PubMed Health⌕ Search

Biomedical subjects

R W Wiley

Publications and source records attributed to R W Wiley.

10 recordsLinked to original sources
PubMed1994

The effect of knowledge of object distance on accommodation during instrument viewing.

We present data in which instrument accommodation was measured while knowledge of object distance was varied. The accommodative feedback loop was 'semiopen'--an intermediate state between the closed-loop and open-loop conditions of previous experiments. The semiopen-loop situation mimicked the degraded-image conditions which are frequently encountered during instrument viewing. The results show that for some subjects knowledge of object distance is a more powerful cue for instrument accommodation than is the optical distance of the object; however, for the majority of subjects this is not the case. We also found that subjects whose accommodation is influenced by knowledge of object distance tend to have a more proximal dark focus than those whose accommodation is independent of knowledge of object distance. We propose that the Mandelbaum effect, in which involuntary accommodation occurs when a transparency is superimposed between the observer and the object of regard, could account for the accommodative behavior of all subjects. However, the Mandelbaum effect would have to be interpreted more broadly than before. In the broader interpretation, the transparency could be cognitive (ie known distance) rather than physical.

Accommodation, Ocular↗
PubMed1992

The effects of pyridostigmine bromide on visual performance.

The effects of pyridostigmine bromide (PB) on selected visual functions were measured on four healthy aviator candidates. Following a pretreatment day during which baseline measurements were completed, subjects were administered currently recommended doses (30 mg, t.i.d.) of PB for 3 d during which their visual functions were assessed using a repeated measures design. Spatial resolution ability was evaluated with high and low contrast visual acuity charts and contrast sensitivity charts at three luminance levels. Dark adaptation was evaluated by measuring visual thresholds for 40 min after a standardized retinal photopigment bleach. Also, refractive error and several oculomotor functions (lateral phoria, fusional vergence, accommodative amplitude, and pupil size) were measured. On days that the subjects ingested PB, only refractive error and pupil diameter were significantly different, and these only minimally. We conclude that the use of PB at doctrinal doses will not significantly compromise an aviator's visual ability.

Accommodation, Ocular↗
PubMed1989

Dark adaptation and recovery from light adaptation: smokers versus nonsmokers.

Because the published data concerning the effects of smoking on visual sensitivity at night are inconsistent, a new study was initiated to obtain ground level comparison data from smoking and nonsmoking Army aviators. Blood samples also were analyzed to compare serum levels of nicotine, cotinine, and carboxyhemoglobin with the visual measures. The present data show no differences in visual sensitivity between smokers and nonsmokers and no significant correlations between the blood and visual measures. The conclusion from these results is that the ability to see the dimmest lights at night is independent of smoking history when scotopic sensitivity is assessed at ground level.

Adult↗
PubMed1987

Recovery of the visual evoked response in the cat following administration of diisopropylfluorophosphate, an irreversible cholinesterase inhibitor.

Visual evoked responses (VER) to counterphased gratings were recorded from area 17 of cat visual cortex prior to and following administration of diisopropylfluorophosphate (DFP). The VER and acetylcholinesterase (AChE) activity of blood, retina, and visual cortex were reduced significantly following DFP administration. Approximately two hours after exposure to 4 mg/kg DFP, the VER began to recover and in some cats returned to base line levels. In contrast, blood, retina, and cortex AChE activity showed little, if any, tendency for recovery throughout the experiment. Since atropine sulfate provided at least partial recovery of the VER following DFP without affecting AChE inhibition, an accumulation of acetylcholine (ACh) probably is involved in the initial visual loss. However, recovery of the VER over time while AChE remained severely inhibited implicates mechanisms other than, or in addition to, accumulation of ACh at receptor sites.

Acetylcholinesterase↗
PubMed1985

The effects of diisopropylfluorophosphate on spatial frequency responsivity in the cat visual system.

Visual-evoked responses to counterphased gratings were recorded from area 17 of cat visual cortex before and after diisopropylfluorophosphate (DFP) administration. DFP produced effects similar to those obtained following physostigmine sulfate administration, in that responses to low spatial frequencies were preferentially reduced. The time course of the effects was quite different for the two types of drugs, and for high doses of DFP responses to all spatial frequencies were approximately uniformly depressed or abolished.

Animals↗
PubMed1984

Contrast sensitivity determined with the spatial bandwidth equalization technique: threshold, suprathreshold, and spatiotemporal measurements.

Contrast sensitivity functions were obtained from normal subjects using a spatial bandwidth equalization (SBE) technique and the more conventional display method. Static sensitivity measurements obtained with the two methods were in good agreement. However, when the patterns were counterphase flickered , sensitivity to the lower spatial frequencies was enhanced using the conventional method while sensitivity measured with the SBE technique was slightly depressed. The SBE method also was used to investigate suprathreshold contrast perception with static and flickering gratings. In general, the perception of contrast was independent of spatial frequency content of the stimulus, especially with increasing contrast levels and flicker frequencies. These studies have shown that the SBE technique is an acceptable method to assess static contrast sensitivity and suprathreshold contrast perception.

Humans↗
PubMed1983

A cholinergic-sensitive channel in the cat visual system tuned to low spatial frequencies.

Visually evoked responses to counterphased gratings were recorded from the cat visual cortex before and after physostigmine administration. Physostigmine markedly reduced the responses to low spatial frequencies, but minimally affected the response to high frequencies. This effect is considered cholinergic since it could be reversed by atropine. These results support at least a two-channel model of spatial frequency responsivity.

Animals↗
PubMed1980

A human performance/workload evaluation of the AN/PVS-5 bifocal night vision goggles.

Eight experienced U.S. Army aviators performed various maneuvers in an instrumented helicopter to test the relative usability of two bifocal-configured night vision goggles. Both configurations were statistically better than the unmodified arrangement when looking at a pilot's ability to fly a standard traffic pattern and to hold a precise altitude at night. The subjective data, supported by comparative flight performances with the two bifocals, further suggested that a 24% bifocal version was more desirable than a 14% configuration. The inference is that the reduced inside field of view presented by the 14% bifocal interferes with a pilot's ability to readily locate instruments once he has directed his attention inside the cockpit.

Aerospace Medicine↗
PubMed1970

Distance effects in human scotopic retinal interaction.

1. Using the threshold for a small, brief test flash as a measure, the effect of light stimulation of small adjacent retinal regions of the human retina was investigated during adaptation to a medium scotopic illuminance.2. Within about (1/2) degrees of the tested area, light causes a desensitization gradually decreasing with distance. Beyond that there is a sensitizing zone which in turn gives way to an outer desensitizing zone. The sign of these effects is reversed if the peripheral stimulus is a patch of darkness.3. Evidence for non-linearity of summation of individual patches was found. Occlusion of each other's sensitizing influence is observed if two regions are closely adjacent to each other.

Adaptation, Ocular↗