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F W Campbell

Publications and source records attributed to F W Campbell.

At least 19 recordsLinked to original sources
PubMed1994

The role of delineation and spatial frequency in the perception of the colours of the spectrum.

The observations of the spectrum made by Newton, Young, Wollaston and Helmholtz are approximated and accounted for. Increasing the number of delineations allows progressively more bands differing in colour to be perceived, in addition to the three blocks of colour seen in the undelineated spectrum. The rate at which further delineation permits more colours to be observed decreases, however, so that up to 30 colours can be perceived in the subdivided spectrum. The wavelength discrimination measurements agree well with previous data. Enhanced colour discrimination is shown to require luminance contrast transients containing only the first few Fourier harmonics.

Adult↗
PubMed1994

Perioperative challenges in the care of the Jehovah's Witness: a case report.

Same day admissions for surgery represent a growing portion of the operating room workload. Vigilance during preanesthetic evaluation and standards of preoperative preparation must be maintained for patients who are undergoing elective procedures. This case study reports the preanesthetic evaluation and perioperative management of a Jehovah's Witness who bled to a hematocrit of 9.0% during a myomectomy. The discussion considers the need for preoperative preparation and conservation of circulating red blood cells. Perioperative management modalities to conserve red blood cells including deliberate, controlled hypotension; autotransfusion; and normovolemic and hypervolemic hemodilution, are presented.

Adult↗
PubMed1992

Motion reveals spatial visual defects.

The question of how we can be unaware of the deficit in our (monocular) visual field, equivalent in size to 76 full moons, is examined. A new method of investigating the response to moving images on and near the blind spot has been found. The image of a computer-generated line, which is made to lengthen with time and pass over the blind spot, is seen as shorter than that of a similar, parallel line which passes outside the blind spot. This perceived difference in length corresponds to the actual width of the blind spot. Our unawareness of blind spots and scotomata is often described as involving some form of 'filling in' process. The rapid variation in cortical receptive field size, recently found to occur in response to stabilized images, may provide a general filling-in mechanism for the removal from perception of otherwise-distracting, stabilizing image regions (such as the shadows of blood vessels and clinical scotomata).

Humans↗
PubMed1992

Study of precorneal tear film thickness and structure by interferometry and confocal microscopy.

Past measurements of precorneal tear film thickness in rabbits and humans gave values of 4-7 microns. These have been the accepted values. However, measurements presented in this report are much higher. Earlier techniques may have changed film thickness or not have fully included the layer containing mucus. Little is known about the mucus component. Thickness was measured in freshly killed animals of 10 species using two independent optical techniques. Coherent light was reflected from eyes and thickness was determined from spacing of interference fringes. Clear images of tissue structure were obtained with confocal microscopy, the tear film was visually identified, and thickness measured. Measurements by the two methods were closely correlated in each animal. No film was detected in trout or carp. In other species, thickness ranged from 9 microns in frogs to 15 microns in gerbils. Values are significantly larger than earlier estimates. Film thickness in three living rabbits was not significantly different from that measured shortly after death. There was no variation in thickness at five positions across the cornea in three species. Mucus content of rat tear film was examined by measuring thinning after application of 4, 8, and 20% (weight/volume) acetylcysteine, a mucolytic agent. Thickness was considerably reduced compared to controls, and the film almost completely removed by the highest concentration. The authors propose that the film is largely composed of mucus, not free aqueous solution. Our methods include such layers, and measurements are correspondingly larger than earlier ones.

Animals↗
PubMed1992

Study of human precorneal tear film thickness and structure using laser interferometry.

The authors previously found that measurements of precorneal tear film thickness in animals, using laser interferometry and confocal microscopy, were larger than earlier estimates. They proposed that this occurred because optical methods did not disturb film structure and measured full thickness, including mucus. In the present study, tear film thickness was measured in humans. Coherent light was reflected from eyes and formed interference patterns. Thickness was determined from spacing of fringes. Mean thickness in six subjects was 34-45 microns, more than four times larger than earlier values. Validity and accuracy of measurements by interferometry were examined in our earlier study using confocal microscopy. Here it provided supportive evidence. Tear film thickness was estimated from optical sections through the corneas of three subjects to be 41-46 microns. Mucus content of the film also was examined. Interferometry was used to measure thinning after application of a mucolytic agent. There was no change in thickness after 5 min exposure to 0.1% (weight/volume) acetylcysteine. Solutions of 20% caused thinning to 11 microns, and thickness slowly increased to reach its original value over 40 min. Thus, the film seemed to be composed substantially of mucus, not aqueous fluid. The results also provided evidence that measurements by interferometry did not include underlying epithelium. Earlier nonoptical methods probably did not include the portion of the film that contained mucus. They seem to have greatly underestimated human tear film thickness.

Adult↗
PubMed1988

A rapid method for estimating weight and resuscitation drug dosages from length in the pediatric age group.

Drug dosages used during pediatric emergencies and resuscitation are often based on estimated body weight. The Broselow Tape, a tape measure that estimates weight and drug dosages for pediatric patients from their length, has been developed to facilitate proper dosing during emergencies. In our study, 937 children of known weight were measured with this tape. Weight estimates generated by the tape were found to be within 15% error for 79% of the children. The tape was found to be extremely accurate for children from 3.5 to 10 kg, and from 10 to 25 kg. Regression lines of estimated compared with actual weight for these children have slopes of 0.98 and 0.96, respectively, not significantly different from the ideal slope of 1.00 (P = 28 and .13). Accuracy was significantly decreased for measured children who weighed more than 25 kg. In a separate group of children (n = 53), the tape was shown to be more accurate than weight estimates made by residents and pediatric nurses (P less than .0001). Use of the Broselow Tape is a simple, accurate method of estimating pediatric weights and drug doses and eliminates the need for memorization and calculation.

Body Height↗
PubMed1988

Visual reaction-time versus action-time.

The reaction-time for movement was found to be around 150 ms and was compared with the time required to take action while two moving lines are on a collision course. Subjects were trained to either avoid or maximize collision. They did so accurately. The action-time was about one-third the reaction-time.

Humans↗
PubMed1988

Sequential visual reaction times.

The reaction-time to a series of successive digits was measured on two subjects. After practice, it was found that whilst the reaction time to the onset of the series was constant at 150 ms, the response time to additional digits became less and less to asymptote to a level of about 50 ms. The time course of this 'chorus-line' phenomenon was studied in greater temporal detail by varying the interval in steps of 20 ms. The effect was greatest at 200 ms. Thereafter, it declined and for long intervals reached the value of a standard reaction time. On a third inexperienced subject, the learning period was established; this was about 300-400 presentations. The implications of these findings are discussed against the background of everyday visual motor behaviour.

Adult↗
PubMed1987

Bad lights stops play.

The visual performance of cricket batsmen is simulated over a wide range of ambient illumination. When illumination falls to the level at which they usually stop batting (the gloom level) a rapid increase in reaction time commences. It is also the level at which office and car sidelights are turned on and the sensation of "gloom" occurs.

Adult↗