Age, degraded viewing environments, and the speed of accommodation.

Subjects were 35 males in an accommodation experiment which utilized a subjective laser optometer. Seven different age groups, from average age 22-52, were measured on the time to change accommodation from a near to an infinity target. During the experiment, room illumination, time duration of reading at a near distance, and the distance of a near-reading task were varied. Results indicated that the time to accommodate from a near to infinity target varied as a function of age, room illumination, and the distance of the near-reading task. During ideal conditions, older subjects could accommodate nearly as quickly as the younger subjects; however, during degraded viewing conditions, the accommodation time for older subjects increased as much as tenfold. Time to accommodate to a distant target also increased solely as a function of time spent reading at a near distance, regardless of age. In accordance with previous reviews of aging and military pilots, it is suggested that the time to accommodate may be used as an objective measure of degraded vision as it relates to age.

The effects of task performance on ocular accommodation and perceived size.

Two studies were conducted to test the hypothesis that performance of cognitive tasks tends to induce outward shifts in ocular accommodation that, in turn, result in changes in perceived size. In the first study, 12 subjects participated in each of 4 conditions; rest or performance of a running-memory task each with either visual or auditory stimuli. In each condition, subjects made four size judgments and their mean accommodation was measured using an infrared optometer. Dark focus of accommodation was measured before and after the experiment. There were no reliable differences among the four conditions, nor between the pre- and postexperiment dark-focus measures. A second study was conducted in which the accommodative state of 10 subjects was recorded during 4 min of rest and 4 min of performing a backward-counting task. The difference between the mean accommodative state during the last minute of rest and task performance approaches statistical reliability. It was concluded that outward shifts in accommodation may be associated with performance of tasks that involve distant targets (e.g., other aircraft in the surrounding airspace) and/or require complex mental transformations (e.g., predicting future position of an intruder aircraft relative to your own aircraft).

Effect of a concurrent counting task on dynamic visual accommodation.

The visual accommodation of four male subjects was selectively recorded over a 3-day period using an objective, continuously recording, infrared optometer to determine the effects of a concurrent counting task on their ability to accommodate to a sinusoidally changing focus stimulus ranging from 0.0 to 3.0 D. There was an increase in their steady-state errors in the direction of negative accommodation of from 0.25 to 0.50 D, but the magnitude of the steady-state error induced by the concurrent task did not change over the three sine wave frequencies used (0.1, 0.2 and 0.4 Hz). The results are discussed in terms of an accommodative "lag" model of sympathetic-parasympathetic arousal induced by superimposing an extraneous mental task.

What you thought you knew about motion sickness isn't necessarily so.

NASA: Motion sickness symptoms, stimuli, and drug therapy are discussed. Autogenic feedback training (AFT) methods of preventing motion sickness are explained. Research with AFT indicates that participants who had AFT could withstand longer periods of Coriolis acceleration, participants with high or low susceptibility to motion sickness could control their symptoms with AFT, AFT for Coriolis acceleration is transferable to other motion sickness stimuli, and most people can learn AFT, though with varying rates of learning.^ieng

Measuring the size of mental images.

Mental images seem to have a size; the experimental problem was to map that image size onto a scale of physical measurement. To this end, two experiments were conducted to measure the size of mental images in degrees of visual angle. In Experiment 1, college students employed light pointers to indicate the horizontal extent of projected mental images of words (the letter string, not the referent). Imagined words covered about 1.0 degress of visual angle per letter. In Experiment 2, a more objective eye-movement response was used to measure the visual angle size of imagined letter strings. Visual angle of eye movement was found to increase regularly as the letter distance between the fixation point and a probed letter position increased. Each letter occupied about 2.5 degrees of visual angle for the four-letter strings in the control/default size condition. Possible relations between eye movements and images are discussed.