Biomedical subjects

T C Handy

Publications and source records attributed to T C Handy.

11 recordsLinked to original sources

PubMed2001

Brain activations associated with shifts in response criterion on a recognition test.

Sensitivity and bias can be manipulated independently on a recognition test. The goal of this fMRI study was to determine whether neural activations associated with manipulations of a decision criterion would be anatomically distinct from neural activations associated with manipulations of memory strength and episodic retrieval. The results indicated that activations associated with shifting criteria (a manipulation of bias) were located in bilateral regions of the lateral cerebellum, lateral parietal lobe, and the dorsolateral prefrontal cortex extending from the supplementary motor area. These regions were anatomically distinct from activations in the prefrontal cortex produced during memory-based retrieval processes (manipulations of sensitivity), which tended to be more medial and anterior. These later activations are consistent with previous studies of episodic retrieval. Determining patterns of neural activations associated with decision-making processes relative to memory processes has important implications for Cognitive Neuroscience, including the use of these patterns to compare memory models in different paradigms.

Adolescent↗

PubMed2001

Position paper on fatal abusive head injuries in infants and young children.

This article represents the work of the National Association of Medical Examiners Ad Hoc Committee on shaken baby syndrome. Abusive head injuries include injuries caused by shaking as well as impact to the head, either by directly striking the head or by causing the head to strike another object or surface. Because of anatomic and developmental differences in the brain and skull of the young child, the mechanisms and types of injuries that affect the head differ from those that affect the older child or adult. The mechanism of injury produced by inflicted head injuries in these children is most often rotational movement of the brain within the cranial cavity. Rotational movement of the brain damages the nervous system by creating shearing forces, which cause diffuse axonal injury with disruption of axons and tearing of bridging veins, which causes subdural and subarachnoid hemorrhages, and is very commonly associated with retinal schisis and hemorrhages. Recognition of this mechanism of injury may be helpful in severe acute rotational brain injuries because it facilitates understanding of such clinical features as the decrease in the level of consciousness and respiratory distress seen in these injured children. The pathologic findings of subdural hemorrhage, subarachnoid hemorrhage, and retinal hemorrhages are offered as "markers" to assist in the recognition of the presence of shearing brain injury in young children.

Battered Child Syndrome↗

PubMed2001

Perceptual load and visuocortical processing: event-related potentials reveal sensory-level selection.

Behavioral evidence suggests that the processing of parafoveal stimuli decreases as the perceptual demands of a task at fixation increase. However, it remains unclear whether or not this effect of perceptual load occurs during initial sensory-level processing at early stages of visuocortical analysis. Using event-related potential measures, we found that increasing the perceptual load of foveal targets led to a significant decrease in the sensory-evoked response to parafoveal stimuli. Moreover, these effects were observed using two different operational definitions of perceptual load. This result indicates that perceptual load affects the flow of information during the initial stages of visuocortical processing.

Adult↗

PubMed2001

Combined expectancies: event-related potentials reveal the early benefits of spatial attention that are obscured by reaction time measures.

Visual spatial attention has been likened to a "spotlight" that selectively facilitates the perceptual processing of events at covertly attended locations. However, if participants have advance knowledge of the likely location of an impending target and the likely response it will require, facilitation in response performance does not occur for targets at the expected (or attended) location that require an unexpected response. Event-related potentials (ERPs) were recorded during a discrimination task in which the most likely target location and target response were simultaneously cued prior to target onset. The ERPs showed evidence of enhanced perceptual-level processing for all targets at attended locations. These results suggest that the lack of response facilitation for unexpected targets at attended locations is likely due to postperceptual processes that are activated by the inclusion of nonspatial stimulus expectancies, response expectancies, or both.

Adult↗

PubMed2000

Capacity theory as a model of cortical behavior.

Growing evidence suggests that a more complete understanding of cortical function requires developing cognitive models that are predictive of multivariate neural behavior (e.g., Raichle, 2000; Shulman et al., 1997). Towards this end, one approach is to interpret population-specific activity in cortex from the perspective of capacity theories of selective attention (e.g., Handy, Hopfinger, & Mangun, in press). In brief, the model is founded on the ideas that (1) processing capacity is limited and (2) different processes may draw on different capacities (e.g., Boles & Law 1998; Polson & Friedman, 1988; see Kramer & Spinks, 1991). Testable hypotheses are then based on whether manipulations of process-specific load will lead to negative or positive covariation between different function-related clusters of activation in cortex--the predicted pattern depends on whether or not the clusters in question are assumed to share a common processing capacity. Expanding on these ideas, the current article addresses several recent issues that have arisen in the effort to apply capacity theory to the study of cortical function.

Cerebral Cortex↗

PubMed2000

Attention and spatial selection: electrophysiological evidence for modulation by perceptual load.

Behavioral data have suggested that perceptual load can modulate spatial selection by influencing the allocation of attentional resources at perceptual-level processing stages (Lavie & Tsal, 1994). To directly test this hypothesis, event-related potentials (ERPs) were recorded for both low- and high-perceptual-load targets in a probabilistic spatial cuing paradigm. The results from three experiments showed that, as measured by the lateral occipital P1 and N1 ERP components, the magnitude of spatially selective processing in extrastriate visual cortex increased with perceptual load. Furthermore, these effects on spatial selection were found in the P1 at lower levels of perceptual load than in the N1. The ERP data thus provide direct electrophysiological support for proposals that link perceptual load to early spatial selection in visual processing. However, our findings suggest a relatively broader model--where perceptual load is but one of many factors mediating early selection.

Adolescent↗

PubMed1999

Hypernatremia and subdural hematoma in the pediatric age group: is there a causal relationship?

Several researchers in the 1950's proposed that hypernatremia causes water to leave brain cells, shrinking the brain, thus tearing the bridging veins and resulting in subdural hematomas. Although the old literature suggests mechanisms linking the two in a cause and effect relationship, there is controversy as to whether hypernatremia leads to subdural bleeding or whether the reverse is true. This issue is important for forensic pathologists who must distinguish natural disease from trauma. An etiologic link between hypernatremia and subdural hematomas was suggested recently, and was proposed originally before Kempe's 1962 paper "The Battered Child Syndrome" which widely disseminated the concepts of child physical abuse, and of subdural bleeding resulting from non-accidental injury. Our study is a multifaceted investigation of infants which includes: a literature review, retrospective chart reviews of both living and deceased hypernatremic infants, a retrospective review of infants hospitalized with subdural hematoma, and a prospective collection of head injured, hypernatremic children. We conclude that hypernatremia, if present in association with subdural hemorrhage, is most likely secondary to intracranial pathology, and that hypernatremia often develops in critically ill infants suffering from a variety of medical conditions.

Child Abuse↗

PubMed1998

Sudden natural death in infants and young children.

This discussion will highlight common natural causes of sudden unexpected death in "healthy" infants and young children. Methods employed to render these diagnoses will be reviewed. Natural causes of sudden death found more commonly in adolescents and young adults will not be discussed.

Cardiovascular Diseases↗

PubMed1998

Postmortem diagnosis of leukodystrophies.

Leukodystrophies are progressive disorders involving the development and maintenance of myelin in the central and peripheral nervous systems. Although relatively uncommon, leukodystrophic disorders may be undiagnosed or misdiagnosed during life, and may appear as "sudden death." In such instances, these victims may be referred to a forensic pathologist. In general, leukodystrophies are inherited in an autosomal recessive manner so that proper postmortem diagnosis by the forensic pathologist is extremely important to the decendant's family for future family planning.

Adrenoleukodystrophy↗

PubMed1996

Spatial distribution of visual attention: perceptual sensitivity and response latency.

Studies of the spatial distribution of visual attention have shown that attentional facilitation monotonically decreases in a graded fashion with increasing distance from an attended location. However, reaction time (RT) measures have typically shown broader gradients than have signal detection (SD) measures of perceptual sensitivity. It is not clear whether these differences have arisen because the stages of information processing indexed by RT measures are different from those indexed by SD measures, or whether these differences are due to methodological confounds in the SD studies. In the present set of experiments, the spatial distribution of attention was studied by using a luminance detection task in an endogenous cuing paradigm that was designed to permit accurate calculations of SD and RT measures for targets at cued and uncued locations. Subjects made target-present/absent decisions at one of six possible cued or uncued upper visual hemifield locations on each trial. The results from three experiments suggest that the differences between broad and focal attentional distributions are not the result of different stages of information processing indexed by RT measures as opposed to SD measures. Rather, the differing distributions appear to reflect variations in attentional allocation strategies induced by the perceptual requirements typical of RT paradigms as opposed to SD paradigms. These findings support numerous prior studies showing that spatial attention affects perceptual sensitivity and that the strategic allocation of attention is a highly flexible process.

Adolescent↗

PubMed1996

Repeat visitors to a pediatric forensic medicine program.

Since the inception in 1990 of a Clinical Forensic Medicine Program at the Louisville Office of the Kentucky Medical Examiner Program, six children have undergone repeat evaluations for physical injuries. Herein, we examine the overall number of cases from January 1991 through December 1994, and the circumstances and outcomes of the six children undergoing reevaluation. Despite the implementation of an organized Forensic Medicine Program, some children in our area suffer repeated episodes of recognized abuse and death.

Child Abuse↗