Topic 2: Memory Revision Notes

Short-Term Memory (STM)

STM is a temporary memory store. Its capacity is typically described as 7 ± 2 items (Miller, 1956), meaning between 5 and 9 pieces of information. However, this can be increased by 'chunking' – grouping items into meaningful units. The duration of STM is very short, usually around 18-30 seconds, unless the information is actively rehearsed (Peterson & Peterson, 1959). Encoding in STM is primarily acoustic, relying on the sound of information.

Long-Term Memory (LTM)

LTM is a permanent memory store with an essentially unlimited capacity. Its duration can range from a few minutes to an entire lifetime. Information is primarily encoded semantically (based on meaning) in LTM, though visual and acoustic encoding also occur. The transfer of information from STM to LTM is crucial for learning and is often achieved through elaborative rehearsal, where information is linked to existing knowledge rather than just repeated.

Differences and Interplay

The key differences between STM and LTM lie in their capacity, duration, and primary encoding methods. STM acts as a 'working space' for current tasks, while LTM serves as a vast reservoir of learned knowledge and experiences. Information must pass through STM to enter LTM, highlighting their sequential relationship in some memory models. Forgetting in STM is often due to decay (information fading over time) or displacement (new information pushing out old), whereas forgetting in LTM can be due to retrieval failure (inability to access stored information) or interference.

Core Stages of Information Processing

The information processing model breaks down memory into three fundamental stages: input, processing, and output. Input refers to all sensory information received from the environment. Processing involves the transformation and manipulation of this input. Output is when processed information is retrieved and used, such as recalling facts or performing an action. This structured approach helps in understanding the flow of information through the memory system.

Key Memory Processes: Encoding, Storage, and Retrieval

Within the processing stage, three distinct subprocesses are crucial. Encoding is the initial conversion of sensory data into a mental representation that can be stored, for instance, turning visual data into an image or auditory data into sound. Storage is the retention of this encoded information over periods ranging from seconds to a lifetime. Retrieval is the operation of bringing stored information into conscious thought or reactivating it for practical application. These processes are interdependent, with effective retrieval relying on successful encoding and storage.

The Computer Analogy for Memory

A widely used analogy compares the human mind to a computer to simplify the complex ideas of the information processing model. In this analogy, input is like data entry via a keyboard or mouse. Encoding resembles converting raw data into a specific file format. Storage is equivalent to saving files on a hard drive or cloud storage. Retrieval is akin to opening a saved file or running a program. While useful, this analogy has limitations as it often oversimplifies the dynamic and emotional aspects of human memory.

Strengths and Weaknesses of the Model

A primary strength of the information processing model is its methodical and testable framework, which has facilitated extensive research into specific memory components and processes. It has led to valuable models like the Multi-Store Model. However, it is often criticised for its reductionist nature, treating human memory too mechanistically and overlooking the influence of emotion, motivation, and social context, which are vital to how humans actually remember and forget.

Structure and Process of the Multi-Store Model

The Multi-Store Model (MSM) by Atkinson and Shiffrin (1968) proposes three memory stores: the sensory register, short-term memory (STM), and long-term memory (LTM). Information from the senses enters the sensory register, which has a large capacity but very brief duration. Attending to this information moves it to STM. STM has a limited capacity (5-9 items) and a limited duration (18-30 seconds) without rehearsal. Rehearsal, particularly maintenance rehearsal, helps keep information in STM and transfers it to LTM. LTM has an unlimited capacity and duration. Retrieval brings information from LTM back to STM.

Evidence and Limitations of the MSM

Supporting evidence for the MSM includes studies on capacity (e.g., Miller, 1956 for STM, Bahrick et al., 1975 for LTM), duration (e.g., Peterson & Peterson, 1959 for STM, Bahrick et al., 1975 for LTM), and the distinction between STM and LTM (e.g., Shallice & Warrington's case study of KF). However, the model is criticised for being oversimplified, suggesting LTM and STM are unitary stores (when they are now known to have multiple components, e.g., working memory model). It also mostly focuses on maintenance rehearsal, ignoring elaborative rehearsal and deeper processing. Memory is more active and complex than proposed by the linear flow in the MSM.

Retrograde Amnesia

Retrograde amnesia is memory loss for events and information that happened before the brain injury or trauma. Symptoms include difficulty remembering personal details like who they are, where they live, or significant life events. The extent of memory loss can vary, from a few months to many years of the past. Older memories are often better preserved than more recent ones, a phenomenon known as Ribot's Law. It is often associated with damage to areas like the temporal lobes or hippocampus, which are crucial for memory consolidation and retrieval.

Anterograde Amnesia

Anterograde amnesia is the inability to form new long-term memories after the onset of amnesia. Individuals can typically remember events from before the amnesia but cannot retain new information for more than a few moments. Symptoms include repeatedly asking the same questions, failing to recognise new people despite multiple introductions, and forgetting recent conversations. This type of amnesia is strongly linked to damage to the hippocampus, a brain structure vital for transferring information from short-term to long-term memory. Famous case studies like H.M. (Henry Molaison) greatly informed our understanding of anterograde amnesia and the role of the hippocampus in memory formation.

Psychological Evidence and Research Methods

Case studies, such as the study of H.M., are a key research method for understanding amnesia. These in-depth investigations of unique individuals with brain damage provide rich qualitative data on the specific deficits and preserved abilities. For example, H.M. demonstrated severe anterograde amnesia but could learn new motor skills, suggesting different memory systems. Neuroimaging techniques like fMRI and CT scans are also used to identify the brain regions affected, providing biological evidence for the causes of amnesia. Ethical considerations in amnesia research include informed consent, especially when capacity for new learning or decision-making is impaired, and protecting the privacy and dignity of participants.

Evaluation of Amnesia Theories

Understanding amnesia informs our understanding of memory models. For instance, the distinction between short-term and long-term memory and different types of long-term memory (e.g., procedural vs. declarative) comes from studying amnesic patients. The dissociation observed in patients like H.M., who could learn new skills but not new facts, supports the idea that long-term memory is not a single, unified system. However, case studies, while rich in detail, have limitations regarding generalisability due to their unique nature. The exact brain regions and mechanisms involved in different forms of amnesia are still under investigation, highlighting the complexity of memory and brain function.