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Biomedical subjects

J Pratt

Publications and source records attributed to J Pratt.

At least 55 records · Page 3Linked to original sources
PubMed1999

The effect of age-related stereotypes on response initiation and execution.

In 2 experiments, the authors investigated the effects of positive and negative stereotypes of older adults on response initiation and execution. College students were first primed with the word young or the word old, and then produced an aimed hand movement in response to a positive or negative trait. Results of the 1st experiment indicated that the participants produced the fastest and most forceful movements when the word "old" primed negative traits; they produced the slowest and least forceful responses when the word old primed positive traits. In a 2nd experiment, the authors replicated these effects by using only the prime old. The results suggest that ageist responses extend beyond reaction time in a social judgment task.

Adult↗
PubMed1999

Examining the effect of practice on inhibition of return in static displays.

In a recent article, Weaver, Lupiáñez, and Watson (1998) reported that both object-based and location-based inhibition of return effects were reduced with practice. The present study was conducted to (1) replicate the reduction of inhibition of return with practice in single-session experiments with a variety of displays and responses and (2) to examine the notion that the reduction was, at least partly, due to habituation. However, no evidence for practice-related changes in the size of the inhibitory effect were found over a series of different inhibition of return experiments using static displays (using various numbers of target locations, types of keypress responses, and number of trials). Overall, the results suggest that inhibition of return is a robust phenomenon and may not, with static displays, be especially sensitive to practice effects.

Adult↗
PubMed1999

Inhibition of return is composed of attentional and oculomotor processes.

Response time can be delayed if a target stimulus appears at a location or object that was previously cued. This inhibition of return (IOR) phenomenon has been attributed to a delay in activating attentional or motor processes to a previously cued stimulus. Two experiments required subjects to localize or identify a target stimulus. In Experiment 1, the subjects' eyes were not monitored. In Experiment 2, the subjects' eyes were monitored, and the subjects were instructed to either execute or withhold an eye movement to a target stimulus. The results indicated that IOR was always present for location and identification responses, supporting an attentional account of IOR. However, IOR was larger when eye movements were executed, indicating that a motor component can contribute to IOR. Finally, when eye movements were withheld, IOR was larger when a target was presented alone than when it was presented with a distractor, suggesting that IOR is larger for exogenous than for endogenous covert orienting. Together, the data indicate that IOR is composed of both an oculomotor component and an attentional component.

Adult↗
PubMed1999

Norbert Elias and the civilized prison.

This paper employs an Eliasian perspective to provide an historical overview to the contemporary crisis in British prisons. It argues that some of the roots of this crisis lie within the very attempts to bring prison development in line with the cultural values of modern society.

History, 19th Century↗
PubMed1998

Hospital admissions. Cold remedies.

The closure of a casualty department provoked a crisis in Hillingdon in the winter of 1996-97. Worried by the publicity, elderly people contacted the health authority to ask what would happen to them if they became ill. An all-day workshop, attended by elderly people, chief executives, nurses, social workers and representatives from the community health council and ambulance services, led to several initiatives, including a rapid response home service, which helped prevent a crisis last winter.

Aged↗
PubMed1998

Glutamate uptake is decreased tardively in the spinal cord of FALS mice.

This study examined high affinity Na+-dependent uptake of glutamate in synaptosomal preparations from spinal cord in mice that express a dominant mutation of human copper/zinc superoxide dismutase (SOD1) and represent an animal model of amyotrophic lateral sclerosis (ALS). Their muscle strength was also monitored by a grip traction test throughout their lifespan. The high affinity Na+-dependent uptake of [3H]glutamate was decreased between 120 and 150 days of age. A marked and significant decrease in Vmax (-40.2%; p < 0.001) on whole spinal cord synaptosomes was observed at 150 days, with no change in Km. This significant decrease was reached a week before the animals died (157.2 +/- 2.2 days) and corresponded to a considerable fall in muscle strength (25% loss between 120 and 140 days, p < 0.001). The FALS mouse model therefore reproduces the decrease in glutamate uptake reported in humans suffering from sporadic or familial ALS. These results are discussed in terms of a possible tardive involvement of glutamate uptake deficiency in human ALS.

Amyotrophic Lateral Sclerosis↗
PubMed1998

Visual fixation offsets affect both the initiation and the kinematic features of saccades.

It is well known that the removal of a fixation point prior to the presentation of a peripheral target dramatically reduces saccadic reaction time (SRT). This effect has become known as the "gap effect". The present study examined several detailed kinematic variables to determine whether the removal of the fixation point also affects the manner in which saccades are produced. The findings indicate that saccades that were initiated after the removal of the fixation point had higher average velocities and reached greater peak velocities, accelerations, and decelerations than did saccades produced in the presence of the fixation point. The results suggest that the removal of the fixation point may affect the force-time curves of saccades in addition to affecting the time needed to initiate the saccades.

Analysis of Variance↗
PubMed1998

Aging and movement: variability of force pulses for saccadic eye movements.

Age-related differences in the trajectories of saccadic eye movements were examined. Younger and older adult subjects produced saccades to predictable target locations. Detailed features of the movements were examined such as the time of peak acceleration and the variability in the magnitude of the peak velocity. These and other measures reveal important details of the force pulses underlying the eye movements and the mental mechanisms that control them. Although minor differences were apparent between the eye movements of younger and older adults, the general patterns were the same across age groups. These results suggest that fundamental details of the brain mechanisms involved in the control of movement are the same for younger and older adults.

Adult↗
PubMed1998

Fixation point offsets facilitate endogenous saccades.

Subjects produced saccades to continuously visible targets that were signaled by the pitch, not the location, of an auditory signal. Such endogenous saccades were initiated more quickly when the visual fixation point disappeared 200 msec before the signal (thus producing a "gap"), even though the alerting benefits of such a warning were eliminated by an earlier warning tone. The presence of the gap effect under these circumstances shows that the effect is more general than was previously believed: Visual fixation point offsets facilitate saccades by affecting oculomotor processes related to both visually elicited (exogenous) and centrally produced (endogenous) saccades. In addition, the magnitude of the gap effect for endogenous saccades was significantly smaller than that for exogenous saccades, suggesting that at least some of the effect arises in relatively early processes, such as those involved in the processing of sensory signals, and not exclusively in later processes, such as those involved in the preparation and production of saccades.

Adult↗
PubMed1997

Initiation and inhibition of saccadic eye movements in younger and older adults: an analysis of the gap effect.

Previous research with young adults has shown that the latency to initiate a saccadic eye movement is typically reduced when the visual fixation stimulus is removed prior to the appearance of a peripheral target stimulus (the "gap effect"). The present study sought to determine whether such fixation offsets would produce similar reductions in reaction time in both younger and older adults. The results indicated that older adults have longer overall latencies to initiate saccadic eye movements and that they exhibit the gap effect. However, the reduction in reaction time due to the fixation offset was approximately equal between younger and older adults relative to the overall saccadic latencies. These findings, along with some other recent evidence, suggest that some of the mechanisms involved in the production of saccadic eye movements may not reveal the changes often found in the skeletal motor system with increasing age. The implications of the findings to age-related differences in inhibitory function are discussed.

Acoustic Stimulation↗
PubMed1997

Evidence for increased synthesis of complement C4 in the renal epithelium of rats with passive Heymann nephritis.

Passive Heymann nephritis (PHN) is a complement-dependent model of immune complex glomerulonephritis. This study investigated the contribution of local complement synthesis by studying gene expression of the classical pathway component C4 in relation to the site of the tissue injury and the development of proteinuria induced by the pathogenic antibody (sheep anti-GP330). This study, using in situ hybridization, found that C4 mRNA expression was increased in the glomerular epithelium and the proximal renal tubular epithelium in a distribution similar to that of the targeted GP330 antigen. The total cortical C4 mRNA expression assessed by semiquantitative polymerase chain reaction (PCR) increased in a time-dependent manner (P < 0.05), coincident with the onset and progression of proteinuria, and peaking 11 to 14 days after the induction of the disease. These data suggest a link, in place and time, between local complement gene expression and glomerular barrier dysfunction induced by anti-GP330. It is postulated that increased epithelial synthesis of C4 stimulated by the engagement of GP330 enhances the formation of the membrane attack complex of complement through its classical pathway, and, hence, the formation of complement-mediated injury.

Animals↗
PubMed1997

Inhibition of return in location- and identity-based choice decision tasks.

Three experiments were conducted to determine whether inhibition of return can be best characterized as an attentional or a motor phenomenon. In the first experiment, subjects made choice keypress responses to the location of a target (left or right) or the identity of the target (X or +) by pressing a left or right response key. In the second experiment, the display was rotated 90 degrees so that there was no direct spatial mapping between the vertically aligned stimulus display and the horizontally aligned response keys. In both experiments, inhibition of return was observed for location-based and identity-based choice responses, although more inhibition was seen in the identity-based responses. The results of the third experiment suggested that this larger inhibitory effect may be specific to the covert orienting of reflexive attention in response to the sudden appearance of a single peripheral stimulus in the identity tasks. Overall, the results are consistent with the attentional, not the motor, explanation of inhibition of return.

Choice Behavior↗
PubMed1996

The effect of riluzole on post-traumatic spinal cord injury in the rat.

This study evaluated treatment with riluzole, a neuroprotective agent, following thoracic spinal cord compression in the rat. Animals received riluzole (2 mg kg-1) or vehicle twice daily for 10 days following the trauma. Motor deficits, somatosensory evoked potentials (SEP) and lesion histology were evaluated. Although paralysis was seen following trauma, seven of 10 animals receiving riluzole recovered motor function and nearly normal behaviour, unlike animals receiving vehicle. Trauma dramatically disturbed SEPs with falls in amplitude and increases in latency. After riluzole SEP returned towards pre-injury levels, while untreated animals showed no recovery. Morphological studies revealed significant (53%) reduction in the degree of spinal cord infarcted after riluzole treatment.

Anesthesia↗
PubMed1996

Spatially diffuse inhibition affects multiple locations: a reply to Tipper, Weaver, and Watson (1996).

S. Tipper, B. Weaver, and F. Watson (1996) suggest that J. Pratt and R.A. Abrams's (1995) failure to find inhibition of return for more than the most recently cued location was because their 2-target display did not adequately capture some of the complexity of real-world visual environments. However, Tipper et al. tested a special case because they always cued 3 out of 4 potential targets (allowing cued and uncued locations to be segregated into 2 spatial regions). The authors show that only the 1 most recently cued location will be inhibited when 2 nonadjacent targets out of 4 possible targets are cued, but both cued locations will be inhibited when they are adjacent. Also, only the 1 most recently cued location was inhibited when 3 nonadjacent targets out of 6 potential target locations were cued. Thus, in a complex environment in which several cued locations are interspersed among noncued locations, inhibition of return will occur for only the 1 most recently attended location, consistent with conclusions of Pratt and Abrams.

Adult↗
PubMed1996

Inhibition of return along the path of attention.

Two experiments were conducted to examine inhibition of return (IOR) at four potential target locations (a near and a far location in each visual hemifield). In the first experiment, the locations were aligned horizontally and IOR was found at the near locations when the cues were presented at the far locations but not at the far locations when the cues were presented at the near locations. In the second experiment, the locations were not horizontally aligned and IOR was not found for near locations when the far locations were cued. The results suggest that IOR may be an attentional phenomenon and that attention may operate in an analog fashion such that locations in the path of the attentional movement may be attended to.

Adult↗
PubMed1996

The gap effect for eye and hand movements.

A temporal gap between fixation point offset and stimulus onset typically yields shorter saccadic latencies to the stimulus than if the fixation stimulus remained on. Several researchers have explored the extent to which this gap also reduces latencies of other responses but have failed to find a gap effect isolated from general warning effects. Experiment 1, however, showed a robust gap effect for aimed hand movements (which required determination of a precise spatial location), regardless of whether the hand moved alone or was accompanied by a saccadic eye movement. Experiment 2 replicated this aimed hand gap effect and also showed a smaller effect for choice manual keypress responses (which required determination of the direction of response only). Experiment 3 showed no gap effect for simple manual keypress responses (which required no spatial determination). The results are consistent with an interpretation of the gap effect in terms of facilitation of spatially oriented responses.

Acoustic Stimulation↗
PubMed1995

Acute effects of irradiation on the rat brain: protection by glutamate blockade.

Riluzole (2-amino-6-trifluorothethoxy benzothiazole), dizocilpine (MK-801; (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine maleate), and lamotrigine (3,5-diamino-6-(2,3-dichlorophenyl)-1,2-triazine), agents reported to have neuroprotective actions, and WR2721 (S-2-(3-aminopropylamino)-ethylphosphorothioic acid), a radioprotector, were evaluated in 15-day-old rats that underwent a 2.5 Gray (Gy) irradiation from a cobalt 60 source. 20 min after irradiation, riluzole (0.5-8 mg/kg), dizocilpine (0.1-1 mg/kg), lamotrigine (25 mg/kg), WR 2721 (75 mg/kg) or vehicle, were injected intraperitoneally. 6 h after irradiation, behavioural and histological evaluations revealed that exposure to 2.5 Gy caused hypolocomotion, stumbling gait and somnolence, which was significantly reduced, from the dose of 4 mg/kg i.p. of riluzole. A dose-dependent protection of neurones in the dentate gyrus, starting from the dose of 1 mg/kg i.p. was also seen. Dizocilpine caused behavioral modifications but significantly reduced neuronal damage. Lamotrigine significantly increased neuronal damage while WR 2721 conferred no protection. In conclusion, two blockers of glutamatergic neurotransmission conferred significant protection against brain damage caused by ionizing irradiation when administered subsequent to exposure.

Amifostine↗