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M I Posner

Publications and source records attributed to M I Posner.

At least 73 records · Page 4Linked to original sources
PubMed1984

Cognition and the basal ganglia. Separating mental and motor components of performance in Parkinson's disease.

Central to the concept of subcortical dementia is the implication that the increased response latencies, which distinguish the syndrome, are due to a slowing of thought processes. The term 'bradyphrenia' has been applied to this presumed slowing of thought in Parkinson's disease and implies (1) that increased response latencies are not strictly motoric but are due to slowed information processing, and (2) that the mental slowing is analogous to the bradykinesia observed in the motor domain and, hence, attributable to dysfunction of dopaminergic basal ganglia mechanisms. The current study attempts to validate this definition of bradyphrenia by seeking a slowing of thought in Parkinson's disease which can be linked directly to bradykinesia. Six parkinsonian patients with end-of-dose akinesia were studied in three experiments which allowed separation of the speed of specific cognitive operations from the speed of motor responses. Serving as their own controls, they were tested both during the parkinsonian 'off' state, and when bradykinesia was alleviated by drug therapy. Four additional patients with newly diagnosed Parkinson's disease were studied before and following successful treatment with L-DOPA/carbidopa. The first experiment measured the rate of memory scanning, the second examined orientating of attention in the visual fields, and the third measured the time required to prepare a manual movement. The results show that overall reaction time increased when patients were in the untreated state, but without a concomitant slowing of purely cognitive components. The slowing of thought often reported in Parkinson's disease does not necessarily accompany bradykinesia and thus may not be related to dopaminergic dysfunction. These findings emphasize the need for caution in inferring a slowing of thought from increased response latencies in subcortical disorders.

Adult↗
PubMed1984

Effects of parietal injury on covert orienting of attention.

The cognitive act of shifting attention from one place in the visual field to another can be accomplished covertly without muscular changes. The act can be viewed in terms of three internal mental operations: disengagement of attention from its current focus, moving attention to the target, and engagement of the target. Our results show that damage to the parietal lobe produces a deficit in the disengage operation when the target is contralateral to the lesion. Effects may also be found on engagement with the target. The effects of brain injury on disengagement of attention seem to be unique to the parietal lobe and do not appear to occur with our frontal, midbrain, and temporal control series. These results confirm the close connection between parietal lobes and selective attention suggested by single cell recording. They indicate more specifically the role that parietal function has on attention and suggest one mechanism of the effects of parietal lesions reported in clinical neurology.

Adult↗
PubMed1982

Neural systems control of spatial orienting.

A peripheral visual cue in an empty field (1) often summons head or eyes, or both, (2) improves efficiency at the cued position while attention is directed to it, even without overt movements, and (3) reduces processing efficiency at the cued position once attention is withdrawn. We have studied the time course and the effects of mid-brain and cortical damage on these components of orienting. The facilitation arises from shifts in covert attention. In cases of mid-brain degeneration due to progressive supranuclear palsy, saccadic movements were abolished, while covert orienting still occurs. However, covert orienting was found to be delayed in directions in which eye movements were most affected, suggesting a role for mid-brain pathways in covert orienting. Parietal lesions can cause massive loss in detection contralateral to the lesion. This is especially true when attention has been directed to the opposite side. These findings relate aspects of covert orienting of attention to neural control systems.

Attention↗
PubMed1980

Attention and the detection of signals.

Detection of a visual signal requires information to reach a system capable of eliciting arbitrary responses required by the experimenter. Detection latencies are reduced when subjects receive a cue that indicates where in the visual field the signal will occur. This shift in efficiency appears to be due to an alignment (orienting) of the central attentional system with the pathways to be activated by the visual input. It would also be possible to describe these results as being due to a reduced criterion at the expected target position. However, this description ignores important constraints about the way in which expectancy improves performance. First, when subjects are cued on each trial, they show stronger expectancy effects than when a probable position is held constant for a block, indicating the active nature of the expectancy. Second, while information on spatial position improves performance, information on the form of the stimulus does not. Third, expectancy may lead to improvements in latency without a reduction in accuracy. Fourth, there appears to be little ability to lower the criterion at two positions that are not spatially contiguous. A framework involving the employment of a limited-capacity attentional mechanism seems to capture these constraints better than the more general language of criterion setting. Using this framework, we find that attention shifts are not closely related to the saccadic eye movement system. For luminance detection the retina appears to be equipotential with respect to attention shifts, since costs to unexpected stimuli are similar whether foveal or peripheral. These results appear to provide an important model system for the study of the relationship between attention and the structure of the visual system.

Attention↗
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↗
PubMed1967

Decay of visual information from a single letter.

If the trace of a letter can be matched more rapidly with a physically identical letter (as in the pair AA) than it can be with a letter having only the same name (as in the pair Aa), then the trace must preserve the visual aspect of the letter. The visual information from a single letter decays in about 1.5 seconds if the task provides little incentive for preservation.

Humans↗