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Perception of faces: disorders in organic and psychopathological states.
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[Are self-perceivable neuropsychological deficits in patients with neuroses or personality disorder diagnoses indicative of later schizophrenia?].
For the first time, the present study assessed the achievable predictive value of early self-experienced neuropsychological deficits for the fater development of schizophrenia. Ninety-six patients with DSM-III-R diagnoses mainly of the formerly neurotic or personality disordered field, of whom 81% had shown such basic disorders at the time of the index examination and therefore were classified as persons at high risk of developing schizophrenia, were re-examined for schizophrenia. After an average follow-up period of about 8 years, more than half of the re-examined sample had developed a schizophrenic disorder according to DSM-III-R. The outcome of schizophrenia versus no schizophrenia was predicted correctly in 77% of cases by the presence or absence of self-experienced disturbances of perception, thought, speech or action.
Ocular scanning and perceptual size distortion in hemispatial neglect: effects of prism adaptation and sequential stimulus presentation.
When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite.
Deficits of spatial localization in children with strabismic amblyopia.
BACKGROUND: Besides loss of visual acuity and binocularity, spatial localization deficits (comprising both increased spatial uncertainty and spatial distortions) are an important feature of strabismic amblyopia. Although they have been extensively investigated in adult amblyopes, there are still many open questions concerning their substrate and relationship to clinical parameters. Our aim was to develop a procedure for assessing vertical alignment, which enabled us to find out whether children with strabismic amblyopia had similar spatial localization deficits, and their relation to the children's clinical condition. METHODS: Vertical alignment was assessed in children by comparing the visual direction in space of three loci along the vertical meridian, separated by 5 deg of visual angle. We tested alignment in the amblyopic and dominant eyes of 32 strabismic and in both eyes of 35 control children from 4.5 to 10 years, together with a careful orthoptic examination. RESULTS: In the amblyopic eyes, increased uncertainty and systematic distortions outside the normal range occurred. Large angles of deviation and pathological fixation patterns were necessary, but not sufficient conditions for gross spatial deficits to occur. The fellow dominant eyes showed spatial localization similar to normal eyes. CONCLUSIONS: Children with strabismic amblyopia exhibited localization deficits and relationship to clinical data similar to those in adult amblyopes. These data are important for further investigations about the substrate, plasticity and the clinical relevance of perceptual distortions.
Oscillopsia associated with dysfunction of visual cortex.
PURPOSE: To investigate the cause of oscillopsia without nystagmus or vestibular dysfunction in a 31-year-old man with no past history of serious illness. METHODS: The changes in the regional cerebral blood flow elicited by visual stimuli were studied by positron emission tomography (PET) in the patient and were compared with changes in normal subjects. The primary visual cortex (PVC) and area V5 were defined on Talairach coordinates, as shown in previous PET studies, and were confirmed with their activation patterns in our subjects. RESULTS: Flicker stimulation (8 Hz) and a stationary random dot pattern activated area V5 in the patient, but not in the six normal controls. A moving random dot pattern activated both the PVC and the extra-striate cortex in both the patient and the controls. CONCLUSIONS: Oscillopsia in this case is associated with dysfunction of the visual cortices and may be caused by it.
Low-level sensory processing in obsessive-compulsive disorder: an evoked potential study.
This study used visual and auditory evoked potentials (VEP and AEP) to study low-level sensory processing in a group of 15 unmedicated subjects with obsessive-compulsive disorder (OCD) and 30 age-matched, gender-matched, and handedness-matched normal controls. EPs were recorded to flash (VEP) and binaural click (AEP) stimulation. OCD subjects were found to have significantly shorter latencies on N1 and P2 of the AEP, and no differences were found in the VEP. Results indicate abnormal information processing states in OCD during low-level auditory processing, but not during low-level visual processing. Neural generators of the VEP and AEP are briefly reviewed and results are discussed in relation to current neurobiological models of OCD.
Behavioral deficits in cats following early selected visual exposure to contours of a single orientation.
The ability of adult cats, whose early visual experience was confined to contours of a single orientation (either vertical or horizontal), to resolve gratings of different orientations was studied by operant methods. Following selective visual exposure during part or all of the first 4 months of life, the cats were trained on a simultaneous discrimination between gratings of various orientations and blank fields of the same mean luminance. The spatial frequency of the gratings was systematically altered in order to obtain an estimate of acuity based upon extrapolation to chance levels of performance. Selectively deprived cats performed as well as normally reared cats on gratings having the same orientation as that of the stripes they saw as kittens, but their performance on gratings orthogonal to these was poorer. The deficits in acuity for gratings perpendicular to the experienced orientation varied between 0.26 and 0.87 of an octave. On the other hand, control cats whose early visual experience alternated between vertical and horizontal stripes, or who were reared in an environment containing randomly oriented contours, failed to show any difference in their acuity for vertical and horizontal gratings. The acuity deficits shown by the selectively deprived animals are long-standing since they remain unchanged even after 30 months of normal visual exposure. It is argued that these perceptual deficits are a consequence of the changes in cortical physiology that other investigators have described in cats who had undergone similar early visual deprivation. Taken together, these findings provide a basis for explaining a number of human perceptual disorders.
Temporal lobe or psychomotor status epilepticus. A case report.
A 22-year-old female with a history of polymorphic and uncontrollable psychomotor seizures in association with unclear disturbances of perception, emotion and intellect is reported. During chronically performed SEEG studies the patient entered a psychomotor status epilepticus with transition from the discontinuous to the continuous type. The electrical findings at surface and depth indicated a primary epileptogenic area in the right hippocampal formation. The typical clinical signs were observed during depth recording. The anatomo-electroclinical correlations therefore could be studied with confidence. Good correlation could be established between distinct seizure patterns and predominant clinical signs. Especially long-lasting hallucinations of music were clearly linked to the ictal involvement of the right gyrus of Heschl, and clouded consciousness and/or memory disturbances were shown to be due to bilateral ictal discharges in the hippocampal formations. Attempts to control the status activity by diazepam intravenously were without striking effects, but very specific acoustic stimuli influenced the discharging pattern of the gyrus of Heschl.
Kinesthetic perceptual disturbance in musculoskeletal disease.
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Two-tone average evoked response in Korsakoff patients.
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Minimal brain dysfunction and the treatment of psychoneuroses.
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Is the spatial deficit in strabismic amblyopia due to loss of cells or an uncalibrated disarray of cells?
We examine two competing explanations for the spatial localization deficit in human strabismic amblyopia, namely neural undersampling and uncalibrated neural disarray. An undersampling hypothesis would predict an associated deficit for contrast discrimination for which we find no evidence in strabismic amblyopia. A neural disarray hypothesis would predict an associated deficit in the degree to which stimuli appear spatially distorted. We find evidence for such a deficit in strabismic amblyopia. We propose that the spatial deficit in strabismic amblyopia is due to a filter-based distortion which is unable to be re-calibrated by higher visual centres.
Clinical assessment of pediatric disorders of higher cerebral function.
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The effects of visual cortex lesions on the perception of rotated shapes.
Monkeys with inferior temporal cortex lesions cannot discriminate between different shapes (e.g., + vs. O) but can discriminate between shapes that differ only in orientation (e.g., 6 vs 9). Lesions of the parietal cortex, on the other hand, impair the discrimination of rotated shapes but spare the ability to discriminate between different shapes. A similar dissociation is found between some visual agnosics who can match but not identify rotated views of objects and other patients who can identify and discriminate objects only if the view is conventional; any change in orientation disrupts performance. In this paper we argue that two mechanisms may be available for the perception of rotated shapes. Which mechanism is used depends on the degree of rotation. It is suggested that the different effects of parietal and temporal lesions reflect the relative contributions of the two areas to the task and disrupt different stages of the two strategies used. A framework for the cortical processing of rotated shapes in the non-human primate is presented.
Canceling out both the real and the spectral lines.
Neglect patients typically show motor perseveration while canceling targets on the ipsilesional side. This behavior can be influenced by the presence vs. absence of targets on the (neglected) contralesional side (). As alternative explanations, the authors proposed (i) directional hypokinesia--the patient cannot perform reaching movements towards detected left-sided targets, and thus carries on canceling on the right side, and (ii) allochiria--the patient misperceives left-sided targets as located on the right side, and cancels them there. We report here data from a patient (EZ) that might confirm the second hypothesis. EZ was presented with 19 displays in which the number and position of cancellation targets on both sides were varied systematically. EZ showed motor perseveration while canceling, but this tendency did not vary across conditions. Interestingly though, EZ also drew cancellation marks in the empty space between the ipsilesional targets, and this phenomenon was significantly more intense when there were more targets on the neglected side. As EZ's comments suggested, such a behavior might reflect the attempt to cancel out delusional targets. Our speculation is that those objects were generated by allochiria.
Hemispheric visual atentional imbalance in patients with traumatic brain injury.
We find a spatially asymmetric allocation of attention in patients with traumatic brain injury (TBI) despite the lack of obvious asymmetry in neurological indicators. Identification performance was measured for simple spatial patterns presented briefly to a locus 5 degrees into the left or right hemifield, after precuing attention to the same (ipsilateral) or opposite (cross-hemifield) side. Though the cue was non-predictive of target location overall, performance was significantly slower for cross than for ipsilateral trials in both patients and controls. We tested 21 TBI patients without overt focal brain damage and nine control subjects. Only patients demonstrated significantly worse performance for left side presentation in the ipsilateral condition. Furthermore, in the cross-hemifield condition, the left-right difference seen in TBI patients was significantly larger-reflecting a failure in producing a leftward attention shift. Again no significant difference was found in controls. These hemifield effects suggest an asymmetry in the ability of TBI patients in shifting attention to the left hemifield, whether from central fixation or from a cue in the contra-lateral hemifield. The results support basic hypotheses regarding visual attention: Attentional control may be asymmetric and attention may be a distributed, rather than localized cortical function.
Selection for action and selection for awareness: evidence from hemispatial neglect.
In bedside testing of patients with hemispatial neglect, we have found that extinction for contralesional stimuli is less when the contralesional and ipsilesional items are different on the dimension to be reported relative to when they are the same. Importantly, a study that investigated this observation found that similarity on visual features that are not necessary for response does not impact the amount of extinction. These findings suggest that response requirements may determine what stimuli will and what stimuli will not gain access to awareness. In a related study, we found that extinction of contralesional stimuli was not determined by perceptual similarity of the ipsilesional and contralesional items but by whether they shared the same semantics (e.g., ONE + 1 ) or the same response (e.g., ONE = WON). Here, we report a single case study in which extinction was determined by whether the competing items shared the same response, regardless of whether they shared or differed in their visual features or semantics. When asked to read the item in each field, there was equivalent extinction in the conditions (ONE + ONE) and (ONE + 1) but less extinction in the condition (ONE + TWO). By contrast, when asked to count the number of characters in each field, there was more extinction in the condition (ONE + TWO) than (ONE + 1). When asked to categorize each item as either a word or digit, the degree of extinction was determined both by whether the items shared the same semantics and by whether they required the same response. The results are consistent with a biased competition model in which competition for selection is resolved flexibly depending on response requirements. Furthermore, the data provide evidence that unattended stimuli are processed to the level of response.