Biomedical subjects

Kenneth F Valyear

Publications and source records attributed to Kenneth F Valyear.

8 recordsLinked to original sources

PubMed2006

The relationship between fMRI adaptation and repetition priming.

Neuroimaging investigations of the cortically defined fMRI adaptation effect and of the behaviorally defined repetition priming effect have provided useful insights into how visual information is perceived and stored in the brain. Yet, although both phenomena are typically associated with reduced activation in visually responsive brain regions as a result of stimulus repetition, it is presently unknown whether they rely on common or dissociable neural mechanisms. In an event-related fMRI experiment, we manipulated fMRI adaptation and repetition priming orthogonally. Subjects made comparative size judgments for pairs of stimuli that depicted either the same or different objects; some of the pairs presented during scanning had been shown previously and others were new. This design allowed us to examine whether object-selective regions in occipital and temporal cortex were sensitive to adaptation, priming, or both. Critically, it also allowed us to test whether any region showing sensitivity to both manipulations displayed interactive or additive effects. Only a partial overlap was found between areas that were sensitive to fMRI adaptation and those sensitive to repetition priming. Moreover, in most of the object-selective regions that showed both effects, the reduced activation associated with the two phenomena were additive rather than interactive. Together, these findings suggest that fMRI adaptation and repetition priming can be dissociated from one another in terms of their neural mechanisms.

Adaptation, Physiological↗

PubMed2006

Human parietal cortex in action.

Experiments using functional neuroimaging and transcranial magnetic stimulation in humans have revealed regions of the parietal lobes that are specialized for particular visuomotor actions, such as reaching, grasping and eye movements. In addition, the human parietal cortex is recruited by processing and perception of action-related information, even when no overt action occurs. Such information can include object shape and orientation, knowledge about how tools are employed and the understanding of actions made by other individuals. We review the known subregions of the human posterior parietal cortex and the principles behind their organization.

Arm↗

PubMed2006

Dissociating arbitrary stimulus-response mapping from movement planning during preparatory period: evidence from event-related functional magnetic resonance imaging.

In the present study, we aimed to dissociate the neural correlates of two subprocesses involved in the preparatory period in the context of arbitrary, prelearned stimulus-response (S-R) associations, namely, S-R mapping and movement planning (MP). We teased apart these two subprocesses by comparing three tasks in which the complexity of both S-R mapping and MP were independently manipulated: simple reaction time (SRT) task, go/no-go reaction time (GNGRT) task, and choice reaction time (CRT) task. We found that a more complex S-R mapping, which is the common element differentiating CRT and GNGRT from SRT, was associated with higher brain activation in the left superior parietal lobe (SPL). Conversely, a greater number of planned finger movements, which is the common difference between CRT and both SRT and GNGRT, was associated with higher brain activation in a number of frontal areas, including the left supplementary motor area (SMA), left dorsal premotor cortex (dPM), and left anterior cingulate cortex (ACC). The left-hemisphere dominance for S-R mapping could be related to the fact that arbitrary S-R mapping is often verbally mediated in humans. Overall, these results suggest a clear dissociation in the preparatory-set period between the more abstract role of left SPL in activating the appropriate S-R associations and the more concrete role played by the SMA, dPM, and ACC in preparing the required motor programs.

Adult↗

PubMed2005

The fusiform face area is not sufficient for face recognition: evidence from a patient with dense prosopagnosia and no occipital face area.

We tested functional activation for faces in patient D.F., who following acquired brain damage has a profound deficit in object recognition based on form (visual form agnosia) and also prosopagnosia that is undocumented to date. Functional imaging demonstrated that like our control observers, D.F. shows significantly more activation when passively viewing face compared to scene images in an area that is consistent with the fusiform face area (FFA) (p < 0.01). Control observers also show occipital face area (OFA) activation; however, whereas D.F.'s lesions appear to overlap the OFA bilaterally. We asked, given that D.F. shows FFA activation for faces, to what extent is she able to recognize faces? D.F. demonstrated a severe impairment in higher level face processing--she could not recognize face identity, gender or emotional expression. In contrast, she performed relatively normally on many face categorization tasks. D.F. can differentiate faces from non-faces given sufficient texture information and processing time, and she can do this is independent of color and illumination information. D.F. can use configural information for categorizing faces when they are presented in an upright but not a sideways orientation and given that she also cannot discriminate half-faces she may rely on a spatially symmetric feature arrangement. Faces appear to be a unique category, which she can classify even when she has no advance knowledge that she will be shown face images. Together, these imaging and behavioral data support the importance of the integrity of a complex network of regions for face identification, including more than just the FFA--in particular the OFA, a region believed to be associated with low-level processing.

Adolescent↗

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

The involvement of the "fusiform face area" in processing facial expression.

We conducted an fMRI investigation to test the widely accepted notion that the fusiform face area (FFA) mediates the processing of facial identity but not expression. Participants attended either to the identity or to the expression of the same set of faces. If the processing of identity is neuroanatomically dissociable from that of expression, then one might expect the FFA to show higher activation when processing identity as opposed to expression. Contrary to this prediction, the FFA showed higher activation for judgments of expression. Furthermore, the FFA was sensitive to variations in expression even when attention was directed to identity. Finally, an independent observation showed higher activation in the FFA for passive viewing of faces when expression was varied as compared to when it remained constant. These findings suggest an interactive network for the processing of expression and identity, in which information about expression is computed from the unique structure of individual faces.

Analysis of Variance↗

PubMed2005

No evidence for visuomotor priming in a visually guided action task.

Craighero et al. showed that grasping movements were initiated more quickly when the goal object shared the same orientation as a previously seen 'prime' object. Because the goal object was never visible in these experiments, however, it is unclear whether the data should be construed as evidence for a general visuomotor priming effect (as the authors contend), or only as evidence for a more specific priming effect on memory-guided actions. In Experiment 1, we demonstrated that memory-guided but not visually guided grasping can be primed by passive viewing of a prime object. In Experiment 2, we compared the effects of a prime object on the grasping and naming of a visible target object. Participants were faster to name the target when its shape was the same as the prime, consistent with well-established perceptual priming effects. Under the identical set of testing parameters, however, reaction time for grasping was unaffected by the orientation or the shape of the prime. In Experiment 3, participants grasped the goal object after either viewing or grasping a prime object. Reaction time for grasping was unaffected by the visual features of the prime in both tasks. Taken together, these results are consistent with the view that perceptual memory -- which presumably underlies visual priming effects -- is largely irrelevant for programming the metrics of actions to visible objects. Visually guided actions are programmed in real-time by dedicated visuomotor modules that appear to be insensitive to the priming effects that are a hallmark of visual perception.

Adolescent↗

PubMed2003

Photostimulation induces rapid growth of song-control brain regions in male and female chickadees (Poecile atricapilla).

To examine the effect of photoperiodic condition on song-control nuclei we examined three groups of male and female black-capped chickadees (Poecile atricapilla). Photorefractory birds were held on long days for several months and had fully regressed gonads. Photosensitive birds were held on short days for several months and had small gonads. Photostimulated birds were transferred to long days for 16 days following several months of short days. Following these photoperiod treatments we determined the volume of the song-control nuclei HVc, Area X, and (RA). There were significant sex differences in HVc and Area X, but not in RA. There were also significant photoperiod effects in HVc and Area X. Thus, sex and photoperiod differences in the song system exist in a species in which both sexes produce learned calls year-round.

Animals↗