functioning:

1. Automatic mode
   This is for routine actions
2. An intermediate, partially automatic mode
   This allows attentional control of actions
3. Deliberate control mode
   This allows non-habitual or novel tasks.

People with damage to the prefrontal cortex or if the prefrontal cortex hasn’t been developed fully yet find it difficult to inhibit responses and switch between tasks. This can be seen in several things:

1. Capture errors
   This involves a failure to override a routine set of actions. A routine action is performed when another action is intended (e.g: when seeing the word “green” in blue letters, people with prefrontal cortex damage can’t say blue, only green).
2. Preservation
   This is the inappropriate repetition of an action (e.g: continuing with the wrong task, because of the previous task). It is difficult to switch tasks.
3. Utilization behaviour
   This refers to dysfunctional automatic reaching for and use of objects in the environment. The person that shows this behaviour fails to inhibit behaviour.

The dysexecutive syndrome refers to a range of deficits reflect problems with executive function and control and is often associated with injury to the frontal areas of the brain. The episodic buffer is a temporary storage structure of limited capacity that is controlled by the central executive and allows information from different sources to be integrated. It is an interface between the modality-specific systems of working memory and long-term memory.