Canadian journal of psychology最新文献

Subjects judged the quality of rigid motion between pairs of three-dimensional drawings that differed by a rotation in depth. The figures were aligned with, and rotated around, either the vertical axis or an axis that was oblique with respect to the XYZ co-ordinate system. Rated quality of motion decreased with increasing angular disparity between the figures and with decreasing stimulus duration, regardless of whether the figures were vertical or oblique. The same subjects then participated in a mental rotation task using the same stimuli and angular disparities. An effect of principal axis emerged, such that subjects took longer to make decisions about obliquely aligned stimuli than about vertically aligned stimuli, especially if they received the oblique stimuli first. These data imply that perceived versus imagined movement through the same trajectory involves different processes. Whereas the apparent motion system performs its computations relatively automatically, the processes involved in mental rotation are more strategic in nature.

Briefly presented target lines are reported more accurately when part of an object-like context than alone (Williams & Weisstein, 1978). Efforts to explain this effect have tended to focus on structural properties that contexts must possess in order to be effective in facilitating target-line discrimination (e.g., Weisstein, Williams, & Harris, 1982). Enns and Prinzmetal (1984) take issue with this approach. They propose that contexts differ more from one another than do target lines presented alone, and it is this fact, and not the general structural properties of contexts, that underlies their effectiveness. Two experiments examined intercontext differences and structural factors as determinants of context effectiveness. Subjects were found to use intercontext differences to narrow the range of possible alternatives, but when this factor was controlled, structural properties determined context effectiveness. The structural interpretation of context effectiveness was found not be as straightforward as generally assumed, however. A third experiment showed context effectiveness to be affected by the character of the discrimination task employed.

Certain instances of neuronal degeneration secondary to brain damage might be functionally beneficial, and steps taken to protect against such degeneration may adversely affect behavioural outcome. After unilateral damage to the intrinsic neurons of the striatum, which includes GABAergic striatonigral projections, delayed trans-synaptic degeneration occurs in the ipsilateral substantia nigra pars reticulata (SNr). This degeneration was prevented by a 2-week regimen of muscimol delivered intraventricularly via osmotic minipumps. Muscimol is a direct-acting GABA agonist that presumably substituted for the absent GABA at the interface between the degenerating striatonigral GABAergic terminals and the GABAergic receptors located on SNr neurons. Sensorimotor asymmetry tests sensitive to unilateral striatal damage were carried out for 4 weeks to determine the functional consequences of the sparing of SNr neurons. Recovery of function was not improved. Instead, tactile extinction and hemiplegia were exaggerated in the contralateral forelimb. Other impairments were unaffected by the muscimol. The experiment was repeated using diazepam, rather than muscimol, to address the possibility that the disruptive effects of muscimol might reflect a more general disruptive influence on recovery processes. Diazepam, which has been shown in our lab to disrupt recovery of function after cortical lesions and to potentiate lesion-associated atrophy in remote subcortical structures, is an indirect-acting GABAergic agonist that requires GABA for its mechanism of action. Because GABAergic terminals at the SNr were destroyed, diazepam (as expected) failed to prevent SNr degeneration. Although diazepam presumably enhanced GABAergic synaptic activity in other brain regions, diazepam had no significant effect on postoperative behavioural function. Apparently, in the first experiment, the prevention of SNr degeneration per se was instrumental in the detrimental effects of muscimol. The rescued SNr neurons may have contributed to dysfunction because they lacked inhibitory GABAergic control. Transsynaptic degeneration secondary to brain damage was discussed as it might relate to release phenomena and their treatment by surgery or transmitter blocking agents in the clinical literature.

The cholinergic hypothesis of geriatric memory dysfunction suggests (a) that basal forebrain lesions in animals should mimic cognitive and mnemonic impairments of human dementia and (b) that cholinergic grafts in the cortex and hippocampus may alleviate such impairments, whether induced by basal forebrain lesions or due to the intrinsic processes of ageing. Our own studies addressing these issues are reviewed. Although aged rats manifest impairments in short-term memory that are reversed by cholinergic grafts in the cortex and hippocampus, basal forebrain lesions have produced ambiguous results, which in part are attributable to nonspecific effects of the lesions. Acetylcholinesterase histochemistry and the topography of NBM-cortical connections indicate that basal forebrain lesions that include the NBM in general spare the cholinergic innervation of the prefrontal cortex, but can damage prefrontal cortical outflows via the globus pallidus. Two experiments are presented to indicate that the medial prefrontal cortex and its ventral striatal outputs provide a critical substrate for normal short-term memory performance in delayed matching and nonmatching tasks. These observations can resolve many of the discrepancies in previous lesion and graft studies.

In this paper we will explore some of the biological and psychosocial factors that appear to be relevant to recovery of function following brain damage, especially in regard to neurorehabilitation programmes. We will also comment on promising areas of research that relate to recovery of function. Our goal is to aid in establishing a conceptual framework for the development of theory- and experiment-based neurorehabilitation.

This report summarizes the behavioural effects of a right occipital stroke in the author. An upper left quandrantanopia resolved over the first 50 poststroke days to leave a scotoma that included the left upper quadrant of the fovea and extended upwards about 6 degrees and lateral about 15 degrees. There was no further reduction in size over the next 4 years. In the early stages of recovery there was an inability to detect consciously either the presence of objects or their motion, except upon reflection once an object entered the intact visual field. This has been referred to previously as blindsight. On about the fourth day poststroke, part of the scotoma became visually active, producing a scintillating aura, which remains. Shortly thereafter colour perception returned in the scotoma, as did motion detection. Although there was little additional change in the field defect after 2 months, the author's visual abilities have continued to improve, in large part because of a shift in fixation such that information at the centre of the visual field now falls about 1.5 degrees into the lower right portion of the fovea. The implications of the visual and behavioural changes are discussed in the context of multiple visual systems and with respect to recovery of function.

A series of experiments examined the potential plasticity of the callosal system in both epileptic patients and in kittens submitted to corpus callosotomy at various ages. The patients were tested for unilateral discrimination and interhemispheric transfer of tactile information. The youngest patient was also required to perform additional inter- and intrahemispheric comparisons of visual and tactile stimuli. The animals were tested for interhemispheric transfer of visual discriminations. The results suggest that in both animals and humans there exists a critical period before which callosal section does not disrupt interhemispheric communication. The results also indicate that the compensatory mechanisms used to achieve interhemispheric transfer in the absence of the corpus callosum may vary according to the sensory modality involved. The possible physiological and/or functional mechanisms responsible for callosal plasticity are discussed.

In this brief review, we argue that a detailed analysis of the spatial and temporal characteristics of visually guided limb movements can provide important insights into the nature of neuropsychological deficits and the functional organization of the brain. In particular, we will show how kinematic analysis of a simple aiming movement can reveal differences that might not be apparent clinically in the behaviour of patients with unilateral brain lesions. We will argue that the subtle but distinctive deficits that follow damage to the left or right hemisphere can be related to the clinical syndromes of manual apraxia and hemispatial neglect, respectively. The fact that these deficits are apparent only with kinematic analysis demonstrates the potential of these techniques for evaluating recovery of function.