Chapter 6: Learning, memory and forgetting Theories of memory generally consider both the architecture of the memory system and the processes operating within that structure. Architecture refers to the way in which the memory system is organised, and process refers to the activities occurring within the memory system. Architecture or structure and process are both important, but some theorists emphasise only one in their theoretical formulations. Learning and memory involve a series of stages. Processes occurring during the presentation of the learning material are known as “encoding”. This is the first stage. As a result of encoding, some information is stored within the memory system. Thus, storage is the second stage. The third, and final, stage is retrieval, which involves recovering or extracting stored information from the memory system. We have emphasised the distinctions between architecture and process and among encoding, storage and retrieval. However, we cannot have architecture without process, or retrieval without previous encoding and storage. It is only when processes operate on the essentially passive structures of the memory system that it becomes active and of use. Architecture of memory The multi-store model is based on common features of different theories. Three types of memory store were proposed: 1. Sensory store: modality specific, brief Most information in the environment is not attended to. The iconic store (or visual store) has limited capacity and duration. Sperling’s (1960) study found that information decayed in about 0.5 seconds. The echoic store is a transient auditory store holding relatively unprocessed input. Ioannides et al. (2003) found evidence for the echoic memory lasting 5 seconds in the left hemisphere and 2 seconds in the right hemisphere. 2. Short-term store: limited capacity and fragile storage Short-term memory is very limited; for example, digit and letter spans typically have a value of 7 plus or minus 2. Miller argued that the capacity of short-term memory should be assessed by number of chunks – integrated pieces of units of information. Span is less for larger chunks. Information is lost from short-term memory through decay and interference. Berman et al. (2009) claim that new information enters short-term memory and disrupts the information already there. INTERACTIVE EXERCISE: Capacity of short-term memory INTERACTIVE EXERCISE: Duration of short-term memory 3. Long-term store: unlimited capacity over long periods Double dissociation indicates that two tasks probably involve different processing mechanisms and provides strong evidence for the distinction between short-term and long-term memory store. Patients with amnesia have impairments of long-term memory but typically have no problem with short-term memory. They typically have damage to the medial temporal lobe. Patients may also have impaired short-term memory but intact long-term memory (see, e.g., Shallice & Warrington, 1974). These patients typically have damage to the parietal and temporal lobes. Some information is attended to and processed by the short-term store. Some information is transferred from short- to long-term store. Transfer to long-term storage depends on rehearsal. While the multi-store model has proven useful in explaining memory, it is oversimplified and some of the assumptions are not correct: The short-term memory is not a gateway to long-term memory (they interact); the model does not account for implicit learning; items that are attended to can be accessed more readily than other items in short-term memory and the model exaggerates the role of rehearsal. Jonides et al. (2008) have argued that the multi-store approach should be replaced with a unitary-store model. It is proposed that amnesic patients have problems with relational memory – forming novel relations or “binding” between items and their context. This is a role played by the hippocampus. Hannula et al. (2006) showed that amnesic patients were able to form strong long-term relational memories, and this could account for their good performance on short-term memory tasks. There is evidence that activation of long-term memory plays a role in short-term memory. However, the unitary-store approach has limitations: It is oversimplified in assuming that short-term memory is only activated long-term memory. Hippocampal involvement is greater in long-term memory than short-term memory and neuroimaging studies do not support the unitary-store model. According to the multi-store theory, there are separate sensory, short-term and long-term stores. There is strong evidence to support the notion of various qualitatively different memory stores, but this approach provides a very oversimplified view. For example, multi-store theorists assumed that there are unitary short-term and long-term stores, but the reality is more complex. Alternatively, unitary-store models assume that short-term memory consists of temporary activations of long-term memory. The difficulties that amnesic patients have are explained by a problem with forming novel relations. There is some evidence for unitary-store models, but these are still oversimplifications of the structure of memory. WEBLINK: An article on techniques for memory retention Working memory Baddeley and Hitch (1974) and Baddeley (1986) replaced the concept of the short-term store with that of working memory. Baddeley (2001) described four components of working memory: Central executive: o modality-free; o limited capacity; o resembles attention; o deals with cognitively demanding tasks. Phonological loop: o holds information in speech-based form; o limited capacity. Visuo-spatial sketchpad: o storage and manipulation of spatial and visual information; o limited capacity. Episodic buffer Assumptions from this theory: If two tasks use the same component, they cannot be performed successfully together. If two tasks use separate components, it should be possible to perform them as well together as separately. In a series of dual-task studies, Robbins et al. (1996) showed that selecting chess moves involved the central executive and visuo-spatial sketchpad but not the phonological loop. Phonological loop The phonological similarity effect is good evidence for the role of the phonological loop in short-term memory tasks. Larsen et al. (2000) found that serial recall was 25% worse if a list of words was phonologically similar. RESEARCH ACTIVITY: Phonemic similarity INTERACTIVE EXERCISE: Encoding in short-term memory The word-length effect (Baddeley et al., 1975) is the finding that memory span is better for shorter words than for longer words, which have a longer articulatory duration.This suggests that capacity of the phonological loop is determined by temporal duration. According to Baddeley (1986, 1990), the phonological loop consists of: a passive phonological store concerned with speech perception; an articulatory process linked to speech production. Baddeley suggests auditory presentation of words has direct access to the phonological store, but visual presentation only has indirect access via subvocal articulation. There is support from research with patients with brain damage. Patients with damage to left inferior parietal cortex have a damaged phonological store but intact articulatory control. Patients with damage to left inferior frontal cortex have intact phonological store but damaged articulatory control. Baddeley et al. (1998) suggest that the phonological loop may be more important in learning new words than familiar ones. The capacity of the phonological loop predicts vocabulary size. Visuo-spatial sketchpad The visuo-spatial sketchpad is used in the temporary storage and manipulation of spatial and visual information. Logie (1995) argues for two components of visuo-spatial working memory: The visual cache o stores form and colour information. The inner scribe o processes spatial and movement information; o rehearses and transfers information from the visual cache to the central executive. There is experimental support for the notion of separate visual and spatial systems. Klauer and Zhao (2004) found a spatial interference task disrupted performance more on a spatial main task than a visual main task. Smith and Jonides (1997) found differences in brain activation during different visual and spatial tasks. The ventral prefrontal cortex is more activated during visual working-memory tasks and the dorsal prefrontal cortex is more activated during spatial working-memory tasks. Many tasks require both components to be used in combination. It is unclear how information from both components is combined and integrated. Central executive The central executive is the most important and versatile component of working memory. It is thought to involve the prefrontal cortex. rTMS to the dorsolateral prefrontal cortex disrupts performance on many complex cognitive tasks. Individuals with dysexecutive syndrome have problems with planning, organising, monitoring and initiating behaviour. They typically have damage within the frontal lobes. The conceptualisation of the central executive has changed over time. Originally, the central executive was viewed as being unitary. More recent proposals highlight several executive processes such as: Baddeley (1996): o Switching of retrieval plans. o Timesharing in dual-task studies. o Selective attention. o Temporary activation of long-term memory. Miyake et al. (2000): o Inhibition function – the ability to deliberately inhibit dominant, automatic or prepotent