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Biomedical subjects

M I Posner

Publications and source records attributed to M I Posner.

18 recordsLinked to original sources
PubMed1992

The neurobiology of selective attention.

Research in the field of selective visual attention has recently seen substantial progress in several areas. Neuroimaging and electrical recording results have indicated that selective attention amplifies neural activity in prestriate areas concerned with basic visual processing. Imaging and cellular studies are delineating the networks of anatomical areas that serve as the source of attentional modulation and have suggested that these networks are anatomically distinct from the sites of the resulting amplifications. Cognitive studies of visual search have explored the role of these amplified computations in the integration of visual features into objects. Attentional effects in normal subjects, and their disruption following brain injury, have revealed the mental representations upon which attention operates.

Animals↗
PubMed1992

Lexical access and the brain: anatomical constraints on cognitive models of word recognition.

Recent studies in the cognitive psychology of reading and many other skilled performances have been dominated by models inspired by neural connectivity (e.g., McClelland & Rumelhart, 1986). Such models have not yet begun to consider the accumulating evidence of considerable anatomical localization of component cognitive operations in the human brain (e.g., Posner, Petersen, Fox, & Raichle, 1988). In this article we apply anatomical findings to the job of building computational models of visual word recognition. Brain imaging studies already provide important constraints on how lexical access should be defined in terms of isolable encoding operations that compute the visual form, phonology, and semantics of words. Brain imaging studies also speak to issues of modularity versus interaction between these encoding operations, distribution versus localization of processing within the operations, and orchestration of operations to accomplish different word processing tasks. We conclude that a combined cognitive and anatomical analysis may be of considerable benefit in developing more adequate models of human information processing.

Brain↗
PubMed1990

Components of neglect from right-hemisphere damage: an analysis of line bisection.

Two versions of a line bisection task were given to patients with posterior right-hemisphere damage and normal control subjects. One, which we refer to as the directed-manual task, was the traditional bisection task in which lines were transected with a pen held in the right hand. In the other task, referred to as the directed-visual task, subjects observed the experimenter move a pen along a line from right-to-left (the left-scan task) or from left-to-right (the right-scan task) and they verbally indicated the subjective midpoint. Patients showed significant left neglect in the manual and the left-scan tasks only. Controls showed no consistent biases and no influence of scanning direction. Right and left cues biased bisection for both groups. The results indicate that when the directed manual response is eliminated, scan direction determined the presence or absence of neglect on bisection. The findings are discussed in terms of the efficiency of visual orienting.

Adult↗
PubMed1989

Covert attention and eye movements during reading.

Eye movements were monitored during the reading of spatially transformed text in order to examine covert attentional processes in reading. In some conditions, the sequence of letters within a word was congruent with (i.e. in the same direction as) the sequence of words in the sentence; in other conditions the direction of letters within words and the direction of words in the sentence were incongruent. In addition, the window of visible text was varied so that in some conditions only the fixated word (and all preceding words) were visible, whereas in other conditions the fixated word and the succeeding word were both visible. Readers were able to extract more parafoveal information from text when the words themselves were normal than when the letters within the words were transformed. However, with practice, readers were able to use some parafoveal information even when the words were transformed. The most important finding was that the congruity of the word and letter order had no reliable effect on the ability to extract parafoveal information and influenced reading performance only when the words themselves were normal. We conclude that covert attention in reading is not a letter-by-letter scan that sweeps across the page, but either an asymmetric spotlight held constant on each fixation or a shifting of an attentional spotlight extending across multiletter units (possibly words) with the direction of shifts of attention closely coupled to the direction of eye movements.

Attention↗
PubMed1989

Left striato-pallidal hyperactivity in schizophrenia. Part II: Phenomenology and thought disorder.

Our previous paper summarized abundant evidence that schizophrenic patients show forms of sensory and motor hemineglect compatible with a left striato-pallidal hyperactivity model of schizophrenia. In this paper we discuss how the model may also account for some of the cognitive and phenomenological aspects of this disorder. Hemineglect can be associated with pallidal hyperactivity through its mediation of the anterior attention system of the frontal lobe. We postulate that this same attentional deficit can also affect higher functions such as the control of language and thought by internal motivations. Many symptoms of schizophrenia can be explained as a form of hemineglect of these higher functions.

Arousal↗
PubMed1989

Hyperactivity of the left striato-pallidal projection. Part I: Lower level theory.

We have observed increased relative blood flow to the left globus pallidus and evidence for subtle forms of right-sided hemineglect in neuroleptic-naive schizophrenic patients. These findings occur in animals following certain lesions such as unilateral destruction of midbrain dopaminergic neurons, and are presumed to be due to left striato-pallidal hyperactivity. A survey of the literature reveals many similarities between animals with unilateral dopaminergic denervation and schizophrenic patients. It has previously been suggested that available evidence does not preclude the possibility that schizophrenic patients have something like a dopaminergic deficiency. Other studies demonstrate that neuroleptics reverse asymmetries in indices of dopamine turnover. A model based upon dopaminergic hemideficiency is outlined, and can potentially explain other abnormalities in schizophrenic patients including eye movement abnormalities and the link between temporal lobe epilepsy and psychosis. A companion article describes how this model can account for some of the phenomenological symptoms of psychosis.

Arousal↗
PubMed1988

Localization of cognitive operations in the human brain.

The human brain localizes mental operations of the kind posited by cognitive theories. These local computations are integrated in the performance of cognitive tasks such as reading. To support this general hypothesis, new data from neural imaging studies of word reading are related to results of studies on normal subjects and patients with lesions. Further support comes from studies in mental imagery, timing, and memory.

Attention↗
PubMed1988

Asymmetries in hemispheric control of attention in schizophrenia.

Investigators have long suggested that schizophrenia might be related to an impairment in the regulation of attention. In this report, the performance of schizophrenic patients was compared with nonschizophrenic control subjects in their ability to direct visual attention. In the first experiment, patients were distinguished from controls by a slower response to a target in the right visual field than to a target in the left visual field when attention was not first directed to the target location. In the second experiment, patients were distinguished from controls by a stronger bias in favor of symbolic information over language information about spatial direction. In both experiments, the patients demonstrated deficits in attention similar to patients from previous studies who had unilateral lesions of the left hemisphere. The identification of performance abnormalities using tasks that are simple, have dissectable cognitive components, have been related to discrete neural systems, and control for nonspecific variables provide the basis for constructing reasonable hypotheses about the cognitive psychology and functional neuroanatomy of schizophrenia.

Adult↗
PubMed1988

Orienting of visual attention in progressive supranuclear palsy.

Orienting of visual attention was studied in 8 patients with progressive supranuclear palsy (PSP) and 8 parkinsonian control subjects. While maintaining fixation on the centre of a visual display, subjects made simple reaction time (RT) key press responses on detecting visual targets which appeared above, below, to the left or right, equidistant from fixation. On each trial the target was preceded by a preparatory cue, either a peripheral luminance change or a central arrow, to summon attention to one of the four locations. The orienting of attention was measured as a facilitation in detection RT at the cued location. For the parkinsonian controls, this facilitation was equal for horizontal and vertical directions, whereas for both types of cues, PSP patients were slower moving attention in the vertical than in the horizontal plane. Midbrain retinotectal pathways are important not only for controlling eye movements, but also for orienting attention.

Aged↗
PubMed1987

How do the parietal lobes direct covert attention?

In cases of unilateral parietal damage patients have trouble with stimuli in the visual hemifield on the side opposite the lesion (contralesional). This deficit is clear when they are first cued to attend to a location on the side of the lesion (ipsilesional) and then given a target on the opposite side of fixation. Our first experiments indicated that these patients do worse when cued to a location in either field and then given a target in the contralesional as compared to the ipsilesional direction. The results of this experiment can be accounted for by a representational or a directional view. A second experiment seeks to discriminate between the two. The results tend to favor the directional view.

Attention↗
PubMed1987

Deficits in human visual spatial attention following thalamic lesions.

There has been speculation concerning the role that thalamic nuclei play in directing attention to locations in visual space [Crick, F. (1984) Proc. Natl. Acad. Sci. USA 81, 4586-4590]. We measured covert shifts of visual attention in three patients with unilateral thalamic hemorrhages shortly after the lesion and after a 6-month recovery period. The experiment measured reaction time to targets that occurred at locations to which attention had been cued (valid trials) or at a currently unattended location (invalid trials). Although the patients showed no deficits in visual fields with perimetry and no neglect in the 6-month follow-up, we found slow reaction times for targets on the side contralateral to the lesion whether or not attention had been cued to that location. Deficits have also been found in this task with cortical and midbrain lesions, but the patterns of performance are quite different. The results with thalamic patients suggest they have a specific deficit in the ability to use attention to improve the efficiency of processing visual targets contralateral to the lesion (engage operation). This finding is in accord with hypotheses of a thalamic link between cortical visual attention and pattern recognition systems proposed by Crick.

Aged↗
PubMed1987

Cognitive neuropsychology and the problem of selective attention.

Cognitive psychologists focus on internal mental operations controlling access to consciousness, memory and responding. They are concerned with the way in which central intentions come to affect sensory and memorial processing. The problem of selective attention to visually presented stimuli provides an important model for integrating this approach with an understanding of underlying neural systems. Studies of humans and alert monkeys show that they can attend selectively to eccentric visual locations while maintaining fixation. The occurrence of a target eccentric to fixation induces a disengagement from the current attentional focus, a movement of attention and an engagement of the target. It has been shown that damage to the parietal lobe affects the ability to disengage, while midbrain injury affects the move component. Each hemisphere appears biased toward processing contralateral targets. In order for the posterior visual selection system to operate it must have access to another more general selective attention system not dedicated to visual spatial information. Thus attentional selectivity requires a multilevel hierarchical system with each level viewed as a network of component mental operations. At one level the component operations are dedicated to particular cognitive systems (e.g., visual-spatial) but at higher levels they seem to be general across different cognitive systems (e.g., visual-spatial and language).

Attention↗
PubMed1986

Does attention affect visual feature integration?

Two questions are investigated in this work: first, whether the integration of color and shape information is affected by attending to the stimulus location, and second, whether attending to a stimulus location enhances the perceptual representation of the stimulus or merely affects decision processes. In three experiments, subjects were briefly presented with colored letters. On most trials, subjects were precued to the stimulus location (valid cue); on some trials, a nonstimulus location was cued (invalid cue). Subjects were less likely to incorrectly combine colors and letter shapes following a valid cue. The attentional facilitation afforded by the cue was not limited to feature integration but also affected the registration of features. However, when the amount of feature information was strictly controlled, attention still affected feature integration. The results indicate that orienting attention to the location of the cue affects the quality of the perceptual representation for features and their integration.

Adolescent↗
PubMed1979

Orthography and familiarity effects in word processing.

Both orthographic regularity and visual familiarity have been implicated as contributors to the efficiency of processing visually presented words. Our studies sought to determine which of the internal codes representing words in the nervous system are facilitated by these two variables. To do this, sets of letter strings in which orthography and familiarity were factorially combined were used as the basis for physical, phonetic, semantic, and lexical judgments. The data indicated consistent effects of orthography on the activation of all codes. These effects were seen in same-different matching and in judgments of stimulus orientation, which are based on visual codes; in judgments of pronounceability based on phonetic codes; in judgments of meaningfulness based on semantic codes; and in lexical decisions, which are based on phonetic and semantic codes together. Familiarity, on the other hand, had a clear influence on the activation of semantic codes and to a lesser extent affected phonetic codes. Despite previous positive results found in matching letter strings, however, no influence of familiarity occurred in judgments based on visual codes once evidence for criterion shifting was eliminated. Our negative results included direct tests of facilitation in matching acronyms (e.g., FBI) and in matching both regular and irregular strings familiarized by specific training. It now appears that earlier findings of visual familiarity effects may be attributed to response biases resulting from the activation of higher level codes sensitive to familiarity, and to the use of small sets of training stimuli that allowed subjects to induce orthographic-like rules. The results obtained so far with our methods seem to reconcile an inconsistent literature by showing that speeded decisions based on visual codes are most strongly influenced by rule-governed processing mechanisms sensitive to orthographic structure, whereas decisions based on phonetic and semantic codes are affected about equally by rule-governed mechanisms and by stimulus-specific mechanisms sensitive to familiarity. This conclusion may lead to changes in notions of how effective various kinds of visual training are likely to be at different stages in the acquisition of reading skill.

Discrimination Learning↗