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Biomedical subjects

D Whitney

Publications and source records attributed to D Whitney.

16 recordsLinked to original sources
PubMed2000

Temporal facilitation for moving stimuli is independent of changes in direction.

A flash that is presented aligned with a moving stimulus appears to lag behind the position of the moving stimulus. This flash-lag phenomenon reflects a processing advantage for moving stimuli (Metzger, W. (1932) Psychologische Forschung 16, 176-200; MacKay, D. M. (1958) Nature 181, 507-508; Nijhawan, R. (1994) Nature 370, 256-257; Purushothaman, G., Patel, S.S., Bedell, H.E., & Ogmen, H. (1998) Nature 396, 424; Whitney, D. & Murakami, I. (1998) Nature Neuroscience 1, 656-657). The present study measures the sensitivity of the illusion to unpredictable changes in the direction of motion. A moving stimulus translated upwards and then made a 90 degrees turn leftward or rightward. The flash-lag illusion was measured and it was found that, although the change in direction was unpredictable, the flash was still perceived to lag behind the moving stimulus at all points along the trajectory, a finding that is at odds with the extrapolation hypothesis (Nijhawan, R. (1994) Nature 370, 256-257). The results suggest that there is a shorter latency of the neural response to motion even during unpredictable changes in direction. The latency facilitation therefore appears to be omnidirectional rather than specific to a predictable path of motion (Grzywacz, N. M. & Amthor, F. R. (1993) Journal of Neurophysiology 69, 2188-2199).

Humans↗
PubMed2000

Illusory spatial offset of a flash relative to a moving stimulus is caused by differential latencies for moving and flashed stimuli.

A flash that is presented adjacent to a continuously moving bar is perceived to lag behind the bar. One explanation for this phenomenon is that there is a difference in the persistence of the flash and the bar. Another explanation is that the visual system compensates for the neural delays of processing visual motion information, such as the moving bar, by spatially extrapolating the bar's perceived location forward in space along its expected trajectory. Two experiments demonstrate that neither of these models is tenable. The first experiment masked the flash one video frame after its presentation. The flash was still perceived to lag behind the bar, suggesting that a difference in the persistence of the flash and bar, does not cause the apparent offset. The second experiment employed unpredictable changes in the velocity of the bar including an abrupt reversal, disappearance, acceleration, and deceleration. If the extrapolation model held, the bar would continue to be extrapolated in accordance with its initial velocity until the moment of an abrupt velocity change. The results were inconsistent with this prediction, suggesting that there is little or no spatial compensation for the neural delays of processing moving objects. The results support a new model of temporal facilitation for moving objects whereby the apparent flash lag is due to a latency advantage for moving over flashed stimuli.

Humans↗
PubMed2000

Motion distorts visual space: shifting the perceived position of remote stationary objects.

To perceive the relative positions of objects in the visual field, the visual system must assign locations to each stimulus. This assignment is determined by the object's retinal position, the direction of gaze, eye movements, and the motion of the object itself. Here we show that perceived location is also influenced by motion signals that originate in distant regions of the visual field. When a pair of stationary lines are flashed, straddling but not overlapping a rotating radial grating, the lines appear displaced in a direction consistent with that of the grating's motion, even when the lines are a substantial distance from the grating. The results indicate that motion's influence on position is not restricted to the moving object itself, and that even the positions of stationary objects are coded by mechanisms that receive input from motion-sensitive neurons.

Humans↗
PubMed2000

Preferred terms for users of mental health services among service providers and recipients.

OBJECTIVE: The terms used to refer to recipients of psychiatric services continue to be controversial. Terms in current use include "patient," "client," "consumer," and "survivor." In this study mental health service recipients and providers were surveyed about their preferences among these terms, and responses were analyzed to identify factors associated with various preferences. METHODS: A total of 550 service providers and 427 recipients at four sites in Ontario-two provincial psychiatric hospitals, a private mental health center, and a psychiatric unit of a general hospital-participated in a brief anonymous survey. RESULTS: Among service providers, 68.4 percent preferred the term "patient," 26.5 percent preferred "client," and.5 percent preferred "consumer." Logistic regression analysis showed that service providers' preferences were associated with age and gender. Among service recipients, 54.8 percent preferred the term "patient," 28.8 percent preferred "client," 7 percent preferred "survivor," and 2.8 percent preferred "consumer." Service recipients' preferences were associated with site, self-reported diagnosis, and employment status. CONCLUSION: The study results indicate lack of universality in preferences for terms for users of mental health services and suggest the need for dialogue about preferred terms between service providers and recipients.

Adult↗
PubMed1999

Gene expression of cellular retinoid-binding proteins: modulation by retinoic acid and dexamethasone in postnatal rat lung.

In rats, septation of gas-exchange saccules occurs during the first 2 postnatal weeks; dexamethasone (DEX) treatment irreversibly impairs septation, and treatment with all-trans retinoic acid (RA) prevents the DEX-induced inhibition of septation. Cellular retinoic acid-binding protein I (CRABP I) and cellular retinol-binding protein I (CRBP I) are important modulators of the cellular metabolism of retinoids. In the present study, therefore, we measured the mRNA concentration of CRABP I and CRBP I in lungs of neonatal rats. In untreated rats, CRABP I and CRBP I mRNA peaked at postnatal d 8, indicating that CRABP I and CRBP I are developmentally regulated at least in part at a pretranslational level during lung septation. Daily treatment of 3- to 8-d-old rats with RA (500 microg/kg/d) had no effect on the level of CRABP I mRNA; treatment with DEX (0.25 microg/d) from d 4 to 8 caused a decrease in CRABP I mRNA that was not prevented by concomitant treatment with RA. These findings suggest that a decrease in CRABP I expression may be important in the DEX-induced block of septation but not in the prevention by RA of DEX-induced inhibition of septation. RA treatment caused an increase of CRBP I mRNA; conversely, treatment with DEX caused a decrease in CRBP I mRNA that was prevented by concomitant treatment with RA. These data suggest CRBP I may play a role in RA-induced septation, in the inhibition of septation caused by DEX, and in the ability of RA to prevent DEX-blocked septation.

Animals↗
PubMed1998

Characterization of large-pore polymeric supports for use in perfusion biochromatography.

Perfusion chromatography is uniquely characterized by the flow of a portion of the column eluent directly through the resin in the packed bed. The benefits of this phenomenon and some of the properties of perfusive resins have been described before, and can be summarized as enhanced mass transport to interior binding sites. Here we extend the understanding of this phenomenon by comparing resins with different pore size distributions. Resins are chosen to give approximately the same specific pore volumes (as shown in the characterization section) but the varying contribution of large pores is used to control the amount of liquid flowing through the beads. POROS R1 has the largest contribution of throughpores, and therefore the greatest intraparticle flow. POROS R2 has a lower contribution of throughpores, and a higher surface area coming from a greater population of diffusive pores, but still shows significant mass transport enhancements relative to a purely diffusive control. Oligo R3 is dominated by a high population of diffusive pores, and is used comparatively as a non-perfusive resin. Although the pore size distribution can be engineered to control mass transport rates, the resulting surface area is not the only means by which binding capacity can be controlled. Surface coatings are employed to increase binding capacity without fundamentally altering the mass transport properties. Models are used to describe the amount of flow transecting the beads, and comparisons of coated resins to uncoated (polystyrene) resins leads to the conclusion that these coatings do not obstruct the throughpore structures. This is an important conclusion since the binding capacity of the coated product, in some cases, is shown to be over 10-fold higher than the precursor polystyrene scaffold (i.e., POROS R1 or POROS R2).

Algorithms↗
PubMed1996

Activation of physiological cell death mechanisms by a necrosis-causing agent.

Cell death is an important physiological process, but it can be triggered by both physiological and nonphysiological stimuli. The product of the bcl-2 gene has the ability to inhibit a physiological cell death process that can be activated by a variety of physiological signals, such as growth factor deprivation. This report describes the use of electron microscopy to examine the effects of two cytotoxic drugs on factor-dependent cells that constitutively express the human bcl-2 gene. Although all cells treated with sodium azide showed changes typical of necrosis, in the absence of Bcl-2 the cells died more rapidly and also displayed features of apoptosis. The fact that Bcl-2 could delay cell death argues that cells can activate internal cell death mechanisms to commit suicide before they are killed by a cytotoxin. Northern analysis showed that growth factor did not preserve viability of the cells through induction of bcl-2. However, growth factor may prevent activation of the physiological cell death mechanisms that bcl-2 can control. This process may constitute a primitive defense response, and blocking it may provide a means of limiting damage caused by otherwise sublethal injuries.

Animals↗
PubMed1988

A clear cell pilar sheath tumor of scalp: case report.

A long-standing tumor of scalp is reported characterized histologically by extensive proliferation of pilar epithelium made up exclusively of cells with small round nuclei and clear cytoplasms containing glycogen granules. The tumor epithelium showed no tendency for keratinization and no cytologic atypia. The growth, however, appeared aggressive and replaced the entire thickness of the dermis and extended into the subcutaneous fat tissue.

Epithelium↗