Biomedical subjects

Christine Whatmough

Publications and source records attributed to Christine Whatmough.

2 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.

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PubMed2004

Common and constrasting areas of activation for abstract and concrete concepts: an H2 15O PET study.

Lesion studies indicate that the lateral and inferior temporal cortex is a critical area of semantic memory storage, but little is known about the cortical organization of semantics within this area. One proposition has been that dominant physical characteristics of objects (structure, motility) are determining factors. A positron emission tomography experiment using the H2(15)O bolus method was performed to test this hypothesis by contrasting activation for concrete and abstract concepts. Unlike previous studies that considered this question, the task required explicit word meaning judgments, and blocks of trials were designed to be of equal difficulty for the two word classes. The task required elderly participants to read aloud the pair of words that was closer in meaning (e.g., spade-shovel vs. spade-carpet). Subtraction analyses that compared the semantic judgment tasks with a baseline condition indicated that both abstract and concrete concepts activated the left lateral temporal cortex. A direct comparison of abstract versus concrete scans indicated differences in the lateralization of fusiform activation. We conclude that although concreteness might be a critical factor in the fusiform cortex, it is not dominant in the lateral temporal cortex. A multistudy overview suggests that tasks that focus on one concept per trial activate areas posterior to y = -40, whereas those that invoke several concepts, as in the present study, activate areas anterior to this. Increased processing complexity may proceed in a posterior-anterior direction in the lateral temporal cortex.

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