Biomedical subjects

M J Riddoch

Publications and source records attributed to M J Riddoch.

At least 19 recordsLinked to original sources

PubMed2005

Don't think twice, it's all right--contralesional dependency for bimanual prehension movements.

In bimanual coordination when moving the hands to two separate objects, subjects tend to initiate and terminate the movements together, even when the targets are at different distances or are of a different size. Additionally, each hand tends to scale its grasp independently to the object to be grasped. Here, we report the performance of a patient, who had previously shown signs of motor neglect, on two experiments investigating coupling and independence in bimanual coordination. The patient showed relatively normal bimanual behaviour for the transport phase of prehension when objects were placed at different distances (Experiment 1), but abnormal behaviour for the grasp component when objects were of different sizes (Experiment 2). Moreover, the contralesional limb demonstrated a dependency of grasp that was related to the object grasped by the ipsilesional limb. We discuss the possible underlying mechanisms of this dependency in relation to competitive motor programming and attentional bias. The results also reinforce the view that the transport and grasp components of prehension are distinct processes.

Aged↗

PubMed2003

Neuropsychometric outcome following aortic arch surgery: a prospective randomized trial of retrograde cerebral perfusion.

BACKGROUND: Aortic surgery requiring hypothermic circulatory arrest is associated with a high incidence of brain injury. However, knowledge of neuropsychometric outcome is limited. Retrograde cerebral perfusion has become a popular adjunctive technique to hypothermic circulatory arrest. The aim of this study was to assess neuropsychometric outcome and compare the 2 techniques. METHODS: In a prospective randomized trial, 38 patients requiring elective aortic arch surgery were allocated to either hypothermic circulatory arrest plus retrograde cerebral perfusion or hypothermic circulatory arrest alone. Neuropsychometric testing was performed preoperatively, and at 6 weeks and 12 to 24 weeks postoperatively. Deficit was defined as a 20% decline in 2 tests or more. Standardized Z scores were calculated for each patient and test. Eighteen patients underwent hypothermic circulatory arrest and 20 patients underwent hypothermic circulatory arrest plus retrograde cerebral perfusion. The mean cardiopulmonary bypass, hypothermic circulatory arrest, and retrograde cerebral perfusion durations were 169, 30, and 25 minutes, respectively. RESULTS: There were 2 deaths and 2 neurological deficits. At 6 weeks postoperatively, 77% of the hypothermic circulatory arrest group and 93% of the hypothermic circulatory arrest plus retrograde cerebral perfusion group had a deficit (P =.22). At 12 weeks this was reduced to 55% and 56%, respectively (P =.93). There was a worse total Z test score in the hypothermic circulatory arrest plus retrograde cerebral perfusion group at 12 weeks (P =.05). Neuropsychometric change did not correlate with hypothermic circulatory arrest duration, presence of aortic atheroma, cannulation technique, or procedure. CONCLUSIONS: Hypothermic circulatory arrest plus/minus retrograde cerebral perfusion is associated with a high incidence of neuropsychometric change despite ostensibly normal clinical outcomes and apparently safe arrest duration. Retrograde cerebral perfusion did not improve outcome in this small study.

Adult↗

PubMed2001

An experimental analysis of unintentional lower limb action.

We provide an experimental analysis of the factors that determine unintentional lower limb action in a patient with cortico-basal degeneration. We show a dissociation between lower limb movements in a novel task and the ability to remember task instructions. In addition, there were effects of the pre-potency of the learned response to the stimulus, with different effects emerging with familiar and unfamiliar stimuli.

Basal Ganglia Diseases↗

PubMed2001

Detection by action: neuropsychological evidence for action-defined templates in search.

How do we detect a target in a cluttered environment? Here we present neuropsychological evidence that detection can be based on the action afforded by a target. A patient showing symptoms of unilateral neglect following damage to the right fronto-temporal-parietal region was slow and sometimes unable to find targets when they were defined by their name or even by a salient visual property (such as their color). In contrast, he was relatively efficient at finding a target defined by the action it afforded. Two other patients with neglect showed an opposite pattern; they were better at finding a target defined by its name. The data suggest that affordances can be effective even when a brain lesion limits the use of other properties in search tasks. The findings give evidence for a direct pragmatic route from vision to action in the brain.

Agnosia↗

PubMed2001

Position-matching in the upper limb: professional ballet dancers perform with outstanding accuracy.

OBJECTIVES: To investigate the accuracy in position-matching in the upper limb in two groups of subjects who were physically fit and movement aware. DESIGN: A mixed-group design was used. Objective measurement of the accuracy in position-matching at the shoulder and elbow in both dominant and nondominant arms consisted of photographic record of the position-matching test, with goniometric measurement. SETTINGS: Physiotherapy department at the Birmingham Royal Ballet and School of Health Science, University of Birmingham. SUBJECTS: Two subject groups: physiotherapy students (n = 10), professional ballet dancers (n = 10). RESULTS: A mixed design analysis of variance found significant differences between the accuracy in position-matching at both the shoulder and elbow joints in the two groups (p < 0.05), with the ballet dancers having greater accuracy then the physiotherapy students. A significant difference in the joint positions tested were demonstrated (p < 0.05) with the positions of abduction at the shoulder and extension of the elbow showing greatest accuracy in matching. There was no significant difference found between the dominant and nondominant upper limb in position-matching. CONCLUSION: Professional ballet dancers demonstrated greater accuracy in position-matching the upper limb, implying that mass and continuing practice can improve a motor sensory skill.

Adult↗

PubMed2000

One more cup of coffee for the road: object-action assemblies, response blocking and response capture after frontal lobe damage.

We report data from a patient, FK, who manifested 'utilisation' behaviour after bilateral lesions of the medial frontal and anterior temporal lobes. In tasks requiring actions to be made with the hand compatible with the orientation of a cup, FK was able to ignore irrelevant distractors that fell in the path of action to the target. However, errors were made when the distractors were other cups. These errors reflected the hand selected on the basis of the properties of the target, suggesting that distractors competed to control the action after selection of the target. When similar in kind to the target, distractors sometimes captured the action. However, distractors that were associated with an action related to the target blocked the usual hand response. These results suggest a complex interlocking of attention and action when grasping responses are made to a target amongst distractors. There is initial selection of the target, but distractors on the path of a reach can then compete for control of the action. Distractors can be inhibited if they do not match the properties of the specified target, and there can also be inhibition of concurrently activated responses. We show that the magnitude of the inhibition is proportional to the strength of learned object-action associations.

Adult↗

PubMed1999

From objects to names: a cognitive neuroscience approach.

To name an object, we need both to recognize it and to access the associated phonological form, and phonological retrieval itself may be constrained by aspects of the visual recognition process. This paper reviews evidence for such constraints, drawing on data from experimental psychology, neuropsychology, functional imaging, and computational modelling. Data on picture identification in normal observers demonstrate that the speed of name retrieval processes differs for natural objects and artifacts, due at least in part to differences in visual similarity between exemplars within these categories. Also, effects of variables on early and late stages of object identification combine in an interactive rather than an additive manner, consistent with object processing stages operating in a continuous rather than a discrete manner. Neuropsychological evidence supports this proposal, demonstrating that subtle perceptual deficits can produce naming problems, even when there is good access to associated semantic knowledge. Functional activation studies further show increased activity in visual processing areas when conditions stress object naming relative to the recognition of familiar object structures. These studies indicate that object naming is based on a series of continuous processing stages and that naming involves increased visual processing relative to recognition tasks. The data can be modelled within an interactive activation and competition framework.

Adult↗

PubMed1999

Memories are made of this: the effects of time on stored visual knowledge in a case of visual agnosia.

We report the effects of the passage of time on the longterm visual knowledge for objects in a patient with visual agnosia (H.J.A.). The naming of real objects was found to have improved, although this was not associated with any change in H.J.A.'s basic perceptual abilities which were stable over a 16-year period. The improvement in object naming was attributed to better use of non-contour-based visual information (such as surface detail and depth cues). In addition, we demonstrate a deterioration in H.J.A.'s long-term memory for the visual properties of objects, and argue that this has occurred as a result of his having impaired perceptual input. The deterioration was only apparent in drawing from memory and in the verbal descriptions of items; with forced-choice testing, H.J.A. operated at ceiling; we propose that current tests of visual imagery may not be sufficiently sensitive to detect subtle impairments of visual memory. Our findings can be taken to indicate that perceptual and memorial processes are not functionally independent, but are linked in an interactive manner.

Aged↗

PubMed1997

Top-down processes in object identification: evidence from experimental psychology, neuropsychology and functional anatomy.

Many models of object identification are bottom-up and serial in nature; processing at a first stage needs to be complete before it is passed on to a subsequent stage, and there is no top-down feedback from the later to the earlier stages. However, data on picture identification in normal observers contradict a strict serial account of processing, since effects of variables on early and late stages of object identification combine in an interactive rather than an additive manner. Recent neuropsychological and functional anatomical data also indicate that object identification involves top-down activation of earlier stages of visual processing. In neuropsychological patients, subtle perceptual deficits can produce naming problems, even when there is good access to associated semantic knowledge; in functional activation studies, there is increased activity in visual processing areas when conditions require object naming relative to object recognition. These studies provide evidence that increased visual processing occurs in identification tasks, suggesting that there is re-current feedback during the identification process.

Form Perception↗

PubMed1997

Luminance and edge information in grouping: a study using visual search.

Preattentive grouping is supported by 2 systems, a brightness system that is contrast polarity sensitive and an edge system that is relatively insensitive to contrast polarity. Search was spatially parallel for pairs of same contrast polarity vertically aligned circles, among horizontal pairs, and serial for pairs of circles that had the opposite contrast polarity (Experiments 1-3). By replacing the circles with squares, the authors investigated the effect of adding collinear edge information. When collinear edges were present, the polarity difference between paired items did not disrupt grouping (Experiments 4-6). These results support models of grouping in which brightness and edge information are processed separately (e.g., S. Grossberg & E. Mingolla, 1985) and models of visual search in which complex relations between stimuli can be computed in parallel across the display.

Adult↗

PubMed1997

A neuropsychological perspective on three schizophrenic patients with midline structural defects.

BACKGROUND: The relationship between midline structural defects and schizophrenia remains unclear, although a number of neuroradiological studies have reported an association between schizophrenia and a range of anomalies. METHOD: Three patients are reported, each diagnosed with schizophrenia and neuroradiological evidence of midline structural anomalies. MRI scans are reported in conjunction with performance over a range of neuropsychological tests designed to assess frontal and lateralised cognitive functions. RESULTS: Evidence of anterior dysfunction was present in all three cases, while on an individual basis patients displayed varying patterns of preserved and dysfunctional cognitive processing. CONCLUSION: The reported findings raise a number of interesting issues regarding the nature of hemispheric involvement in schizophrenia.

Adult↗

PubMed1996

Visual processing in patients with Frégoli syndrome.

We investigated four paranoid schizophrenic patients diagnosed with Frégoli delusion, and four matched psychotic controls. Neuropsychological testing included visual and verbal recognition memory, in addition to a comparison of left and right hemispheric processing of two different classes of stimuli, animate and inanimate objects. Performance on the recognition memory test failed to discriminate between the two psychotic groups on the basis of facial recognition, however, the patients with Frégoli delusion failed to show the right hemisphere processing advantage for the animate class of stimuli found for the set of norms and also present in the psychotic control group. These results are discussed in the context of both current theories of the delusional misidentification syndromes in general, and models of facial recognition in particular.

Journal Article↗

PubMed1994

Non-spatial extinction following lesions of the parietal lobe in humans.

Efficient behaviour in the visual environment requires selection between stimuli competing for control of action. Many current models of selection are spatial: relevant objects are chosen by attending to their locations. The unilateral stimulus extinction observed following lesions of the parietal lobe provides evidence for spatial selection. Such patients may identify a single stimulus presented in their contralesional field, but can fail to detect the same stimulus when a competing stimulus is shown simultaneously on the ipsilesional side. Here we demonstrate that extinction need not be spatial in nature, but may be determined by characteristics of the objects to be selected. In two patients with parietal lobe lesions and poor spatial localization, pictures extinguished words and closed shapes extinguished open shapes. This object-based extinction indicates the existence of biases within non-spatial selection mechanisms which are independent of biases produced by spatial selection mechanisms. We suggest that selection of objects for action requires that the 'winners' produced by the independent competitive biases for selection are bound together within distinct neural areas concerned with object properties and space.

Brain Diseases↗

PubMed1994

Recognition impairments and face imagery.

We investigated face imagery for H.J.A. and P.H., who experience profound difficulties in recognising familiar faces. H.J.A.'s problems involve a perceptual impairment that compromises the integration of features into a coherent representation, and he does not show covert recognition of faces in indirect tests. In contrast, P.H. has shown extensive covert recognition effects, leading to the suggestion that his deficit occurs at a higher level of visual processing than H.J.A.'s. H.J.A. and P.H. were given tasks intended to explore their ability to answer questions that depended on imaging single faces, and on configuration-based or feature-based comparisons of imaged sets of three faces. For all of these face imagery tasks, P.H.'s overall performance was severely impaired. H.J.A., though, showed preserved face imagery when imaging single faces and when making feature-based comparisons between imaged faces. However, when configuration-based comparisons were demanded H.J.A. also showed a severe and stable impairment of face imagery. These observations are inconsistent with the idea that face recognition impairments have a unitary underlying cause and vary only in severity. Instead, they imply multi-stage causation, with the nature of consequent impairments of face imagery being determined by the level at which the recognition deficit arises.

Adult↗

PubMed1993

Expression is computed separately from facial identity, and it is computed separately for moving and static faces: neuropsychological evidence.

We report data contrasting the processing of facial identity from static photographs, and facial expression from static and moving images, in two patients with face processing impairments. One patient is markedly impaired at perceiving facial identity and he is poor at discriminating facial expression and gender from static photographs of faces. In contrast, he performs normally when required to make judgements of facial expression and gender to faces depicted by sets of moving light dots. The second patient is relatively good at perceiving facial identity, but poor at judging emotional expression from both static and moving faces. The data are consistent with the existence of separate processes for encoding face identity and facial expression, and, furthermore, indicate the separate encoding of expression from moving and static images.

Cerebrovascular Disorders↗

PubMed1993

Object agnosias.

Explore the source record for details and available documents.

Agnosia↗

PubMed1992

Parallel pattern processing and visual agnosia.

A series of visual search experiments are reported examining pattern processing in a visual agnosic patient. We examined search for targets defined by: (I) the combination of their features relative to homogeneous distractors; (2) the combination of their features relative to heterogeneous distractors; and (3) a single feature difference relative to the distractors (their orientation). Normal subjects demonstrate evidence of spatially parallel search when combined-feature targets are detected against homogeneous distractors, and when targets are defined by a salient feature difference. There are non-linear effects of the number of distractors present, and absent responses can be as fast as present. In contrast, search times for combined-feature targets amongst heterogeneous distractors increase linearly with display size, with the slope for absent responses about twice that for present. The contrast between search for combined-feature targets amongst homogeneous and heterogeneous distractors can be attributed to the effects of grouping between distractors and between distractors and targets (Duncan & Humphreys, 1989, 1992; Humphreys & Muller, in press). Grouping between homogeneous distractors facilitates search. An agnosic patient, HJA, showed normal search functions for single-feature targets and for combined-feature targets amongst heterogeneous distractors. However, he was impaired at search for combined-feature targets amongst homogeneous distractors. This suggests that HJA is selectively impaired at grouping conjunctions of form features. The relations between HJA's agnosia and his problem in the parallel grouping of form conjunctions are discussed, as are the implications of the work for understanding normal vision.

Adult↗

PubMed1991

Parallel computation of primitive shape descriptions.

This article reports evidence that parallel search functions can occur when heterogeneous conjunction elements configure into a single object description. Experiment 1 demonstrates parallel search for form conjunctions presented in displays of heterogeneous nontargets when closure and good continuation between display elements are exhibited. When closure and good continuation are absent, reaction times increase linearly with set size (Experiment 2). Experiment 3 demonstrates a halfway stage between these two extremes, in which displays have closure but not good continuation. Finally, selection of object descriptions is shown to be temporally limited to one object at a time (Experiment 4). The data are incompatible with both local feature-based and distractor similarity-based accounts of visual search; however, they are compatible with there being an important role for preattentive feature combinations forming primitive object descriptions. Parallel search functions can occur when heterogeneous conjunctions configure into a single object description.

Adult↗