Biomedical subjects

Martin Arguin

Publications and source records attributed to Martin Arguin.

10 recordsLinked to original sources

PubMed2005

Establishing visual category boundaries between objects: a PET study.

Individuals with Alzheimer's disease (AD) often have problems in recognizing common objects. This visual agnosia may stem from difficulties in establishing appropriate visual boundaries between visually similar objects. In support of this hypothesis, showed that AD subjects have difficulties in establishing visual category boundaries between continuously graded shapes. In an attempt to investigate the neural basis of these impairments, the current study required a group of neurologically healthy elderly participants to categorically classify a series of ellipses varying in width while regional blood flow changes were measured using positron emission tomography (PET). Two categorization conditions were compared in order to isolate changes in cortical activity that dissociated the categorization of shapes situated either near or far from a category boundary that divided the width continuum. The participants produced a discontinuity in the probability and speed of categorizing the shapes at some point along the continuum, suggesting that the objects were classified into distinct categories. Moreover, a comparison of the PET scans obtained while the subjects were categorizing the shapes situated near vs. far form the category boundary revealed significant differences in cortical activity in the parietal and frontal brain areas. These findings suggest that both visuo-spatial and decision making mechanisms may be involved in establishing categorical distinctions between continuously graded stimuli. It is proposed that the functional role of the parietal and frontal cortical regions in establishing visual boundaries between categories of objects may be relevant for understanding object recognition impairments in AD.

Aged↗

PubMed2005

The structure of three-dimensional object representations in human vision: evidence from whole-part matching.

This article examines how the human visual system represents the shapes of 3-dimensional (3D) objects. One long-standing hypothesis is that object shapes are represented in terms of volumetric component parts and their spatial configuration. This hypothesis is examined in 3 experiments using a whole-part matching paradigm in which participants match object parts to whole novel 3D object shapes. Experiments 1 and 2, consistent with volumetric image segmentation, show that whole-part matching is faster for volumetric component parts than for either open or closed nonvolumetric regions of edge contour. However, the results of Experiment 3 show that an equivalent advantage is found for bounded regions of edge contour that correspond to object surfaces. The results are interpreted in terms of a surface-based model of 3D shape representation, which proposes edge-bounded 2-dimensional polygons as basic primitives of surface shape.

Form Perception↗

PubMed2005

How to make the word-length effect disappear in letter-by-letter dyslexia: implications for an account of the disorder.

The diagnosis of letter-by-letter (LBL) dyslexia is based on the observation of a substantial and monotonic increase of word naming latencies as the number of letters in the stimulus increases. This pattern of performance is typically interpreted as indicating that word recognition in LBL dyslexia depends on the sequential identification of individual letters. We show, in 7 LBL patients, that the word-length effect can be eliminated if words of different lengths are matched on the sum of the confusability (visual similarity between a letter and the remainder of the alphabet) of their constituent letters. Additional experiments demonstrate that this result is mediated by parallel letter processing and not by any compensatory serial processing strategy. These findings indicate that parallel processing contributes significantly to explicit word recognition in LBL dyslexia and that a letter-processing impairment is fundamental in causing the disorder.

Dyslexia, Acquired↗

PubMed2004

Recovery from aphasia: a longitudinal study on language recovery, lateralization patterns, and attentional resources.

Despite the large body of evidence on the neural basis of the recovery from aphasia, the role of either cerebral hemisphere remains controversial. This paper reports the results of a longitudinal single-case study on the patterns of lateralization for lexical semantic processing during the recovery from aphasia. The experimental protocol included a lateralized lexical decision task (LDT), an attentional task and a language test. There was no presentation site effect on the LDT, and the performance was jointly influences by attentional and language factors. These findings suggest that the recovery of lexical semantic processing may be sustained by both cerebral hemispheres, and highlights the importance of experimental protocols that allow examining both language and attentional factors modulating factors modulating the recovery from aphasia.

Analysis of Variance↗

PubMed2004

Independent processing of parts and of their spatial organization in complex visual objects.

A visual search experiment using synthetic three-dimensional objects is reported. The target shared its constituent parts, the spatial organization of its parts, or both with the distractors displayed with it. Sharing of parts and sharing of spatial organization both negatively affected visual search performance, and these effects were strictly additive. These findings support theories of complex visual object perception that assume a parsing of the stimulus into its higher-order constituents (volumetric parts or visible surfaces). The additivity of the effects demonstrates that information on parts and information on spatial organization are processed independently in visual search.

Humans↗

PubMed2004

Two-way interactions between music and language: evidence from priming recognition of tune and lyrics in familiar songs.

A priming technique was employed to study the relations between melody and lyrics in song memory. The procedure involved the auditory presentation of a prime and a target taken from the same song, or from unrelated but equally familiar songs. To promote access to memory representations of songs, we varied the format of primes and targets, which were either spoken or sung, using the syllable /1a/. In each of the four experiments, a prime taken from the same song as the target facilitated target recognition, independently of the format in which it occurred. The facilitation effects were also found in conditions close to masked priming because prime recognizability was very low, as assessed in Experiment 1 by d' measures. Above all, backward priming effects were observed in Experiments 2, 3, and 4, where song order was reversed in the prime-target sequence, suggesting that words and tones of songs are not connected by strict temporal contingencies. Rather, the results indicate that, in song memory, text and tune are related by tight connections that are bidirectional and automatically activated by relatively abstract information. Rhythmic similarity between linguistic stress pattern and musical meter might account for these priming effects.

Adult↗

PubMed2003

Distinct mechanisms account for the linear non-separability and conjunction effects in visual shape encoding.

In a series of visual search experiments involving simple 2D shapes, Arguin and Saumier (2000) showed that targets that were made of conjunctions of distractor features or that were a linear combination of distractor features were searched at significantly slower rates than single-feature linearly separable targets. The present study assessed whether these conjunction and linear nonseparability effects can be attributed to distinct mechanisms. Specifically, we studied the impact of target-distractor similarity on the search rates for single-feature, conjunction, and linearly nonseparable targets. The results replicate the conjunction and linear nonseparability effects obtained by Arguin and Saumier. They also show that the conjunction and linear separability effects are differently modulated by variations in target-distractor similarity. This dissociation demonstrates that both effects are based on distinct mechanisms. The possible nature of these mechanisms is discussed.

Adult↗

PubMed2003

Orientation invariance in visual object priming depends on prime-target asynchrony.

Two experiments are reported in which orientation effects on visual object recognition latency were examined. In Experiment 1, we assessed picture-naming performance as a function of image-plane stimulus orientation and found increasing response times with increased misorientation of the stimulus. In Experiment 2, we examined the repetition priming effect on the identification of upright targets as a function of prime orientation. With time delays of 100, 200, or 500 msec between the onset of the prime and that of the target (i.e., stimulus onset asynchrony [SOA]), the magnitude of the priming effect decreased with increasing misorientation of the prime. These results contrast with the orientation-invariant priming effects reported in some previous repetition priming studies. These investigations all used relatively long prime-target SOAs. Confirming the crucial role of the latter variable, Experiment 2 shows that the magnitude of the repetition priming effect is invariant across prime orientations with an SOA of 1,000 msec. The possible implications of the present observations with respect to the issue of orientation invariance versus dependency of the visual object recognition processare discussed.

Adult↗

PubMed2002

The contribution of the right cerebral hemisphere to the recovery from aphasia: a single longitudinal case study.

We examined the role of the right cerebral hemisphere in the recovery from aphasia of HJ, a 50-year-old right-handed and unilingual man who suffered from severe aphasia caused by an extensive left hemisphere (LH) lesion. He was followed-up over 10 months at 4-month intervals, with a lateralized lexical decision task (LDT), an attentional task, and a language battery. Testing started when HJ was 2 months poststroke. In the LDT, words were presented to central vision or lateralized to the left or right visual hemifield. At each test period, we examined the effect of the degree of imageability (high vs. low), and the grammatical class (noun vs. verb) of the targets on HJ's response times and error rates, with left visual field, right visual field, and central vision presentations. The results of the experiment showed that the pattern obtained with the LDT could not be accounted for by fluctuations in attention. There was an interaction of grammatical class with degree of imageability with left visual field displays only. The right hemisphere (RH) was faster with high-imageability words than with low-imageability words, regardless of their grammatical class. There was also an overall RH advantage on response times at 2 and 6 months after onset. This RH predominance coincided with a major recovery of language comprehension and the observation of semantic paralexias, while no major change in language expression was observed at that point. Ten months after onset, the pattern of lateralization changed, and response times for the LDT with either presentation site were equivalent. This LH improvement coincided with some recovery of language expression at the single-word level. The results of this study suggest that, in cases of severe aphasia caused by extensive LH lesions, the RH may play an important role in the recovery process. Furthermore, these results show that the contribution of the two cerebral hemispheres to recovery may vary overtime and affect specific aspects of language.

Aphasia↗

PubMedDate not supplied

Visual object agnosia as a problem in integrating parts and part relations.

Current models of vision generally assume that the recognition of visual objects is achieved by encoding their component parts, as well as the spatial relations among parts. The current study examined how the processing of parts and their configurations may be affected in visual agnosia due to brain damage. Both a visual agnosic patient (AR) and healthy control subjects performed a visual search task in which they had to discriminate between targets and distractors that varied according to whether they shared their parts and/or their configuration. The results show that AR's visual search rates are disproportionally slow when targets and distractors share the same configuration than when they have different configurations. AR is also found to be disproportionately slow in discriminating targets and distractors that share identical parts when the targets and distractors share the same configuration. With differently configured targets and distractors, AR shows no part sharing effect. For controls, in contrast, the part and configuration sharing effects occur independently of one another. It is concluded that AR's object recognition deficit arises from difficulties in discriminating objects that share their configuration, and from an abnormal dependency of part information processing upon object configuration.

Adult↗