Biomedical subjects

Greg Davis

Publications and source records attributed to Greg Davis.

6 recordsLinked to original sources

PubMed2006

The microgenesis of global perception in autism.

Several studies have reported that individuals with autism and Asperger's syndrome show a local processing bias on tasks involving features and configurations. This study assessed whether this bias results from differences in the perception of features or a cognitive bias to attend to features in autism as a consequence of a deficit in attending to configurations. Children with autism and typically developing children performed a task assessing the initial perceptual representation of features and configurations following a 50 ms stimulus display and the development of the perceptual representation by grouping processes following an 800 ms stimulus display. No differences were observed between the two groups, suggesting that the perceptual and attentional mechanisms marshalled by this task operate typically in children with autism.

Attention↗

PubMed2005

The natural history of white coat hypertension during pregnancy.

OBJECTIVE: White coat hypertension (WCH) is a common phenomenon with a long term prognosis intermediate between those with true hypertension and true normotension. The natural history of this phenomenon throughout pregnancy remains unknown. We assessed the likelihood of women with an initial diagnosis of WCH developing pre-eclampsia (PE) as their pregnancy progressed. DESIGN: Prospective observational study. SETTING: St George Hospital, a teaching and University hospital. POPULATION: Two hundred and forty-one pregnant women with an early pregnancy diagnosis of essential hypertension (EH). METHODS: Eighty-six women had this diagnosis (EH) confirmed pre-pregnancy by 24-hour ambulatory blood pressure monitoring (ABPM) or repeated automated home blood pressure (BP) self-measurement. The remaining 155 underwent 24-hour ABPM in early pregnancy to establish their diagnosis. Women found to have WCH did not receive antihypertensives during their pregnancy, whereas those with confirmed EH received oxprenolol or methyldopa. Women with WCH had repeated 24-hour ABPM and/or BP assessments in a pregnancy day assessment unit until delivery. MAIN OUTCOME MEASURE: The development of PE in women with WCH or EH. RESULTS: The overall prevalence of WCH was 32%. Half retained this phenomenon throughout pregnancy and had good pregnancy outcomes. Forty percent developed (benign) gestational hypertension and also had good pregnancy outcomes while 8% developed proteinuric PE, significantly fewer than in women with confirmed EH (22%), P= 0.008. No BP parameter at study entry permitted discrimination between those women with WCH who retained this phenomenon and those who developed GH or PE. CONCLUSION: WCH is a common phenomenon in pregnant women who appear to have EH according to routine BP measurement early in pregnancy. Antihypertensives may be withheld from this group initially and they can be advised they will have better pregnancy outcomes than women with true EH. However, continued monitoring throughout pregnancy remains important to detect the small group of white coat hypertensives who develop PE.

Adult↗

PubMed2005

What is enumerated by subitization mechanisms?

Subitization, the rapid enumeration of small numbers of objects, is often held to reflect a general ability to process three or four items simultaneously. However, questions as to which types of visual representations count as items for subitization have, thus far, received relatively little attention. In several new experiments, we instructed participants to enumerate three or four colored regions in a display. In some trials, all of these regions belonged to separate visual objects, whereas in others, two or more belonged to the same object(s). We found far slower enumeration in the latter case than in the former case, a result that cannot be attributed to Stroop interference from the number of attended objects in a display. We conclude that subitization mechanisms cannot operate on small fragments of shape and color alone, even when such fragments are easily individuated from one another. Rather, such mechanisms are compelled to operate on object representations.

Adult↗

PubMed2005

The capacity of visual short-term memory is not a fixed number of objects.

Luck and Vogel (1997) have reported several striking results in support of the view that visual short-term memory (VSTM) has a fixed capacity of four objects, irrespective of how many relevant features those objects comprise. However, more recent studies have challenged this account, indicating only a weak effect of the number of objects once other factors are more evenly equated across conditions. Here, we employed a symmetry manipulation to verify object segmentation in our displays, to demonstrate that when spatial and masking factors are held constant, the number of objects per se has no effect on VSTM. Instead, VSTM capacity may reflect the number of object "parts" or feature conjunctions in a given display.

Adult↗

PubMed2004

Characteristics of attention and visual short-term memory: implications for visual interface design.

Although the human retina can code many object images simultaneously, observers are often aware of only a tiny fraction of this information. These processing limitations of the visual brain have evolved to prioritize particularly relevant features of a scene while ignoring other irrelevant features. However, such selectivity has its drawbacks. In information-rich environments, such as driving a car or landing an aircraft, vision can fail to cope, and accidents can result. Accordingly, much recent research in psychophysics and ergonomics has examined how display characteristics affect our ability to process multiple features of the visual environment simultaneously. The majority of these experiments has found that performance can be optimized by combining several features into one visual 'object'. In contrast, several recent studies from my own laboratory have found the opposite pattern, indicating that information sources can often be more efficiently processed when they belong to separate objects. Indeed, these data suggest that the number of objects has no general effect on our perceptual performance. Instead, I argue for a two-pathway approach to understanding human visual capacities, and suggest that this approach may have important implications for a diverse range of display technologies, including cockpit displays.

Attention↗

PubMed2003

Androgenetic alopecia in a postmenopausal woman as a result of ovarian hyperthecosis.

A 65-year-old woman presented with an 8-year history of progressive frontotemporal alopecia and hirsutism. She had elevated serum levels of testosterone, androstenedione and estradiol. Ultrasound and computed tomography imaging suggested a right ovarian mass, while bilateral ovarian venous sampling demonstrated increased testosterone levels originating from both ovarian veins. Histology obtained following bilateral oophorectomy demonstrated bilateral ovarian hyperthecosis. Six months after surgery, the patient remains well with no progression of the alopecia. Ovarian hyperthecosis is a rare cause of androgenetic alopecia in postmenopausal women. The role of hyperthecosis and its relationship to androgenetic alopecia is reviewed.

Aged↗