Summary

This chapter examines object-oriented bimanual coordination and reviews studies which have furthered our understanding of how the central nervous system coordinates the movement of the two hands. Each section deals with different aspects of bimanual coordination and the relevant underpinning neurobiology. First, we describe how bimanual behavior is inherently constrained by the sensorimotor system which preferentially processes and executes symmetrical movements. Second, we discuss how the dynamics of the two hands are integrated to maintain the equilibrium of bimanual performance using anticipatory mechanisms. The third section deals with handedness and how the inherent laterality of our motor system influences bimanual behavior. In the final section, we show how some of the lateral preferences may be over-ridden according to the demands of certain tasks.

Introduction

One hand affords reaching, grasping and manipulation of objects of various shapes and sizes. However, two hands dramatically increase the capacity and range of human dexterity to include larger, heavier objects and to permit greater relative motions of manipulated parts. To achieve coordinated bimanual actions, the kinematics and dynamics of each hand need to be temporally and spatially orchestrated. We consider a number of bimanual manipulative tasks, both in terms of behavioral control issues and also in terms of the underlying neuroanatomy and physiology. A key issue in object manipulation is the use of an appropriate grip force (GF) to maintain stability of the grasped object. Prior to considering bimanual coordination of grasping, we briefly review relevant work on unimanual manipulation of objects.

Summary

We describe constraints on grip points in reaching and lifting objects. Most objects afford a choice of points providing stable grip with thumb and index finger. We overview experiments showing how micro (surface texture determining friction) and macro (local shape for determining direction of the surface normal relative to interdigit force, and global shape for determining center of mass) geometric features affect precision grip. We summarize the roles of visual and haptic cues in selection of grip points and describe how planning takes account not only of the object but also the intended action in directing grasp to these points. We support our arguments with evidence taken from studies of normal and disordered motor behavior.

Introduction

In characterizing the sensorimotor control of grasping, other chapters in this book have emphasized coordination between the hand, which shapes to and grasps the object, and the arm, which moves the hand to the object and lifts both hand and object through space (Jones & Lederman, 2006; see also Chapters 1, 11–13). Generally, the object concerned has been provided with vertical and parallel sides, the grasp has been a precision grip, and the goal of the action has been to maintain a stable grip so that the object neither translates nor rotates relative to the hand.

Summary

With the invention of strain gauges, isometric finger forces such as those produced during grasping an object could be measured continuously, precisely and without major constraints to the grip. In the precision grip between thumb and index finger, elementary performance aspects such as maximum grip force, ability to maintain a constant force, fast force changes or tracking of a dynamic target have been studied. In 1984, Johansson and Westling presented their paradigm based on the measurement of grip and load forces during grasping and lifting of an object. Their studies inspired a great deal of scientific interest in this aspect of fine motor control examined in healthy subjects as well as in patients with peripheral or central nervous system diseases. Research in this field progressed by introducing other motor tasks with specific demands on the control system, such as the compensation of inertial forces during movements of grasped objects. In addition, methods improved by technical developments such as 6-degree-of-freedom force/torque sensors, autonomous measurement devices, or force matrices to measure pressure distributions at grasping surfaces. Thus, measurements of isometric grip forces during object manipulation became a widely used method in neurophysiological and clinical motor sciences.

Control of isometric grip forces

Historically, the typical way to measure the force generated by the fingers or the whole hand was via compression of springs (e.g. Du Mensil de Rochemont, 1926). In addition, objects with known weights were used to load the hand or the fingers with a defined force (Truschel, 1913).

Summary

Objective and quantitative measures to assess the severity and progression of Huntington's disease (HD) are desirable. Several studies have demonstrated quantifiable deficits in the coordination of precision grasping in patients with Huntington's disease. Correlation analysis revealed that the amount of grip force variability while holding an object was correlated to the total motor score of the Unified Huntington's Disease Rating Scale (UHDRS) in a cross-sectional study. In addition, grip force variability increased in all HD patients during a 3-year follow-up. The UHDRS total motor score did not change significantly in the same subjects. The results suggest that neurophysiological analysis of isometric grip forces may detect disease progression more sensitively than clinical rating scales. The applicability of the assessment of grip forces in clinical studies is currently tested in large multicenter studies. Possible applications of the technique as a biomarker in clinical studies in HD are discussed.

Introduction

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder with a prevalence of about 7–10 symptomatic patients per 100,000 individuals and about double the number of pre-symptomatic gene carriers (Harper, 1996). Expansion of a CAG-repeat within exon 1 of the HD gene results in the development of the HD phenotype (The Huntington's Disease Collaborative Research Group, 1993), with longer repeats associated with earlier manifestation and faster progression of disease (Andrew et al., 1993).

Summary

The development of skilled hand movements such as grasping and object manipulation is of fundamental importance to the ability to perform everyday life activities. The purpose of this chapter is to provide an overview on development of grasping and object manipulation. The first part describes developmental characteristics of prehension, i.e. reaching and grasping. The second part deals with the development of independent finger movements, which is an important prerequisite for both grip formation and object manipulation. In the third part, aspects of manipulation of unstable and stable objects are discussed. This includes discussion of the development of sensory control mechanisms, i.e. adaptation to friction and weight of the manipulated object. Finally, the concept of neuronal group selection, a concept that implies that development is the result of complex interaction between genes and environment, is described.

Introduction

Prehension (i.e. reaching and grasping) and manipulation of objects are motor skills that are fundamentally important for exploration and interaction with the environment. Although human infants can grasp from an early age, it takes several years before children are able to perform these skills in a mature pattern. The development of these skilled hand movements and underlying neural mechanisms is the focus of this chapter.

Prehension involves two main components, i.e. reaching and grasping. First, the hand has to be moved to the location of the object. Second, the grip must be adapted to size, shape, orientation and the intended use of the object (see also Chapters 1 and 12).

Summary

This chapter underlines the multifaceted nature of reach and grasp behavior by reviewing several computational models that focus on selected features of reach-to-grasp movements. An abstract meta-model is proposed that subsumes previous modeling efforts, and points towards the need to develop computational models that embrace all the facets of reaching and grasping behavior.

Introduction

Hand transport and hand (pre)shaping are basic components of primate grasping. The different views on their dependence and coordination lead to different explanations of human control of grasping. One can view these two components as being controlled independently but coordinated so as to achieve a secure grasp. The alternative view is that the hand and the arm are taken as a single limb and controlled using a single control mechanism. Needless to say, this distinction is not very sharp; but it becomes a choice to be made by a control engineer when it is necessary to actually implement a grasp controller. The experimental findings so far point towards the view that human grasping involves independent but coordinated control of the arm and the hand (see Jeannerod et al., 1998) (see also Chapter 10). However, reports against this view do exist as it has been suggested that human grasping is a generalized reaching movement that involves movement of digits so as to bring the fingers to their targets on the object surface (Smeets & Brenner, 1999, 2001). Although theoretically both control mechanisms are viable, from a computational viewpoint, the former is more likely.

Summary

Stroke results in irreversible brain damage, with the type and severity of symptoms dependent upon the location and the amount of injured brain tissue. The most common neurological impairment caused by stroke is partial weakness, called paresis, reflecting a reduced ability to voluntarily activate spinal motoneurons. In conjunction with the general reduced ability to voluntarily activate spinal motoneurons, there is often a reduced ability to selectively activate the spinal motoneuron pools, i.e. turning on some neurons while not turning on others. Together, these mechanisms result in altered movement control of many muscles, especially the contralesional hand and arm muscles used for grasping. Because of the altered muscle control, a variety of kinematic and kinetic alterations are observed during grasping in people with paresis post stroke. Impairments in grasping are related to the inability to use the hand for functional activities during daily life. In rare instances, stroke affects the posterior parietal lobe, resulting in distinct grasping deficits that are substantially different from grasping deficits seen after corticospinal system damage. Future studies investigating grasping post stroke could include the examination of both kinematic and kinetic aspects of grasping in the same subject samples, the examination of different types of grasping (e.g. palmar, precision), and the examination of different time points post stroke.

General information about stroke

Stroke is an acute neurological event that is caused by an alteration in blood flow to the brain.

Summary

Our knowledge about an object small enough to be grasped with the hand usually begins first with a visual appreciation of its size and shape. However, in the dark or when searching a deep pocket or purse, vision is impossible. Consequently a haptic exploration procedure is the only course of action and scanning an object's surface with the fingertips provides information about friction, shape, compliance, temperature and friction that is unattainable by visual inspection. This initial information is of particular importance to subsequent object manipulation and dexterous handling. Both exploratory hand movements and object manipulation make efficient use of specialized low-threshold mechanoreceptors in the skin which are selectively sensitive to both normal and tangential (shearing) forces as well as slip on the skin. This cutaneous feedback guides the exploratory movements and provides a signal of when a tactile target is encountered. These primary afferent signals are subsequently transformed by cell assemblies in the somatosensory cortex to generate central representations or internal models of the object's salient physical features. Neuronal signals encoding the internal model of shape, friction and center of mass are then relayed directly by cortico-cortical projections from the somatosensory cortex to motor cortex. The subsequent dexterous object manipulation is driven by anticipatory motor control strategies based on the internal model of the object's features which are used to direct grip forces and finger positions.

Summary

Dopaminergic medication or deep brain stimulation of the subthalamic nucleus (STN DBS) impact on many aspects of the grip–lift task in idiopathic Parkinson's disease (PD). The rate of both grip- and load-force generation were normalized by the levodopa test, whereas the maximum vertical acceleration was not improved in all studies. Other dopa-responsive factors included load preparation time, which was shortened, and maximal grip force that showed an extra increase in the test. The overflow of grip force and maximum negative load force was correlated with the intensity of levodopa-induced dyskinesias (LID) in patients affected by this symptom. Maximal negative load force and tremor were not dopa-sensitive. Subthalamic nucleus DBS exerted a dopa-like effect on most parameters of the grip–lift task except for grip force in the long-term comparison. In patients with LID the preoperative overflow of force in on-state and the severity of LID were both ameliorated by STN-DBS, although the force level did not return to normal values in all studies. A dopa-resistant action tremor of higher frequency can be seen during the grip–lift task, while the rest tremor of PD is suppressed at onset of the movement. Further therapies involve facilitation of movements with a training augmented by external cues like auditory or visual signals to overcome akinesia. The grip–lift task offers a valuable instrument to study therapeutic effects in PD.

Introduction

Dopaminergic medication or deep brain stimulation of the subthalamic nucleus impact on almost any aspect of motor deficits in idiopathic Parkinson's disease (PD).

An individual's autobiographical memory is made up of their episodic memory, memory for specific episodes of their lives, and their conceptual, generic, and schematic knowledge of their personal history: their autobiographical knowledge. In a typical act of remembering, these two types are brought together and a specific memory from one's life is recalled. These autobiographical memories are the content of the self. They locate us in sociohistorical time, they locate us in our societies and in our social groups, they define the self. In important ways, autobiographical memories allow the self to develop and at the same time they constrain what we can become. In this chapter we outline a little of what is known about the representation of autobiographical memories in the mind and how they are constructed in consciousness. With this in mind, we then turn to the function that autobiographical memories have in defining the self by making certain networks of memories that ground the self in making a specific experienced reality highly accessible.

AN INTRODUCTION TO AUTOBIOGRAPHICAL MEMORY RESEARCH

Although the formal scientific study of memory has been in existence for at least a century, since the early work of scientists such as Ebbinghaus (1885/1964), Galton (1883), and Ribot (1882), the study of autobiographical memory was neglected during much of this period as a result of the complexities associated with this type of recall.

After the attacks on the World Trade Center and Pentagon on September 11, 2001, the Princeton historian Bernard Lewis explained the thinking and behavior of Muslims to the American public in a New Yorker article (Lewis, 2001). Lewis wrote that, unlike Americans, Muslims know and care about history:

Lewis implies that Americans' (and presumably most Westerners') historical memories are not “nourished from the pulpit, by the schools, and by the media.” He further implies that Americans' historical memories are accurate, even if they do not care much about history.

In this chapter, we dispute each of these claims. Muslims are not unique in their use or abuse of history. People's memories of the histories of the national, ethnic, or religious groups to which they belong (ingroups) are often tilted in favor of their ingroups and against other groups. We present evidence that historical memories are skewed, in part, because children and adults are presented with selective and biased depictions of the past. Educators, religious leaders, politicians, and media all play an important role by influencing the knowledge available.

Culture is no explanation – that much is (or should be) obvious to all social scientists. Saying that people do this or believe that “because that's their culture” is at most a descriptive statement – telling us that the behavior or belief in question is widespread in the particular group we are considering – but it begs the question: Why are those behaviors or beliefs common in that group?

Surprisingly, this is a rather new interest in the social sciences. Chiefly responsible for this odd lack of interest was the perennial reluctance of many social scientists to consider micro-processes and their aggregation – that is, the way that individual processes and behaviors create large-scale social phenomena (Schelling, 1978). However, in the last twenty years, a new anthropology and psychology of cultural transmission has emerged, founded on the systematic study of micro-processes – the field has its theoretical foundations (Boyd & Richerson, 1985; Sperber, 1985; Tooby & Cosmides, 1992), its mathematical formalisms (McElreath & Boyd, 2007), and droves of empirical studies (see e.g., Atran, 1990; Boyer, 1994; Hirschfeld, 1996 and many others). The main thrust in most of these studies is the study of particular cognitive dispositions and their consequences for cultural transmission, a domain that Pascal Boyer surveys in the final chapter of this book.

One of the ancestors of this field is Milman Parry, who as a young classicist in the 1930s proposed an original (and to many scholars scandalous) explanation of Homeric formulae, these recurrent pairs of nouns and epithets (“rose-fingered Dawn,” “fleet-footed Achilles,” “heifer-eyed Aphrodite,” “Apollo, rouser of armies,” etc.

Almost nothing renders us human as much as our unique capacity for memory. Other animals surely have memory in biological and even social forms. They can do amazing things in flocks and herds. But no other creatures can use memory to create, to record experience, to forge self-conscious associations, to form and practice language, to know, collect, narrate, and write their pasts. We not only can know at least some of our past; we know that we can know it. Sometimes it seems that memory really is the root, the fountain of human intelligence. It is this deeply human power of memory that makes it so ubiquitous, so essential to human life, but also such a problem and such a subject of inquiry. As the Israeli philosopher Avishai Margalit has written: “Memory is knowledge from the past. It is not necessarily knowledge about the past” (Margalit, 2004). In everyday life, and in the world of scholarship (whether cognitive psychology, neuroscience, anthropology, literature, or history), all considerations of memory seem perpetually to ride on the teeter-totter of trust and distrust, up and down, with distrust carrying the most weight, and trust struggling to keep the teeter-totter moving at all. Can we believe what memory provides us? Can we afford not to?

This chapter is about the cultural memory and transmission of oral traditions, especially those that use poetics and music. The latter include many of the best studied and most stable forms of oral traditions, including children rhymes, ballads, songs, and epic poetry. Oral traditions are of interest because, unlike written traditions, they depend primarily on memory for their survival. Thus, by examining the products of long periods of oral transmission, we can learn something about the processes of memory used. Working in the other direction, by using our knowledge of memory, we can better understand how the products came into being and what their likely limitations are. Although they are often viewed only as art forms in current times, oral traditions did, and often still do, transmit valuable practical and moral information and in many forms, such as the epics sung in the Balkans, give insight into major conflicts (Foley, 1991; Havelock, 1978; Lord, 1960; Ong, 1982).

In large part, this chapter is drawn from my earlier work on oral traditions (e.g., Rubin, 1995), but here I intend to show how it provides a more general view of memory as used in the cultural transmission of information. My goal is to show that current theories of memory need to be expanded in principled and theoretically well-supported ways if they are going to be maximally useful in helping us understand individual and collective memory.