Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

Bartlett viewed thinking as a high level skill exhibiting ballistic properties that he called its “point of no return”. This paper explores one aspect of cognition through the use of a simple model...

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Orienting of attention

The two basic phenomena that define the problem of visual attention can be illustrated in a simple example. Consider the arrays shown in each panel of Figure 1. In a typical experiment, before the arrays were presented, subjects would be asked to report letters appearing in one color (targets, here black letters), and to disregard letters in the other color (nontargets, here white letters). The array would then be briefly flashed, and the subjects, without any opportunity for eye movements, would give their report. The display mimics our. usual cluttered visual environment: It contains one or more objects that are relevant to current behavior, along with others that are irrelevant. The first basic phenomenon is limited capacity for processing information. At any given time, only a small amount of the information available on the retina can be processed and used in the control of behavior. Subjectively, giving attention to any one target leaves less available for others. In Figure 1, the probability of reporting the target letter N is much lower with two accompa­ nying targets (Figure la) than with none (Figure Ib). The second basic phenomenon is selectivity-the ability to filter out un­ wanted information. Subjectively, one is aware of attended stimuli and largely unaware of unattended ones. Correspondingly, accuracy in identifying an attended stimulus may be independent of the number of nontargets in a display (Figure la vs Ie) (see Bundesen 1990, Duncan 1980).

Neural Mechanisms of Selective Visual Attention

: The concept of attention as central to human performance extends back to the start of experimental psychology, yet even a few years ago, it would not have been possible to outline in even a preliminary form a functional anatomy of the human attentional system. New developments in neuroscience have opened the study of higher cognition to physiological analysis, and have revealed a system of anatomical areas that appear to be basic to the selection of information for focal (conscious) processing. The importance of attention is its unique role in connecting the mental level of description of processes used in cognitive science with the anatomical level common in neuroscience. Sperry describes the central role that mental concepts play in understanding brain function. As is the case for sensory and motor systems of the brain, our knowledge of the anatomy of attention is incomplete. Nevertheless, we can now begin to identify some principles of organization that allow attention to function as a unified system for the control of mental processing. Although many of our points are still speculative and controversial, we believe they constitute a basis for more detailed studies of attention from a cognitive-neuroscience viewpoint. Perhaps even more important for furthering future studies, multiple methods of mental chronometry, brain lesions, electrophysiology, and several types of neuro-imaging have converged on common findings.

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The Attention System of the Human Brain

Attention deficit hyperactivity disorder (ADHD) comprises a deficit in behavioral inhibition. A theoretical model is constructed that links inhibition to 4 executive neuropsychological functions that appear to depend on it for their effective execution: (a) working memory, (b) self-regulation of affect-motivation-arousal, (c) internalization of speech, and (d) reconstitution (behavioral analysis and synthesis). Extended to ADHD, the model predicts that ADHD should be associated with secondary impairments in these 4 executive abilities and the motor control they afford. The author reviews evidence for each of these domains of functioning and finds it to be strongest for deficits in behavioral inhibition, working memory, regulation of motivation, and motor control in those with ADHD. Although the model is promising as a potential theory of self-control and ADHD, far more research is required to evaluate its merits and the many predictions it makes about ADHD.

/pdf/behavioral-inhibition-sustained-attention-and-executive-3s4ta68l66.pdf

Behavioral inhibition, sustained attention, and executive functions: Constructing a unifying theory of ADHD.

When interacting with objects in their environment, patients with Parkinson's disease (PD) often make hypometric movements (e.g., micrographia). The purpose of this study was to learn if patients with PD, in the absence of overt actions or environmental stimuli, have egocentric (body-centered) conceptual (representational) hypometria. Actions can take place in either proximal or distal peri-personal space. Normally, the right hemisphere has a distal and the right a proximal attentional bias. We also want to learn if a patient with onset of disease in the right hemisphere would have a greater conceptual action hypometria than individuals with left hemispheric onset. Seventeen subjects with PD and 15 age-matched controls were given a questionnaire evaluating subjective perception of personal action space. The questionnaire asked individuals to rate, using a 0–5 scale, the distances between their body and hand when performing the various actions that take place in peri-personal space. When compared to contro...

Conceptual Hypometria? An evaluation of conceptual mapping of space in Parkinson's disease

Background
Total knee arthroplasty improves quality of life but is associated with postoperative cognitive dysfunction in older adults. This prospective longitudinal pilot study with a parallel control group tested the hypotheses that: 1) nondemented adults would exhibit primary memory and executive difficulties after total knee arthroplasty, and 2) reduced preoperative hippocampus/entorhinal volume would predict postoperative memory change, whereas preoperative leukoaraiosis and lacunae volumes would predict postoperative executive dysfunction.

A Pilot Study Evaluating Presurgery Neuroanatomical Biomarkers for Postoperative Cognitive Decline After Total Knee Arthroplasty in Older Adults

Despite the frequency of visuospatial complaints in patients with dementia of the Alzheimer type, little is understood about the mechanisms underlying those symptoms. Letter-cancellation tasks were obtained from 50 patients with a clinical diagnosis of Alzheimer's disease (AD). Twenty-two of the 50 subjects (44%) made a total of 36 errors in which they failed to cancel a target letter. There were no differences in mean age, education, gender, or Mini-Mental StateExamination score between error-makers and those making no errors. The distribution of errors on the page was not random. When compared to previously reported results of healthy subjects on the same task, the proportion ofAD subjects making errors was higher (44% vs. 26%), but the number of errors per error-maker did not differ. AD subjects demonstrated a high proportion of errors in the central region ofthe page, but did not show the normally expected performance bias to the left or distant halfofthe page. The pattern of errors reinforces past findings that deficits in the allocation and movement of visual attention across space occur in AD and that disorganization in visual search may contribute to AD patients' visuospatial dysfunction.

Letter cancellation performance in Alzheimer's disease

Liepmann (1900 and 1905): A Definition of Apraxia and a Model of Praxis

BACKGROUND/OBJECTIVE: Grapheme-to-phoneme conversion (GPC) allows the pronunciation of nonword letter strings and of real words with which the literate reader has no previous experience. Although cross-modal association between visual (orthographic) and auditory (phonemic-input) representations may contribute to GPC, many cases of deep or phonologic alexia result from injury to anterior perisylvian regions. Thus, GPC may rely upon associations between orthographic and articulatory (phonemic-output) representations. METHOD/RESULTS/CONCLUSION: Detailed analysis of a patient with phonologic alexia suggests that defective knowledge of the position and motion of the articulatory apparatus might contribute to impaired transcoding from letters to sounds.

Kenneth M. Heilman

Papers

Conceptual Hypometria? An evaluation of conceptual mapping of space in Parkinson's disease

A Pilot Study Evaluating Presurgery Neuroanatomical Biomarkers for Postoperative Cognitive Decline After Total Knee Arthroplasty in Older Adults

Letter cancellation performance in Alzheimer's disease

Liepmann (1900 and 1905): A Definition of Apraxia and a Model of Praxis

Articulatory processes and phonologic dyslexia.