Biomedical subjects

David Westwood

Publications and source records attributed to David Westwood.

3 recordsLinked to original sources

PubMed2005

A double dissociation between sensitivity to changes in object identity and object orientation in the ventral and dorsal visual streams: a human fMRI study.

We used an event-related fMR-adaptation paradigm to investigate changes in BOLD activity in the dorsal and ventral visual streams as a function of object identity and object orientation. Participants viewed successive paired images of real-world, graspable objects, separated by a visual mask. The second image of each pair was either: (i) the same as the first image, (ii) different only in identity, (iii) different only in orientation, or (iv) different in both identity and orientation. A region in the parieto-occipital cortex (dorsal stream) showed a selective increase in BOLD activity with changes in object orientation, but was insensitive to changes in object identity. In contrast, a region in the temporo-occipital cortex (ventral stream) showed a selective increase in activity with changes in identity, but was insensitive to changes in orientation. The differential sensitivity to orientation and identity is consistent with the idea that the dorsal stream plays a critical role in the visual control of object-directed actions while the ventral stream plays a critical role in object perception.

Brain Mapping↗

PubMed2005

Manipulability and living/non-living category effects on object identification.

Object naming studies have generally observed that both normal and brain damaged individuals are faster and more accurate at identifying non-living objects than living objects (). However, a potential confounding variable, manipulability, has been present in past studies that may mediate this effect. Previous studies that have observed a non-living advantage have often used manipulable and non-manipulable exemplars to represent the non-living and living groups, respectively. Under conditions which controlled for object manipulability and familiarity, results demonstrated advantages for the identification of non-manipulable and for living objects.

Adolescent↗

PubMed2003

Selective dysfunction of tool-use: a failure to integrate somatosensation and action.

Apraxia is thought to reflect a disruption to high-level perceptual, cognitive and motor systems that form a distributed praxis network. Some authors suggest that apraxic deficits are unique to the neurology clinic; however, mounting evidence suggests that apraxic deficits are observable in natural contexts (e.g. Foundas et al., 1995). Naturalistic gesture production involves the integration of conceptual knowledge, gesture ideation, visual and somatosensory cues, and executive processes. Impairments in this context are therefore of interest from a clinical and theoretical standpoint. We present the case of a young female stroke patient (CK) demonstrating a novel limb praxis profile. CK's conceptual, evocation and praxis executive stages were evaluated: performance was contrasted to 30 healthy controls. CK was able to pantomime and imitate transitive gestures, suggesting that her ideational, executive and visual analytic systems were intact. Moreover, CK showed a good conceptual understanding of tools, objects and actions. However, CK demonstrated poor gesture production when actually using the tool associated with the action--a chronic and bilateral deficit that persisted at a 5-year follow-up assessment. Thus, CK's deficit appears to represent a specific and chronic disruption to high-level praxis systems that incorporates tactile inputs into the unfolding gesture production sequence.

Adult↗