Search Results

There have been wide-spread disagreements about the nature of short-term memory. What distinguishes it from long-term memory? Is the information in short-term memory forgotten as a function of time (memory decay)? Is it susceptible to a limit in capacity, the number of items that can be held at once? This chapter proposes that there are two mechanisms of short-term memory: the activated portion of long-term memory, and the subset of activated elements that are in the focus of attention. It is suggested that the activated portion has a time limit (as well as being susceptible to interference) whereas the focus of attention has a capacity limit. Some unresolved issues with that approach are discussed, along with the neurophysiology of short-term memory. The commonly-used term “working memory” is conceived as a combination of both short-term memory mechanisms, along with direction from central executive processes.

This chapter discusses visual short-term memory (VSTM) system. It compares VSTM system with visual long-term memory system. It then discusses the measurement of VSTM, the storage capacity of VSTM, the reasons why VSTM capacity is limited, the nature of VSTM representations, VSTM processes, and the functions of the VSTM process.

This historical chapter examines the fundamental relation between memory and attention. Information that is temporarily in or near conscious awareness is in the focus of attention, so attention and memory can be viewed as two sides of the same coin. The emerging information processing field led to the model proposed in a 1988 Psychological Bulletin article by the author, upon which the book is based. The model distinguishes between two sources of short-term memory: the currently, temporarily activated elements from long-term memory and the subset of activated elements that are in the focus of attention. Presumably, although relatively unprocessed elements of long-term memory can be automatically activated, new associations between items, and between each item and its context, may be set up only in the focus of attention. Attention is controlled partly by volition (central executive processes) and partly by changes in stimulation that recruit attention.

This chapter discusses neuropsychological disorders of visual short-term memory (VSTM) and the importance of these disorders for theories of VSTM. It emphasizes the role of VSTM not only in “bottom-up” processes (forming a memory for new material from the environment) but also in “top-down” processing, as when visual images are formed from material from long-term memory (LTM). It is argued that just as VSTM is involved when we need to remember new visual input, so visual imagery recruits VSTM, which then serves as a medium for retrieving stored visual memories. Thus, the same processes (and brain regions) that play a part in typical laboratory studies of VSTM using relatively simple visual displays may also be involved when people make judgments about the visual characteristics of objects retrieved from LTM.

This chapter reviews research examining visual memory for complex, natural environments. It is divided into two main sections. The first concerns the use of visual memory to construct online representations of natural scenes (i.e., the representation produced as one is actively viewing a scene). The second concerns longer-term scene memory stored after a scene is no longer in view.

The ability to hold visual information in mind beyond the duration of the initial sensory stimulation critically underpins many higher-level cognitive functions. In particular, visual short-term memory (VSTM) provides the perceptual continuity that is necessary for visual information to guide behavior across short temporal delays. This chapter explores how the mechanisms of attention optimize VSTM. First, it considers how top-down attention biases VSTM encoding to favor information that is most likely to be relevant to behavior. Next, it looks at more recent evidence that top-down attention can also bias representations already stored within VSTM. Flexible allocation of attention within VSTM enables the visual system to prioritize and update stored representations to accommodate changing task demands.

This chapter summarizes the various visual memory systems that are discussed in this book, focusing on the nature of the representations used by these systems, their temporal dynamics, their neutral substrates, and their functional role in visually guided behavior. It discusses the definition of visual memory. It then describes the three main subsystems of visual memory: visual sensory memory, visual short-term memory (VSTM), and long-term memory (LTM).

Working memory is an elaboration short term memory, the capacity to hold items briefly in consciousness and then repeat or identify them, and involves the important addition of mental “work”, that is, cognitive processing and its combination with “memory”. In addition, working memory is a form of declarative memory, because this sort of processing goes on in consciousness and involves relational and inferential judgments, and is accessible to explicit forms of expression. Working memory relies critically on the functions of the prefrontal cortex, which studies on humans and animals show is essential to executive functions involving holding and manipulating information in mind, and for searching for stored memories and formulating appropriate behavioral strategies.

In everyday parlance, memory is understood to be the ability to remember the mental traces of experience, of past events, and learned facts. This common view of memory is essentially based on the conscious acquisition and recall of information. Cognitive science and neuropsychology, however, have now made it imperative to broaden that definition. This chapter discusses the cortical substrate and mechanisms of memory. First, the making, organization, and retrieval of cognit, now as an item of memory, are explored. The formation of short-term memory, perceptual memory, and executive memory is considered, together with retrieval of memory. This chapter shows that memories are formed in cortical networks by associative principles and mechanisms; perceptual memory networks are hierarchically organized in posterior cortex of association; executive memory networks are hierarchically organized in frontal cortex; memory retrieval consists in the associative reactivation of its network, that is, the increased excitability and firing of its neurons; organized behavior results from the joint activation of perceptual and executive memory networks.

The chapter emphasizes a level of analysis at which subdivisions are avoided until shown to be fundamental. It helps especially in investigations of short-term memory, selective attention, and the relationship between them. Fundamental, seemingly obvious concepts actually have been questioned in the literature and so are revisited. The chapter summarizes ways in which memory and attention appear to be closely interrelated. This is important because it includes observations that could be drawn only by aggregating across previous chapters. Directions for evolution of the theoretical framework are considered. The cognitive concepts are mapped onto brain structures. Moreover, both behavioral and brain research methods are challenged to make the best use of multiple levels of analysis. In this regard, even positing a homunculus, a portion of the mind that somehow carries out volition, is useful to divide human information processing into subcategories, allowing some of them to be better understood.

Studies using animals provide unique insights into the role of the hippocampus in memory not possible through studies on humans. Efforts to model amnesia in non-human primates have shown that hippocampal damage results in selective deficits in memory, and preserved short term and working memory as well as perceptual, motor, and non-memory cognitive capacities. Further studies show that the parahippocampal cortical region surrounding the hippocampus is also critical for memory, in particular for the capacity to recognize individual stimuli over extended periods. The hippocampus is not critical for this ability, but is essential for more complex tasks requiring memory for relations among stimuli.

Visual sensory memory lasts for the duration of the response in the retina. Visual short-term memory may comprise up to 10 objects during the first second, and drops to 4 after that. Only a few items can be remembered from the scene before a saccade and carried forward to be combined with the scene seen after a saccade. What is remembered is affected by where attention is directed. Visual long-term memory may last a lifetime, and it can be divided into declarative and nondeclarative, with further subdivisions. Traces of memory are found all over the visual system, particularly in the temporal lobe for declarative memory but also in lower areas.

This chapter points to a feature of serial recall that is less commonly considered, namely that recall is better for real words than it is for nonwords, letters or digits. Performance is even better if the word list comprises a meaningful sentence. This demonstrates an important role for semantic knowledge in immediate serial recall tasks. Conversely, this chapter reports evidence from patients with verbal short-term memory deficits who nevertheless have intact language comprehension, showing that the latter skill does not depend on adequate functioning of the phonological loop. Moreover, amnesic patients appear able to retain semantic information over short periods of time, despite their severe difficulty in accessing long-term memory.

This chapter examines the outputs of the ventral visual processing stream, from the inferior temporal visual cortical areas in particular. It explains that neuronal outputs provide a distributed representation of ‘what’ object or face is being viewed, while specialized subregions, such as the cortex in the superior temporal sulcus, provide evidence about face expression and about movements of objects and people. The chapter describes how attentional bias could be implemented by the operation of short-term-memory systems, explains why short-term memory must be separate from the temporal lobe and parietal lobe perceptual systems, and proposes a theory on how these short-term-memory systems work.

Studies on the amnesic patient H.M. began the modern era of the cognitive neuroscience of memory. These studies, and other case studies, showed that damage limited to the hippocampal region results in an impairment that is selective to memory and spares other perceptual, motor, emotional, or cognitive functions. Furthermore, the amnesic deficit is selective to the permanent establishment of new declarative memories. Thus H.M. and other patients with hippocampal damage have intact short-term and working memory, and can form long-term memories that do not rely on remembering specific past events or on the flexible use of memories to solve new problems. These and other characteristics of amnesia following hippocampal damage indicate that the hippocampal memory system is essential to relational memory, the ability to associate multiple events with one other and with their spatial and temporal context, and the ability to integrate many memories into a network of knowledge.

Memory is composed of multiple dissociable systems, varying according to the length of retention interval, level of consciousness, and modality of information to be learned. Memory systems are differentially affected in amnesia, depending from localization and aetiology of brain lesions. One of the main dissociations in memory concerns the duration of storage systems. Short-term memory holds information active in the mind over limited time periods, while long-term memory stores information durably. Dissociation of these systems is common in amnesia. Amnesic patients tend to show relatively preserved short-term memory, but fail to encode information into a more durable and stable trace.