11/84. Visual and tactile size distortion in a patient with right neglect.One typical feature of the neglect syndrome in patients with right hemisphere damage is that they bisect horizontal lines to the right of centre. It has been argued that to a large extent these bisection errors can be attributed to a perceptual change whereby the patient experiences the left half of a line as shorter than the right half, causing them to set the midpoint of the line towards the right. We describe here a patient with a left hemisphere lesion and rightward neglect, who consequently makes bisection errors in a leftward direction. We carried out a series of tests which confirmed that he shows a subjective visual distortion in the converse direction, i.e. a perception of horizontal extents on the right as shorter than extents on the left. We also found that he shows a similar distortion in his tactile perception. The association of visual and tactile distortions in this patient is compatible with the view that the distortion effects have a rather high-level origin. Multiple single-case studies will, however, be required to establish whether this association of deficits is typical, or whether visual and tactile size distortions are separable symptoms associated with neglect.- - - - - - - - - - ranking = 1keywords = perception (Clic here for more details about this article) |
12/84. Unilateral right parietal damage leads to bilateral deficit for high-level motion.patients with right parietal damage demonstrate a variety of attentional deficits in their left visual field contralateral to their lesion. We now report that patients with right lesions also show a severe loss in the perception of apparent motion in their "good" right visual field ipsilateral to their lesion. Three tests of attention were conducted, and losses were found only in the contralesional fields for a selective attention and a multiple object tracking task. Losses in apparent motion, however, were bilateral in all cases. The deficit in apparent motion in the parietal patients supports previous claims that this relatively effortless percept is mediated by attention. However, the bilateral deficit suggests that the disruption is due to a bilateral loss in the temporal resolution of attention to transient events that drive the apparent motion percept.- - - - - - - - - - ranking = 0.5keywords = perception (Clic here for more details about this article) |
13/84. Agenesis of the corpus callosum with hypothermia.A patient with episodic hypothermia and agenesis of the corpus callosum had no direct evidence of hypothalamic-pituitary dysfunction. However, it is speculated on the basis of a recent clinicopathologic case study that selective hypothalamic involvement is the cause of the hypothermia. Electroencephalograms and treatment with antiseizure medication did not support an epileptic genesis for the episodic hypothermia. Double, simultaneous, tachistoscopic stimulation studies revealed an asymmetry of response that can be explained by either a functional disconnection of the cerebral hemispheres or bilateral independent and asymmetrical representation of speech mechanisms.- - - - - - - - - - ranking = 0.0085098355516829keywords = speech (Clic here for more details about this article) |
14/84. Phantom smelling.A case of phantom smelling (phantosmia) is described in a 28-yr.-old man who developed permanent bilateral anosmia after a serious injury to olfaction-related brain structures at the age of 25 years. The findings indicate that, even years after loss of input from olfactory receptors, the neural representation of olfactory perception can still recreate olfactory sensations without any conscious recall of them. This indicates that the neural representation of olfactory sensations remains functional and implies that neuronal activity in the olfactory organ or in other brain structures gives rise to olfactory experiences perceived as originating from the perception of original odor substances. The report suggests the intriguing possibility that the olfactory perception is not a passive process that merely reflects its normal input from the olfactory system but is continuously generated by a neural representation in the olfactory organ or in other olfaction-related brain structures, based on both genetic and sensory determinants. To the author's knowledge this is the first reported case of its kind.- - - - - - - - - - ranking = 1.5keywords = perception (Clic here for more details about this article) |
15/84. Direction-specific motion blindness induced by focal stimulation of human extrastriate cortex.Motion blindness (MB) or akinetopsia is the selective disturbance of visual motion perception while other features of the visual scene such as colour and shape are normally perceived. Chronic and transient forms of MB are characterized by a global deficit of direction discrimination (pandirectional), which is generally assumed to result from damage to, or interference with, the motion complex MT /V5. However, the most characteristic feature of primate MT-neurons is not their motion specificity, but their preference for one direction of motion (direction specificity). Here, we report that focal electrical stimulation in the human posterior temporal lobe selectively impaired the perception of motion in one direction while the perception of motion in other directions was completely normal (unidirectional MB). In addition, the direction of MB was found to depend on the brain area stimulated. It is argued that direction specificity for visual motion is not only represented at the single neuron level, but also in much larger cortical units.- - - - - - - - - - ranking = 1.8823914587443keywords = perception, discrimination (Clic here for more details about this article) |
16/84. Neural correlates of conscious and unconscious vision in parietal extinction.brain areas activated by stimuli in the left visual field of a right parietal patient suffering from left visual extinction were identified using event-related functional magnetic resonance imaging. Left visual field stimuli that were extinguished from awareness still activated the ventral visual cortex, including areas in the damaged right hemisphere. An extinguished face stimulus on the left produced robust category-specific activation of the right fusiform face area. On trials where the left visual stimulus was consciously seen rather than extinguished, greater activity was found in the ventral visual cortex of the damaged hemisphere, and also in frontal and parietal areas of the intact hemisphere. These findings extend recent observations on visual extinction, suggesting distinct neural correlates for conscious and unconscious perception.- - - - - - - - - - ranking = 0.5keywords = perception (Clic here for more details about this article) |
17/84. Dissociation of affective modulation of recollective and perceptual experience following amygdala damage.It has been suggested that similar neural mechanisms may underlie the affective modulation of both recollective and perceptual experience. A case is reported of a patient who has bilateral amygdala damage and marked impairment in the perception of emotion, particularly fear. The patient DR and 10 healthy control subjects (matched for school leaving age, intelligence quotient, and non-emotional memory performance) were shown a series of slides accompanied by an emotionally arousing narrative. One week later DR and the controls were given a surprise memory test for this material. In addition, they completed a verbal memory test using emotionally arousing stimuli. Both DR and the healthy control subjects showed a normative pattern of enhanced memory for emotional material. On the basis of these results and the previously demonstrated impairment of perception of emotion in this patient, it is concluded that different neural mechanisms may underlie affective modulation of recollective and perceptual experience.- - - - - - - - - - ranking = 1keywords = perception (Clic here for more details about this article) |
18/84. A case of acute loss of binocular vision and stereoscopic depth perception. (The misery of acute monovision, having been binocular for 68 years).PURPOSE: There are few personal reports in the literature, by knowledgeable vision scientists, of the loss of binocular vision. This case is reported. CASE REPORT: This 68 year old retired pediatric ophthalmologist suffered an almost total loss of vision, OD, as a result of a sudden massive hemorrhage into the vitreous body from a bridging retinal vessel, which remained after repair of a spontaneous large horseshoe retinal tear. This caused significant problems with both remaining monocular vision, cognition, and space perception. It was surprisingly disabling. A diary is included. RESULT: The author now appreciates better: 1. that the overlap and cross compensation of monocular vision is quite significant; 2. that monocular depth perception may be impaired by any type of intervening optical media; 3. that a two dimensional world is very different and vastly inferior to a three dimensional world. comment: Such problems are not ordinarily expected or described in these circumstances, but considering what is in the literature, they may be more common and serious than assumed by eye care professionals, and should be taken into consideration in rendering eye care in similar situations. Loss of binocular vision results in a significant handicap even when the vision remaining in the good dominant eye is normal. It is truly remarkable to this victim that so many mature patients are willing to accept this situation in the form of surgical or optical monovision to avoid spectacles for presbyopia.- - - - - - - - - - ranking = 3keywords = perception (Clic here for more details about this article) |
19/84. Different spatial processing for stimulus-centered and body-centered representations.The authors describe a patient who experienced two successive strokes in the right hemisphere. After the first stroke, she showed stimulus-centered left neglect confined to right space on a circle discrimination task, which resolved. After the second stroke, she showed body-centered left neglect on the same task. These observations of two types of left neglect in the same patient suggest there are at least two distinct spatial attentional systems in the brain: global and focal attentional systems.- - - - - - - - - - ranking = 0.38239145874427keywords = discrimination (Clic here for more details about this article) |
20/84. Use of a forced-choice test of tactile discrimination in the evaluation of functional sensory loss: a report of 3 cases.The loss of sensation is not an uncommon associated finding after injury to the peripheral nerves and the spinal cord. However, the sensory examination is prone to the influence of nonphysiologic factors, and one cannot use it to determine whether functional sensory loss reflects unconscious or intentional symptom production. This distinction has important implications for differential diagnosis and for decision making in the context of workers' compensation claims and personal injury litigation. We present 3 cases of patients with chronic pain and nondermatomal patterns of loss of fine-touch sensation, whose sensory loss was examined by a sensory forced-choice symptom validity test. Their below-chance scores showed intentionally produced sensory symptoms. The use of this methodology in differential diagnosis is discussed.- - - - - - - - - - ranking = 1.5295658349771keywords = discrimination (Clic here for more details about this article) |
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