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J M Findlay

Publications and source records attributed to J M Findlay.

At least 55 records · Page 3Linked to original sources
PubMed1997

Studying expertise in music reading: use of a pattern-matching paradigm.

Two experiments are described that make use of a pattern-matching paradigm to investigate perceptual processing of music notation. In Experiment 1, it is reported that the speed of comparing two visually presented musical sequences is related to the sight-reading skill of the subjects. The effect of the temporal and pitch structure of the comparison stimuli is also assessed. In Experiment 2, eye-movement recordings were taken as subjects performed the task. These data demonstrated that more experienced musicians are able to perform the comparisons with fever, and shorter, glances between the patterns. These and other findings suggest that skilled sight-reading is associated with an ability to rapidly perceive notes or groups of notes in the score, and confirm that the pattern-matching paradigm is a useful tool in examining expertise in music reading.

Adolescent↗
PubMed1997

Current management of aneurysmal subarachnoid hemorrhage guidelines from the Canadian Neurosurgical Society.

Published medical evidence pertaining to the management of aneurysmal subarachnoid hemorrhage (SAH) was critically reviewed in order to prepare practice guidelines for this condition. SAH should be considered as a possible cause of all sudden and/or unusual headaches, and every attempt should be made to recognize mild SAHs, as they are still frequently misdiagnosed. The first test for SAH is computed tomography (CT), followed by lumbar puncture when the CT is negative for intracranial bleeding (the case in only several per cent of patients within 24 hours of aneurysm bleeding). Urgent cerebral angiography is necessary to detect the underlying cerebral aneurysm. The advantage of rapid diagnosis of SAH followed by early aneurysm repair is minimizing the risk of catastrophic aneurysm rebleeding. Early surgery for aneurysm repair is often possible and is recommended, unless the aneurysm location or size renders it technically difficult to expose in clot-laden subarachnoid cisterns beneath an acutely swollen brain. Aneurysm ablation is optimally accomplished with open microsurgery and clipping of the aneurysm neck, although other options include proximal parent artery occlusion, "trapping" of the aneurysmal segment of the artery, and embolization of thrombogenic materials (e.g., platinum "microcoils") directly into the aneurysm dome using endovascular techniques. Neurological outcome following SAH is also optimized through the prevention of secondary SAH complications, and further management specific for ruptured cerebral aneurysms can include anticonvulsants, neuroprotectants, and various agents and techniques to prevent or reverse delayed-onset cerebral vasospasm. All patients with aneurysmal SAH should be treated with the calcium antagonist nimodipine, and in certain circumstances patients should receive anticonvulsants. Induced arterial hypertension, hypervolemia and in some instances percutaneous balloon angioplasty are recommended to reverse vasospasm causing symptomatic cerebral ischemia prior to cerebral infarction.

Humans↗
PubMed1996

Saccadic eye movement programming in unilateral neglect.

The present study examined the eye movements made by patients with unilateral neglect under fixation gap and overlap conditions. The prior offset of fixation in a + 100 msec gap condition did not produce an increase in the numbers of contralesional saccades made by 3 out of 4 patients. This finding is incompatible with the view that the deficit in producing contralesional saccades reflects an inability to disengage visual attention from fixation. A significant reduction in saccade latency was, however, obtained in the gap condition ('gap effect'). The latency reduction in the gap condition is consistent with models which attribute the gap effect to warning signal effects and the release of an ocular rather than an attentional disengagement mechanism. Saccade latency was not increased when two targets were presented bilaterally and simultaneously in both hemifields (in contrast to the increase in latency shown by normal subjects). The lack of a normal 'bilateral target effect' in neglect is attributed to an imbalance in the level of activity in the saccadic system. Three patients showed visual 'extinction' and did not make saccades to the contralesional bilateral targets. In contrast R.R. who shows object-based neglect did not show extinction and made saccades to the contralesional bilateral targets. This suggests that visual extinction may be influenced by the form of neglect shown by the patient. The effects on saccade amplitude of presenting two targets in the same hemifield were also examined in a global effect task. One patient showed a much greater global effect than normal when pairs of targets were presented in his ipsilesional hemifield. In contrast R.R. showed a normal magnitude global effect. It appears that the form of neglect shown by a patient is a factor that influences their eye movement behaviour on simple saccade tasks and these eye movement abnormalities cannot be accounted for by a deficit of attentional disengagement.

Cognition Disorders↗
PubMed1996

Aneurysmal subarachnoid hemorrhage associated with weight training: three case reports.

Weight training is a popular component of physical fitness in North America. This form of training remains relatively safe with few cases of life-threatening injuries. However, a series of studies have demonstrated that repetitive upper- and lower extremity weight training incorporating a Valsalva maneuver can increase arterial pressure to values as high as 480/350 mm Hg. This marked increase in arterial pressure is transmitted to the cerebral vasculature and increases cerebral arterial transmural pressure and may have the potential to initiate the rupture of a previously innocuous intracranial aneurysm. We report three cases of subarachnoid hemorrhage (SAH) associated with arm (bicep) curls and leg press weight training and discuss the possible link between this form of exercise and aneurysmal SAH.

Adolescent↗
PubMed1995

Independent contributions of the orienting of attention, fixation offset and bilateral stimulation on human saccadic latencies.

In a series of experiments we examined the effects of the endogenous orienting of visual attention on human saccade latency. Three separate manipulations were performed: the orienting of visual attention, the prior offset of fixation (gap paradigm) and the bilateral presentation of saccade targets. Each of these manipulations was shown to make an independent contribution to saccade latency. In experiments 1 and 2 subjects were instructed to orient their attention covertly to a location by a verbal pre-cue; targets could appear in the attended hemifield (valid) or in the non-attended hemifield (invalid) together with a no-instruction (neutral) condition. Saccades were made under fixation gap and overlap conditions, to either single target or two bilaterally presented targets which appeared at equal and opposite eccentricities in both hemifields. The results showed a large increase (cost) of saccade latency to invalid targets and a small non-significant decrease (benefit) of saccade latency to valid targets. The cost associated with invalid targets replicates the "meridan crossing effect" shown in manual reaction time experiments and is consistent with the hemifield inhibition and premotor models of attentional orienting. The use of a "gap" procedure produced a generalised facilitation of saccade latency, which was not modified by the prior orienting of visual attention. The magnitude of the gap effect was similar for saccades made to attended and non-attended stimulis. This suggests that the gap effect may be due to ocular motor disengagement, or a warning signal effect, rather than to the prior disengagement of visual attention. When two targets were presented simultaneously, one in each hemifield, saccade latency was slowed compared with the single target condition. The magnitude of this slowing was unaffected by the prior orienting of visual attention or by the fixation condition. The slowing was examined in more detail in experiment 3, by presenting targets with brief offset delays. The latency increase was maximal if the two targets were presented simultaneously and decreased if the distractor appeared at short intervals (20-80 ms) before or after the saccade target onset. If the non-attended stimulus was presented at greater intervals (160, 240 ms) before the saccade target, then a facilitation effect was observed. This demonstrates that the onset of a distractor in the non-attended hemifield can have both an inhibitory and a facilitatory effect on a saccade production.

Attention↗
PubMed1995

A probability vector and transition matrix analysis of eye movements during visual search.

This report describes a new method for analysing eye movement records during free viewing. The proposed new measures originate from a categorisation of saccade directions. The proportion of each categorised direction and the transition matrix of each two successive categorised directions are then calculated. These new measures are proposed as objective indicators of the strategies employed by an observer engaged in a visual search task. It is concluded that the probability vector and transition matrix analysis are particularly suitable as measures of observer strategies in relation to performance on VDU-based tasks. The relation between these measures and other measures related to search efficiency are also discussed.

Attention↗
PubMed1995

Combined microneurosurgical and thoracoscopic removal of neurogenic dumbbell tumors.

The resection of posterior mediastinal dumbbell tumors has until now required laminectomy and some form of open access to the thoracic cavity. Over a 1-year period, a novel surgical approach combining posterior microneurosurgical and anterior video-assisted thoracoscopy techniques was used in 4 patients. In 3 patients, the tumor was removed successfully with minimal postoperative discomfort and rapid recovery. In the fourth patient, limited thoracotomy became necessary to control bleeding. This new approach, which combines modern-day neurosurgical and general thoracic surgical techniques, appears safe and could become the preferred method for removing most benign posterior mediastinal dumbbell tumors.

Adult↗
PubMed1995

Pharmacological and morphological effects of in vitro transluminal balloon angioplasty on normal and vasospastic canine basilar arteries.

Despite growing clinical use of transluminal balloon angioplasty (TBA) to treat cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH), the precise mechanism of action of balloon dilation on the cerebral arterial wall is unknown. In this experiment the authors examined the pharmacological and morphological changes in 10 normal and 12 vasospastic canine basilar arteries following in vitro silicone microballoon TBA. For the SAH group in which the double-hemorrhage model was used, vasospasm was confirmed by angiography and the animals were killed on Day 7 after the first SAH. In vitro TBA was performed on basilar arteries from normal and SAH dogs immediately after sacrifice and removal of the brain. The procedure was performed while the arteries were maintained in oxygenated Krebs buffer. In the pharmacological studies, potassium chloride, prostaglandin F2 alpha, serotonin, and noradrenaline were used as vasoconstrictors, and bradykinin and calcium ionophore A23187 were used to produce an endothelium-dependent dilation. In both normal and vasospastic groups, the pharmacological responses of dilated segments of basilar arteries were compared to those of nondilated segments of the same arteries. Vessels from all groups were examined using scanning electron microscopy (EM) and transmission EM. Scanning EM was used to study the intact vessel wall, the smooth-muscle cell layer obtained after digestion with hydrochloric acid, and the extracellular matrix obtained after digestion with bleach. Cross-sections of the vessel wall were examined using transmission EM. The most striking finding was that immediately after in vitro TBA of both normal and vasospastic canine basilar arteries, there was a significant reduction (p < 0.05) of responses to both vasoconstrictors and vasorelaxants. As revealed by scanning EM and transmission EM, both normal and vasospastic vessels dilated with TBA showed flattening and patchy denudation of the endothelium, and straightening and occasional rupturing of the internal elastic lamina. In addition, vasospastic vessels dilated with TBA showed decreased surface rippling and mild stretching and straightening of smooth-muscle cells, and mild thinning of the tunica media. There was no gross vascular disruption or obvious change in the extracellular matrix of the vessel walls of either normal or vasospastic arteries after TBA. These results suggest that functional impairment of vasoreactivity in the vessel wall as a result of mechanical stretching of the smooth-muscle layer plays a more important role than structural alteration, at least in the immediate dilation produced in vasospastic arteries by TBA.

Analysis of Variance↗
PubMed1995

Visual search: eye movements and peripheral vision.

The visual search task allows investigation of the way in which central processes can influence the programming of saccadic eye movements. In this paper, a simple search task is studied in which a target is presented in a ring-shaped display of eight stimuli. The subject is required to locate the target with a saccadic eye movement. Targets were colored disks and the task was to search for a target of a particular color. Sensory factors (when all nontargets are identical, the target stands out) and central factor (prespecification of the target) both contribute to search efficiency. When the display contains a double target, saccades sometimes land at an intermediate position between the two targets. This shows that the signal delivered by the search procedure is not necessarily highly localized.

Adult↗
PubMed1995

A randomized trial of intraoperative, intracisternal tissue plasminogen activator for the prevention of vasospasm.

A multicenter, randomized, blinded, placebo-controlled trial was conducted to study the possible role of intracisternally administered fibrinolytic agent recombinant tissue plasminogen activator (rt-PA) in preventing delayed onset cerebral vasospasm following aneurysmal subarachnoid hemorrhage (SAH). The target population was patients with ruptured saccular aneurysms causing severe SAH, placing them at high risk for vasospasm. Treatment consisted of a single 10 ml intraoperative injection of either vehicle buffer solution or rt-PA (1 mg/ml) into the opened basal subarachnoid cisterns immediately following aneurysm clipping. The major efficacy endpoint in this trial was angiographic vasospasm, and the major safety concern was intracranial hemorrhage. One hundred patients were randomized, 49 to placebo and 51 to rt-PA treatment. Baseline population characteristics were similar between the two groups. Severity of intracranial hemorrhage on computed tomographic scans was also similar between groups: 87.2% of both placebo and rt-PA treated patients had thick subarachnoid clots, and the rates for intracerebral and intraventricular hemorrhage were, respectively, 16.3% and 22.5% for placebo and 23.5% and 21.6% for rt-PA. Nine randomized patients did not receive treatment in the operating room, and in 8 this was due to conditions felt unsafe for the administration of a fibrinolytic agent. The overall incidence of angiographic vasospasm measured between the seventh and eleventh day following SAH was similar between the two groups, with arterial narrowing detected in 74.4% of dosed placebo patients and 64.6% of rt-PA treated patients. However, there was a trend toward lesser degrees of vasospasm in the rt-PA treated group. The rates for no or mild, moderate, and severe vasospasm were 69%, 16% and 15% in the rt-PA treated group, versus 42%, 35% and 23% in the placebo group (P = 0.07). When only those patients with thick subarachnoid clots were considered at the treating centers, there was a 56% relative risk reduction of severe vasospasm in the rt-PA treated group, which was significant (P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Fatal rebleeding from a dural arteriovenous malformation of the posterior fossa: case report with pathological examination.

A seventy-year-old woman suffered a fatal cerebellar rehemorrhage from a large venous aneurysm associated with a dural arteriovenous malformation (AVM) of the posterior fossa. The malformation, fed by branches of the right vertebral, occipital and middle meningeal arteries, had a nidus in the transverse sinus wall with a pedunculated extension reaching the pial surface of the adjacent cerebellum, from where the malformation drained exclusively into an aneurysmal cerebellar vein. There was no associated venous sinus obstruction. Histopathological examination of the venous sinuses, arteriovenous malformation and venous drainage is described and these findings as they relate to the pathogenesis of dural AVMs are discussed. Vascular malformations of the dura mater do not appear to be a single clinical or pathological entity. The serious risk of hemorrhage from a parenchymal venous aneurysm is emphasized.

Aged↗